key: cord-0017492-7moqw9lo authors: Shi, Chunhu; Dumville, Jo C; Cullum, Nicky; Rhodes, Sarah; Leung, Vannessa; McInnes, Elizabeth title: Reactive air surfaces for preventing pressure ulcers date: 2021-05-07 journal: Cochrane Database Syst Rev DOI: 10.1002/14651858.cd013622.pub2 sha: 5425554742048e8b64cfaaf48f816b7512e851d4 doc_id: 17492 cord_uid: 7moqw9lo BACKGROUND: Pressure ulcers (also known as pressure injuries, pressure sores, decubitus ulcers and bed sores) are localised injuries to the skin or underlying soft tissue, or both, caused by unrelieved pressure, shear or friction. Reactive air surfaces (beds, mattresses or overlays) can be used for preventing pressure ulcers. OBJECTIVES: To assess the effects of reactive air beds, mattresses or overlays compared with any support surface on the incidence of pressure ulcers in any population in any setting. SEARCH METHODS: In November 2019, we searched the Cochrane Wounds Specialised Register; the Cochrane Central Register of Controlled Trials (CENTRAL); Ovid MEDLINE (including In‐Process & Other Non‐Indexed Citations); Ovid Embase and EBSCO CINAHL Plus. We also searched clinical trials registries for ongoing and unpublished studies, and scanned reference lists of relevant included studies as well as reviews, meta‐analyses and health technology reports to identify additional studies. There were no restrictions with respect to language, date of publication or study setting. SELECTION CRITERIA: We included randomised controlled trials that allocated participants of any age to reactive air beds, overlays or mattresses. Comparators were any beds, overlays or mattresses that were applied for preventing pressure ulcers. DATA COLLECTION AND ANALYSIS: At least two review authors independently assessed studies using predetermined inclusion criteria. We carried out data extraction, 'Risk of bias' assessment using the Cochrane 'Risk of bias' tool, and the certainty of the evidence assessment according to Grading of Recommendations, Assessment, Development and Evaluations methodology. If a reactive air surface was compared with surfaces that were not clearly specified, then we recorded and described the concerned study but did not included it in further data analyses. MAIN RESULTS: We included 17 studies (2604 participants) in this review. Most studies were small (median study sample size: 83 participants). The average participant age ranged from 56 to 87 years (median: 72 years). Participants were recruited from a wide range of care settings with the majority being acute care settings. Almost all studies were conducted in the regions of Europe and America. Of the 17 included studies, two (223 participants) compared reactive air surfaces with surfaces that were not well described and therefore could not be classified. We analysed data for five comparisons: reactive air surfaces compared with (1) alternating pressure (active) air surfaces (seven studies with 1728 participants), (2) foam surfaces (four studies with 229 participants), (3) reactive water surfaces (one study with 37 participants), (4) reactive gel surfaces (one study with 66 participants), and (5) another type of reactive air surface (two studies with 223 participants). Of the 17 studies, seven (41.2%) presented findings which were considered at high overall risk of bias. Primary outcome: Pressure ulcer incidence Reactive air surfaces may reduce the proportion of participants developing a new pressure ulcer compared with foam surfaces (risk ratio (RR) 0.42; 95% confidence interval (CI) 0.18 to 0.96; I(2) = 25%; 4 studies, 229 participants; low‐certainty evidence). It is uncertain if there is a difference in the proportions of participants developing a new pressure ulcer on reactive air surfaces compared with: alternating pressure (active) air surfaces (6 studies, 1648 participants); reactive water surfaces (1 study, 37 participants); reactive gel surfaces (1 study, 66 participants), or another type of reactive air surface (2 studies, 223 participants). Evidence for all these comparisons is of very low certainty. Included studies have data on time to pressure ulcer incidence for two comparisons. When time to pressure ulcer incidence is considered using a hazard ratio (HR), low‐certainty evidence suggests that in the nursing home setting, people on reactive air surfaces may be less likely to develop a new pressure ulcer over 14 days' of follow‐up than people on alternating pressure (active) air surfaces (HR 0.44; 95% CI 0.21 to 0.96; 1 study, 308 participants). It is uncertain if there is a difference in the hazard of developing new pressure ulcers between two types of reactive air surfaces (1 study, 123 participants; very low‐certainty evidence). Secondary outcomes Support‐surface‐associated patient comfort: the included studies have data on this outcome for three comparisons. We could not pool any data as comfort outcome measures differed between included studies; therefore a narrative summary is provided. It is uncertain if there is a difference in patient comfort responses between reactive air surfaces and foam surfaces over the top of an alternating pressure (active) air surfaces (1 study, 72 participants), and between those using reactive air surfaces and those using alternating pressure (active) air surfaces (4 studies, 1364 participants). Evidence for these two comparisons is of very low certainty. It is also uncertain if there is a difference in patient comfort responses between two types of reactive air surfaces (1 study, 84 participants; low‐certainty evidence). All reported adverse events: there were data on this outcome for one comparison: it is uncertain if there is a difference in adverse events between reactive air surfaces and foam surfaces (1 study, 72 participants; very low‐certainty evidence). The included studies have no data for health‐related quality of life and cost‐effectiveness for all five comparisons. AUTHORS' CONCLUSIONS: Current evidence is uncertain regarding any differences in the relative effects of reactive air surfaces on ulcer incidence and patient comfort, when compared with reactive water surfaces, reactive gel surfaces, or another type of reactive air surface. Using reactive air surfaces may reduce the risk of developing new pressure ulcers compared with using foam surfaces. Also, using reactive air surfaces may reduce the risk of developing new pressure ulcers within 14 days compared with alternating pressure (active) air surfaces in people in a nursing home setting. Future research in this area should consider evaluation of the most important support surfaces from the perspective of decision‐makers. Time‐to‐event outcomes, careful assessment of adverse events and trial‐level cost‐effectiveness evaluation should be considered in future studies. Trials should be designed to minimise the risk of detection bias; for example, by using digital photography and adjudicators of the photographs being blinded to group allocation. Further review using network meta‐analysis will add to the findings reported here. People treated with reactive air surfaces may be at lower risk of developing a new pressure ulcer than those treated with alternating pressure (active) air surfaces over 14 days of follow-up in the nursing home setting. Support surface associated patient comfort (median follow-up duration 11 days, minimum 5 days, maximum 14 days) The 4 studies report a range of different measures for this outcome and they cannot be pooled. -1364 (4 RCTs) ⊕⊝⊝⊝ Very low d,e It is uncertain if there is a difference in support surface associated patient comfort between reactive air surfaces and alternating pressure (active) air surfaces. Included studies did not report this outcome. Included studies did not report this outcome. Cost-effectiveness Included studies did not report this outcome. Reactive air surfaces may reduce the proportion of participants developing new pressure ulcers compared with foam surfaces. Included studies did not report this outcome. Support surface associated patient comfort Allman 1987 reported this outcome in which participants were asked to choose a response to a com--72 ⊕⊝⊝⊝ Very low c,d It is uncertain if there is a difference in patient comfort re-Follow-up: 13 days fort-related question from categories: 'Very comfortable', 'Comfortable', 'Uncomfortable', or 'Very uncomfortable'. More people using reactive air surfaces may have responded that they were comfortable or very comfortable than those using foam surfaces on top of an alternating pressure (active) air surfaces (P = 0.04). (1 RCT) sponses between reactive air surfaces and foam surfaces on top of an alternating pressure (active) air surfaces. All reported adverse events Follow-up: 13 days Only Allman 1987 (72 participants) reported this outcome (see Table 1 ). -72 (1 RCT) It is uncertain if there is a difference in adverse event rates between reactive air surfaces and foam surfaces. Health-related quality of life Included studies did not report this outcome. Cost-effectiveness Included studies did not report this outcome. *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect. a Downgraded once for risk of bias (1 study contributing 8% weight in the meta-analysis had domains other than performance bias at high risk of bias and all the remaining studies had domains other than performance bias at low or unclear risk of bias). b Downgraded once for imprecision as, despite the fact that the optimal information size was met, the 95% CI crossed RR = 0.75. c Downgraded once for unclear risk of bias. d Downgraded twice for imprecision due to the small sample size. It is uncertain if there is a difference in the proportion of participants developing a new ulcer between reactive air surfaces and reactive water surfaces. Time to pressure ulcer incidence The included study did not report this outcome. Follow-up: 13 days The included study did not report this outcome. All reported adverse events Follow-up: 13 days The included study did not report this outcome. Health-related quality of life The included study did not report this outcome. Cost-effectiveness The included study did not report this outcome. *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect. a Downgraded once for unclear overall risk of bias. b Downgraded twice for substantial imprecision because the OIS was not met and the confidence interval was very wide and crossed RRs = 0.75 and 1.25. It is uncertain if there is a difference in the proportion of participants developing a new ulcer between reactive air surfaces and reactive gel surfaces. Time to pressure ulcer incidence The included study did not report this outcome. Support surface associated patient comfort Follow-up: 13 days The included study did not report this outcome. All reported adverse events Follow-up: 13 days The included study did not report this outcome. Trusted evidence. Informed decisions. Better health. Cochrane Database of Systematic Reviews Pressure ulcers -also known as pressure injuries, pressure sores, decubitus ulcers and bed sores -are localised injuries to the skin or underlying so tissue (or both) caused by unrelieved pressure, shear or friction (NPIAP 2016) . Pressure ulcer severity is generally classified as follows, using the National Pressure Injury Advisory Panel (NPIAP) system (NPIAP 2016). • Stage 1: intact skin with a local appearance of non-blanchable erythema • Stage 2: partial-thickness skin loss with exposed dermis • Stage 3: full-thickness skin loss • Stage 4: full-thickness skin and tissue loss with visible fascia, muscle, tendon, ligament, cartilage or bone • Unstageable pressure injury: full-thickness skin and tissue loss that is obscured by slough or eschar so that the severity of injury cannot be confirmed • Deep tissue pressure injury: local injury of persistent, nonblanchable deep red, maroon, purple discolouration or epidermal separation revealing a dark wound bed or bloodfilled blister The stages described above are consistent with those described in another commonly used system, the International Classification of Diseases for Mortality and Morbidity Statistics (World Health Organization 2019). Pressure ulcers are complex wounds that are relatively common, a ecting people across di erent care settings. A systematic review found that prevalence estimates for people a ected by pressure ulcers in communities of the UK, USA, Ireland and Sweden ranged from 5.6 to 2300 per 10,000 depending on the nature of the population surveyed (Cullum 2016) . A subsequent cross-sectional survey of people receiving community health services in one city in the UK estimated that 1.8 people per 10,000 have a pressure ulcer (Gray 2018 ). Pressure ulcers confer a heavy burden in terms of personal impact and use of health-service resources. Having a pressure ulcer may impair physical, social and psychological activities (Gorecki 2009). Ulceration impairs health-related quality of life (Essex 2009); can result in longer institution stays (Theisen 2012); and increases the risk of systemic infection (Espejo 2018) . There is also substantial impact on health systems: a 2015 systematic review of 14 studies across a range of care settings in Europe and North America showed that costs related to pressure ulcer treatment ranged between EUR 1.71 and EUR 470.49 per person, per day (Demarré 2015). In the UK, the annual average cost to the National Health Service for managing one person with a pressure ulcer in the community was estimated to be GBP 1400 for a Stage 1 pressure ulcer and more than GBP 8500 for more severe stages (2015 /2016 Guest 2018) . In Australia, the annual cost of treating pressure ulcers was estimated to be AUD 983 million (95% confidence interval (CI) 815 million to 1151 million) at 2012/2013 prices (Nguyen 2015) . The serious consequences of pressure ulceration have led to an intensive focus on their prevention. Pressure ulcers are considered largely preventable. Support surfaces are specialised medical devices designed to relieve or redistribute pressure on the body, or both, in order to prevent pressure ulcers (NPIAP S3I 2007) . Types of support surface include, but are not limited to, integrated bed systems, mattresses and overlays (NPIAP S3I 2007) . The NPIAP Support Surface Standards Initiative (S3I) system can be used to classify types of support surface (NPIAP S3I 2007) . According to this system support surfaces may: • be powered (i.e. require electrical power to function) or nonpowered; • passively redistribute body weight (i.e. reactive pressure redistribution), or mechanically alternate the pressure on the body to reduce the duration of pressure (i.e. active pressure redistribution); • be made of a range of materials, including but not limited to: air cells, foam materials, fibre materials, gel materials, sheepskin for medical use and water-bags; • be constructed of air-filled cells that have small holes on the surface for blowing out air to dry skin (i.e. low air-loss feature) or have fluid-like characteristics via forcing filtered air through ceramic beads (i.e. air-fluidised feature), or have neither of these features. Full details of classifications of support surfaces are listed in Appendix 1. A widely used type of support surface is the reactive air bed or mattress (traditionally termed static air-filled bed or mattress). These beds or mattresses are made of air cells that remain constantly inflated with or without using electrically powered pumps (i.e. being static rather than dynamic) (Clark 2011 ; NPIAP S3I 2007) . Reactive air beds or mattresses can have low-airloss features designed to influence the microclimate environment by keeping the skin dry (since moisture is thought to potentially increase friction on skin and increase the risk of skin damage) (Clark 2011 ; Wounds International 2010) . Some reactive air mattresses can have air-fluidised features. Types of reactive air beds or mattresses include: powered or nonpowered reactive air mattresses (e.g. Repose static air mattress); powered or non-powered reactive low-air-loss mattresses (e.g. Low Air Loss mattress); and powered or non-powered reactive airfluidised air mattresses (e.g. Clinitron air-fluidised bed) (Shi 2018a ). The aim of using support surfaces to prevent pressure ulceration is to redistribute pressure beneath the body, thereby increasing blood flow to tissues and relieving the distortion of skin and so tissue (Wounds International 2010) . Reactive support surfaces achieve pressure redistribution by passive mechanisms, including immersion (i.e. 'sinking' of the body into a support surface) and envelopment (i.e. conforming of a support surface to the irregularities in the body). These devices distribute the pressure over a greater area, thereby reducing the magnitude of the pressure at specific sites (Clark 2011). national guidelines (EPUAP/NPIAP/PPPIA 2019 ; NICE 2014). Since the publication of the Cochrane Review, 'Support surfaces for pressure ulcer prevention' (McInnes 2015) , there has been a substantial increase in the number of relevant randomised controlled trials published in this area. The NPIAP S3I 2007 support surface-related terms and definitions have also been internationally recognised, and Cochrane has developed new methodological requirements, such as the use of GRADE assessments (Guyatt 2008) . These developments necessitate an update of the evidence base. In considering this evidence update, we took into account the size and complexity of the previously published review (McInnes 2015) , which includes all types of support surface. An alternative approach is to split the original review into multiple new titles, each with a narrower focus. We consulted on this splitting option via an international survey in August 2019. The potential new titles suggested were based on clinical use, the new terms and definitions related to support surfaces (NPIAP S3I 2007), a relevant network meta-analysis (Shi 2018a) , and current clinical practice guidelines (EPUAP/NPIAP/PPPIA 2019; NICE 2014). We received responses from 29 health professionals involved in pressure ulcer prevention activity in several countries (Australia, Belgium, China, Italy, the Netherlands and the UK). In total, 83% of respondents supported splitting the review into suggested titles and 17% were unsure (no respondent voted against splitting). The new review titles are as follows: • alternating pressure (active) air surfaces for preventing pressure ulcers • foam surfaces for preventing pressure ulcers • reactive air surfaces for preventing pressure ulcers • alternative reactive support surfaces (non-foam and non-airfilled) for preventing pressure ulcers We will bring the results of these new reviews together in an overview with a network meta-analysis (Salanti 2012) , in order to simultaneously compare all support surfaces and to rank them based on the probabilities of each being the most e ective for preventing pressure ulcers. This particular review compares reactive air beds, mattresses or overlays with any surface. To assess the e ects of reactive air beds, mattresses or overlays compared with any support surface on the incidence of pressure ulcers in any population in any setting. We included published and unpublished randomised controlled trials (RCTs), including multi-armed studies, cluster-RCTs and crossover trials, regardless of the language of publication. We excluded studies using quasi-random allocation methods (e.g. alternation). We included studies in any population, including those defined as being at risk of ulceration, as well as those with existing pressure ulcers at baseline (when the study measured pressure ulcer incidence). This review focused on reactive air beds or mattresses in general. Eligible studies included a specific bed, overlay or mattress with reactive or static pressure redistribution capabilities. These included, but were not limited to, specific reactive air mattresses identified in Shi 2018a; namely: • powered or non-powered reactive air mattresses (e.g. So lex static air mattress); or • powered or non-powered reactive low-air-loss mattresses (e.g. low-air-loss Hydrotherapy); or • powered or non-powered reactive air-fluidised mattresses (e.g. Clinitron air-fluidised bed). We included studies where two or more support surfaces were used sequentially over time or in combination, where the support surface(s) of interest were included in one of the study arms. We included studies comparing eligible reactive air beds, overlays or mattresses against any comparator defined as a support surface. Comparators could be: • non-reactive air surfaces, including: alternating pressure (active) air surfaces such as alternating pressure (or dynamic) air mattresses, foam mattresses, and non-foam and non-air-filled surfaces (e.g. reactive gel surfaces such as a gel pad used on an operating table, reactive fibre surfaces such as Silicore fibre overlay, reactive water surfaces, reactive sheepskin surfaces such as Australian Medical Sheepskins overlay), or • a di erent type of reactive air surface. We included studies in which co-interventions (e.g. repositioning) were delivered, provided that the co-interventions were the same in all arms of the study (i.e. interventions randomised were the only systematic di erence). We considered the primary and secondary outcomes described below. If a study did not report any review-relevant outcomes but was otherwise eligible (i.e. eligible study design, participants and interventions), we contacted the study authors (where possible) to clarify whether they had measured a relevant outcome but did not report it. We considered the study as 'awaiting classification' if we could not establish whether it measured an outcome or not. We excluded the study if the study authors confirmed that they did not measure any review-relevant outcomes. If a study measured an outcome at multiple time points, we considered the outcome measures at three months to be the primary endpoint for this review (Schoonhoven 2007) , regardless of the time points specified as being of primary interest by the study. If the study did not report three-month outcome measures, we considered those closest to three months. Where a study only reported a single time point, we included this in this review. Where the study did not specify a time point for outcome measurement, we assumed this was the final duration of follow-up noted. Trusted evidence. Informed decisions. Better health. Our primary outcome was pressure ulcer incidence. We recorded two outcome measures (the proportion of participants developing a new pressure ulcer; and time to pressure ulcer incidence), where available. We considered the proportion of participants developing a new pressure ulcer as the primary outcome for this review. Our preferred measure was time to pressure ulcer incidence; however, we did not expect it to be reported in many studies. We extracted and analysed time-to-event data but focused on the binary outcome in our conclusions. We accepted the study authors' definitions of an incident ulcer regardless of which pressure ulcer severity classification system was used to measure or grade new pressure ulcers. We also considered the outcome of pressure ulcer incidence irrespective of whether studies reported ulcers by stages or as a non-stratified value. We did not consider subjective outcome measures (e.g. 'better' or 'worse' skin condition) as measures of pressure ulcer incidence. • Support-surface-associated patient comfort. We considered patient comfort outcome data in this review only if the evaluation of patient comfort was pre-planned and was systematically conducted across all participants in the same way in a study. The definition and measurement of this outcome varied from one study to another; for example, the proportion of participants who report comfort, or comfort measured by a scale with continuous (categorical) numbers. We planned to include these data with di erent measurements in separate meta-analyses when possible. • All reported adverse events (measured using surveys or questionnaires, other data capture process or visual analogue scale). We included data where study authors specified a clear method for collecting adverse event data. Where available, we extracted data on all serious and all non-serious adverse events as an outcome. We recorded where it was clear that events were reported at the participant level or whether multiple events per person were reported, in which case appropriate adjustments were required for data clustering (Peryer 2019). We considered the assessment of any event in general defined as adverse by participants, health professionals, or both. • Health-related quality of life (measured using a standardised generic questionnaire such as EQ-5D (Herdman 2011), 36item Short Form (SF-36; Ware 1992), or pressure ulcer-specific questionnaires such as the PURPOSE Pressure Ulcer Quality of Life (PU-QOL) questionnaire (Gorecki 2013), at noted time points). We did not include ad hoc measures of quality of life or qualitative interviews of quality of life because these measures were unlikely to be validated. • Cost-e ectiveness: within-trial cost-e ectiveness analysis comparing mean di erences in e ects with mean cost di erences between the two arms. We extracted data on incremental mean cost per incremental gain in benefit (incremental cost-e ectiveness ratio (ICER)). We also considered other measures of relative cost-e ectiveness (e.g. net monetary benefit, net health benefit). We searched the following electronic databases to identify reports of relevant clinical trials: • We identified other potentially eligible studies or ancillary publications by searching the reference lists of retrieved included studies, as well as relevant systematic reviews, meta-analyses and health technology assessment reports. When necessary, we contacted authors of key papers and abstracts to request further information about their trials. We did not perform a separate search for adverse e ects of interventions used. We considered adverse e ects described in included studies only. Trusted evidence. Informed decisions. Better health. We carried out data collection and analysis according to the methods stated in the published protocol (Shi 2020) , which were based on the Cochrane Handbook for Systematic Reviews of Interventions (Li 2019). Changes from the protocol or previous published versions of the review are documented in Di erences between protocol and review. One review author re-checked the RCTs included in McInnes 2015 for eligibility (CS). Two review authors or researchers (CS and Asmara Jammali-Blasi, or JCD) independently assessed the titles and abstracts of the new search results for relevance using Rayyan (Ouzzani 2016) (Di erences between protocol and review), and then independently inspected the full text of all potentially eligible studies. The two review authors or researchers (CS and Asmara Jammali-Blasi, or JCD) resolved any disagreements through discussion or by involving another review author if necessary. One review author checked data from the studies included in McInnes 2015 and extracted additional data where necessary (CS). A second review author or researcher checked any new data extracted (SR, VL, EM, Zhenmi Liu, Gill Norman, or Melanie Stephens) . For new included studies, one review author (CS) independently extracted data and another review author or researcher checked all data (SR, VL, EM, Zhenmi Liu, Gill Norman, or Melanie Stephens) (Di erences between protocol and review). Any disagreements were resolved through discussion and, if necessary, with the involvement another review author. Where necessary, we contacted the authors of included studies to clarify data. We extracted these data using a pre-prepared data extraction form: • basic characteristics of studies (first author, publication type, publication year and country); • funding sources; • care setting; • characteristics of participants (trial eligibility criteria, average age in each arm or in a study, proportions of participants by gender and participants' baseline skin status); • support surfaces being compared (including their descriptions); • details on any co-interventions; • duration of follow-up; • the number of participants enrolled; • the number of participants randomised to each arm; • the number of participants analysed; • participant withdrawals with reasons; • the number of participants developing new ulcers (by ulcer stages where possible); • data on time to pressure ulceration; • support-surface-associated patient comfort; • adverse event outcome data; • health-related quality of life outcome data; and • cost-e ectiveness outcome data. We (CS and NC) classified specific support surfaces in the included studies into intervention groups using the NPIAP S3I support surface-related terms and definitions (NPIAP S3I 2007) . Therefore, to accurately assign specific support surfaces to intervention groups, we extracted full descriptions of support surfaces from included studies, and when necessary supplemented the information with that from external sources such as other publications about the same support surface, manufacturers' or product websites and expert clinical opinion (Shi 2018b ). If we were unable to define any of the specific support surfaces evaluated in an included study, we extracted available data and reported these as additional data outside the main review results. Two review authors or researchers (CS and SR, VL, EM, Zhenmi Liu, Gill Norman, or Melanie Stephens) independently assessed risk of bias of each included study using the Cochrane 'Risk of bias' tool (see Appendix 3). This tool has seven specific domains: sequence generation (selection bias), allocation concealment (selection bias), blinding of participants and personnel (performance bias), blinding of outcome assessment (detection bias), incomplete data (attrition bias), selective outcome reporting (reporting bias), and other issues (Higgins 2017) . We assessed performance bias, detection bias and attrition bias separately for each of the review outcomes (Higgins 2017) . We noted that it is o en impossible to blind participants and personnel in device trials. In this case, performance bias may be introduced if knowledge of treatment allocation results in deviations from intended interventions, di erential use of co-interventions or care between groups not specified in the study protocol that may influence outcomes. We attempted to understand if, and how, included studies compensated for challenges in blinding; for example, implementing strict protocols to maximise consistency of cointerventions between groups to reduce the risk of performance bias. We also noted that pressure ulcer incidence is a subjective outcome. Compared with blinded assessment, non-blinded assessment of subjective outcomes tends to be associated with more optimistic e ect estimates of experimental interventions in RCTs (Hróbjartsson 2012). Therefore, we judged non-blinded outcome assessment as being at high risk of detection bias. In this review, we included the issues of di erential diagnostic activity and unit of analysis under the domain of 'other issues'. For example, unit of analysis issues occurred where a cluster-randomised trial had been undertaken but analysed at the individual level in the study report. For the studies included in McInnes 2015, one review author (CS) checked the 'Risk of bias' judgements and, where necessary, updated them. A second review author or researcher (SR, VL, EM, Zhenmi Liu, Gill Norman, or Melanie Stephens) checked any updated judgement. We assigned each 'Risk of bias' domain a judgement of high, low, or unclear risk of bias. We resolved any discrepancy through discussion and by involving another review author where necessary. Where possible, useful and feasible, when a lack of reported information resulted in a judgement of unclear risk of bias, we planned to contact study authors for clarification. We present our assessment of risk of bias for the proportion of participants developing a new pressure ulcer outcome using two 'Risk of bias' summary figures. One is a summary of bias for each item across all studies, and the second shows a cross-tabulation of each study by all of the 'Risk of bias' items. Trusted evidence. Informed decisions. Better health. Once we had given our judgements for all 'Risk of bias' domains, we judged the overall risk of bias for each outcome across studies as: • low risk of bias, if we judged all domains to be at low risk of bias; • unclear risk of bias, if we judged one or more domains to be at unclear risk of bias and other domains were at low risk of bias but no domain was at high risk of bias; or • high risk of bias, as long as we judged one or more domains as being at high risk of bias, or all domains had unclear 'Risk of bias' judgements, as this could substantially reduce confidence in the result. We resolved any discrepancy between review authors through discussion and by involving another review author where necessary. For studies using cluster randomisation, we planned to consider the risk of bias in relation to recruitment bias, baseline imbalance, loss of clusters, incorrect analysis and comparability with individually randomised studies (Eldridge 2019; Higgins 2019; Appendix 3). However, we did not include any studies with a cluster design. For meta-analysis of pressure ulcer incidence data, we present the risk ratio (RR) with its 95% confidence interval (CI). For continuous outcome data, we present the mean di erence (MD) with 95% CIs for studies that use the same assessment scale. If studies reporting continuous data used di erent assessment scales, we planned to report the standardised mean di erence (SMD) with 95% CIs. However, this was not undertaken in the review. For time-to-event data (time to pressure ulcer incidence), we present the hazard ratio (HR) with its 95% CI. If included studies reporting time-to-event data did not report an HR, when feasible, we estimated this using other reported outcomes (such as numbers of events) through employing available statistical methods (Parmar 1998; Tierney 2007) . We noted whether studies presented outcomes at the level of cluster (e.g. ward, research site) or at the level of participants. We also recorded whether the same participant was reported as having multiple pressure ulcers. Unit of analysis issues may occur if studies randomise at the cluster level but the incidence of pressure ulcers is observed and data are presented and analysed at the level of participants (clustered data). We noted whether data regarding participants within a cluster were (incorrectly) treated as independent within a study, or were analysed using within-cluster analysis methods. If clustered data were incorrectly analysed, we recorded this as part of the 'Risk of bias' assessment. If a cluster-RCT was not correctly analysed, we planned to use the following information to adjust for clustering ourselves where possible, in accordance with guidance in the Cochrane Handbook for Systematic Reviews of Interventions . • The number of clusters randomly assigned to each intervention, or the average (mean) number of participants per cluster. • Outcome data ignoring the cluster design for the total number of participants. • Estimate of the intra-cluster (or intra-class) correlation coe icient (ICC). However, we did not identify any cluster-RCTs in this review. For cross-over trials, we only considered outcome data at the first intervention phase (i.e. prior to cross-over) as eligible. If a study had more than two eligible study groups, where appropriate, we combined results across these arms to make single pair-wise comparisons . Data are commonly missing from study reports. Reasons for missing data could be the exclusion of participants a er randomisation, withdrawal of participants from a study, or loss to follow-up. The exclusion of these data from analysis may break the randomisation and potentially introduces bias. Where there were missing data, and where relevant, we contacted study authors to pose specific queries about these data. In the absence of other information, for pressure ulcer incidence we assumed that participants with missing data did not develop new pressure ulcers for the main analysis (i.e. we added missing data to the denominator but not the numerator). We examined the impact of this assumption through undertaking a sensitivity analysis (see Sensitivity analysis). When a study did not specify the number of randomised participants prior to dropout, we used the available number of participants as the number randomised. Assessing heterogeneity can be a complex, multifaceted process. Firstly, we considered clinical and methodological heterogeneity; that is, the extent to which the included studies varied in terms of participant, intervention, outcome, and other characteristics including duration of follow-up, clinical settings, and overall studylevel 'Risk of bias' judgement (Deeks 2019). In terms of the duration of follow-up, in order to assess the relevant heterogeneity, we recorded and categorised assessment of outcome measures as follows: • up to eight weeks (short-term); • more than eight weeks to 16 weeks (medium-term); and • more than 16 weeks (long-term). We supplemented this assessment of clinical and methodological heterogeneity with information regarding statistical heterogeneity assessed using the Chi 2 test. We considered a P value of less than 0.10 to indicate statistically significant heterogeneity given that the Chi 2 test has low power, particularly in the case where studies included in a meta-analysis have small sample sizes. We carried out this statistical assessment in conjunction with the I 2 statistic (Higgins 2003) , and the use of prediction intervals for randome ects meta-analyses (Borenstein 2017; Riley 2011). The I 2 statistic is the percentage of total variation across studies due to heterogeneity rather than chance (Higgins 2003 Cochrane Database of Systematic Reviews heterogeneity (Higgins 2003) . For random-e ects models where the meta-analysis had more than 10 included studies and no clear funnel plot asymmetry, we also planned to present 95% prediction intervals (Deeks 2019). We planned to calculate prediction intervals following methods proposed by Borenstein 2017. Random-e ects analyses produce an average treatment e ect, with 95% confidence intervals indicating where the true population average value is likely to lie. Prediction intervals quantify variation away from this average due to between-study heterogeneity. The interval conveys where a future study treatment e ect estimate is likely to fall based on the data analysed to date (Riley 2011). Prediction intervals are always wider than confidence intervals (Riley 2011). It is important to note that prediction intervals reflect heterogeneity of any source, including from methodological issues as well as clinical variation. For this reason some authors have suggested that prediction intervals are best calculated for studies at low risk of bias to ensure intervals that have meaningful clinical interpretation (Riley 2011). We had planned to calculate prediction intervals for all analyses to assess heterogeneity and then to explore the impact of risk of bias in subgroup analysis stratified by study risk of bias assessment as detailed below. However, we did not calculate any prediction interval because all conducted metaanalyses contained fewer than 10 studies. We followed the systematic framework recommended by Page 2019 to assess risk of bias due to missing results (non-reporting bias) in the meta-analysis of pressure ulcer incidence data. To make an overall judgement about risk of bias due to missing results, we did the following. • Identified whether pressure ulcer incidence data were unavailable by comparing the details of outcomes in trials registers, protocols or statistical analysis plans (if available) with reported results. If the above information sources were unavailable, we compared outcomes in the conference abstracts or in the methods section of the publication, or both, with the reported results. If we found non-reporting of study results, we then judged whether the non-reporting was associated with the nature of findings by using the 'Outcome Reporting Bias In Trials' (ORBIT) system (Kirkham 2018). • Assessed the influence of definitely missing pressure ulcer incidence data on meta-analysis. • Assessed the likelihood of bias where a study had been conducted but not reported in any form. For this assessment, we considered whether the literature search was comprehensive and planned to produce a funnel plot for meta-analysis for seeking more evidence about the extent of missing results, provided there were at least 10 included studies (Peters 2008; Salanti 2014). However, we did not produce a funnel plot for any meta-analysis because all analyses in this review had fewer than 10 included studies. We summarised the included studies narratively and synthesised included data by using meta-analysis where applicable. We structured comparisons according to type of comparator and then by outcomes, ordered by follow-up period. We considered clinical and methodological heterogeneity and undertook pooling when studies appeared appropriately similar in terms of participants, support surfaces, and outcome type. Where statistical synthesis of data from more than one study was not possible or considered inappropriate, we conducted a narrative review of eligible studies. Once the decision to pool was made, we used a random-e ects model, which estimated an underlying average treatment e ect from studies. Conducting meta-analysis with a fixed-e ect model in the presence of even minor heterogeneity may provide overly narrow confidence intervals. We used the Chi 2 test and I 2 statistic to quantify heterogeneity but not to guide choice of model for meta-analysis (Borenstein 2009). We exercised caution when metaanalysed data were at risk of small-study e ects because use of a random-e ects model may be unsuitable in this situation. In this case, or where there were other reasons to question the choice of a fixed-e ect or random-e ects model, we assessed the impact of the approach using sensitivity analyses to compare results from alternate models (Thompson 1999). We performed meta-analyses largely using Review Manager 5.4 (Review Manager 2020). We presented data using forest plots where possible. For dichotomous outcomes, we presented the summary estimate as a RR with 95% CIs. Where continuous outcomes were measured, we presented the MD with 95% CIs; we planned to report SMD estimates where studies measured the same outcome using di erent methods. For time-to-event data, we presented the summary estimates as HRs with 95% CIs. When important heterogeneity occurred, we planned to follow these steps, proposed by Cipriani 2013 and Deeks 2019, to investigate further: • check the data extraction and data entry for errors and possible outlying studies; • if outliers existed, perform sensitivity analysis by removing them; and • if heterogeneity was still present, we planned to perform subgroup analyses for study-level characteristics (see below) in order to explain heterogeneity as far as possible. However, we did not undertake any subgroup analysis because metaanalyses in this review included fewer than 10 studies. We investigated heterogeneity using the methods described in the Cochrane Handbook for Systematic Reviews of Interventions (Deeks 2019). We planned to perform subgroup analyses for binary and categorical factors (or meta-regression for continuous factors) to determine whether the size of treatment e ects was influenced by these four study-level characteristics: • risk of bias (binary: low or unclear risk of bias; and high risk of bias (Schulz 1995)); • settings (categorical: acute care and other hospital settings; long-term care settings; operating theatre setting; and intensive care unit); • baseline skin status (categorical: participants at risk, of mixed skin status or non-reporting; non-blanchable erythema; existing ulcers of Stage 2 or serious (Shi 2018c)); and • follow-up duration (continuous). We did not perform subgroup analysis or meta-regression when the number of studies included in the meta-analysis was not reasonable (i.e. fewer than 10). We planned to compare subgroup findings using the 'Test for Subgroup Di erences' in Review Manager 5.4 (Review Manager 2020). We conducted sensitivity analyses for the following factors, to assess the robustness of meta-analysis of data on pressure ulcer incidence. • Impact of the selection of pressure ulcer incidence outcome measure. The proportion of participants developing a new pressure ulcer was the primary outcome measure for this review but we also analysed time to pressure ulcer development, where data were available. • Impact of missing data. The primary analysis assumed that participants with missing data did not develop new pressure ulcers. We also analysed pressure ulcer incidence by only including data for the participants for whom we had endpoint data (complete cases). We noted that when a study only had complete case data (i.e. missing data or the numbers of participants randomised were not reported), complete case data were considered in the related main analysis (Di erences between protocol and review). • Impact of altering the e ects model used. We used a randome ects model for the main analysis followed by a fixed-e ect analysis. We presented the main, pooled results of the review in 'Summary of findings' tables, which we created using GRADEpro GDT so ware. These tables present key information concerning the certainty of evidence, the magnitude of the e ects of the interventions examined and the sum of available data for the main outcomes (Schünemann 2019). The tables also include an overall grading of the certainty of the evidence associated with each of the main outcomes that we assessed using the GRADE approach. The GRADE approach defines the certainty of a body of evidence as the extent to which one can be confident that an estimate of e ect or association is close to the true quantity of specific interest. The GRADE assessment involves consideration of five factors: within-trial risk of bias, directness of evidence, heterogeneity, precision of e ect estimates, and risk of publication bias (Schünemann 2019). The certainty of evidence can be assessed as being high, moderate, low or very low; RCT evidence has the potential to be high-certainty. We did not downgrade the certainty of evidence for the risk of bias factor in a specific circumstance. That is, if the blinding of participants and personnel was the only domain resulting in our judgement of overall high risk of bias for the included studies; however for these studies it was impossible to blind participants and personnel. When downgrading for imprecision, we followed the methods described in Guyatt 2011: either considering both the optimal information size (OIS) and the 95% CI of each meta-analysis if they were estimable; or considering the sample size, the number of events and other e ectiveness indicators if the calculation of OIS and undertaking a meta-analysis were not applicable. Where necessary, we used the GRADE 'default' minimum important di erence values (RR = 1.25 and 0.75) as the thresholds to judge if a 95% CI was wide (imprecise) so as to include the possibility of clinically important harm and benefit (Guyatt 2011 ). We presented a separate 'Summary of findings' table for all but one comparison evaluated in this review. The exception was the comparison of reactive air surfaces versus another type of reactive air surface (Di erences between protocol and review). We presented these outcomes in the 'Summary of findings' tables: • proportion of participants developing a new pressure ulcer; • time to pressure ulcer incidence; • support-surface-associated patient comfort; • all reported adverse events; • health-related quality of life; and • cost-e ectiveness. We prioritised the time points and method of outcome measurement specified in Types of outcome measures for presentation in 'Summary of findings' tables. Where we did not pool data for some outcomes within a comparison, we conducted a GRADE assessment for each of these outcomes and presented these assessments in a narrative format in 'Summary of findings' tables (Di erences between protocol and review). See Characteristics of included studies; Characteristics of excluded studies; Characteristics of studies awaiting classification; Characteristics of ongoing studies. Cochrane Database of Systematic Reviews as well as the clinical practice guidelines listed in Searching other resources. In total, we included 17 studies (with 19 publications) in the review, of which one was an unpublished report (Cobb 1997) . See Figure 1 . Cochrane Database of Systematic Reviews Included studies Of the 17 included RCTs, 16 had a parallel group design; 15 with two arms, and one with three arms (Sideranko 1992). One study was a two-arm, cross-over design trial and we only considered data prior to cross-over in this review (Van Leen 2013). Of the 17 studies, four were conducted at more than one research site ( 1987; Bennett 1998; Cobb 1997; Finnegan 2008; Lazzara 1991; Sideranko 1992) . Of the included studies, the median of the duration of follow-up was 14 days (range: five days to six months). The 17 included studies enrolled a total of 2604 participants (median study sample size: 83 participants; range: 16 to 1074). The average participant age was specified for 16 studies and ranged between 56 and 87 years (median: 72 years). Bennett 1998 did not specify the average participant age but stated that all participants were more than 80 years old. The sex of the participants was specified for 2511 participants in the 17 studies: 1125 (44.8%) were male and 1386 (55.2%) were female. Of the 17 studies, 13 (2335 participants) recruited people at risk of having a new ulcer with risk assessed largely using the Waterlow, Norton or Braden scales. In 10 of the 13 studies, 2033 (87.1%) participants were free of pressure ulcers at baseline. In three studies, 302 (12.9%) participants with superficial ulcers were enrolled (Bennett 1998; Cavicchioli 2007; Malbrain 2010) . In two studies, 112 participants with existing severe full-thickness pressure ulcers were enrolled (Allman 1987; Finnegan 2008). One study (100 participants; Inman 1993) did not specify the skin status at baseline, and the final included study (57 participants; Sideranko 1992) stated that all participants were free of ulcers at baseline. Participants were recruited from a variety of settings, including: • Cochrane Database of Systematic Reviews participants and RIK® microfluid static overlay for the remaining 50 of 55 control participants (Vermette 2012) . Eleven studies specified the co-interventions they applied (e.g. repositioning, cushions) (Beeckman 2019; Bennett 1998; Cooper 1998; Finnegan 2008; Inman 1993; Jiang 2014; Malbrain 2010; Price 1999; Van Leen 2011; Van Leen 2013; Vermette 2012) . All but one of these stated or indicated that the same co-interventions were applied in all study groups. However, Inman 1993 stated that twohourly repositioning was applied in the standard hospital surface arm but did not specify if any co-intervention was applied in the reactive air surfaces arm. Of the 17 studies, 12 specified the details of funding sources, including nine that were completely or partly funded by industry or received mattresses under evaluation from industries (Allman 1987; Beeckman 2019; Bennett 1998; Cooper 1998; Finnegan 2008; Inman 1993; Lazzara 1991; Price 1999; Takala 1996) . Jiang 2014 was supported by public funding, and two studies noted no funding support (Van Leen 2011; Vermette 2012). We excluded 154 studies (with 201 records). The main reasons for exclusion were: irrelevant or ineligible interventions (67 studies); ineligible study design (e.g. non-RCT, reviews, commentary articles; 52 studies); studies focused on the treatment rather than prevention of pressure ulcers (20 studies); incorrect randomisation and non-randomised methods (eight studies); studies with ineligible outcomes (four studies); clinical trials that were withdrawn (two studies; NCT02634892; NCT02735135); and ineligible participants (healthy subjects; one study). We also identified eight duplicates in screening the full-texts (see Figure 1 ). We did not identify any ongoing studies. There were six studies (six records) for which we could not make eligibility decisions. In one case (Gardner 2008), we were unable to determine whether the study used foam surfaces. For the five remaining studies, we were unable to obtain the full-texts (in part due to more limited access to intra-library loans during the COVID-19 period) despite making extensive e orts (Chaloner 2000b; Henn 2004; Knight 1999; Mastrangelo 2010a; Melland 1998 ). We summarise 'Risk of bias' assessments for the primary outcome of this review in Figure 2 and Cochrane Database of Systematic Reviews Random sequence generation (selection bias) Allocation concealment (selection bias) Blinding of participants and personnel (performance bias): All outcomes Blinding of outcome assessment (detection bias): All outcomes Incomplete outcome data (attrition bias): All outcomes Selective reporting (reporting bias) Other bias Random sequence generation (selection bias) Allocation concealment (selection bias) Blinding of participants and personnel (performance bias): All outcomes Blinding of outcome assessment (detection bias): All outcomes Incomplete outcome data (attrition bias): All outcomes Selective reporting ( We ran a comprehensive search and considered the risk of having missed published reports to be low. We were able to locate one study from other resources and one unpublished report (Allman 1987 and Cobb 1997, respectively) . We were unable to assess the risk of non-publication of studies with negative findings as we could not present funnel plots given the small number of included studies in each analysis. See: Summary of findings 1 Reactive air surfaces compared with alternating pressure (active) air surfaces for pressure ulcer prevention; Summary of findings 2 Reactive air surfaces compared with foam surfaces for pressure ulcer prevention; Summary of findings 3 Reactive air surfaces compared with reactive water surfaces for pressure ulcer prevention; Summary of findings 4 Reactive air surfaces compared with reactive gel surfaces for pressure ulcer prevention See Summary of findings 1; Summary of findings 2; Summary of findings 3; Summary of findings 4. Unless otherwise stated, random-e ects analysis was used throughout. Each pooled result presented is an average e ect, rather than a common e ect and should be interpreted as such. We have not reported data from the three studies with comparator group surfaces that we could not classify in the main body of the results (Bennett 1998; Inman 1993; Vermette 2012) . For completeness, we summarise the results of these studies in Appendix 4. We performed data analyses for the following comparisons and outcomes. Where applicable, we performed pre-specified sensitivity analyses as noted in Sensitivity analysis. Sideranko 1992) and their data were pooled. It is uncertain if there is a di erence in the proportion of participants developing a new ulcer between reactive air surfaces (19/849 (2.2%)) and alternating pressure (active) air surfaces (32/799 (4.0%)). The RR is 0.62 (95% CI 0.35 to 1.11; I 2 = 3%; Analysis 1.1). Evidence is of very low certainty, downgraded twice for high risk of bias in domains other than performance bias for four studies contributing over 54% weight in the meta-analysis, and once for imprecision as, despite the fact that the OIS was met, the 95% CI was wide and crossed RR = 0.75. We considered the studies in Analysis 1.1 as heterogeneous in terms of care settings, skin status at baseline and overall 'Risk of bias. However, we did not perform any pre-specified subgroup analysis because, as noted in Subgroup analysis and investigation of heterogeneity, the number of included studies was fewer than 10, meaning it would be di icult to meaningfully interpret the results. • Sensitivity analysis with complete case data . This resulted in a RR of 0.62 (95% CI 0.35 to 1.11; I 2 = 3%). The result was consistent with the main analysis (Appendix 5). Cochrane Database of Systematic Reviews of 0.58 (95% CI 0.34 to 1.00; I 2 = 3%) and this was consistent with the main analysis (Appendix 5). Beeckman 2019 (308 participants) reported this outcome. Lowcertainty evidence suggests that people treated with reactive air surfaces may be at lower risk of developing a new pressure ulcer than those treated with alternating pressure (active) air surfaces over 14 days' follow-up in a nursing home setting (HR 0.44, 95% CI 0.21 to 0.96; Analysis 1.2). These results are sensitive to the choice of format for the primary outcome measure so they should be interpreted cautiously. Evidence certainty was downgraded twice for high risk of detection bias (Appendix 5). Support-surface-associated patient comfort (median follow-up duration 11 days, minimum 5 days, maximum 14 days) Four studies (1364 participants) reported this outcome (Cavicchioli 2007; Finnegan 2008; Jiang 2014; Price 1999) . The four studies reported a range of di erent measures for this outcome and they cannot be pooled (see Table 2 ). We are uncertain if there is a di erence in patient comfort between reactive air surfaces and alternating pressure (active) air surfaces. Evidence was of very low certainty, downgraded once for high overall risk of bias in three small studies but unclear risk of bias in one large study, and twice for substantial inconsistency. Not reported. Not reported. Not reported. Four studies (236 participants) compared reactive air surfaces with foam surfaces (Allman 1987; Takala 1996; Van Leen 2011; Van Leen 2013) . Of these studies, Allman 1987 compared reactive air surfaces with the use of foam surfaces (19 mm thick foam pad) on top of alternating pressure (active) air surfaces. Proportion of participants developing a new pressure ulcer (follow-up duration minimum 13 days, maximum 6 months) All four studies (236 participants) reported this outcome and the data of 229 participants were available for analysis. Reactive air surfaces (12/113 (10.6%)) may reduce the proportion of participants developing a new pressure ulcer compared with foam surfaces (32/116 (27.6%)); however, the evidence is of low certainty. The RR is 0.42 (95% CI 0.18 to 0.96; I 2 = 25%; Analysis 2.1). Evidence certainty was downgraded once for risk of bias (one study contributing 8% weight in the meta-analysis had domains other than performance bias at high risk of bias and all the remaining studies had domains other than performance bias at unclear risk of bias) and once for imprecision as, despite the fact that the OIS was met, the 95% CI crossed RR = 0.75. The included studies did not report data on time to pressure ulcer incidence. We considered the studies in Analysis 2.1 as heterogeneous in terms of follow-up durations, care settings, and overall 'risk of bias' and there was an indication of statistical heterogeneity (Tau 2 = 0.21, Chi 2 test P value = 0.26 and I 2 = 25%). We did not perform any prespecified subgroup analysis because, as noted in Subgroup analysis and investigation of heterogeneity, the number of included studies was fewer than 10, meaning it would be di icult to meaningfully interpret the results. • Sensitivity analysis with fixed-e ect (rather than randome ects) model . The use of a fixed-e ect model resulted in a RR of 0.40 (95% CI 0.23 to 0.72; I 2 = 25%). This remained consistent with the main analysis (Appendix 5). Only Allman 1987 (72 participants) reported this outcome in which participants were asked to choose a response to a comfort-related question from these categories: 'Very comfortable', 'Comfortable', 'Uncomfortable', or 'Very uncomfortable'. It is uncertain if there is a di erence in patient comfort responses between reactive air surfaces and foam surfaces on top of an alternating pressure (active) air surface (P = 0.04; very low-certainty evidence). Evidence certainty was downgraded once for unclear risk of bias, and twice for imprecision due to the small sample size. Only Allman 1987 (72 participants) reported this outcome (see Table 1 ). It is uncertain if there is a di erence in adverse event rates between reactive air surfaces and foam surfaces (very low-certainty evidence). Evidence certainty was downgraded once for unclear risk of bias, and twice for imprecision due to the small sample size. Not reported. Not reported. Sideranko 1992 compared reactive air surfaces with a reactive water mattress. Proportion of participants developing a new pressure ulcer (follow-up duration 9.5 days) Sideranko 1992 (37 participants) reported this outcome. It is uncertain if there is a di erence in the proportion of participants developing a new ulcer between reactive air surfaces (1/20 (5%)) and reactive water surfaces (2/17 (11.8%)). The RR is 0.43 (95% CI 0.04 to 4.29; Analysis 3.1). Evidence is of very low certainty, downgraded once for unclear overall risk of bias and twice for Cochrane Database of Systematic Reviews substantial imprecision because the OIS was not met and the 95% CI was very wide and crossed both RRs = 0.75 and 1.25. The included study did not report data on time to pressure ulcer incidence. Not reported. Lazzara 1991 compared reactive air surfaces with a reactive gel mattress. Lazzara 1991 (74 participants) reported this outcome and had analysable data for 66 participants. It is uncertain if there is a di erence in the proportion of participants developing a new ulcer between reactive air surfaces (10/33 (30.3%)) and reactive gel surfaces (8/33 (24.2%)). The RR is 1.25 (95% CI 0.56 to 2.77; Analysis 4.1). Evidence is of very low certainty, downgraded once for unclear overall risk of bias and twice for imprecision because the OIS was not met and the confidence interval was very wide, and crossed both RRs = 0.75 and 1.25. The included study did not report data on time to pressure ulcer incidence. Not reported. Two studies compared two di erent types of reactive air surfaces with each other: that is, EHOB versus KinAir (Cobb 1997) and So lex versus ROHO (Cooper 1998). We did not pool data from the two studies. We summarised study findings narratively below, and presented key outcome data in Table 3 . Both studies (223 participants) reported this outcome; see Table 3 . Neither study found a di erence in the proportions of participants developing a new pressure ulcer between EHOB and KinAir reactive air surface or between So lex and ROHO reactive air surface. Evidence is of very low certainty, downgraded once for unclear risk of bias (both studies were at unclear risk of bias in at least one domain), and twice for imprecision: sample sizes were small, there were very few events and both reported CIs crossed RRs = 0.75 and 1.25. Cobb 1997 (123 participants; follow-up duration 40 days) reported time to pressure ulcer incidence but did not report analysable data. Cobb 1997 reported no statistically significant di erence in survival analysis between the two types of reactive air surfaces (EHOB versus KinAir). Evidence is of very low certainty, downgraded once for unclear risk of bias, and twice for imprecision as the sample size was small and there were very few events. Only Cooper 1998 (84 complete cases) reported this outcome, defined as the participants' perception of comfort, rated using a 5-point visual rating scale. None of the participants selected 'Very uncomfortable' in either reactive air surface group; five selected 'Uncomfortable' (all using ROHO); eight selected 'Adequate' (four in each group); 48 selected 'Comfortable' (24 in each group), and 23 selected 'Very comfortable' (13 using So lex and 10 using ROHO). If we only considered the responses of 'Comfortable' and 'Very comfortable' for this outcome, it is uncertain if there is a di erence in the support-surface-associated patient comfort between the two specific reactive air surfaces under evaluation (low-certainty evidence). Evidence certainty was downgraded once for unclear risk of bias and once for imprecision due to the small sample size. Not reported. Not reported. Not reported. We report evidence from 17 RCTs on the e ects of reactive air surfaces compared with any support surface on the incidence of pressure ulcers in any population in any setting. We did not analyse data reported in the three studies that compared reactive air surfaces with surfaces that could not be classified. This review had evidence for five comparisons: reactive air surfaces compared with alternating pressure (active) air surfaces, foam surfaces, reactive water surfaces, reactive gel surfaces, and comparisons between two types of reactive air surface (EHOB versus KinAir, and So lex versus ROHO). We summarise key findings across these comparisons below. Five comparisons have evidence for this outcome. However, for most of these comparisons, it is uncertain if there is a di erence in the proportions of participants developing a new pressure ulcer between reactive air surfaces and alternating pressure (active) air surfaces (six studies with 1648 participants), reactive water surfaces (one study with 37 participants), reactive gel surfaces (one study with 66 participants), or another type of reactive air surface (two studies with 223 participants). Using reactive air surfaces may reduce the risk of developing new pressure ulcers compared with foam surfaces (four studies with 229 participants; low-certainty evidence). Two studies have evidence for this outcome. Low-certainty evidence suggests that people treated with reactive air surfaces are Cochrane Database of Systematic Reviews at a lower risk of developing a new pressure ulcer than those treated with alternating pressure (active) air surfaces over 14 days' followup in a nursing home setting (one study with 308 participants). However, it is uncertain if there is a di erence in the risk of developing new pressure ulcers between two types of reactive air surfaces (one study with 123 participants). This review has evidence on this outcome for three comparisons. It is uncertain if there is a di erence in patient comfort responses between reactive air surfaces and foam surfaces on top of an alternating pressure (active) air surface (one study with 72 participants; very low-certainty evidence); and between two types of reactive air surfaces under evaluation (one study with 84 participants; low-certainty evidence). It is uncertain if there is a di erence in patient comfort responses between reactive air surfaces and alternating pressure (active) air surfaces (four studies with 1364 participants; very low-certainty evidence). This review has adverse events evidence for one comparison only. It is uncertain if there is a di erence in adverse events between reactive air surfaces and foam surfaces (one study with 72 participants; very low-certainty evidence). This review did not identify evidence for this outcome. This review did not include data for this outcome for all five comparisons. As detailed in Search methods for identification of studies, we ran a comprehensive set of literature searches to maximise the relevant research included here. The international pressure ulcer guideline recommends considering using a reactive air surface for people at risk for developing pressure ulcers (EPUAP/NPIAP/PPPIA 2019). Whilst this appears to recommend the applicability of reactive air surfaces for adults and children in any settings, all participants in included studies were adults (with the reported average age ranging from 56 to 87 years, median of 72 years). Across the included studies, more than half (55.2%) of enrolled participants were female. Almost all of enrolled participants (2335/2604; 89.7%) were at (high) risk of pressure ulceration, with risk assessed using a risk assessment tool (e.g. the Braden scale) and most of the 2335 participants (87.1%) were ulcer-free at the time of being recruited. Three included studies (with 302 participants) did include participants with superficial pressure ulcers at baseline. Most of the included studies were small (half had fewer than 83 participants), whilst eight studies enrolled more than 100 participants, with two enrolling more than 200 participants. These eight studies together accounted for 80.7% (2101/2604) of the participants in this review. The geographical scope of included studies was limited: almost all the studies were from Europe and North America, and one small study was from China (Jiang 2014). Included studies recruited participants from a variety of care settings including: acute care settings (seven studies), community and long-term care settings (four studies), or both (two studies); and intensive care units (four studies). Whilst three of the five comparisons included studies from a variety of care settings, due to a limited number of included studies for these comparisons we could not perform pre-specified subgroup analysis by di erent care settings. Thus, for these three comparisons we are unable to drawn conclusions about potential modification of treatment e ects in di erent care settings. Each of the remaining two comparisons only included one study: one was in an intensive care unit and another was in a nursing home. Therefore, their evidence is very limited. These comparisons are reactive air surfaces compared with reactive water surfaces, or reactive gel surfaces. Additionally, there were no data for operating rooms. We recognise that reactive air surfaces can have a range of other features (e.g. air-fluidised, low-air-loss;.see Included studies). In this review, we considered all specific types of reactive air surfaces as generic reactive air surfaces since they have the same underlying mechanism of redistributing pressure activity (i.e. distributing the pressure over a greater area via immersion and envelopment). We did not synthesise evidence for each specific type of reactive air surface. There were no data for the comparison of reactive air surfaces versus reactive fibre surfaces. Further planned review work using network meta-analysis will add to the findings reported here. We did not analyse data reported in the three studies that compared reactive air surfaces with undefined surfaces as these comparator group surfaces could not be classified using the NPIAP S3I 2007 support surfaces terms and definitions. However, for completeness of all relevant evidence, we reported the data from these studies in Appendix 4. Another limitation in the included studies was the large variation in terms of follow-up durations (with a range of five days to six months, median of 14 days). This is partly because di erent followup durations are appropriate in di erent care settings. For example, participants staying at acute care settings are more likely to be discharged a er a short-term hospital stay whilst those staying at community and long-term care settings can have long-term follow-up. The short median duration of follow-up may contribute to an under-estimation of pressure ulcer incidence across study groups of the included studies because most pressure ulcers would occur in the first two to four weeks a er hospital admission (Schoonhoven 2007), and some incident pressure ulcers may have been missed in these studies. We implemented the GRADE approach for assessing the certainty of the evidence and found that most of the included evidence from our 10 meta-analyses or syntheses across five comparisons was of low or very low certainty. Downgrading of evidence was all due to the unclear or high risk of bias of findings, and/or imprecision due to the small numbers of participants, events, wide confidence intervals that failed to exclude important benefits or harms, or all of these. Trusted evidence. Informed decisions. Better health. We downgraded once or twice for study limitations for all evidence. We assessed risk of bias according to seven domains: sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, selective outcome reporting, incomplete follow-up, and other potential biases. Of the 17 studies, we judged ten as being at unclear overall risk of bias; and seven at high overall risk of bias. The prevalence of high overall risk of bias is partly due to the non-blinding of participants and personnel for most comparisons. We acknowledged that such blinding of participants and personnel is impractical for most comparisons. Therefore, we did not downgrade certainty of evidence for studies at high overall risk of bias that was solely due to the possible presence of performance bias. Five studies were also at high risk of bias due to unblinded outcome assessment. Unblinded assessment has been found to exaggerate odds ratios (from subjective binary outcomes) by, on average, 36% (Hróbjartsson 2012). The outcome assessment of pressure ulcer incidence is subjective, and blinded assessmentwhilst operationally challenging -can be undertaken (e.g. masked adjudication of photographs of pressure areas) (Baumgarten 2009). Therefore, we considered unblinded pressure ulcer incidence assessment could substantially bias e ect estimates in the included studies and downgraded the certainty of evidence for detection bias on a study-by-study basis. We did not downgrade any result for indirectness of evidence. This was because we considered that the participants, interventions and outcomes in the included studies were within the scope of the published review protocol and there was no indirectness. Statistical heterogeneity was low for nine of the 10 evidence syntheses we performed and we did not downgrade for inconsistency for them. We downgraded for inconsistency for the support-surface-associated patient comfort outcome in the comparison of reactive air surfaces versus alternating pressure (active) air surfaces; and the included studies of this synthesis reported heterogenous results. The low statistical heterogeneity was partly because seven of the 10 syntheses included only one study. None of the remaining meta-analyses or narrative syntheses included more than six studies. Despite the fact that we found heterogeneity in overall risk of bias, care settings, outcome measurement methods, or follow-up durations between included studies, we considered that heterogeneity (inconsistency) was low and explained, and we decided not to downgrade evidence certainty. We have to note that although we planned to calculate prediction intervals to understand the implications of heterogeneity, all analyses included a small number (up to six) of included studies which was fewer than the 10 needed for this calculation. We downgraded for imprecision for all pieces of evidence from the 10 evidence syntheses. Study sample sizes were small in most cases (median sample size: 83) with o en a small number of events and wide associated confidence intervals around e ect estimates. Confidence intervals o en crossed the line of null e ect, thus meaning we could not discern whether the true population e ect was likely to be beneficial or harmful. We did not downgrade the certainty of evidence for publication bias in all meta-analyses. This is because (1) we have confidence in the comprehensiveness of our literature searches; and (2) we did not find any clear evidence of non-reporting bias of study results. Although we planned to perform funnel plots for meta-analysis to visually inspect for publication bias, there was no analysis including more than ten studies. We followed pre-specified methods to review evidence in order to prevent potential bias in the review process. For example, we ran comprehensive electronic searches, searched trials registries and checked the references of systematic reviews identified in electronic searches. This review also has limitations. Firstly, some included studies may have considered co-interventions as 'usual care' but did not fully describe them. We assumed that all studies had provided cointerventions equally to participants in their study groups if there was nothing to indicate that this was not the case. Secondly, we did not implement pre-specified subgroup analysis as we mentioned above, mainly because no analysis included more than ten studies. Thirdly, the study with time to pressure ulcer data in this review, Beeckman 2019, did not fully report time-to-event data, and the HR and CI we used in Analysis 1.2 were calculated using the methods described in Tierney 2007. We recognise that those calculated data (and associated meta-analyses) might be inaccurate. Fourthly, two studies termed their controls as 'standard hospital surfaces' but did not specify the construction materials of these surfaces. Although we made e orts to collect information on these surfaces, we were not able to classify them. Traditionally, 'standard hospital surfaces' meant foam surfaces, but we felt adopting that assumption was unwarranted. Accurate classification of these surfaces in the future might change the results of some comparisons (e.g. reactive air surfaces versus foam surfaces). Finally, we were not able to prespecify the comparisons included in this review. This is because specific support surfaces applied could only be known and defined once eligible studies were included. However, we pre-planned to use the NPIAP S3I 2007 support surface terms and definitions to define specific support surfaces in order to avoid any potential bias. To our knowledge, among the 14 systematic reviews or metaanalyses we identified through electronic searches for this review ( Cochrane Database of Systematic Reviews As mentioned above, the types of reactive air surfaces used in the included studies varied, and we labelled all these types as a single generic group 'reactive air surfaces'. However, Shi 2018a and McInnes 2015 considered individual types of reactive air surfaces (e.g. air-fluidised bed, low-air-loss hydrotherapy) separately in di erent comparisons. For example, McInnes 2015 classified support surfaces into 'low-tech' and 'high-tech' groups in general, and included 'static air mattresses' into low-tech 'constant low-pressure devices' but considered low-air-loss surfaces as 'hightech' regardless of whether they were active or reactive. Shi 2018a grouped some interventions under the term 'standard hospital surfaces' but concluded that the types of surfaces labelled in this way varied over time, and by setting. We noted that the NPIAP S3I 2007 recommends that the use of 'standard hospital surfaces' term should be avoided and the surface characteristics should be specified. In this review, we made great e orts to define surfaces, where these surfaces were described as a 'standard hospital surface' in the included studies to ensure they were placed in the correct comparisons. We classified those 'standard hospital surfaces' that had no characteristic details or could not be classified using the NPIAP S3I 2007 terms and definitions as undefined surfaces. The re-definitions and re-classifications of specific support surfaces discussed above can explain some of the inconsistency between these reviews, but importantly, Shi 2018a was a network metaanalysis. Shi 2018a considered pressure ulcer incidence and supportsurface-associated patient comfort outcomes only, whilst this review added adverse e ect evidence to the evidence base. Using reactive air surfaces may reduce the risk of developing new pressure ulcers within 14 days compared with alternating pressure (active) air surfaces in people in a nursing home setting. Also, the use of reactive air surfaces may reduce pressure ulcer incidence compared with foam surfaces. However, evidence is uncertain about the relative e ects of reactive air surfaces versus foam surfaces, reactive water surfaces, reactive gel surfaces, or another type of reactive air surface in preventing pressure ulcers. Given the large number of di erent support surfaces available, future studies should prioritise which support surfaces to evaluate on the basis of the priorities of decision-makers. For example, reactive air surfaces versus alternating pressure (active) air surfaces may be a high priority for future evaluation. All interventions used should be clearly described using the current classification system. Researchers should avoid use of some terms, such as 'standard hospital surfaces'. Limitations in included studies are largely due to small sample size and sub-optimal RCT design. The incidence of pressure ulcers can be low in certain settings and this needs to be considered in sample size calculations and when considering the feasibility of trial conduct. Under-recruitment or over-estimation of event rates that then fail to occur, or both, can lead to imprecision and less robust e ect estimates. Future studies should also consider carefully the choice of outcomes they report; time-to-event data for pressure ulcer incidence should be used in trials. Careful and consistent assessment and reporting of adverse events needs to be undertaken to generate meaningful data that can be compared between studies. Likewise, patient comfort is an important outcome but it is poorly defined and reported, and this needs to be considered in future research studies. Further studies should aim to collect and report health-related quality of life using validated measures. Finally, future studies should nest cost-e ectiveness analysis in their conduct where possible. Any future studies must be undertaken to the highest standard possible. Whilst it is challenging to avoid the risk of performance bias in trials of support surfaces as blinding of participants and personnel is seldom possible, stringent protocols -for example, in terms of encouraging consistent care and blinded decisionmaking -can help to minimise risk. It is also important to fully describe co-interventions (e.g. repositioning) and ensure protocols mandate balanced use of co-interventions across trial arms. The risk of detection bias can also be minimised with the use of digital photography and adjudicators of the photographs being masked to support surfaces (Baumgarten 2009). Follow-up periods should be for as long as possible and clinically relevant in di erent settings. Where possible and useful, data collection a er discharge from acute care settings may be considered. The authors are grateful to the following peer reviewers who provided feedback on both the protocol and the review: Julie Bruce and Zena Moore. Thanks are also due to Jessica Sharp for copyediting the protocol, to Denise Mitchell for additional copy-edit feedback, to Faith Armitage for copy-editing the review and to Nicole Pitcher for writing the Plain Language Summary. We also would like to thank Asmara Jammali-Blasi for screening search records; and to thank Zhenmi Liu, Gill Norman and Melanie Stephens for double-checking data extraction and risk of bias assessment for this review. Cochrane Database of Systematic Reviews Interventions Air-fluidised bed Cochrane Database of Systematic Reviews • Outcome type: binary • Time points: median 13 days • Reporting: partially reported • Definition and measurement method (e.g. scale, self-reporting): patients developing complications • Dropouts and reasons: 7 withdrawn prior to follow-up and excluded from analysis (6 died, 1 withdrew due to nausea and dislike of the air-fluidised bed) • Data and results: 8 died, 2 pneumonia, 10 urinary tract infections, 6 hypotension, 5 hypernatraemia, 5 oliguria, 7 sepsis, 16 fever, and 3 heart failure on air-fluidised bed; 7 died, 4 pneumonia, 7 urinary tract infections, 7 hypotension, 5 hypernatraemia, 8 oliguria, 6 sepsis, 22 fever, and 6 heart failure on conventional therapy • Notes (e.g. other results reported): some patients appeared to have multiple adverse events • Not reported • Not reported Outcomes that are not considered in this review but reported in trials: • Ulcer healing • Change in total surface area • Patients improved • 50% reduction in total surface area • Pain response This is a treatment trial that contains ulcer incidence data. Random sequence generation (selection bias) Low risk Quote: "Patients were randomly allocated to treatment groups in two strata in balanced blocks of six with stratification … The randomization sequence was determined using a table of random numbers …" Comment: low risk of bias due to the use of a proper randomisation method. Unclear risk Quote: "… treatment allocations were placed in envelopes sealed and numbered sequentially. After establishing eligibility, one of the investigators selected the unopened envelope with the lowest number in the appropriate strata and allocated the patient to the treatment indicated on the enclosed card" Comment: unclear risk of bias because information is still insufficient to ensure if concealment is performed properly (e.g. it is unclear if the envelopes are opaque). Blinding of participants and personnel (performance bias) All outcomes Unclear risk Comment: no information provided. Blinding of outcome assessment (detection bias) All outcomes Comment: no information provided. Incomplete outcome data (attrition bias) All outcomes Comment: low risk of bias because of the low rate of attrition (7/72, 9.7%). Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre-specified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Study objective: to compare the effectiveness and cost of static air support surfaces versus alternating air pressure support surfaces in a nursing home population at high risk for pressure ulcers All reported adverse events using allocated support surfaces • Reporting: not reported • Reporting: not reported • Reporting: not reported • Notes: purchase costs of the support surfaces calculated per participant per day given the 2-year lifespan for a static air mattress and 7-year for an alternating air pressure mattresses. The average lifespan of 2 years for a static air mattress resulted in a daily cost of 0.20 Euro; the average lifespan of 7 years for an alternating air pressure mattress resulted in a daily cost of 0.53 Euro. Outcomes that are not considered in this review but reported in trials: • None Random sequence generation (selection bias) Low risk Quote: "The random allocation sequence was based on a computer-generated list of random numbers using an online tool (www.randomization.com)." Comment: low risk of bias because of the use of a proper randomisation method. Unclear risk Quote: "When the participants met the inclusion criteria and an informed consent was obtained, they received an allocation number (first available number on the computer-generated list)." Quote: "Subsequently, a random allocation of each eligible participant was performed based on a computer-generated list of random numbers." Comment: unclear risk of bias because the process of allocation is not clear for judging if concealment is properly performed and it is unclear who performed allocation. Blinding of participants and personnel (performance bias) All outcomes Quote: "The study was not blinded due to the obvious visible difference between the support surfaces (e.g. external control unit)." Comment: high risk of bias because of the understandable challenge of performing blinding. Blinding of outcome assessment (detection bias) All outcomes Quote: "The study was not blinded due to the obvious visible difference between the support surfaces (e.g. external control unit). Both support surface types were presented to ward nurses ..." Quote: "During the follow-up period (days 1-14), the ward nurses collected all data" Quote: "Researchers performed independent and unannounced skin assessments and technical controls weekly" Cochrane Database of Systematic Reviews Comment: high risk of bias because of the understandable challenge of performing blinding. Incomplete outcome data (attrition bias) All outcomes Low risk Quote: "An intention-to-treat analysis was performed." Comment: low risk of bias. Selective reporting (reporting bias) Low risk Comment: the study protocol is available and it is clear that the published reports include all outcomes, including those that were prespecified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Study objective: to determine whether low-air-loss hydrotherapy reduces the incidence of new skin lesions associated with incontinence in hospitalised patients ... compared with standard care. To assess subjectively patient and nursing satisfaction related to using low-air-loss hydrotherapy beds. Duration of follow-up: 60 days; median 4 (range 1 to 60) days in low-air-loss hydrotherapy; median 6 (range 1 to 62) days in standard care Single centre or multi-sites: multi-sites Setting: acute and chronic hospital wards Inclusion criteria: (1) incontinence of urine and/or liquid faeces was present; (2) treatment in bed for 16 hours or longer per day was expected; (3) the length of hospitalisation was expected to be 3 or more days; (4) in the opinion of the attending physician, death was not expected within the next 7 days; and (5) no other condition was present, e.g. excessive combativeness or morbid obesity, which, in the opinion of the principal investigator, would preclude the patient from fulfilling the objectives of the project Interventions Low-air-loss hydrotherapy • Description of interventions: low-air-loss hydrotherapy beds (Clensicair, Support Systems International/Hill-Rom, Charleston, SC) used to maximise the amount of time incontinent patients remain dry; similar to low-air-loss beds e.g. Flexicair therapy beds in which air escapes continuously through the semipermeable fabric used to construct the multiple air cushions of the surface (Bennett 1998); "Model Clensicair; Power needed; Kind -Low air loss with incontinence management system" from product search http://www.medwow.com/med/alternating-pressure-bed/hill-rom/clensicair/15595.model-spec. • NPUAP S3I classification: powered, reactive low-air-loss air surface • Temperature on the first study day after enrolment • Assessment of subjective nursing and patient satisfaction This cannot be regarded as an ulcer healing trial. Random sequence generation (selection bias) Low risk Quote: "Subjects ... were stratified based on whether any pressure sores were present at enrolment ... randomization of subjects ... was done by unblocked allocation using a table of random numbers stratified by pressure sore and by setting" Comment: low risk of bias due to the use of random number table. Unclear risk Comment: no information provided. Blinding of participants and personnel (performance bias) All outcomes Comment: no information provided. Blinding of outcome assessment (detection bias) All outcomes Quote: "... the study nurse and/or research technicians ... performed a thorough examination of the truncal skin ... to identify new truncal skin lesions, including pressure sores, blisters, bruises, abrasions, chemical irritations, and candidiasis ... categorised all skin lesions based on objective appearance and/ or treatment prescribed ..." Comment: unclear risk of bias because insufficient information to permit judgement of low or high risk of bias. Incomplete outcome data (attrition bias) All outcomes Comment: high risk of bias because (1) 16 of 58 individuals in low-air-loss hydrotherapy; and 2 of 58 in standard care were excluded from analysis; (2) 6 participants receiving low-air-loss hydrotherapy exited because of patient or family member complaints (e.g. being wet, cold or uncomfortable). Two participants were removed by researchers as a result of hypothermia. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Study objective: to determine whether alternating low pressure or continuous low pressure is most effective in reducing the incidence of pressure ulcers in high risk patients Inclusion criteria: those admitted to the unit or deemed "at risk" of pressure ulceration as defined by the Braden Pressure Ulcer Risk Assessment Scale (a total Braden score of ≤ 17 and mobility and activity sub-scores of ≤ 3); their admission was expected to last at least 2 weeks and they had up to 1 grade I pressure ulcer Cochrane Database of Systematic Reviews dropouts in continuous low pressure (5 died, 4 discharged prior to assessment, 4 did not complete study due to non-concordance and not agreeing to use the modality) • Notes (e.g. other results reported): 2 of 69 individuals (1 stage 1 and 1 stage 2) in alternating low pressure; 1 of 71 individuals (stage 2) in continuous low pressure • Reporting: not reported Support -surface-associated patient comfort • Reporting: not reported • Notes: 5 dropouts due to discomfort and/or not agreeing to use the assigned modality in Alternating low pressure; 4 dropouts due to discomfort and/or not agreeing to use the assigned modality in continuous low pressure All reported adverse events using allocated support surfaces • Reporting: not reported • Reporting: not reported • Reporting: not reported • Not available Random sequence generation (selection bias) Unclear risk Quote: "Patients in the treatment group were randomised to receive either continuous or alternating low pressure on the high-tech mattress" Comment: the method of randomisation was not reported. Unclear risk Comment: no information provided. Blinding of participants and personnel (performance bias) All outcomes Quote: "... independently from the blinded randomised treatment group (who received the Duo2 high-tech mattress)." Comment: low risk of bias because blinding method was implemented. Blinding of outcome assessment (detection bias) All outcomes Quote: "As there is no visible difference between these two modes, the external observer was blinded as to which one was in use. The external observers assessed all study patients' ... presence (or absence) and grade of both existing and new pressure ulcers" Comment: low risk of bias because outcome assessment was blinded. Incomplete outcome data (attrition bias) All outcomes Comment: high risk of bias because of high proportions of dropouts in both groups and probably using incorrect analysis methods to address missing data. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre-specified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Study objective: to compare outcomes related to pressure ulcer development when high-risk patients were placed on a KinAir specialty bed, a rented low-air-loss bed, compared to an EHOB Waffle air mattress, a purchased, 1-patient use, static air mattress overlay Figure 1 ) "there is no statistically significant difference between the EHOB Waffle mattress or the KinAir bed, although the EHOB survival curve is lower than the KinAir curve"; no further data. Random sequence generation (selection bias) Unclear risk Quote: "Patients were placed into one of the study groups by random selection of a treatment card by a nurse not involved in the study" Comment: unclear risk of bias because the method of proper randomisation is not clearly specified. Low risk Quote: "Patients were placed into one of the study groups by random selection of a treatment card by a nurse not involved in the study" Comment: low risk of bias because concealment of the allocation process is likely through the involvement of an independent nurse. Blinding of participants and personnel (performance bias) All outcomes Quote: "No attempt was made to alter the medical plan of care related to use of specialty beds/overlays" Comment: unclear risk of bias because of the lack of specific information on performance bias though no attempt to change care plan is stated. Comment: no information provided. Blinding of outcome assessment (detection bias) All outcomes Quote: "A skin assessment tool was used to document presence or absence of skin breakdown, the stage of injury when it occurred, and progression of the skin breakdown. The skin assessment tool also included an anterior and posterior diagram of the human body that allowed the investigator to draw the site of pressure ulcer(s)" Comment: unclear risk of bias because of lack of relevant information. Comment: no information provided. Incomplete outcome data (attrition bias) All outcomes Comment: no attrition identified. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre-specified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Cobb 1997 (Continued) Reactive air surfaces for preventing pressure ulcers ( Methods Study objective: to compare 2 dry-flotation pressure-reducing surfaces in pressure sore incidence, patient comfort and the appropriate use of equipment in 100 orthopaedic patients • Reporting: not reported: • Reporting: not reported Outcomes that are not considered in this review but reported in trials: • Equipment setting Random sequence generation (selection bias) Unclear risk Quote: "The subjects were then randomly allocated to one of the two types of mattress using consecutively numbered sealed opaque envelopes" Comment: the method of randomisation was not described. Low risk Quote: "The subjects were then randomly allocated to one of the two types of mattress using consecutively numbered sealed opaque envelopes" Cochrane Database of Systematic Reviews Comment: low risk of bias due to the use of proper concealment method. Blinding of participants and personnel (performance bias) All outcomes Comment: no information provided. Blinding of outcome assessment (detection bias) All outcomes Quote: "The patient's skin integrity was assessed ... " Comment: unclear risk of bias because efforts to prevent detection bias were not described. Quote: "the patients' perception of comfort was recorded using a standardised question and a five-point visual rating scale" Comment: high risk of bias because comfort outcome is self-reported and blinding is impossible. Incomplete outcome data (attrition bias) All outcomes Quote: "16 patients had withdrawn ... four had died in the Sofflex group, and three in the ROHO group. The remaining nine patients were withdrawn ...: five were transferred to other specialities and four were discharged..." Comment: unclear risk of bias because 16% of 100 participants missed. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Study objective: to compare the effectiveness of a specialised alternating air pressure mattress replacement system and an air-fluidised integrated bed in the management of post-operative flap patients Inclusion criteria: 18 years or older who were admitted for reconstructive surgery to repair a tissue deficit (full-thickness pressure ulcer involving muscle, fascia and, in some cases, bone) in the sacralcoccygeal, trochanteric or ischial region Exclusion criteria: unlikely or unwilling to comply with the treatment protocol, which included a minimum of 7 days bed rest within the surgical unit, or unable to consent • Integrity of the surgical site Random sequence generation (selection bias) Low risk Quote: "allocation was determined by using web-based random-number software" Comment: low risk of bias due to the use of a proper randomisation method. Unclear risk Quote: "Groups were concealed in sealed envelopes" Comment: unclear risk of bias because a proper concealment method is not specified. Blinding of participants and personnel (performance bias) All outcomes Comment: no information provided. Blinding of outcome assessment (detection bias) All outcomes Quote: "Tissue integrity on discharge was not blinded and determined by the surgical team responsible for this pilot phase." Comment: high risk of bias because no blinding was undertaken. Comment: unclear risk of bias because it is not specified if patients who reported comfort data were blinded. Incomplete outcome data (attrition bias) All outcomes Quote: "four subjects in Group A and three subjects in Group B did not receive the allocated intervention (Fig. 2) and were not included in the follow-up" Comment: unclear risk of bias because a fair proportion of subjects lost to follow-up. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Study objective: to determine, in critically ill patients at risk, both the clinical utility and cost-effectiveness of using an air suspension bed in the prevention of pressure ulcers Interventions Air suspension bed • Description of interventions: air suspension bed (KinAir, Kinetic Concepts Inc, San Antonio, Tex) ... provides a smooth, low-friction, low-shear surface with a high moisture vapor transmission rate, decreasing physical stresses on the skin (Inman 1993); the patent of this product can be seen in https:// patentimages.storage.googleapis.com/27/6f/0f/f80303c8fcec2a/US5983429.pdf. • NPIAP S3I classification: powered, reactive low-air-loss air surface • Co-interventions: not described • Measurement method (e.g. scale, self-reporting): cost-effectiveness estimated from a third-party payer's perspective; effectiveness measured as the number of ICU patients at risk in whom pressure ulcers developed and expressed per 100 patients at risk; cost estimates reported in both US and Canadian 1988 dollars; incremental cost-effectiveness ratio calculated (the cost per pressure ulcer prevented). • Notes: cost per 100 patients at risk 56,347.40 Canadian dollars in standard bed vs 50,044.80 Canadian dollars in air suspension; cost saved per 100 patients at risk 6302.60 Canadian dollars due to air suspension; pressure ulcers prevented per 100 patients at risk 64 due to air suspension; cost-effectiveness ratio (cost per pressure ulcer prevented) < 0 (air suspension bed), meaning air suspension bed was dominant, providing increased effectiveness in the form of fewer pressure ulcers, for less money than the current program of standard ICU bed and frequent patient rotation. Outcomes that are not considered in this review but reported in trials: • No Random sequence generation (selection bias) Unclear risk Quote: "... consecutive patients were randomly assigned to receive treatment with either the air suspension bed or a standard ICU bed" Comment: the method of randomisation is not described. Unclear risk Comment: no information provided. Blinding of participants and personnel (performance bias) All outcomes Comment: no information provided. Blinding of outcome assessment (detection bias) All outcomes Quote: "... a visual skin inspection of 13 bony prominences was performed by a trained critical care research nurse, and the presence or absence of pressure ulcers was recorded" Comment: unclear risk of bias because blinding of outcome assessment is not described. Incomplete outcome data (attrition bias) All outcomes Quote: "Of the 100 patients randomised, 98 successfully completed the study protocol. One patient from each study group was excluded from the analysis, as they did not have an ICU stay of at least 3 days. Neither of these patients developed a pressure ulcer during their hospitalisation" Comment: low risk of bias due to the small proportion of missing data. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Trusted evidence. Informed decisions. Better health. Methods Study objective: to investigate the efficacy of static low-air-loss mattress (static LALM) and power pressure air mattress (PPAM) in prevention of pressure ulcers • Not reported • Not reported • Not reported Outcomes that are not considered in this review but reported in trials: Random sequence generation (selection bias) Low risk Quote: "We used a random number table to randomize and parallel control design" Comment: low risk of bias because the sequence generation process is proper. Allocation concealment (selection bias) Trusted evidence. Informed decisions. Better health. Blinding of participants and personnel (performance bias) All outcomes Unclear risk Comment: no information provided. Blinding of outcome assessment (detection bias) All outcomes Unclear risk Comment: no information provided. Incomplete outcome data (attrition bias) All outcomes Comment: low risk of bias because intention-to-treat (ITT) analysis performed. Comment: unclear risk of bias because the rates of missing data in both groups is between 10% to 20%. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Study objective: to compare the effectiveness of 2 pressure-reducing devices [an air-filled overlay and a gel mattress] in a group of elderly nursing home residents Interventions SofCare overlay • Description of interventions: air-filled overlay (SofCare overlay) Gaymar Industries. Additional source of information "Gaymar SofCare air mattress ... composed of three distinct layers of more than 300 compensating air cells. The cells are interconnected through a series of air channels. As the cells exchange air, the patient's weight is redistributed over the entire surface of the cushion ... SofCare is unlike any other inflated device ... SofCare looks as so as it feels, "customizing" itself to the body weight and configuration of each individual patient. By conforming to the patient ... (http://www.rehabmart.com/pdfs/gaymar_sof_care_overlay_brochure.pdf)" • NPIAP S3I classification: non-powered, reactive air surface • Co-interventions: not described Cochrane Database of Systematic Reviews Notes Random sequence generation (selection bias) Low risk Quote: "Using a table of random numbers, each subjected was placed into ..." Comment: low risk of bias because a proper randomisation was done. Unclear risk Comment: no information provided. Blinding of participants and personnel (performance bias) All outcomes Unclear risk Comment: no information provided. Blinding of outcome assessment (detection bias) All outcomes Quote: "Patients in both study groups were assessed by the same researcher for the presence of pressure ulcer development over areas of bony prominence" Comment: unclear risk of bias because no information on blinding was reported. Incomplete outcome data (attrition bias) All outcomes Quote: "... the initial study population was 76 subjects ..." Quote: "A total of 74 subjects were in the study ... Two subjects were excluded from the study ... Those subjects who participated in the study for four to six months were included in the data analysis. Eighteen residents developed pressure ulcers during the course of the study, nine residents had preexisting pressure ulcers, and 36 residents did not develop a pressure ulcer" Comment: unclear risk of bias because the patient flow is not clear enough and the proportion of missing data is probably between 10/74 (13.5%) and 13/74 (17.6%). Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Study objective: to compare pressure ulcer outcomes in medical intensive care unit (ICU) patients nursed on either a reactive mattress overlay (ROHO®, ROHO Inc, Belleville, IL, USA) or an active alternating pressure mattress (NIMBUS®3, ArjoHuntleigh, Luton Bedfordshire, UK) Cochrane Database of Systematic Reviews Duration of follow-up: not specified; mean study duration reported 12.2 days (SD 5.5) in ROHO and 15 (14) in NIMBUS 3 Single centre or multi-sites: single centre Study start date and end date: not described Outcomes that are not considered in this review but reported in trials: • Pressure ulcer healing outcome (reported but not extracted because patients with ulcers are not units of randomisation) Random sequence generation (selection bias) Low risk Quote: "Randomisation of patients to products was performed blinded by the insertion of equivalent numbers of labels written with ''active'' or ''reactive'' placed in identical sealed envelopes that were shuffled and placed in a box and drawn in sequence" Comment: low risk of bias because a simple randomisation was applied. Unclear risk Quote: "Randomisation of patients to products was performed blinded by the insertion of equivalent numbers of labels written with ''active'' or ''reactive'' placed in identical sealed envelopes that were shuffled and placed in a box and drawn in sequence. When a patient was admitted who fulfilled the inclusion criteria the next envelope was opened by a ward nurse and the patient was assigned to the mattress on the label" Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Study objective: to compare the effects on pressure damage prevalence by using 2 different support systems in patients with fractured neck of femur who were at high risk Cochrane Database of Systematic Reviews • Description of interventions: a low-unit-cost system (Repose) ... comprising a low-pressure inflatable mattress and cushion that are readily portable and require little maintenance ... manufactured using a special polyurethane material that has a multidirectional stretch, is vapour permeable, waterproof and x-ray translucent • NPIAP S3I classification: non-powered, reactive air surface • Co-interventions: standard best practice as appropriate to condition, including regular repositioning Outcomes that are not considered in this review but reported in trials: • No Random sequence generation (selection bias) Low risk Quote: "a concealed computer generated list was used to randomise eligible consecutive consenting patients to one of the support systems" Comment: low risk of bias because of the use of a proper randomisation method. Allocation concealment (selection bias) Low risk Quote: "a concealed computer generated list was used to randomise eligible consecutive consenting patients to one of the support systems" Comment: low risk of bias because of a proper concealment method. Blinding of participants and personnel (performance bias) All outcomes Comment: high risk of bias because blinding is not possible for this comparison. Blinding of outcome assessment (detection bias) All outcomes Quote: "Patients were not assessed blindly as it was considered that displacement for examination would cause excessive discomfort. A team of trained researchers completed all assessments" Comment: high risk of bias because no blinding is done. Incomplete outcome data (attrition bias) All outcomes High risk Outcome group: primary outcome Quote: "No patient was excluded from all the analyses" Quote: "Data were not available for the 14-day follow-up assessment for a further 12 patients who were transferred to wards or hospitals that were not involved in the study or were discharged home" Comment: high risk of bias because 16 in Repose and 14 in NIMBUS II plus Alpha TranCell actually missed and were not included in analysis. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Sideranko 1992 Outcomes that are not considered in this review but reported in trials: • Interface pressure Random sequence generation (selection bias) Unclear risk Quote: "... subjects were randomly assigned to be placed on one of the three surfaces studied" Comment: unclear risk of bias because the method of randomisation was not specified. Unclear risk Comment: no information provided. Blinding of participants and personnel (performance bias) All outcomes Unclear risk Comment: no information provided. Blinding of outcome assessment (detection bias) Unclear risk Comment: no information provided. Cochrane Database of Systematic Reviews Incomplete outcome data (attrition bias) All outcomes Comment: no missing assumed. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre-specified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Random sequence generation (selection bias) Unclear risk Quote: "Those with an expected ICU stay exceeding five days were randomly assigned to be treated on either ..." Comment: unclear risk of bias because a proper randomisation criteria is unspecified. Allocation concealment (selection bias) High risk Comment: randomisation influenced by mattress availability, therefore, allocation not concealed. Blinding of participants and personnel (performance bias) All outcomes High risk Outcome group: pressure ulcer outcome Quote: "The study was not blinded, since the severity of illness of the patients precluded their transfer for evaluation of the skin condition by a blinded reviewer, and the type of mattress in the bed could not be blinded" Comment: high risk of bias because this statement implies blinding of participants and personnel is likely impossible. Blinding of outcome assessment (detection bias) All outcomes Quote: "The study was not blinded, since the severity of illness of the patients precluded their transfer for evaluation of the skin condition by a blinded reviewer, and the type of mattress in the bed could not be blinded" Comment: high risk of bias as it is clearly stated. Incomplete outcome data (attrition bias) All outcomes Quote: "Sequential analysis of the primary outcome variable (pressure sore formation) on an intention-to-treat basis was done after each block of four patients had completed the treatment" Comment: low risk of bias because intention-to-treat (ITT) analysis was conducted. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Study objective: to evaluate the clinical efficacy of combining a standard 15 cm cold foam mattress with a static air overlay mattress versus a cold foam mattress alone in preventing pressure ulcers Outcomes that are not considered in this review but reported in trials: • Treatment data on the new ulcers reported but not extracted Random sequence generation (selection bias) Unclear risk Quote: "Randomization into two groups was performed after informed consent using numbered envelopes" Comment: unclear risk of bias because the randomisation method used is not sufficiently clear. Unclear risk Comment: no information provided. Blinding of participants and personnel (performance bias) All outcomes Comment: no information provided. Blinding of outcome assessment (detection bias) All outcomes Quote: "A weekly inspection of the skin to assess the possible occurrence of a skin lesion was done by an independent nurse" Comment: low risk of bias because the attempt was made to blind outcome assessment. Incomplete outcome data (attrition bias) All outcomes Comment: no attrition identified. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre-specified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Van Leen Outcomes that are not considered in this review but reported in trials: • Treatment data on the new ulcers reported but not extracted Authors' judgement Support for judgement Random sequence generation (selection bias) Low risk Quote: "Patients were randomised into 2 groups using numbered envelopes" Comment: low risk of bias because the randomisation method is not sufficiently clearly presented in the paper; author response suggests remote computer randomisation sequence generation. Unclear risk Comment: unclear risk of bias because author responded that sealed envelopes were opened by nurse but it's unclear if envelopes were sequentially numbered and opaque. Blinding of participants and personnel (performance bias) All outcomes Comment: no information provided. Blinding of outcome assessment (detection bias) All outcomes Quote: "Patients' skin was inspected weekly to assess the possible occurrence of a skin lesion" Comment: no information provided on the blinding of outcome assessment. Incomplete outcome data (attrition bias) Cochrane Database of Systematic Reviews All outcomes Comment: no attrition identified; 2 cases were transferred to low-air-loss bed treatments after they developed category III ulcers. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre-specified. Other bias Low risk Comment: the study appears to be free of other sources of bias. Methods Study objective: to compare the efficacy of different surfaces in the prevention of pressure ulcers; to compare costs associated with the use of an inflated static overlay (ISO) with the standard treatment, which in the first author's facility consists of renting a microfluid static overlay (MSO) or a low-air-loss dynamic mattress (LALDM) with pulsation for moderate-risk to very high-risk patients; to evaluate patient comfort Outcomes that are not considered in this review but reported in trials: • Costs Random sequence generation (selection bias) Low risk Quote: "Participants were randomly assigned a rented surface (MSO or LALDM) or an ISO. Once subject consent was obtained and signed, the allocation sequence for mattress type was done by draw by the research nurse using an opaque envelope and the subject witnessing the draw" Comment: low risk of bias because it is likely trial used a proper randomisation method. Unclear risk Quote: "The allocation sequence was concealed from the research nurse enrolling and assessing the participants" Comment: unclear risk of bias because concealment approach is not specified. Blinding of participants and personnel (performance bias) All outcomes Quote: "The purpose of this unblinded, randomised, prospective study ..." Quote: "Blinding was not obtained for the patient, the clinical sta , or the research evaluator because the surfaces were visible" Comment: high risk of bias because non-blinding is clearly stated. Blinding of outcome assessment (detection bias) All outcomes Quote: "The purpose of this unblinded, randomised, prospective study ..." Quote: "Blinding was not obtained for the patient, the clinical sta , or the research evaluator because the surfaces were visible" Comment: high risk of bias because non-blinding is clearly stated. Incomplete outcome data (attrition bias) All outcomes Quote: "Analyses were performed in intention-to-treat involving all 110 randomly assigned patients" Comment: intention-to-treat (ITT) analysis conducted. Quote: "Of the 110 participants, 68 expressed opinions regarding comfort" Comment: high risk of bias because 42 of 110 missed. Selective reporting (reporting bias) Low risk Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre-specified. Other bias Low risk Comment: the study appears to be free of other sources of bias. S24 TI decubitus or AB decubitus S23 TI ( bed sore* or bedsore* ) or AB ( bed sore* or bedsore* ) S22 TI ( pressure ulcer* or pressure sore* ) or AB ( pressure ulcer* or pressure sore* ) S21 (MH "Pressure Ulcer") S20 S1 OR S2 OR S3 OR S4 OR S5 OR S6 OR S7 OR S8 OR S9 OR S10 OR S11 OR S12 OR S13 OR S14 OR S15 OR S16 OR S17 OR S18 OR S19 S19 TI net bed* or AB net bed* S18 TI ( kinetic therapy or kinetic table* ) or AB ( kinetic therapy or kinetic table* ) S17 TI ( turn* bed* or tilt* bed* ) or AB ( turn* frame* or tilt* frame* ) S16 TI sheepskin OR AB sheepskin Cochrane Database of Systematic Reviews S15 TI water suspension or AB water suspension S14 TI air bag* or AB air bag* S13 TI air suspension or AB air suspension S12 TI alternat* pressure or AB alternat* pressure S11 TI static air or AB static air S10 Appendix 3. Risk of bias 1 'Risk of bias' assessment in individually randomised controlled trials The study authors describe a random component in the sequence generation process, such as referring to a random number table, using a computer random number generator, coin tossing, shu ling cards or envelopes, throwing dice, drawing of lots. Trusted evidence. Informed decisions. Better health. Any one of the following. • Insu icient information to permit a judgement of low or high risk of bias. • The study did not address this outcome. Any one of the following. • No missing outcome data. • Reasons for missing outcome data unlikely to be related to true outcome (for survival data, censoring unlikely to be introducing bias). • Missing outcome data balanced in numbers across intervention groups, with similar reasons for missing data across groups. • For dichotomous outcome data, the proportion of missing outcomes compared with observed event risk is not su icient to have a clinically relevant impact on the intervention e ect estimate. • For continuous outcome data, the plausible e ect size (di erence in means or standardised di erence in means) among missing outcomes is not su icient to have a clinically relevant impact on observed e ect size. • Missing data have been imputed using appropriate methods. Any one of the following. • Reason for missing outcome data is likely to be related to the true outcome, with either imbalance in numbers or reasons for missing data across intervention groups. • For dichotomous outcome data, the proportion of missing outcomes compared with observed event risk is su icient to induce clinically relevant bias in intervention e ect estimate. • For continuous outcome data, the plausible e ect size (di erence in means or standardised di erence in means) among missing outcomes is su icient to induce clinically relevant bias in the observed e ect size. • 'As-treated' analysis done, with substantial departure of the intervention received from that assigned at randomisation. • Potentially inappropriate application of simple imputation. Any one of the following. • Insu icient reporting of attrition/exclusions to permit judgement of low or high risk of bias (e.g. number randomised not stated; no reasons for missing data provided). • The study did not address this outcome. Any of the following. • The study protocol is available and all of the study's prespecified (primary and secondary) outcomes that are of interest in the review have been reported in the prespecified way. • The study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified (convincing text of this nature may be uncommon). Any one of the following. • Not all of the study's prespecified primary outcomes have been reported. • One or more primary outcomes are reported using measurements, analysis methods or subsets of the data (e.g. subscales) that were not prespecified. • One or more reported primary outcomes were not prespecified (unless clear justification for their reporting is provided, such as an unexpected adverse e ect). • One or more outcomes of interest in the review are reported incompletely so that they cannot be entered in a meta-analysis. • The study report fails to include results for a key outcome that would be expected to have been reported for such a study. GRADE: an emerging consensus on rating quality of evidence and strength of recommendations GRADE guidelines: 4. Rating the quality of evidencestudy limitations (risk of bias) Development and preliminary testing of the new fivelevel version of EQ-5D (EQ-5D-5L) Measuring inconsistency in meta-analyses Cochrane Handbook for Systematic Reviews of Interventions version 5.2.0 (updated Cochrane Handbook for Systematic Reviews of Interventions version 6 #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10 OR #11 OR #12 OR #13 OR #14 OR #15 OR #16 OR #17 OR #18 OR #19 OR #20 OR #21 AND INREGISTER *:ti,ab,kw #3 (foam or transfoam):ti,ab Reactive air surfaces for preventing pressure ulcers (Review) Copyright © 2021 The Authors. Cochrane Database of Systematic Reviews published by John Wiley & Sons, Ltd. on behalf of The Cochrane Collaboration ):ti,ab,kw #13 "static air":ti,ab,kw #14 (alternat* next pressure):ti,ab,kw #15 (air next suspension*):ti,ab,kw #16 (air next bag*):ti,ab,kw #17 (water next suspension*):ti,ab,kw #18 sheepskin:ti,ab,kw #19 (turn* or tilt*) next (bed* or frame*):ti,ab,kw #20 kinetic next Pressure Ulcer] explode all trees #24 (pressure next (ulcer* or sore* or injur*)):ti,ab,kw #25 (decubitus next (ulcer* or sore*)):ti,ab,kw #26 ((bed next sore*) or bedsore*):ti,ab Copyright © 2021 The Authors. Cochrane Database of Systematic Reviews published by John Wiley & Sons, Ltd. on behalf of The Cochrane Collaboration Copyright © 2021 The Authors. Cochrane Database of Systematic Reviews published by John Wiley & Sons, Ltd. on behalf of The Cochrane Collaboration Cochrane Database of Systematic Reviews random* or factorial* or crossover* or cross over* or cross-over* or placebo* or assign* or allocat* or volunteer*).ti,ab Copyright © 2021 The Authors In the case that a meta-analysis includes, for example, both cluster-randomised and individually randomised trials, potential di erences in the intervention e ects between di erent trial designs should be considered. This is because the "contamination" of intervention e ects may occur in cluster-randomised trials, which would lead to underestimates of e ect. The contamination could be known as a "herd e ect", i.e. within clusters, individuals' compliance with using an intervention may be enhanced • Two studies (216 participants) that compared reactive air surfaces with undefined 'standard hospital surfaces' reported inconsistent results: Bennett 1998 (116 participants) suggested no difference in the proportion of participants developing a new ulcer between reactive air surfaces and undefined surfaces (RR 2.00, 95% CI 0.64 to 6.28) whilst Inman 1993 (100 participants) suggested reactive air surfaces reduced the risk of having new pressure ulcers 110 participants) compared reactive air surfaces with alternating pressure (active) air surfaces or RIK® microfluid static overlay (MSO), and reported that: 6 of 55 in MSO or low-airloss dynamic mattress (LALDM); 2 of 55 in ISO (3.6%) using reactive air surfaces developed a new pressure ulcer and 6 of 55 (10.9%) using undefined reactive surfaces developed new ulcers Vermette 2012 (110 participants) compared reactive air surfaces with alternating pressure (active) air surfaces or RIK® microfluid static overlay, and defined this outcome as participants self-rated comfort on a scale of 1 to 5 with 1 indicating very comfortable and 5 indicating not comfortable. In total, 68 participants rated comfort: 27 of 30 participants using undefined reactive surfaces and 29 of 34 using reactive air surfaces responded Only Inman 1993 (100 participants; compared reactive air surfaces with undefined standard hospital surfaces) reported this outcome but did not express it as the incremental cost per health benefit gained. Inman 1993 reported that, when reactive air surfaces were used, the cost saved per 100 patients at risk was 6302.6 Canadian dollars conceived the review; designed the review; coordinated the review; extracted data; analysed or interpreted data; undertook quality assessment; performed statistical analysis; produced the first dra of the review review; analysed or interpreted data; checked quality of statistical analysis; produced the first dra of the review; contributed to writing or editing the review; advised on the review; secured funding conceived the review; designed the review; coordinated the review; checked quality of data extraction; contributed to writing or editing the review; advised on the review; secured funding conceived the review; designed the review; checked quality of statistical analysis Vannessa Leung: checked quality of data extraction; checked quality assessment Elizabeth McInnes: conceived the review; designed the review; coordinated the review; checked quality of data extraction; checked quality assessment Editor): edited the protocol; advised on methodology, interpretation and content; approved the final protocol prior to publication Managing Editor): coordinated the editorial process Information Specialist): designed the search strategy and edited the search methods section Editorial Assistant): edited the reference sections of the protocol and the review Research for Patient Benefit, Evidence synthesis for pressure ulcer prevention and treatment, PB-PG-1217-20006). I received support from the Tissue Viability Society to attend conferences unrelated to this work. The Doctoral Scholar Awards Scholarship and Doctoral Academy Conference Support Fund (University of Manchester) also supported a PhD and conference attendance respectively The study authors describe a non-random component in the sequence generation process. Usually, the description would involve some systematic, non-random approach, for example, sequence generated by odd or even date of birth, sequence generated by some rule based on date (or day) of admission, sequence generated by some rule based on hospital or clinic record number.Cochrane Database of Systematic Reviews Insu icient information to permit judgement of low or high risk of bias. It is likely that the majority of studies will fall into this category. The study appears to be free of other sources of bias. There is at least one important risk of bias. For example, the study:• had a potential source of bias related to the specific study design used; or • has been claimed to have been fraudulent; or • had some other problem. There may be a risk of bias, but there is either:• insu icient information to assess whether an important risk of bias exists; or • insu icient rationale or evidence that an identified problem will introduce bias. Recruitment bias (or identification bias) is the bias that occurs in cluster-RCTs if the personnel recruiting participants know individuals' allocation, even when the allocation of clusters has been concealed appropriately. The knowledge of the allocation of clusters may lead to bias because the individuals' recruitment in cluster trials is o en behind the clusters' allocation to di erent interventions; and the knowledge of allocation can determine whether individuals are recruited selectively.This bias can be judged through considering the following questions.• Were all the individual participants identified/recruited before randomisation of clusters?• Is it likely that selection of participants was a ected by knowledge of the intervention?• Were there baseline imbalances that suggest di erential identification or recruitment of individual participants between arms? Baseline imbalance between intervention groups can occur due to chance, problems with randomisation, or identification/recruitment bias. The issue of recruitment bias has been considered above.In terms of study design, the risk of chance baseline imbalance can be reduced by the use of stratified or pair-matched randomisation.Minimisation -an equivalent technique to randomisation -can be used to achieve better balance in cluster characteristics between intervention groups if there is a small number of clusters.Concern about the influence of baseline imbalance can be reduced if trials report the baseline comparability of clusters, or statistical adjustment for baseline characteristics. Similar with missing outcome data in individually randomised trials, bias can occur if clusters are completely lost from a cluster trial, and are omitted from the analysis.The amount of missing data, the reasons for missingness and the way of analysing data given the missingness should be considered in assessing the possibility of bias. Data analyses, which do not take the clustering into account, in cluster trials will be incorrect. Such analyses lead to a "unit of analysis error" and over-precise results (overly small standard error) and overly small P values. Though these analyses will not result in biased estimates of e ect, they (if not correctly adjusted) will lead to too much weight allocated to cluster trials in a meta-analysis.Note that the issue of analysis may not lead to concern any more and will not be considered substantial if approximate methods are used by reviewers to address clustering in data analysis. • Two review authors independently assessed the titles and abstracts of the new search results for relevance using Rayyan rather than using Covidence. • For new included studies, one review author independently extracted data and another review author checked all data, rather two review authors independently carrying out data extraction. • When a study only had complete case data, we considered complete case data in the related main analysis (i.e. assuming no missing data issue). This was not pre-planned. • We presented separate 'Summary of findings' tables for four of the five comparisons evaluated in this review. We did not present the table for the comparison between di erent types of reactive air surfaces. • Where we did not pool data, we conducted a GRADE assessment and presented these assessments in a narrative format in 'Summary of findings' tables. This was not pre-planned.