key: cord-1039109-oojc3ouf
authors: Sorbello, Massimiliano; Rosenblatt, William; Hofmeyr, Ross; Greif, Robert; Urdaneta, Felipe
title: Opening Pandora’s Box: Aerosol boxes and barrier enclosures for airway management in COVID-19 patients – a scoping review and narrative synthesis
date: 2020-09-03
journal: Br J Anaesth
DOI: 10.1016/j.bja.2020.08.038
sha: 115fbd4f62f687dbf5c998136251005f68fdc6a9
doc_id: 1039109
cord_uid: oojc3ouf

BACKGROUND: Exposure of healthcare providers to SARS-CoV-2 is a significant safety concern during COVID-19 pandemic, requiring contact/droplet/airborne precautions. Due to global shortages, limited availability of personal protective equipment has motivated the development of barrier-enclosure systems such as aerosol boxes, plastic drapes, and similar protective systems. We examined the available evidence and scientific publications about barrier-enclosure systems for airway management in suspected/confirmed COVID-19 patients. Medline/EMBASE/Google Scholar databases (December 1/2019 - May 27/2020) were searched for all articles on barrier enclosures for airway management in COVID-19, including references and websites. All sources were reviewed by a panel of experts using a Delphi method with a modified nominal-group technique. RESULTS: Fifty-two articles were reviewed for their results and level of evidence regarding barrier device feasibility, advantages, protection against droplets and aerosols, effectiveness, safety, ergonomics, and cleaning/disposal. The majority of analysed papers were expert opinion, small case-series, technical descriptions, small-sample simulation studies, and pre-print proofs. CONCLUSIONS: The use of barrier-enclosure devices adds to the complexity of airway procedures with potential adverse consequences, especially during airway emergencies. Concerns include limitations on the ability to perform airway interventions and the aid that can be delivered by an assistant, patient injuries, compromise of PPE integrity, lack of evidence for added protection of healthcare providers including secondary aerosolization upon barrier removal, and lack of cleaning standards. Enclosure barriers for airway management are no substitute for adequate PPE, and their use should be avoided until adequate validation studies can be reported.

According to Greek mythology, when Prometheus stole fire from the gods, Zeus took his revenge by introducing Prometheus' brother, Epimetheus, to Pandora. This curious lady opened a box she had been given for safekeeping, thereby unleashing disease, death, and uncountable evils into the world.

Since then, "Pandora's Box" has become an idiom representing "any source of great and unexpected troubles" or "a present which seems valuable, but which in reality is a curse". 1 COVID- 19 may not have been one of the maladies contained in Pandora's box, but the pandemic provides an opportunity to discuss similar mysterious new coffers.

Regional shortages of personal protective equipment (PPE) have triggered concerns regarding the transmission of SARS-CoV-2 by respiratory droplets and aerosols during airway management. A large number of aerosol boxes, plastic covers, tents and sheets, and similar barrier enclosure systems have been proposed to augment or adjunct PPE. None of these barrier devices have undergone rigid evaluation and validation. This review aims to highlight the features of the variously proposed solutions, and discuss limitations, potential pitfalls and dangers related to their use as tools to prevent healthcare provider (HCP) contamination and infection during airway management.

A literature review was performed in Medline, EMBASE, and Google Scholar databases, including publications from December 1, 2019, to May 27, 2020. Articles pertaining to barrier enclosures for airway management in the context of COVID-19 in any language were retrieved. The employed search strategy included the following search terms: "(((COVID OR COVID-19 OR coronavirus) AND (airway OR airway management OR intubation) AND (aerosol box OR intubation box OR airway box OR barrier enclosure OR tent OR barrier OR sheet OR protection OR shield OR drape OR aerosol-generating procedure OR droplet OR safety))) AND ("2019/12/01"[Date -Publication] : "3000" [Date -Publication] )" (appendix 2). A hand search of references cited in the selected papers was performed by an expert panel. An additional Google search was undertaken to identify grey literature evidence and online guidelines of scientific societies, pre-print articles, relevant documents published by governmental or health care agencies, professional associations, and medical educators and innovators.

The database search returned 109 papers, with an additional 32 publications (including 6 websites) found on manual search. Two papers were eliminated as duplicates. Applying inclusion and exclusion criteria, 87 papers were removed. A total of 52 articles and six websites were included in this review ( Figure 1 , Appendix 1). All documents were reviewed by the expert panel and assessed for article type, study design, type of barrier (intervention), sample size, study setting, a summary of interventions (outcomes), main findings, and relevance (Table I) . A narrative synthesis was drafted and referenced. The final result was obtained through a discussion with a modified Delphi method using a modified Nominal Group Technique (mNGT). Given the limitations imposed by the pandemic lockdown and geographical distances, all mNGT discussion rounds (literature search; definitions of questions; literature selection; literature comparison and evaluation; elaboration of conclusions and statements) were performed virtually using email, WhatsApp (https://www.whatsapp.com) and Zoom (https://www.zoom.us) platforms during a sixweek time span.

We found a considerable number of relevant reports and studies. Due to the high heterogeneity, small sample sizes, and limited patient data, we elected to write a scoping review resulting in a narrative summary.

This review included 52 written reports and 6 websites ( Table I) . All were published between December 1 st , 2019 to May 27, 2020. There were nineteen correspondences, 4-22 sixteen letters to the editor, 23-38 ten original articles, 39-48 three research letters, [49] [50] [51] one guideline 52 , one short recommendation, 53 one case report, 54 and one quality improvement study 55 . Of these reports, there were only six case reports or small case series. 6, 15, [41] [42] [43] 54 The most common barrier enclosure types were plastic wraps or tents (25 reports), 5, 9, 12, 15, 17, 23-29, 31, 33, 37, 38, 40, 41, 43, 45, 46, 51, 52, 54, 56 acrylic aerosol boxes (19 reports), 4-6, 8, 11, 16, 18, 19, 22, 24, 34, 35, 42, 44, 50, 53, 57, 58 combinations of aerosol boxes and plastic wraps (8 reports). 6, 8, 13, 15, 32, 36, 42, 48 Eleven reports included other types of barrier enclosures (modified incubator hood, 7 carton box, 8 acrylic panels, 49 surgical retractors, frames and anesthetic poles, 21, 41, 43, 47 external fixators, 14 suspension laryngoscopy support, 40, 55 modified packaging tray 39 ). In ten cases a smoke evacuator/aspirator was reported. 5, 16, 17, 32, 40, 41, 45, 55, 59, 60 Sample sizes were often not given. 5, 6, 8-11, 13, 14, 17-21, 23, 25-27, 29-31, 33, 39, 40, 45, 47, 52, 53, 57, 58 Cases of barrier enclosure use with one manikin or one human was noted in eight reports, 12, 15, 16, 41, 49, 54, 61, 62 five cases in three reports , 22, 24, 43 and series of 25 or more cases in three reports. 36, 44, 46 The reported settings were simulations with manikins in 20 cases, 4-6, 11-13, 16, 19, 21-23, 25-28, 38, 40, 44, 48, 60 simulations with study volunteers in two cases, 9, 50 use in adult patients in 11 cases, 7, 15, 23, 27, 31, 36, 41, 43, 46, 49, 55 and four in pediatric patients. 40, 42, 52, 56 . In 24 reports, there was either no setting described, or there was a barrier enclosure description without demonstration. 6-8, 10, 13, 14, 17, 18, 20, 24-26, 29-32, 37, 39, 45, 51-54, 58 Types of interventions and outcomes J o u r n a l P r e -p r o o f After the original concept was reported by a Taiwanese physician, 57 Canelli and colleagues described a transparent plexiglass barrier enclosure intended to minimize the spread of aerosolized particles during intubation. 4 Their seemingly elegant simulation of a cough (with and without an "aerosol box" in place) demonstrated various particle diffusion patterns and the potential for contamination of personnel charged with airway management. Worldwide, many HCP's have rushed to adopt similar barrier enclosures, and papers describing boxes have been published. 5, 6, 53, 54, 58 Reusable protective shields, 31, 39, 49 and disposable plastic covers for airway management procedures 9, 10, 23, 24, 40, 46, 52 that include intubation, 11, 25-27 placement of supraglottic airway devices, 28 extubation, 12, 29, 51 tracheostomy, 41, 43, 55 bronchoscopy, 42 tracheal tube exchange, pediatric airway management, 40, 52, 56 and other aerosol-generating procedures (AGPs) 13, 14, 41, 43, 55 have been proposed. More recently, hand-made and 3-D printed boxes ( Figure  2 ), adapted neonatal incubator hoods, 7 and even carton-plastic enclosures have been introduced. 8 Many of these devices provide limited or no access for an assistant, and no or limited accommodations for advanced airway management techniques (e.g., flexible scope aided tracheal intubation).

Feldman and colleagues 48 concurred with Canelli's findings in adult and pediatric simulated scenarios. 4, 62 This group confirmed that many airway procedures are AGPs. Extubation may generate more aerosol particles than intubation, 61 and HCPs charged with airway management have higher exposure, increased transmission risk, and should don airborne-level personal protective equipment (PPE) when performing AGPs. 20, 63, 64 Based on these findings, it has been suggested that in cases where adequate PPE is not available, barrier enclosures might mitigate HCP exposure. However, due to the large variability of the approaches, the often-small sample sizes, sparse patient data, and no evidence of decrease viral transmission with their use, many questions remain to be addressed. Therefore, in this narrative, the expert panel proposes that the following issues should be investigated in a controlled fashion before widespread adoption or recommendation of barrier interventions:

While still under investigation, data from the SARS and MERS pandemics, 20 and more recent reports 65-69 strongly suggest airborne transmission results in HCP exposure, especially during airway management procedures. 70, 71 Disease spread and clinical illness incidence appear to be directly proportional to viral load and exposure time, 64 which are higher and longer during airway management, 70 because of the proximity of the HCP to the airway.

Schlieren imaging (a passive imaging method for direct visualization of refractive index changes used to assess small particle spread) of a coughing volunteer showed that considerable amounts of air moved out of the aerosol box from the distal open-end, and through the operative holes. 47, 50 Simulations with e-cigarettes and propylene glycol vapors that (contain large aerosol particles ranging from 40 to 200 micrometers in diameter) suggest that neither the boxes nor the plastic barriers provide sufficient protection from the spread of aerosols, and may even channel or contain them into a higher concentration close to HCPs managing the airway (Appendix 3, Video 1). Trapped aerosols may later be unknowingly released upon removal of the barrier ("secondary aerosolization"). Alternative solutions might include the addition of plastic tents to the boxes, 10, 12, 29, 31, 48, 60 negative pressure systems, 7, 20, 32, 39, 42, 45, 51, 61-64 or rapid vacuum aspiration, that in itself might be more effective than the use of barriers (See Marriot Extractor, Appendix 3, Video 2). 59, 60 Are the rigid boxes ergonomically practical?

Although many of the aerosol box simulations have been performed in an operating room environment, these devices may be used in other patient settings, with different patient surfaces, sizes, and types (e.g., intensive care unit, radiology suite, ambulance). A box placed above the patient's head might not fit (e.g., the obese patient), maybe uncomfortable, or provoke claustrophobia, anxiety, restlessness, and combativeness. Furthermore, they are not usable in situations of severe respiratory distress, where patients are often sitting upright or semirecumbent to maintain respiratory function. Demonstrations of barrier models that are wider, possibly more stable, that allow for ramped positioning and increased maneuverability have been suggested, 13, 36 but there remains no evidence that they improve airway management performance. If an intubation introducer 18 or a bulky or hyperangulated video laryngoscope is used, there may not be sufficient intra-box space to allow for unencumbered manipulation. 19 A simulation study comparing intubation success with or without two generations of aerosol boxes demonstrated that the boxes were associated with higher intubation failure rates and prolonged intubation times. 44 In contrast, other simulations have shown that the use of powered respirator PPE does not affect the time-to-intubation and first-pass success of video laryngoscope aided tracheal intubation. 72 We must also consider how monitor cables, intravenous tubing, breathing circuits, suction tubing, and bedding might interfere with barrier use and be disrupted by barrier placement and removal. Employment of advanced features of supraglottic airway devices (i.e., gastric tube placement, position-check tests, optically guided tracheal intubation) might be limited. 20 A concern for accidental tracheal extubation through entanglement during barrier removal must be considered. Appreciating the time pressure, cognitive load, and stress associated with airway management in patients with anatomically and/or physiologically difficult airways, 73 and the limitations imposed by PPE, 18 the addition of another physical barrier seems counterintuitive.

It has been argued that physical barriers might be more useful for the extubation phase of airway management, but controlled investigations are likewise needed. 20, 51 At the time of anesthetic emergence still more questions arise: How will a waking patient react to a confining barrier? What happens in cases of patient coughing after extubation or the need for airway suctioning? If emergency reintubation is needed, can the operator maneuver properly? Will the confines of the barrier enclosure hinder the use of an airway exchange catheter? What are the proper procedures for managing airway compromise on awakening?

Cases of failed tracheal intubation or extubation requiring reintubation, rescue maneuvers (including the use of alternative devices such as facemask or supraglottic airway ventilation), or emergency surgical airway access may be necessary. One simulation has demonstrated that in the case of difficult airway resuscitation, the ability of an assistant to aid the intubator was encumbered. 21 If a barrier must be rapidly removed during an airway emergency, this may cause delay and/or be hazardous to the patient, airway operator or assistant. 74 It is not difficult to demonstrate through simulation how this approach could make an airway crisis more difficult to handle, including the added task of barrier enclosure removal to provide adequate access to the patient (See Appendix 3, Video 3). Furthermore, should cardiopulmonary resuscitation and defibrillation be needed, the box or tent may represent a flammable oxygen reservoir, increasing the risk of fire. 40, 75

SARS-CoV-2 can survive on plastic surfaces for 3-5 days, 76 and although sensitive to available disinfectants, 77 there is little information on reliable methods of cleaning reusable barrier devices. 40 A variety of reusable barrier enclosure designs with features such as evacuation systems have been reported. 5, 16, 55 Each variation introduces new recesses for which effective cleaning will need to be demonstrated. As alluded to above, the issue of aerosol viral particle load within the confines of a barrier and its release on removal ("secondary aerosolization") will need to be addressed. 22, 69 In parallel with the observation of increased contamination risk during PPE doffing, 78 we might inadvertently create a "secondary aerosolization" risk upon barrier enclosure removal. 30

Concerns exist that there may be a false sense of security among HCPs using these barrier devices, leading to less attentive use of suitable PPE, or that organizations may compromise on providing PPE, using the provision of aerosol boxes or other barrier enclosures as a substitute. We want to raise concerns against such practices, as recent guidelines have advised. 79 Furthermore, aerosol boxes can disrupt or damage the intubator's PPE, 18 as demonstrated in a recent simulation study. 44 Throughout the world, a delicate balance exists between the need for maximal protection and PPE shortages. 80 A recent Cochrane review suggests that ambiguous, constantly changing, or contradictory PPE guidelines might result in PPE underuse and resistance to adhere to infection prevention guidelines. 81 The unquestioned use of barrier enclosure systems might dangerously contribute to this phenomenon. As in all other areas of Medicine, application of unproven devices and tools that otherwise appear to be technical or common-sense solutions can be fraught with harm to patient and HCPs. It appears more rational to adopt correct individual and social protective behaviors, 82 develop PPE prioritization strategies, 61, 68, 78, 80, 82 establish boundaries for non-clinical working areas, 83 and recommend suitable protection levels of PPE for AGPs. 68, 84, 85 

It must be acknowledged that most data regarding the COVID-19 outbreak should be considered of low-level evidence given that many of the analysed papers were expert opinion, technical reports, small simulation studies, small case series, pre-print proofs, or narrative reviews based on previous SARS and MERS outbreaks. Hence, the expert panel could not perform a systematic review. The expert panel highlighted some crucial gaps in knowledge that need to be addressed in future research.

• The ability of barrier enclosure systems to contain or limit aerosols.

• Effects of barrier enclosure systems on basic, advanced, and difficult airway management.

• Implications of barrier enclosure systems on the integrity of PPE, adoption of adequate PPE levels, and adherence to guidelines.

• Implications of barrier enclosure systems on the safety of healthcare providers and patients.

• Definition of clear and univocal protocols for cleaning, disinfection, or disposal of barrier enclosure systems.

There is a growing interest in, and enthusiastic dissemination 58, 86 of barriers such as aerosol boxes, additional covers, and other creative solutions. 87 However, until these modalities show clear advantages and safety after undergoing adequate levels of scrutiny and testing in laboratory examination, simulation, 88, 89 and a practical demonstration in low-risk patient care scenarios, the authors strongly advise to resist their use in hazardous patient care situations. In the absence of this evidence, the opinion of this expert panel is that "aerosol boxes" increase task loading and complexity, add additional barriers to effective airway management, may become reservoirs for contact transmission, may damage or compromise PPE, and, fundamentally, do not stop aerosols.

We are in desperate times: many hard-hit areas resemble battlefield hospitals. In this setting, we need tried-and-true battlefield solutions. Evidence tells us that only properly selected, tested, and fitted PPE will protect healthcare practitioners. In time and with appropriate scientific investigation, it may be possible to demonstrate whether these barriers are of benefit in the fight against the virus, or, like their ancestor in Pandora's curious hands, are "a gift which seems valuable, but is, in reality, a curse. " Authors' contributions Massimiliano Sorbello idea and writing; Felipe Urdaneta idea and writing; Ross Hofmeyr literature search, review and critical appraisal; Robert Greif methodology, search strategy and text critical review; William Rosenblatt final review.

Funding (no external funding for this article)

Medical, Verathon Medical and DEAS Italia, is a patent co-owner (no royalties) of DEAS Italia and has received lecture grants and travel reimbursements from MSD Italia. RH directs a fellowship program which is funded in part by an unrestricted educational grant from Karl Storz. RG is European Resuscitation Council Director of Training and Education, ILCOR Task Force Chair on Education, Implementation, and Teams. FU is part of an Advisory Board for Vyaire Medical and consultant for Medtronic. WR declares travel reimbursement from Ambu. 

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Simulation of a cannot intubate / cannot oxygenate airway scenario without and with an aerosol box. The box appeared to hinder the ability of an assistant to help in the airway resuscitation. The assistant had "hands-on" the patient 42 and 8 seconds, respectively

Acknowledgments (The authors wish to thank all healthcare providers involved in critical care of COVID-19 patients.)

Breaches or damage to PPE: 8 in AB, none without AB.Qualitative comments on their experience: discomfort (50%) and increased cognitive load (33%) with AB.