key: cord-1038481-3ajjzn3o authors: Thurairatnam, S.; Gawecki, F.; Strangeways, T.; Perks, J.; Santhirapala, V.; Myers, J.; Tighe, H. C.; Howard, L. S.; Shovlin, C. L. title: Triage assessment of cardiorespiratory risk status based on measurement of the anaerobic threshold, and estimation by patient-reported activity limitation date: 2020-03-30 journal: nan DOI: 10.1101/2020.03.27.20045203 sha: ad7531e069a50f480fbdf1d4f8aa08758e247e06 doc_id: 1038481 cord_uid: 3ajjzn3o BACKGROUND: Rapid triaging, as in the current COVID-19 pandemic, focuses on age and pre-existing medical conditions. In contrast, preoperative assessments use cardiopulmonary exercise testing (CPET) to categorise patients to higher and lower risk independent of diagnostic labels. Since CPET is not feasible in population-based settings, our aims included evaluation of a triage/screening tool for cardiorespiratory risk. METHODS: CPET-derived anaerobic thresholds were evaluated retrospectively in 26 patients with pulmonary arteriovenous malformations (AVMs) who represent a challenging group to risk-categorise. Pulmonary AVM-induced hypoxaemia secondary to intrapulmonary right-to-left shunts, anaemia from underlying hereditary haemorrhagic telangiectasia and metabolic equivalents derived from the 13-point Veterans Specific Activity Questionnaire (VSAQ) were evaluated as part of routine clinical care. Pre-planned analyses evaluated associations and modelling of the anaerobic threshold and patient-specific variables. RESULTS: In the 26 patients (aged 21-77, median 57 years), anaerobic threshold ranged from 7.6-24.5 (median 12.35) ml.min-1kg-1 and placed more than half of the patients (15, 57.7%) in the >11 ml.min-1kg-1 category suggested as lower-risk for intra-abdominal surgeries. Neither age nor baseline SpO2 predicted anaerobic threshold, or lower/higher risk categories, either alone or in multivariate analyses, despite baseline oxygen saturation (SpO2) ranging from 79 to 99 (median 92)%, haemoglobin from 108 to 183 (median 156)g.L-1. However, lower haemoglobin, and particularly, arterial oxygen content and oxygen pulse were associated with increased cardiorespiratory risk: Modelling a haemoglobin increase of 25g.L-1 placed a further 7/26 (26.9%) patients in a lower risk category. For patients completing the VSAQ, derived metabolic equivalents were strongly associated with anaerobic threshold enabling risk evaluations through a simple questionnaire. CONCLUSIONS: Baseline exercise tolerance may override age and diagnostic labels in triage settings. These data support approaches to risk reduction by aerobic conditioning and attention to anaemia. The VSAQ is suggested as a rapid screening tool for cardiorespiratory risk assessment to implement during triage/screening. umbrella of "pre-existing medical conditions". There is particular concern that as for health insurance, 38 lack of familiarity with rare diseases may lead to an inappropriately negative weighting, with no time 39 to redress in an acute triage setting. In pre-operative assessments, anaesthetists increasingly use cardiopulmonary exercise testing (CPET) 42 to identify patients who may be unable to appropriately respond to increased cardiorespiratory demands 43 of surgery due to reduced cardiorespiratory reserve. [1, 2] The CPET-derived measure of anaerobic 44 threshold (AT) of <11 ml.min -1 kg -1 has been identified in multiple studies and systematic reviews to 45 be associated with adverse outcomes, mortality, and longer lengths of stay in a variety of surgeries, 46 including intra-abdominal and intra-thoracic procedures. [2] [3] [4] The AT represents the point where ATP generation cannot be met by mitochondrial metabolism. It is considered a good measure as it reflects 48 oxygen delivery and patient conditioning, and is not dependent on the patient's motivation during 49 exercise. [2] 50 51 The rapid assessment tool selected for evaluation was the Veteran's Specific Activity Questionnaire THURAIRATNAM Patients with pulmonary AVMs can demonstrate pronounced physiological abnormalities, including 61 significant hypoxaemia, [12] [13] [14] [15] [16] [17] [18] increased minute ventilation ( V̇E) for given increases in CO2 62 production (V̇E/ V̇CO2 slope) [16, 17] , high cardiac output states [19] , and often iron deficiency and 63 anaemia due to inadequate replacement of haemorrhagic iron losses from underlying hereditary 64 haemorrhagic telangiectasia (HHT) [20, 21] There is no published guidance on management of individuals with pulmonary AVMs or HHT undergoing anaesthesia, and each year, our service receives 66 requests regarding suitability for surgery and insurance, and/or reports that surgery or insurance has 67 been withheld because of the perceived risks of pulmonary AVMs/HHT. Our goal was to evaluate commonly used assessment criteria, and examine the potential role for a rapid 70 assessment tool that could distinguish lower risk individuals in an emergency setting, based on usual 71 cardiorespiratory status. The detailed study aims were to explore which variables may be associated 72 with cardiorespiratory risk defined by the anaerobic threshold in order to inform triage and develop 73 approaches to help guide pre-exposure [23] or pre-operative [1] [2] [3] [4] 10] Additionally, to further support the robustness of data analysis, regression analyses were performed 111 All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The copyright holder for this this version posted March 30, 2020. The CPET-evaluated total oxygen consumption at peak exercise (peak V̇O2) has also been used for high Other measurements that were associated with the higher risk status were higher serum bicarbonate and We used the derived relationship between and AT and VSAQ to model the expected cut off by age on 231 the VSAQ that might indicate an individual in a lower risk category based on the established AT of 11 232 ml.min -1 .kg -1 . As noted in Figure 4 , this differs by patient age such that a VSAQ of 8 would be 233 All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The copyright holder for this this version posted March 30, 2020. suggestive of lower risk irrespective of age, whereas older individuals in the "best" New York Heart 234 Association (NYHA) category [25] could still fall into the higher risk category defined by AT 235 <11ml.min -1 .kg -1 . In younger individuals, lower risk would be assigned even in the setting of more 236 limited exercise capacity, (VSAQ 4-7, NYHA II). In other words, the VSAQ provided sufficient 237 granularity to indicate where age-related physiology would be 'offset' in particularly active older adults, 238 and where there may be more concern for a much less active younger individual. maximal CPET did not improve following embolisation treatments that obliterated the pulmonary 261 AVM(s) and improved SpO2. [16] However, the issue is how best to capture this good exercise 262 tolerance. We have previously reported the ease of use with the VSAQ in a pre-assessment clinic. [18] 263 We have now adjusted to send the VSAQ to patients by email so they can report back the lowest number 264 at which they needed to stop at a subsequent teleconsultation, thus conveying complex physiological 265 information in seconds (Onabanjo et al, manuscript in preparation) . While measurements in acute 266 settings do not reflect the patient's baseline, usual activity could be captured by the VSAQ either before 267 or at the time of triage assessment. Potential mechanisms for the association between lower anaerobic threshold and less successful surgical 270 outcomes have been put forward, including the suggestion that regular exercise stimulates ischaemic 271 preconditioning and lessens surgical demand by enabling the body to adjust to ischaemia and better 272 utilise oxygen. Additionally, endurance exercise has been found to increase mitochondrial mass, which 273 can therefore delay the start of anaerobic respiration by enhancing the utilisation of oxygen by 274 mitochondria. [6] "Prehabilitation" or pre-operative exercise therapy has been found to improve post-275 operative outcomes in other disease groups and has been proposed to help prepare for COVID-19 276 infection. [23] Herein we also show that addressing anaemia is likely to be an additional strategy to 277 reduce cardiorespiratory risk status. In summary, high proportions of patients with a label that might be expected to mean "pre-existing 280 cardiorespiratory condition" do not fall into classical high risk categories when more carefully 281 evaluated. Given the need for appropriate allocation of ward/critical care resources, whether for 282 surgery, or in infective setting, we suggest the VSAQ offers a cost-effective tool that can be easily 283 integrated into triages or anaesthetic pre-assessments to assist with rapid evaluation of cardiorespiratory 284 risk. All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The lowest 10 VSAQ scores and associated exercise limitations are plotted against age. Horizontal bands indicate the respective New York Heart Association (NYHA [25] ) categories of I (no symptoms on ordinary physical activity), II (limited on ordinary activity), III (limited at 20-100m), and IV (limited at rest). To indicate lower and higher risk categories, the regression line is plotted for an anaerobic threshold of 11 ml.min -1 .kg -1 . To provide an indication of confidence limits, and the direction and scale of variation if this threshold scale were to be adjusted, regression lines for anaerobic thresholds of 10 and 12 ml.min -1 .kg -1 are also plotted. 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Diseases of the Heart and Blood Vessels Nomenclature and Criteria for diagnosis The authors thank the patients for their willing cooperation in these studies. The authors have no conflicts of interests to declare.