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Diagnostic Accuracy of Subjective Dyspnoea in Detecting Hypoxaemia Among Outpatients with COVID-19: a Retrospective Cohort Study

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Diagnostic Accuracy of Subjective Dyspnoea in Detecting Hypoxaemia Among Outpatients with COVID-19: a Retrospective Cohort Study Open access Original research BMJ Open: first published as 10.1136/bmjopen-2020-046282 on 8 March 2021. Downloaded from Diagnostic accuracy of subjective dyspnoea in detecting hypoxaemia among outpatients with COVID-19: a retrospective cohort study Linor Berezin,1 Alice Zhabokritsky,1 Nisha Andany,1,2 Adrienne K Chan,1,2 Jose Estrada- Codecido,2 Andrea Gershon,1,3 Philip W Lam,1,2 Jerome A Leis,1,2 Scott MacPhee,4 Samira Mubareka,2,5 Andrew E Simor,1,2 Nick Daneman 1,2 To cite: Berezin L, ABSTRACT Strengths and limitations of this study Zhabokritsky A, Andany N, Objectives The majority of patients with mild- to- et al. Diagnostic accuracy of moderate COVID-19 can be managed using virtual subjective dyspnoea in detecting ► This is the first study to evaluate the diagnostic ac- care. Dyspnoea is challenging to assess remotely, hypoxaemia among outpatients curacy of subjective dyspnoea in detecting hypoxae- with COVID-19: a retrospective and the accuracy of subjective dyspnoea measures in mia in the setting of COVID-19. cohort study. BMJ Open capturing hypoxaemia have not been formally evaluated ► The diagnostic accuracy of patient-reported pres- 2021;11:e046282. doi:10.1136/ for COVID-19. We explored the accuracy of subjective ence of dyspnoea in capturing hypoxaemia was bmjopen-2020-046282 dyspnoea in diagnosing hypoxaemia in COVID-19 evaluated across a range of oxygen saturation patients. ► Prepublication history and (SpO2) cutoffs from 92% to 97% and stratified supplemental material for this Methods This is a retrospective cohort study of based on age, presence of lung disease and date of paper is available online. To consecutive outpatients with COVID-19 who met criteria symptom onset. view these files, please visit for home oxygen saturation monitoring at a university- ► Objective dyspnea scales, including the modified the journal online (http:// dx. doi. affiliated acute care hospital in Toronto, Canada from 3 Medical Research Council dyspnoea scale and Roth org/ 10. 1136/ bmjopen- 2020- April 2020 to 13 September 2020. Dyspnoea measures score were also evaluated. 046282). were treated as diagnostic tests, and we determined ► Methodological limitations of the study include the Received 28 October 2020 their sensitivity (SN), specificity (SP), negative/positive retrospective study design and small sample size. http://bmjopen.bmj.com/ Revised 23 January 2021 predictive value (NPV/PPV) and positive/negative likelihood ► This study was limited to patients who were con- Accepted 24 February 2021 ratios (+LR/−LR) for detecting hypoxaemia. In the primary sidered high risk for severe COVID-19, and the data analysis, hypoxaemia was defined by oxygen saturation collected for this study were from single patient as- <95%; the diagnostic accuracy of subjective dyspnoea sessments and did not assess whether changes in was also assessed across a range of oxygen saturation dyspnoea correlate with changes in SpO2 over time. cutoffs from 92% to 97%. Results During the study period, 89/501 (17.8%) INTRODUCTION of patients met criteria for home oxygen saturation monitoring, and of these 17/89 (19.1%) were diagnosed As of 19 January 2021, there have been more on September 29, 2021 by guest. Protected copyright. with hypoxaemia. The presence/absence of dyspnoea than 93 million laboratory- confirmed novel had limited accuracy for diagnosing hypoxaemia, with COVID-19 cases and 2 million deaths docu- 1 SN 47% (95% CI 24% to 72%), SP 80% (95% CI 68% to mented globally. The spectrum of disease 88%), NPV 86% (95% CI 75% to 93%), PPV 36% (95% CI of COVID-19 ranges from asymptomatic or 18% to 59%), +LR 2.4 (95% CI 1.2 to 4.7) and −LR 0.7 mild symptoms, to severe respiratory failure (95% CI 0.4 to 1.1). The SN of dyspnoea was 50% (95% and death.2 Approximately 20% of patients CI 19% to 81%) when a cut- off of <92% was used to with COVID-19 experience dyspnoea, which define hypoxaemia. A modified Medical Research Council is more commonly associated with severe © Author(s) (or their dyspnoea score >1 (SP 98%, 95% CI 88% to 100%), Roth disease.3 Fatal cases of COVID-19 have higher employer(s)) 2021. Re- use maximal count <12 (SP 100%, 95% CI 75% to 100%) and rates of dyspnoea, lower blood oxygen satu- permitted under CC BY-NC. No Roth counting time <8 s (SP 93%, 95% CI 66% to 100%) commercial re- use. See rights ration (SpO2) and greater rates of compli- and permissions. Published by had high SP that could be used to rule in hypoxaemia, but cations such as acute respiratory distress BMJ. displayed low SN (≤50%). syndrome.4 5 For numbered affiliations see Conclusions Subjective dyspnoea measures have In an effort to reduce avoidable hospitalisa- end of article. inadequate accuracy for ruling out hypoxaemia in high- tions, healthcare contacts and transmission, risk patients with COVID-19. Safe home management most patients with COVID-19 can be managed Correspondence to of patients with COVID-19 should incorporate home in the community using virtual healthcare Dr Nick Daneman; oxygenation saturation monitoring. Nick. Daneman@ sunnybrook. ca platforms, and transferred to hospital only if Berezin L, et al. BMJ Open 2021;11:e046282. doi:10.1136/bmjopen-2020-046282 1 Open access BMJ Open: first published as 10.1136/bmjopen-2020-046282 on 8 March 2021. Downloaded from they develop progressive respiratory disease.6 Subjective investigator (either AZ or SM). For the analysis, values dyspnoea can be assessed remotely using patient interview, were obtained from the patient’s initial virtual care assess- and augmented by surrogate measures such as the Roth ment with a pulse oximeter, and subjective dyspnoea score7 and modified Medical Research Council (mMRC) measures were taken at the same time as the objective dyspnoea Scale.8 However, the accuracy of these measures measure of hypoxia. has not been formally evaluated in the context of COVID- 6 7 19. Of great concern is the risk of false reassurance if Predictor variables patients develop hypoxaemia without the subjective sensa- The primary predictor of interest was patient-reported tion of dyspnoea. ‘Silent hypoxaemia’, or low SpO2 in the presence of dyspnoea. Secondary predictor variables absence of dyspnoea, has been reported in the setting of were patient- reported breathing faster at rest, breathing COVID-19 and clinicians have speculated that it may be harder than normal, feeling more breathless today than 9 associated with increased out- of- hospital mortality ; case yesterday, as well as dyspnoea as measured by the mMRC reports have described patients presenting to hospital dyspnoea scale and the Roth score. with rapid deterioration and respiratory failure without 10–12 The mMRC dyspnoea scale has been studied extensively signs of respiratory distress. in a variety of respiratory conditions.8 It is composed of Previous studies of the utility of dyspnoea measure- five categories that describe the degree of activity limita- ment in diagnosing hypoxaemia in other respiratory tion due to worsening breathlessness. The participant conditions such as chronic obstructive pulmonary disease assigns themselves a score ranging from 0 to 4 based on (COPD), congestive heart failure and lung cancer have 13–16 their perception of which activities result in dyspnoea, yielded conflicting results. The association has not with higher scores indicating a greater impairment in been studied during the COVID-19 pandemic despite the their ability to perform daily activities. highly publicised concept of ‘silent hypoxaemia’. There- The Roth score is a tool for quantifying the severity of fore, we sought to determine the diagnostic accuracy of dyspnoea, in which the patient is asked to count audibly subjective dyspnoea measures in diagnosing hypoxaemia to 30 in their native language, and the maximal count among a cohort of outpatients with COVID-19. and counting time are recorded. A prior validation study demonstrated a strong positive correlation between pulse oximetry measurement and both counting time (r=0.59; METHODS p<0.001) and maximal count (r=0.67; p<0.001) achieved Study participants in one breath.7 All consecutive patients with laboratory- confirmed COVID-19 followed as outpatients by the Sunnybrook Outcomes Health Sciences Centre COVID-19 Expansion to Outpa- The reference measure was SpO2 as measured by a http://bmjopen.bmj.com/ tients (COVIDEO) virtual care service from 3 April 2020 ChoiceMMed pulse oximeter (model MD300C20). In to 13 September 2020 were included in this retrospective the primary outcome definition, hypoxaemia was consid- cohort study. The patients were diagnosed based on a posi- ered to be present if SpO2 was <95% in order to provide tive mid- turbinate or nasopharyngeal swab for COVID-19 sufficient power to estimate the diagnostic test character- RNA detected by real- time PCR. COVIDEO is a virtual istics. Secondary outcomes included hypoxaemia cut-offs care model for monitoring of outpatients with COVID-19 varying from 92% to 97%. Patients received instructions at Sunnybrook Health Sciences Centre, and is the basis 17 on correct pulse oximeter use and were told to wait 5–10 s of similar programmes at other hospitals. Patients were on September 29, 2021 by guest. Protected copyright. for readings to calibrate prior to recording the SpO2 contacted by an infectious diseases physician for assess- measurements. ment and monitoring either by telephone or through the Ontario Telemedicine Network virtual platform. A portable pulse oximeter was delivered to the homes Statistical analysis of high- risk patients as defined by age >60 years, preg- In the primary analysis, the subjective dyspnoea measures nancy, extensive comorbidities or presence of cardiore- were treated as diagnostic tests, and the specificity (SP), spiratory symptoms, such as chest pain or dyspnoea. The sensitivity (SN), positive predictive value (PPV), negative requirement for informed consent was waived.
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