A substantial proportion of patients with coronavirus disease 19 (COVID-19) develop severe respiratory failure and require mechanical ventilation, most often fulfilling criteria for acute respiratory distress syndrome (ARDS).1 The characteristics of these patients are heterogeneous, consistent with what is known about ARDS.1,2 Inflammatory edema leads to varying degrees of lung collapse resulting in ventilation perfusion ratio (V̇/Q̇) mismatching, including a significant shunt fraction. Additionally, lung microthrombi are suspected and result in different levels of dead space and inefficient ventilation.3 In sedated patients, gravitational forces lead to lung atelectasis occurs in the dependent lung regions, and the remaining aerated lung available for gas exchange becomes small. Insufficient hypoxic vasoconstriction, another feature of ARDS that contributes to V̇/Q̇ mismatch, is suggested by the finding of hypoxemia with relatively preserved compliance in some patients.4
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Corresponding Author: Laurent Brochard, MD, Interdepartmental Division of Critical Care Medicine, Li Ka Shing Knowledge Institute, St Michael's Hospital, 209 Victoria St, Room 408, Toronto, ON M5B 1T8, Canada (firstname.lastname@example.org).
Published Online: May 15, 2020. doi:10.1001/jama.2020.8539
Conflict of Interest Disclosures: Dr Brochard reported receiving grants from Medtronic Covidien, and Fisher Paykel and nonfinancial support from SenTec, Air Liquide, and Philips and having a patent issued through General Electric. Dr Telias reported receiving personal fees from MBMed SA and Argentina and grants from CIHR, Canada, outside of the submitted work. No other disclosures were reported.
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