Exertional hypoxia in patients without resting hypoxia is an early predictor of moderate to severe COVID-19.

The importance of exertional hypoxia without resting hypoxia in COVID-19 is unknown and may help objectively identify high-risk patients. Interventions may be initiated earlier with sufficient lead-time between development of exertional hypoxia and other outcome measures. We performed a retrospective study of adult patients hospitalized with COVID-19 from March 1, 2020 to October 30, 2020 in an integrated academic medical system in the Chicagoland area. We analyzed patients who had daily exertional oximetry measurements taken. We defined exertional hypoxia as SpO2 < 90% with ambulation. We excluded patients who had first exertional oximetry measurements or first exertional hypoxia after the use of oxygen therapies. We determined the association of exertional hypoxia without resting hypoxia with the eventual need for nasal cannula or advanced oxygen therapies (defined as high flow nasal cannula, Bi-PAP, ventilator, or extracorporeal membrane oxygenation). We also calculated the time between development of exertional hypoxia and the need for oxygen therapies. Of 531 patients included, 132 (24.9%) had exertional hypoxia. Presence of exertional hypoxia was strongly associated with eventual use of nasal cannula (OR 4.8, 95% CI 2.8-8.4) and advanced oxygen therapy (IRR 7.7, 95% CI 3.4-17.5). Exertional hypoxia preceded nasal cannula use by a median 12.5 h [IQR 3.25, 29.25] and advanced oxygenation by 54 h [IQR 25, 82]. Exertional hypoxia without resting hypoxia may serve as an early, non-invasive physiologic marker for the likelihood of developing moderate to severe COVID-19. It may help clinicians triage patients and initiate earlier interventions.