The mystery of the pandemic's ‘happy hypoxia’

Abstract

Among the many surprises of the new coronavirus is one that seems to defy basic biology: infected patients with extraordinarily low blood oxygen levels, or hypoxia, scrolling through their phones, chatting with doctors, and generally describing themselves as comfortable. Clinicians call them the happy hypoxics. A normal blood oxygen saturation is at least 95%. In most lung diseases, such as pneumonia, falling saturations accompany other physiologic changes, including stiff or fluid-filled lungs, or rising levels of carbon dioxide because the lungs can9t expel it efficiently. It9s these features that leave us feeling short of breath—not, counterintuitively, low oxygen saturation itself. Doctors are keen to understand this hypoxia in COVID-19, and when and how to treat it—including whether patients should monitor their oxygen saturations at home with inexpensive devices called pulse oximeters.