Happy hypoxia in COVID-19: pathophysiology and pulse oximetry accuracy

Wilson-Baig, Noamaan

Many patients with COVID-19 have presented to emergency departments with arterial hypoxaemia but without breathlessness;this is called 'happy hypoxia' or, more accurately, 'silent hypoxaemia'. Hypoxaemia needs to be identified correctly in patients with COVID-19 as it is associated with in-hospital mortality. The aetiology of silent hypoxia is unclear, and the pathophysiological processes involved in the relationship between the response to hypoxaemia and the sensation of dyspnoea may explain its clinical presentation. Pulse oximetry is used routinely to measure oxygen saturation. However, recent literature has questioned its accuracy in patients with COVID-19. Inaccuracies in readings, which arise for several reasons, could in part explain silent hypoxaemia. Caution should be taken when interpreting pulse oximeter readings or patients could be given a higher inspired oxygen fraction than necessary. Silent hypoxaemia may also mask disease severity in patients with COVID-19.