A left shift in the oxyhaemoglobin dissociation curve in patients with severe coronavirus disease 2019 (COVID‐19)

Critically ill patients with coronavirus disease 2019 (COVID‐19) present with hypoxaemia and are mechanically ventilated to support gas exchange. We performed a retrospective, observational study of blood gas analyses ( n = 3518) obtained from patients with COVID‐19 to investigate changes in haemoglobin oxygen (Hb–O 2 ) affinity. Calculated oxygen tension at half‐saturation (p 50 ) was on average (±SD) 3·3 (3·13) mmHg lower than the normal p 50 value (23·4 vs. 26·7 mmHg; P < 0·0001). Compared to an unmatched historic control of patients with other causes of severe respiratory failure, patients with COVID‐19 had a significantly higher Hb–O 2 affinity (mean [SD] p 50 23·4 [3·13] vs. 24·6 [5.4] mmHg; P < 0·0001). We hypothesise that, due to the long disease process, acclimatisation to hypoxaemia could play a role.