Hypoxaemia in the early stage of COVID-19: prevalence of physical or biochemical factors?

We read with interest the reply from B usana et al. [1] to our correspondence [2]. We fully agree with the authors and with the cited references [3–6] stating that the affinity of haemoglobin (Hb) for oxygen (O 2 ) is not affected in the arteries or in the veins of coronavirus disease 2019 (COVID-19) patients. The confusion arises as our concept is based on the biochemical shunt due to the quaternary conformational change of Hb with a temporary decrease of Hb–O 2 affinity, which is applicable only to the affected alveolar-capillary bed. The ventilation–perfusion mismatch can't explain the high P aCO 2 – P ETCO 2 gap in the setting of COVID-19 induced hypoxaemia and cannot be considered as the sole pathophysiological basis for the treatment in the early stage of COVID-19 https://bit.ly/3BKmGxJ