TY - JOUR T1 - Biochemical shunt: where and how? JF - European Respiratory Review JO - EUROPEAN RESPIRATORY REVIEW DO - 10.1183/16000617.0148-2022 VL - 31 IS - 165 SP - 220148 AU - Mattia Busana AU - Luigi Camporota AU - Luciano Gattinoni Y1 - 2022/09/30 UR - http://err.ersjournals.com/content/31/165/220148.abstract N2 - G. Harutyunyan and co-workers, in their reply to our correspondence, introduce the fascinating concept of “biochemical shunt” to help explain some of the gas exchange abnormalities reported in patients with early coronavirus disease 2019 (COVID-19). In brief, they assert the plausibility that the oxyhaemoglobin dissociation curve (ODC), which may be normal in the arterial and venous blood, could be altered (i.e. reduced oxygen affinity) in the pulmonary blood flowing through diseased alveolar capillaries. It is not easy for us to understand which COVID-19-related factors, or metabolites, might alter the ODC specifically in the pulmonary circulation, and to what extent they involve the lung parenchyma (partially or totally, where and why). Let us suppose, for example, that the biochemical shunt occurs in the whole parenchyma (nearly fully ventilated in early COVID-19).Response to Harutyunyan et al. “Hypoxaemia in the early stage of COVID-19: prevalence of physical or biochemical factors?” https://bit.ly/3K1NSKu ER -