Novel gas exchange analysis in COVID-19 lung disease

Abstract

The study by H arbut et al. [1] reported in this issue of the European Respiratory Journal analyses gas exchange in patients with acute coronavirus disease 2019 (COVID-19) lung disease; arterial oxygen and carbon dioxide tension ( P O 2 and P CO 2 ) and the mean (or mixed) value for alveolar (A̅) P O 2 and P CO 2 (not an “ideal” [2] but the actual value) were measured, when patients (and healthy controls) were breathing air. From the mean alveolar to arterial P O 2 and arterial to mean alveolar P CO 2 gradients (A̅a P O 2 and aA̅ P CO 2 ), the authors computed intrapulmonary shunt and alveolar dead space using the classical three compartment model of R iley and C ournand [2] (but, with important differences: see later). H arbut et al. [1] argued that intrapulmonary shunt should be a marker for alveolar consolidation, as in lobar pneumonia, but at a more microscopic level; alveolar dead space, on the other hand, should be a surrogate for pulmonary microvascular obstruction and thrombosis, e.g. following severe endothelial injury.