Intrapulmonary shunting is a key contributor to hypoxia in COVID-19: an update on the pathophysiology

Data from every patient over 18 years old admitted to the two centres for clinically and/or laboratory-confirmed COVID-19 was recorded. Patients were only included if they were hypoxic on admission and required supplemental oxygen. Patients were excluded if they were pregnant, self-discharged against medical advice before treatment completion, or if there was no documentation of oxygen saturations on admission. Oxygen saturations measured using fingertip pulse oximetry by the ambulance crew and emergency departments were collected. Oxygen flow (litres/min) was converted to FiO2 according to predetermined conversion charts. Baseline saturations on air followed by saturations after administration of oxygen were collected and used to construct the oxygen dissociation curve (ODC). The calculation has been previously described in detail. Intrapulmonary shunt and VA/Q mismatch were estimated using software based on the algorithm developed by Lockwood et al which produces ODCs using a two-compartment model. Epidemiological, clinical, laboratory, and radiological characteristics were collected in addition to treatments and outcome (discharge or death).