Using pulmonary gas exchange to estimate shunt and deadspace in lung disease: theoretical approach and practical basis

Identifying pulmonary vascular obstruction in the presence of pneumonia (e.g., in COVID-19) is difficult. We present here conversion of bedside measurements of arterial and alveolar Po 2 and Pco 2 into values for shunt and deadspace—when both coexist—using Riley and Cournand’s 3-compartment gas exchange model. Deadspace values higher than expected from shunt alone indicate high ventilation/perfusion ratio areas likely reflecting (micro)vascular obstruction.