Modelling lung diffusion-perfusion limitation in mechanically ventilated SARS-CoV-2 patients

This is the first study to describe the daytime evolution of respiratory parameters in mechanically ventilated COVID-19 patients. The data base refers to patients hospitalised in the intensive care unit (ICU) at Arequipa Hospital (Peru, 2335 m) in 2021. In both survivors (S) and non-survivors (NS) patients, a remarkable decrease in respiratory compliance was observed, revealing a proportional decrease in inflatable alveolar units. The S and NS patients were all hyperventilated and their SatO₂ was maintained at >90%. However, while S remained normocapnic, NS developed progressive hypercapnia. We compared the efficiency of O₂ uptake and CO₂ removal in the air blood barrier relying on a model allowing to partition between diffusion and perfusion limitations to gas exchange. The decrease in O₂ uptake was interpreted as diffusion limitation, while the impairment in CO₂ removal was modelled by progressive perfusion limitation. The latter correlated with the increase in positive end-expiratory pressure (PEEP) and plateau pressure (Pplat), leading to capillary compression, increased blood velocity, and considerable shortening of the air-blood contact time.