Mechanisms of Hypoxia in COVID-19 Patients: A Pathophysiologic Reflection
Mohana Nitsure, Bhakti Sarangi, Guruprasad Hassan Shankar, Venkat Sandeep Reddy, Ajay Walimbe, Varsha Sharma
Abstract
COVID-19 causes severe hypoxemia which fulfills the criteria of ARDS but is not accompanied by typical features of the syndrome. The combination of factors including low P/F ratios, high A-a gradient, relatively preserved lung mechanics, and normal pulmonary pressures may imply a process occurring on the vascular side of the alveolar-capillary unit. The scant but rapidly evolving data available on the pathophysiology are seemingly conflicting, indicating the relative dominance of intrapulmonary shunting or dead space in different studies. In this hypothesis paper, we attempt to gather and explain these observations within a unified conceptual framework by invoking the relative contributions of microvascular thrombosis, along with two proposed vascular mechanisms of capillary flow redistribution and flow through intrapulmonary arteriovenous anastomoses (IPAVA).