The respiratory distress syndrome accompanying a subset of severe COVID-19 may be distinctfrom classic ARDS. There is relatively well-preserved lung mechanics despite the severity ofhypoxemia, characterized by high respiratory compliance and high shunt fraction, and increasingrecognition of systemic features of a hypercoaguable state in this disease. Therefore, thepathology and pathophysiology of COVID-19 might differ from that of typical ARDS. Wesought to define the role of complement activation and microvascular thrombosis in cases ofpersistent, severe COVID-19.