Do thrombotic and bleeding phenotypes differ in patients with severe COVID-19 compared to other viral pneumoniasin the context of extracorporeal membrane oxygenation?

Background : Respiratory failure is a major complication in patients with COVID-19. Some patients rapidly develop severe acute respiratory distress syndrome (ARDS) with profound hypoxaemia despite mechanical ventilation and rescue therapies such as nitric oxide and require veno-venous extracorporeal membrane oxygenation (VVECMO). Bleeding and thrombosis are major complications in patients treated with ECMO irrespective of the cause for underlying respiratory failure. Thrombosis, mainly pulmonary thrombosis or pulmonary embolism, is frequently seen in patients with severe COVID-19. Aims : To compare thrombosis, bleeding and mortality rates in a cohort of patients with severe COVID-19 pneumonia to a matched cohort of patients with other viral pneumonia, supported with VV-ECMO. Methods : A retrospective single-centre observational study in a tertiary ECMO referral centre. Fifty-four COVID-19 patients admitted for VV-ECMO from 17/3/20 to 26/5/20 were compared with a matched sample of 44 patients received VV-ECMO for non-COVID-19 viral pneumonia from 5/4/18 to 18/1/19. Thrombosis, bleeding and mortality rates were compared. Results : Baseline characteristics were comparable between cohorts. COVID-19 patients had higher admission platelet count and fibrinogen level. Sixty-nine thrombotic events occurred in 43/54 (80%) COVID-19 patients, compared to 34 events in 26/44 (59%) non-COVID-19 patients. Unlike the non-COVID-19 cohort, the majority of thromboses were pulmonary (57%), diagnosed early in the course of VV-ECMO. Twenty-four major bleeding (MB) events occurred in 19/54 (35%) COVID-19 patients and 11 in 9/44 (20%) non-COVID-19 patients. All 21 major haemorrhages during VV-ECMO in the COVID-19 cohort were preceded by thrombosis. Mortality rate was comparable: 9/54 (17%) versus 7/44 (16%). 5/9 COVID-19 fatalities were caused by MB;haemorrhagic transformation of ischemic stroke, versus none in the non-COVID-19 cohort. Conclusions : COVID-19 patients receiving VV-ECMO are at higher risk of thrombosis and fatal MB than patients receiving VV-ECMO for non-COVID-19 viral pneumonia. Further work is required to characterise the COVID-19/VV-ECMO coagulopathies and optimise anticoagulation strategy.