Prone Position and the Risk of Venous Thrombosis in COVID-19 Patients with Respiratory Failure

Despite the small sample size of these studies and the lack of randomized clinical trials specifically addressing the risk of developing VTE in the prone versus supine position during mechanical ventilation, preliminary results suggest that prone positioning may contribute to increase an already elevated risk of developing venous thrombosis in COVID-19 patients with respiratory failure, likely due to position related reduction in venous blood flow, up to stasis. Although regional perfusion remains relatively unchanged in patients with non-COVID ARDS placed in the prone position, the combination of gravity and impaired perfusion due to the increased burden of vascular occlusion (caused by in situ pulmonary thrombosis) may ultimately compromise regional lung perfusion in ARDS of COVID-19 patients. Therefore, as lung injury advances, the benefit of maintaining a prone positioning to improve gas exchange diminishes, with patients instead placed at increased risk of thrombosis. Therefore, specific thrombosis prophylaxis protocols should be defined for COVID-19 patients with ARDS who are placed in the prone position for a prolonged period of time, especially those requiring mechanical ventilation or ECMO. Moreover, due to such increased risk of developing venous thrombosis, it may be advisable to refrain from maintaining prone positioning in the so-called “non-responders” (i.e., in those with ARDS but without significant respiratory improvement after pronation) immediately after the initial pronation sessions.