Apnea testing for brain death confirmation in VV-ECMO patients with very low sweep flow: a case reports and practical physiological insights

In recent years, venovenous extracorporeal membrane oxygenation has become a critical therapeutic tool for patients with severe respiratory failure. Neurological complications, including brain death, are common in this population, and confirming brain death in venovenous extracorporeal membrane oxygenation-supported patients presents unique challenges. In Brazil, an apnea test is mandatory for confirming brain death. However, its application in patients on venovenous extracorporeal membrane oxygenation, which predominantly addresses venoarterial extracorporeal membrane oxygenation cases, is not well defined in the literature. This report outlines our standardized approach for conducting apnea tests in three patients with suspected brain death during ongoing venovenous extracorporeal membrane oxygenation support. We describe three cases from a cohort of 93 extracorporeal membrane oxygenation patients treated for severe respiratory failure. The apnea test was conducted after 24 hours of observation without sedation. Given the physiological nuances of extracorporeal membrane oxygenation, where carbon dioxide clearance is primarily influenced by sweep flow, we adopted a low-sweep-flow protocol (200mL/minute) to achieve a partial pressure of carbon dioxide greater than 55mmHg, consistent with brain death criteria. In cases of severe hypoxemia during the test, extracorporeal membrane oxygenation blood flow can be temporarily increased to maintain oxygenation. All patients received concurrent renal support, which also facilitated carbon dioxide clearance. Our findings suggest that the apnea test with very low sweep flow is a safe and feasible method for diagnosing brain death in venovenous extracorporeal membrane oxygenation-supported patients. This physiologically grounded approach provides a clinically viable strategy for managing the complex interplay between gas exchange, oxygenation, and carbon dioxide clearance during the apnea test.