Apnea Testing for the Determination of Brain Death in Patients Supported by Extracorporeal Membrane Oxygenation

Abstract

The neurological criteria for brain death include coma, absent brain stem reflexes, and apnea. For patients on extracorporeal membrane oxygenation (ECMO), routine apnea testing is not possible because gas exchange occurs entirely through the membrane oxygenator. We describe the protocol we used to perform the apnea test and declare brain death in a patient on ECMO and review the literature of brain death testing in patients on ECMO. A 39-year-old female presented with cardiogenic shock followed by pulseless electrical activity (PEA) and eventually started on veno-arterial (VA) ECMO. Neurology was consulted for prognostication. Initial exam 48 hours after arrest showed absent brain stem reflexes. Another neurological exam 72 hours after arrest was compatible with brain death, so apnea test was performed. The apnea test involved preoxygenation, then she was disconnected from ventilator and the gas sweep rate decreased to 1 L/ minute while maintaining the same blood flow rate. At 10 minutes, the PCO 2 level needed to declare brain death was achieved. With increasing use of ECMO to support critically ill patients, physicians should become familiar with the challenges this technology has created when testing for apnea in the determination of brain death. In this case report, we showed that apnea testing can be done in patients on ECMO without the need for ancillary testing. The mainstay of performing apnea testing on these patients is decreasing the gas sweep rate to 0.5 -1 L/minute while maintaining the same blood flow rate.

Clinical Determination of Brain Death in Children Supported by Extracorporeal Membrane Oxygenation

“…As reported previously [11][12][13][14][16][17][18][19] and demonstrated in our cohort of pediatric patients, decreasing the sweep gas flow rate can serve as an effective means of increasing carbon dioxide to a level sufficient for successful apnea testing. In a subset of patients, however, decreasing the sweep gas flow rate may be insufficient to permit an adequate rise in PaCO 2 as PaCO 2 also depends on the rate of blood flow through the ECMO circuit, intrinsic cardiac output, the degree of lung injury, and the metabolic rate.…”

“…The determination of brain death by clinical criteria requires apnea testing to demonstrate a failure of medullary respiratory centers. While this has historically been viewed as challenging in patients supported by ECMO given that ventilation and oxygenation are controlled by the ECMO circuit [10], case reports and small case series, primarily in adults, suggest that apnea testing is feasible in this population [11][12][13][14][15][16][17][18]. Three cases of apnea testing have also been reported in pediatric patients on ECMO [19].…”

Apnea test for brain death diagnosis in adults on extracorporeal membrane oxygenation: a review

“…Although more frequent than arterial hypotension, it was described by only four studies. ( 10 , 12 , 13 , 23 )…”

“…Disconnection from the ventilator was performed in most of the reviewed cases, combined with supplemental oxygen therapy via catheter or T-piece. ( 10 , 12 - 14 , 16 , 17 , 22 , 23 ) The use of PEEP was also frequent. In these cases, an external valve attached to the endotracheal tube was instituted via a T-piece (CPAP 5 - 10cmH 2 O) or attached to the resuscitation bag (bag-valve or AMBU ® bag).…”

“…( 16 , 17 ) The most frequently used values were 0.5 - 1.0L/minute. ( 2 , 10 , 12 , 13 , 15 , 18 - 23 - 25 ) In addition, most studies recommend against reducing the sweep flow to below 0.5L/min, as this may predispose patients to hypoxemia and derail the completion of the test.…”