The use of continuous flow of oxygen and PEEP during apnea in the diagnosis of brain death.

The establishment of apnea for the diagnosis of brain death by disconnecting the patient from the ventilator may lead to dangerous hypoxemia at the end of the test period. We established apnea for 4 min in 8 patients with suspected brain death, both by disconnecting them from the ventilator after 10 min ventilation with FIO2 = 1.0 (method "A"), and by leaving them attached to an IMV ventilator circuit with a continuous flow of 100% O2 and PEEP of 4-8 cm H2O without mechanical ventilation (method "B"). PaO2 decreased during the apneic period by 143 +/- 65 (SD) mmHg using method "A", and by 48 +/- 28 mmHg using method "B" (p less than 0.002). The changes in PaCO2 and pH were similar following both apneic methods. We conclude that it is safer to test for apnea by leaving the patients on a continuous flow of 100% oxygen and low PEEP than to disconnect them from the ventilator.