Validation of the Apnea Test Performed by High-flow Oxygen Therapy in Patients With Clinical Brain Death

The protocol is based on performing two consecutive apnea tests on a patient in clinical brain death in intensive care unit. The first apnea test will be conducted under standard oxygen therapy and confirms clinical brain death (standard procedure). The second apnea test (for the study) will be conducted under high-flow oxygen therapy. Only patients whose apnea test is initially validated under standard oxygen therapy will have the second apnea test under high-flow oxygen therapy. After a standardized preoxygenation, the 1st apnea test will be performed under standard oxygen therapy through the endotracheal tube (flow at 8L/min) for 10 minutes. An arterial blood gas sampling will be sampled every 2 minutes during the1st apnea test. The confirmation of clinical brain death by validating the apnea test under standard oxygen therapy will be done if the following two conditions are met: 1) absence of a spontaneous respiratory movements AND 2) an arterial capnia \> 60 mmHg or an increase \> 20 mmHg (compared to the capnia at the end of preoxygenation). Then the patient will be reconnected to the ventilator for 15 minutes. A second standardized preoxygenation will be performed before the 2nd apnea test. The second apnea test will be performed under high-flow oxygen therapy through the endotracheal tube (flow at 50L/min, FiO2 100%) for 10 minutes. An arterial blood gas sampling will be sampled every 2 minutes during the1st apnea test. Then the patient will be reconnected to the ventilator with the same settings before the start of the study.