[Definition of apnea in the diagnosis of brain death].

Apnea is an essential criterion for the diagnosis of brain death and is often difficult to determine in artificially ventilated patients. Absolute apnea is the absence of respiration when the respiratory center is maximally stimulated by hypercapnia. In a study of 13 cases we show that measuring PaCO2, which must be equal or superior to 50 mm Hg, is mandatory in confirming the stimulation of the respiratory center. The duration of apnea necessary to reach this level is highly variable. It does not induce hypoxemia when the technique of apneic oxygenation is used.