Apnea testing for the determination of brain death: a modified protocol. Technical note.

The absence of spontaneous respirations at a PaCO2 of 60 mm Hg or above has traditionally been accepted as the respiratory criteria for the determination of brain death. The testing of patients for the presence or absence of apnea has been complicated because the rate of PaCO2 elevation may vary substantially from patient to patient, and a nonlinear relationship exists between the rate of PaCO2 increase and the duration of apnea. In an attempt to refine the apnea test and to further elucidate the physiology of hypercapnia in humans, 11 patients who met all but the respiratory criteria for brain death were evaluated using a modification of a previously utilized apnea testing protocol. All patients were brought to a PaCO2 of 40 mm Hg or above prior to the apnea test. Baseline PaCO2 ranged from 40 to 45 mm Hg in six patients (Group I) and from 46 to 51 mm Hg in five patients (Group II). The mean rate of PaCO2 increase was 5.1 +/- 1.4 mm Hg/min in Group I and 6.7 +/- 3.1 mm Hg/min in Group II. No problems with cardiovascular instability or hypoxia were encountered during testing in this series. This refinement of the apnea test allows for a streamlined and safe approach to brain death detection.