Safety of apnea testing for the diagnosis of brain death: a comprehensive study on neuromonitoring data and blood gas analysis

Here, we studied the safety of apnea testing (AT) for the determination of brain death with regard to intracranial pressure (ICP), cerebral perfusion and arterial blood gas parameters. We hypothesized that ICP only increases when cerebral perfusion pressure (CPP) remains positive during AT.A total of 34 patients who fulfilled brain death criteria were identified by chart review (2009-2017). We analysed ICP, CPP and mean arterial pressure (MAP) prior to AT, during AT and after AT, as well as arterial pH, paCO2 , paO2 and arterial O2 saturation at the start and end of AT.Intracranial pressure was 87.9 ± 17.7 mmHg (mean ± SD) prior to AT, 89.9 ± 17.2 mmHg during AT and 86.4 ± 15.2 mmHg after AT (P = 0.9). CPP was -6.9 ± 12.8 mmHg prior to AT, -7.1 ± 13.7 mmHg during AT and -8.6 ± 13.0 mmHg after AT (P = 0.98), respectively. MAP was 82.9 ± 14.6 mmHg prior to AT, 84.7 ± 13.9 mmHg during AT and 79.7 ± 9.6 mmHg after AT (P = 0.57), respectively. A total of 10 patients had positive CPP (8.6 ± 4.3 mmHg), but ICP did not increase during AT. Arterial pH decreased from 7.43 ± 0.06 to 7.22 ± 0.06 (P < 0.05), paCO2 increased from 38.6 ± 4.2 to 69.6 ± 8.0 mmHg (P < 0.05), paO2 decreased from 416.3 ± 113.4 to 289.2 ± 146.5 mmHg (P < 0.05), and O2 saturation was stable at 99.8 ± 0.4% and 98.2 ± 3.2% (P = 0.39).Apnea testing had no detrimental effect on ICP, CPP, MAP or oxygenation, regardless of the presence of an initially positive CPP. The lack of further ICP elevations is presumably explained by critical closing pressures above individual CPP levels during AT.