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

Background and purpose 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 . Methods 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 , pa CO 2 , paO 2 and arterial O 2 saturation at the start and end of AT . Results 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), pa CO 2 increased from 38.6 ± 4.2 to 69.6 ± 8.0 mmHg ( P  < 0.05), paO 2 decreased from 416.3 ± 113.4 to 289.2 ± 146.5 mmHg ( P  < 0.05), and O 2 saturation was stable at 99.8 ± 0.4% and 98.2 ± 3.2% ( P  = 0.39). Conclusions 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 .