Sympathetic cardiovascular hyperactivity precedes brain death

The time preceding brain death is associated with complex dysregulation including autonomic dysfunction that may compromise organ perfusion, thus inducing final organ failure. In this study, we assessed autonomic function in patients prior to brain death.

In 5 patients (2 women, median 60 years, age range 52–75 years) with fatal cerebral hemorrhage or stroke and negative prognosis, we monitored RR-intervals (RRI), systolic and diastolic blood pressure (BP), and oxygen saturation. Adjustment of mechanical ventilation remained constant. We assessed autonomic function from spectral powers of RRI and BP in the mainly sympathetic low- (LF, 0.04–0.15 Hz) and parasympathetic high-frequencies (HF, 0.15–0.5 Hz), and calculated the RRI-LF/HF-ratio as index of sympathovagal balance. Three patients required norepinephrine (0.5–1.6 mg/h) for up to 72 h to maintain organ perfusion. Norepinephrine was reduced to 0.2–0.5 mg/h within 2 h before brain death was diagnosed according to the criteria of the German Medical Association. Wilcoxon test compared average values of ten 2-min epochs determined 2–3 h (measurement 1) and 1 h (measurement 2) before brain death.

We found higher systolic (127.3 ± 15.9 vs. 159.4 ± 44.8 mmHg) and diastolic BP (60.1 ± 15.6 vs. 74.0 ± 15.2 mmHg), RRI-LF/HF-ratio (1.2 ± 1.6 vs. 3.9 ± 4.0), and BP-LF-powers (2.7 ± 4.8 vs. 23.1 ± 28.3 mmHg²) during measurement 2 than during measurement 1 (p < 0.05).

The increase in BPs, in sympathetically mediated BP-LF-powers, and in the RRI-LF/HF-ratio suggests prominent sympathetic activity shortly before brain death. Prefinal sympathetic hyperactivity might cause final organ failure with catecholamine-induced tissue damage which impedes post-mortem organ transplantation.