Abstract P89: The Induction of Mild Hypothermia Accelerates the Recovery of Autonomic Function After Cardiac Resuscitation in Pigs
The induction of mild hypothermia (MH, 33°C) has become guideline therapy to prevent hypoxic brain injury after cardiac arrest. In awake patients, cooling causes shivering and an activation of the sympathetic nervous system. Whether or not the induction of MH after resuscitation during anaesthesia and muscular relaxation causes the same effects has not been investigated, yet. In 16 anesthetized and relaxed pigs (64±2 kg), ventricular fibrillation (VF, 5 min) was induced electrically. After resuscitation, pigs were assigned either to normothermia (38°C, n=8, NT) or MH (33°C, n=8, intravascular cooling device). At baseline and at 10 min, 1 h, 2 h, 4 h and 6 h after return of spontaneous circulation (ROSC), the spectrum of a 15 min ECG sample (intracardiac catheter, 1 kHz sampling frequency) was analyzed. The high frequency fraction (HF, 0.07–0.5 Hz, AU=arbitrary units) indicated parasympathetic tone, the ratio between low (LF, 0.01–0.07 Hz) frequency fraction and HF indicated sympathetic tone. HF decreased in both groups at 10 min after ROSC. At 2 h after ROSC, HF was higher in MH than in NT. At 6 h after ROSC, HF was back to control values in both groups. An inverse pattern was seen with LF/HF. The induction of MH accelerates the decrease of a temporarily higher symathetic tone after VF and resuscitation. This might represent a protective effect of MH in the recovery of the resuscitated heart.