Autonomic regulation during mild therapeutic hypothermia in cardiopulmonary resuscitated patients

We investigated whether there are differences in autonomic cardiovascular regulation in resuscitated patients undergoing therapeutic hypothermia (TH) in relation to the clinical outcome.

Between 2005 and 2007, 18 consecutive resuscitated patients were enrolled. ECG and blood pressure data were recorded for 48 h during hypothermia and warming up to a body core temperature of 36°C. Autonomic regulation was assessed by applying time, frequency, and non-linear dynamics domain methods from heart rate and blood pressure variability (HRV/BPV) analyses.

Nine patients survived with good neurological recovery, and nine patients died during the ICU stay. In both groups, we found a decreased HRV presented by standard deviation of R-R intervals (sdNN) below 50 ms(2) at each time of measurement. Immediately after recovery to a body core temperature of 36°C, a significant higher HRV was found in survivors compared to non-survivors by means of indices sdNN (40.2 ± 19.5 vs. 10.9 ± 4.1 ms(2), P = 0.01), R-R intervals distribution histogram [shannon] (3.7 ± 0.6 vs. 2.2 ± 0.4, P = 0.008), very low frequency band [VLF] (152.2 ± 99.3 vs. 3.4 ± 1.9, P = 0.001) and the variance of the time series of R-R intervals [Wsdvar] (1.16 ± 0.52 vs. 0.29 ± 0.25, P = 0.02) . A decreased spontaneous BPV was found only among survivors comparing blood pressure characteristics within stable hypothermia to the initial state before hypothermia.

Resuscitated patients show a significantly reduced HRV before, during and after TH. Compared to survivors, the non-survivors show a further and significantly decrease of HRV immediately after hypothermia.