Improving neurological outcomes post-cardiac arrest in a rat model: Immediate hypothermia and quantitative EEG monitoring

Objectives: Therapeutic hypothermia (TH) after cardiac arrest (CA) improves outcomes in a fraction of patients. To enhance the administration of TH, we studied brain electrophysiological monitoring in determining the benefit of early initiation of TH compared to conventional administration in a rat model. Methods: Using an asphyxial CA model, we compared the benefit of immediate hypothermia (IH, T = 33 degrees C, immediately post-resuscitation, maintained 6h) to conventional hypothermia (CH, T = 33 degrees C, starting 1 h post-resuscitation, maintained 12 h) via surface cooling. We tracked quantitative EEG using relative entropy (qEEG) with outcome verification by serial Neurological Deficit Score (NDS) and quantitative brain histopathological damage scoring (HDS). Thirty-two rats were divided into 4 groups based on CH/IH and 7/9-min duration of asphyxial CA. Four sham rats were included for evaluation of the effect of hypothermia on qEEG. Results: The 72-h NDS of the IH group was significantly better than the CH group for both 7-min (74/63; median, IH/CH, p<0.001) and 9-min (54/47, p = 0.022) groups. qEEG showed greater recovery with IH (p < 0.001) and significantly less neuronal cortical injury by HDS (IH: 18.9 +/- 2.5% versus CH: 33.2 +/- 4.4%, p = 0.006). The 1-h post-resuscitation qEEG correlated well with 72-h NDS (p < 0.05) and 72-h behavioral subgroup of NDS (p < 0.01). No differences in qEEG were noted in the sham group. Conclusions: Immediate but shorter hypothermia compared to CH leads to better functional outcome in rats after 7- and 9-min CA. The beneficial effect of IH was readily detected by neuroelectrophysiological monitoring and histological changes supported the value of this observation. (c) 2007 Elsevier Ireland Ltd. All rights reserved.