Impact of high intracranial pressure on neurophysiological recovery and behavior in a chronic porcine model of hypothermic circulatory arrest

Objective: This review was undertaken to determine whether high intracranial pressure (ICP) during reperfusion after hypothermic circulatory arrest (HCA) correlates with evidence of suboptimal cerebral protection in a chronic porcine model. Methods: In concurrent studies of cerebral protection, 48 control pigs (24-31 kg) underwent 90 min of HCA at 20°C using a strictly standardized protocol. Hemodynamic measurements, ICP and neurophysiological data (EEG, SSEP) were assessed before HCA and until 3 h postoperatively. ICP was measured using a Codman microtip catheter inserted directly into brain parenchyma. Neurological/behavioral evaluation (9=full recovery) was carried out daily through postoperative day (POD) 3. Results: There were no significant hemodynamic or metabolic differences between individual animals. ICP (mmHg) increased significantly for the first 3 h after HCA: from baseline levels of 6.2±2.1 to 10±2.6 at 1 h, 11±3.2 at 2 h and 10±3.6 mmHg at 3 h; P<0.001 for the trend. EEG recovery 3 h after HCA was observed in 13 animals (27%), and correlated with lower ICP during reperfusion (P<0.001): with each 1 mmHg increase in ICP at 3 h, the odds of early EEG recovery decreased by a factor of 0.72. Lower ICP during reperfusion was also significantly associated with higher behavioral scores on POD 1 and 2, P<0.001. Conclusions: A significant rise in ICP may help explain the prolonged obtundation and confusion often seen clinically after HCA. If these small but consistent increases in ICP contribute to rather than reflect ischemic neuronal damage, simple maneuvers to reduce ICP may improve cerebral recovery after HCA.