Effect of rewarming speed during hypothermic cardiopulmonary bypass on cerebral pressure-flow relation

Background: Cerebral blood flow is less dependent on arterial blood pressure during hypothermic cardiopulmonary bypass (CPB) compared to warm CPB. Fast rewarming has a more pronounced effect on cognitive performance in the elderly and causes an increased arterio-jugular oxygen content difference. We studied the effect of rewarming and rewarming speed on cerebral pressure-flow relation in adult patients undergoing elective coronary artery bypass surgery with mild hypothermic CPB. Methods: Fifty patients were randomly assigned to either a slow rewarming strategy (0.24degreesC/min) or a fast rewarming strategy (0.5degreesC/min). Cerebral pressure-flow relation was assessed by a transcranial Doppler derived index for cerebral pressure-flow relation (Pressure-flow Index, PFI). The effect of rewarming speed on cerebral pressure-flow relation was assessed by comparing the absolute PFI value after rewarming between the two treatment groups. Results The mean PFI decreased significantly from 0.73 (standard deviation: 0.28) before rewarming to 0.54 (0.35) after rewarming in the slow rewarming group and from 0.63 (0.29) to 0.48 (0.30) in the fast rewarming group. Absolute PFI after rewarming was not significantly different (mean PFI difference = 0.06; 95% CI = -0.13; 0.26) between both rewarming strategies. Conclusion: Rewarming from mild hypothermic CPB might result in pressure-dependent cerebral blood flow velocity but rewarming speed did not aggravate the effect of rewarming on pressure-flow dependency.