Minimum cerebral blood flow in selective cerebral perfusion for brain protection within a limited period of time

Abstract

We experimentally evaluated the minimum cerebral bral blood flow required for brain protection during 90 min of selective cerebral perfusion (SCP) at moderate hypothermia ranging from 24° to 28°C, using short-latency somatosensory evoked potentials (SSEPs) as a monitor for cerebral electrical activity. Twenty mongrel dogs were divided into two groups of 10. In group A the brain temperature was lowered to 26°–28°C by core cooling using cardiopulmonary bypass (CPB), and in group B the brain was cooled to 24°C. Each group was subdivided into high-flow (H) and low-flow (L) groups according to the flow rate of SCP. In the high-flow subgroups of group A (group AH,n=5) and group B (group BH,n=5), the flow rate of SCP was maintained at 5 ml/kg/min. In the low-flow subgroups of group A (group AL,n=5) and group B (group BL,n=5), the SCP flow was 3 ml/kg/min. After systemic hypothermia and circulatory arrest, SCP was performed for 90 min via the innominate artery. In the high-flow subgroups (AH + BH), all SSEP wave components from P1 to N2 were completely preserved in 9 of the 10 dogs after 90 min of SCP, with 90% recovery rate of SSEPs. In the low-flow subgroups (AL+BL), the recovery rate of SSEPs was 30%. In four dogs without full recovery of SSEPs in group AL, all components of SSEPs were abolished; however, P1N1 waves, which are regarded as an electrical activity originating from the subcortical pathway, were restored in two of the three in group BL. Therefore, it might be suggested that more than 5 ml/kg/min of SCP is needed as a minimum cerebral blood flow for 90 min at hypothermia of 24° to 28°C, but 3 ml/kg/min is insufficient to protect the whole brain.