Hypothermic extracorporeal circulation in immature swine: a comparison of continuous cardiopulmonary bypass, selective antegrade cerebral perfusion and circulatory arrest

Objective: Selective antegrade cerebral perfusion (SCP) has been widely used during complex congenital heart surgery and theoretically affords some degree of neuroprotection. There are limited data to support this claim, however. This study was designed to compare, at profound hypothermia, continuous cardiopulmonary bypass, SCP and circulatory arrest in a survival model of extracorporeal circulation in immature swine. Methods: Fifteen piglets (5.9 ± 1.1 kg) were placed on cardiopulmonary bypass (CPB), cooled to a rectal temperature of 15 °C and subjected to 90 min of hypothermic circulatory arrest (HCA), selective cerebral perfusion (30 ml kg^-1 min^-1) (SCP) or systemic full-flow perfusion (FF; 100 ml kg^-1 min^-1). Piglets were weaned from CPB and extubated. Daily neurologic assessments were performed for 5 days using neurologic deficit scoring (NDS) and overall performance categories (OPC). On postoperative day (POD) 5, all brains were perfusion-fixed and assigned a total histologic score (THS) of neuronal injury by a neuropathologist blinded to the study groups. Results: The median POD 1 NDS/OPC was 0 (range 0-115)/1(range 1-2) for FF, 130 (range 0-195)/2 (range 1-3) for HCA and 0 (range 0-30)/1 for SCP. Although there was a trend for the neurologic status in the HCA group to be worse on POD 1, this did not achieve significance, and both NDS and OPC scores for HCA animals normalised by POD 5. Median THS was 9 (range, 0-11) for FF, 12 (range, 4-14) for HCA and 9 (range, 0-11) for SCP with no statistically significant difference between the groups. Conclusions: In this survival model of hypothermic extracorporeal circulatory support in immature swine, histologic brain injury was similar in piglets subjected to FF, SCP or HCA. Although the HCA group tended to have worse early neurologic outcome, any difference clearly disappeared by POD 5. These data raise the possibility that profound hypothermia alone during extracorporeal support may produce this observed brain injury. Additional study is required to define the precise aetiology of the brain injury observed in this animal model.