Brain preservation with selective cerebral perfusion for operations requiring circulatory arrest: protection at 25 degrees C is similar to 18 degrees C with shorter operating times.

Background: Hypothermic circulatory arrest (HCA) is employed for aortic arch and other complex operations, often with selective cerebral perfusion (SCP). Our previous work has demonstrated real-time evidence of improved brain protection using SCP at 18 degrees C. The purpose of this study was to evaluate the utility of SCP at warmer temperatures (25 degrees C) and its impact on operating times.

Methods: Piglets undergoing cardiopulmonary bypass (CPB) and 60 min of HCA were assigned to three groups: 18 degrees C without SCP, 18 degrees C with SCP and 25 degrees C with SCP (n=8 animals per group). CPB flows were 100 ml kg(-1) min(-1) using pH-stat management. SCP flows were 10 ml kg(-1) min(-1) via the innominate artery. Cerebral oxygenation was monitored using NIRS (near-infrared spectroscopy). A microdialysis probe placed into the cerebral cortex had samples collected every 15 min. Animals were recovered for 4h after separation from CPB. All data are presented as mean+/-standard deviation (SD; p<0.05, significant).

Results: Cerebral oxygenation was preserved during deep and tepid HCA with SCP, in contrast to deep HCA without SCP (p<0.05). Deep HCA at 18 degrees C without SCP resulted in significantly elevated brain lactate (p<0.01) and glycerol (p<0.01), while the energy substrates glucose (p<0.001) and pyruvate (p<0.001) were significantly depleted. These derangements were prevented with SCP at 18 degrees C and 25 degrees C. The lactate/pyruvate ratio (L/P) was profoundly elevated following HCA alone (p<0.001) and remained persistently elevated throughout recovery (p<0.05). Piglets given SCP during HCA at 18 degrees C and 25 degrees C maintained baseline L/P ratios. Mean operating times were significantly shorter in the 25 degrees C group compared to both 18 degrees C groups (p<0.05) without evidence of significant acidemia.

Conclusion: HCA results in cerebral hypoxia, energy depletion and ischaemic injury, which are attenuated with the use of SCP at both 18 degrees C and 25 degrees C. Procedures performed at 25 degrees C had significantly shorter operating times while preserving end organs.