Brain preservation with selective cerebral perfusion for operations requiring circulatory arrest: protection at 25 °C is similar to 18 °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 °C. The purpose of this study was to evaluate the utility of SCP at warmer temperatures (25 °C) and its impact on operating times. Methods: Piglets undergoing cardiopulmonary bypass (CPB) and 60 min of HCA were assigned to three groups: 18 °C without SCP, 18 °C with SCP and 25 °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 4 h 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 °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 °C and 25 °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 °C and 25 °C maintained baseline L/P ratios. Mean operating times were significantly shorter in the 25 °C group compared to both 18 °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 °C and 25 °C. Procedures performed at 25 °C had significantly shorter operating times while preserving end organs.