Effect of temperature and PaCO2 on cerebral embolization during cardiopulmonary bypass in swine

Background. Patients experience cerebral embolization during cardiopulmonary bypass (CPB). This study determined if alterations in temperature and/or PaCO2 can reduce cerebral and ocular embolization. Methods and Results. Forty-four pigs underwent CPB: 24 animals at 28°C, and 20 at 38°C. The two temperature groups were randomized to undergo embolization (67-μm fluorescent microspheres) at either hypercarbia or hypocarbia. Before and after embolization, cerebral and ocular blood flow were determined at normocarbia. Reducing temperature or PaCO2 reduced cerebral and ocular embolization. Hypocarbia reduced cerebral embolization by 60% and 45% in normothermic and hypothermic groups, respectively (p< 0.0001 and p< 0.05). Relative to normothermic animals, hypothermia reduced cerebral embolization by 37% under an elevated CO2 condition (p< 0.05), but not under hypocarbic conditions. Similarly, regardless of temperature, fewer emboli were delivered to the eye in hypocarbic animals (p< 0.05), but hypothermia did not reduce ocular embolization. Conclusions. Cerebral embolization is determined by both temperature and PaCO2 at the time of embolization. In CPB practice, reductions in temperature and/or PaCO2 during periods of embolic risk may reduce brain injury.