Selective convective brain cooling during normothermic cardiopulmonary bypass in dogs

Objective: Although normothermic cardiopulmonary bypass results in improved cardiac outcome, patients do not benefit from hypothermic-mediated brain protection and thus may be at high risk for ischemic brain injury. The present study evaluated the efficacy of selective forced-air cerebral cooling. Methods: Sixteen dogs were anesthetized with either intravenous pentobarbital or inhaled halothane (n = 8 for each group). Temperatures were monitored in the esophagus (i.e., core), parietal epidural space, and brain parenchyma. Normothermic atrial-femoral cardiopulmonary bypass and forced- air pericranial cooling (to approximately 13°C) were maintained for 150 minutes. Data between groups were compared by means of repeated-measures analysis of variance and two-sample t test. Within each group, brain-to-core temperature gradients were compared to zero by means of the one-sample t test. Results: In pentobarbital-anesthetized dogs, after 30 minutes of cerebral cooling, temperatures in the parietal epidural space and 1 cm and 2 cm beneath the dura were 3.3°± 1.4°C (mean ± standard deviation), 2.6°± 13°C, and 1.1 ± ± 0.6°C cooler than the core temperature, respectively. At the conclusion of the study (i.e., 150 minutes), these temperatures were 4.5°± 1.8°C, 3.9°± 1.6°C, and 2.0°± 0.9°C cooler than the core temperature, respectively. Similar changes were observed in halothane-anesthetized dogs. Conclusions: Regardless of the background anesthetic, the magnitude of selective cerebral cooling observed in our study was larger than the 1°to 2°Γ changes previously reported to modulate ischemic brain injury.