SELECTIVE CONVECTIVE BRAIN COOLING DURING NORMOTHERMIC CARDIOPULMONARY BYPASS IN DOGS

Objective: Although normothermic cardiopulmonary bypass results in imp roved cardiac outcome, patients do not benefit from hypothermia-mediat ed brain protection and thus may be at high risk for ischemic brain in jury. 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 card iopulmonary bypass and forced-air pericranial cooling (to approximatel y 13 degrees C) were maintained for 150 minutes. Data between groups w ere compared by means of repeated-measures analysis of variance and tw o-sample t test. Within each group, brain-to-core temperature gradient s 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 beneat h the dura were 3.3 degrees +/- 1.4 degrees C (mean +/- standard devia tion), 2.6 degrees +/- 1.3 degrees C, and 1.1 degrees +/- 0.6 degrees C cooler than the core temperature, respectively. At the conclusion of the study (i.e., 150 minutes), these temperatures were 4.5 degrees +/ - 1.8 degrees C, 3.9 degrees +/- 1.6 degrees C, and 2.0 degrees +/- 0. 9 degrees C cooler than the core temperature, respectively. Similar ch anges were observed in halothane-anesthetized dogs. Conclusions: Regar dless of the background anesthetic, the magnitude of selective cerebra l cooling observed in our study was larger than the 1 degrees to 2 deg rees C changes previously reported to modulate ischemic brain injury.