Selective convective brain cooling during normothermic cardiopulmonary bypass in dogs

Although normothermic cardiopulmonary bypass results in improved cardiac outcome, patients do not benefit from hypothermia-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.

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 degrees 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.

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 degrees +/- 1.4 degrees C (mean +/- standard deviation), 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 changes were observed in halothane-anesthetized dogs.

Regardless of the background anesthetic, the magnitude of selective cerebral cooling observed in our study was larger than the 1 degree to 2 degrees C changes previously reported to modulate ischemic brain injury.