Temperature Management During Cardiopulmonary Bypass: Effect of Rewarming Rate on Cognitive Dysfunction

Abstract

Hypothermia is a very strong neuroprotective agent during cerebral ischemia. However, several randomized clinical trials have failed to demonstrate a protective effect of hypothermic cardiopulmonary bypass on postoperative cognitive deficits. The lack of neuroprotection may be due to rapid rewarming, which in turn may result in cerebral hyperthermia. The purpose of this study was to detennine if rapid rewarming at the end of cardiopulmonary bypass is associated with an increased risk of postoperative neuropsychologic impairment.

Methods: A battery of neuropsychologic tests were administered preand postoperatively to patients undergoing elective coronary bypass surgery. Patients were allowed to drift to 34°C then rewarmed to 37.5°C at the end of cardiopulmonary bypass. Patients were divided into 2 groups according to the median time to rewarm (21 minutes): a rapid group (n = 70) and a slow group (n = 76).

Results: The 2 groups of patients were similar for all pre-, intra-, and postoperative variables, with the exception of rewarming times (15 ± 4 minutes [mean ± SD]) in the rapid group versus 30 ± 9 minutes in the slow group, p < 0.001). The rapid group had a significantly higher prevalence of neuropsychologic impairment 1 week postoperatively than the slow group (82% versus 57%, p < 0.05), as well as worse mean scores on all neuropsychologic tests. There was a nonsignificant trend toward increased neuropsychologic impairment 3 months postoperatively in the rapid group, as well as worse mean scores on 8 of the 10 tests.

Conclusions: Rapid rewarming at the end of cardiopulmonary bypass may increase the risk of postoperative cognitive impairment. Until further studies are performed, rapid rewarming should be avoided in order to minimize the risk of cerebral hyperthermia.

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