Systemic Temperature During CPB
Systemic hypothermia has traditionally been used during cardiac surgical procedures to provide a degree of myocardial, cerebral, and somatic protec-tion. In the past few years, however, there has been growing recognition that moderate degrees of systemic hypothermia (ie, 28°C) may not produce additional benefit over mild hypothermia (ie, 34°C) in terms of cerebral or cardiac preservation. As a result, there has been a trend toward the use of mild hypothermia during most cardiac surgical procedures, unless deep hypothermia (ie, <20°C) is needed for circulatory arrest. The single randomized, controlled trial of mild vs moderate hypothermia in CABG patients reported significantly less postoperative AF in the mild hypothermia group. Postoperative AF was identified only retrospectively from chart review, which leaves open the possibility that some arrhythmias were not detected, however. The data from the current trial confirm the pilot data reported by this same group of investigators in a much smaller group of patients. The authors speculated that significant increases in sympathetic nerve activity during rewarming may have been responsible for an increased frequency of postoperative AF in patients who experienced moderate degrees of hypothermia. There have been no studies, however, that address this possibility directly.