Alterations in Sympathetic Nervous System Activity with Intraoperative Hypothermia during Coronary Artery Bypass Surgery: Catecholamine FindingsThe changes observed in plasma catecholamines are probably not related to the anesthetic agent, heparin, or to the extracorporeal bypass machine because these variables were constant throughout the fall in core temperature. Also, the changes in catecholamines probably cannot be ascribed to the antihypertensive drugs received by some of these patients preoperatively, because there was no statistical difference between patients who were, and were not, receiving these medications. The two sites of blood sampling should not affect our results, because the central venous NE levels should be no more than 30 percent higher than simultaneous arterial NE values in striking contrast to the 250 percent elevation we describe. Similarly, central venous EPI values should be at least 30 percent lower than similar arterial samples, not elevated as we describe.
We believe that hypothermia-induced alterations of the SNS occur in humans as they do in nonhuman primates. The ventricular dysrhythmias and hemodynamic instability encountered during deep hypothermia are difficult to manage and may be terminal events. Based upon our catecholamine data, we speculate the following: (1) hypotension associated with hypothermia below core temperatures of 28┬░C either in the operating room or emergency department which does not respond to intravascular volume, may improve with the administration of systemic catecholamines, and (2) likewise, four hours after rewarming, an overactivity of the SNS may occur, at which time arrhythmias and hypertension would be best treated with short acting adrenergic receptor blockade.
Changes in Thyroid Hormone
A postoperative fall in the serum concentration of T3, with or without systemic hypothermia, is a common postoperative finding and is consistent with previously published data about T3 reductions in postoperative CABS patients.