Histamine Release during Morphine and Fentanyl Anesthesia

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Abstract
High doses of morphine produce peripheral vasodilation and frequently significant hypotension. These effects may be due, in part, to the release of histamine. One putative advantage of high-dose fentanyl anesthesia is its relatively small effect on peripheral vascular resistance. The hemodynamic differences between morphine and fentanyl might be attributable to histamine release. Patients (15) were studied prior to coronary artery bypass surgery. Subjects received an infusion of morphine (1 mg/kg, i.v. at 100 .mu.g/kg per min [ n = 8]) or fentanyl (50 .mu.g/kg at 5 .mu.g/kg per min [n = 7]). Patients in the morphine group had an average 750% peak increase in plasma histamine accompanied by a significant decrease in mean arterial pressure (-27 mmHg) and systemic vascular resistance (-520 dyne .cntdot. s/cm5). The greatest decrease in systemic vascular resistance occurred in those patients with the highest levels of plasma histamine (r = -0.81). Patients in the fentanyl group had no change in plasma histamine and no decrease in arterial pressure or systemic vascular resistance. Cardiac output and heart rate were comparable between the 2 groups. Differences in the release of histamine account for most, if not all, of the different effects of morphine and fentanyl on the peripheral vasculature.