<α>1-Adrenergic Responsiveness during Coronary Artery Bypass Surgery

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Abstract
Elevated catecholamines and <β>-adrenergic receptor hyporesponsiveness (or desensitization) have been demonstrated in failing human myocardium, but the role of the <α>-adrenergic receptor remains unclear. The authors tested the hypothesis that <α>1-adrenergic responsiveness decreases in patients with impaired ventricular function undergoing coronary artery revascularization. Impaired ventricular function was defined prospectively by left ventricular ejection fraction ± 40% (group I, n = 12), and normal ventricular function by ejection fraction > 40% (group II, n = 22). Phenylephrine (Phe) pressor dose-response curves were established prior to anesthesia, during fentanyl anesthesia, and during fentanyl anesthesia plus hypothermic cardiopulmonary bypass at the time of aortic cross-clamp (anes + CPB/AXC). Polynomial regression of the Phe dose response curve estimated the Phe dose required to increase mean arterial blood pressure 20%, designated Ph20. Although pre-anesthesia PD20 and anes + CPB/AXC PD20 values were not affected by ejection fraction, significant differences in PD20 (P < 0.05) between groups occurred during fentanyl anesthesia (group I = 2.28 ± 1.60 <μ>g.kg−1, group II 1.57 ± 0.98 μ.kg−1; mean ± SD). Anes + CPB/AXC was associated with a significant reduction in PD20 in both groups compared with pre-anesthesia (P < 0.01). Our results suggest impairment of <α>1-adrenergic responsiveness occurs during fentanyl anesthesia in patients with ejection fractions ± 40% (evidenced by greater PD20 values). Although this impairment may be due to altered Phe pharmacokinetics, these results also support the possible existence of <α>1-adrenergic receptor desensitization in this group. Reduction in PD20 during anes + CPB/AXC in all patients points to more powerful effects than fentanyl anesthesia alone; such influencing effects may include hemodilution, hypothermia, elevated plasma catecholamines, exclusion of the pulmonary circulation, or altered Phe pharmacokinetics.