Altered Hemodynamic Response to Dobutamine in Relation to the Degree of Preoperative β-Adrenoceplor Blockade

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Abstract
The relationship between the extent of preoperative .beta.-adrenoceptor blockade and the hemodynamic properties of dobutamine was investigated in patients scheduled for elective myocardial revascularization during isoflurane-nitrous oxide anesthesia. Twenty patients had been treated with .beta.-adrenoceptor blocking drugs for at least 4 weeks before the study; 11 unblocked patients served as control group. The extent of clinical .beta.-adrenoceptor blockade was quantified using the isoproterenol sensitivity test. The dose of isoproterenol required to increase heart rate by 25 beats/min was defined as the CD25 (chronotropic dose 25), representing the degree of .beta.-adrenoceptor blocking drugs. The authors found a significant inverse relationship between CD25 values and changes in cardiac index in response to three dobutamine infusion rates (1.0, 2.0, and 4.0 .mu.g .cntdot. kg-1 min-1), the correlation coefficients being -0.78, -0.79, and -0.82, respectively. Compared to unblocked patients, almost no change, or even a decrease, of the cardiac index was observed at higher degrees of clinical .beta.-adrenoceptor index was observed at higher degrees of clinical .beta.-adrenoceptor blockade. Moreover, there was a significant linear correlation (r = 0.66-0.75) between CD25 values and the effects of dobutamine on systemic vascular resistance index (SVRI), i.e., SVRI decreased in control patients, but increased in patients with high degrees of preoperative .beta.-adrenoceptor blockade. This unmasked vasoconstrictive response to dobutamine was observed despite the fact that the majority of our patients had received cardioselective adrenergic blocking drugs. No correlation existed between the extent of .beta.-blockade and the effects of dobutamine on mean arterial blood pressure, and there was no difference in the effect of dobutamine on mean arterial blood pressure, whether the patient was beta blocked or not. The authors conclude that these results could have important clinical implications for the use of dobutamine in patients undergoing coronary artery bypass surgery who are receiving .beta.-adrenoceptor blocking drugs for control of angina pectoris, hypertension, or arrhythmias.