Monitoring of beta-receptor sensitivity in cardiac surgery

Objective: To determine the repeatability of the hemodynamic response to re peated isoproterenol challenge doses to validate the standardized isoproter enol sensitivity test as an index of cardiovascular beta-receptor function. Design: Prospective, single-blind, nonrandomized clinical trial. Setting: University department of cardiothoracic anesthesia. Participants: Twenty middle-aged men scheduled for primary elective coronar y artery bypass surgery 10 of whom had been treated with cardioselective be ta(1)-antagonists for more than 3 months. Interventions: After induction of anesthesia and baseline hemodynamic evalu ation, cardiac beta-receptor sensitivity was estimated from the chronotropi c/inotropic responses to four intravenous 4-mu g isoproterenol bolus doses. Measurements and Main Results: Baseline cardiovascular function and pharmac odynamic response to the four isoproterenol challenge doses were monitored with catheters in the radial and pulmonary arteries (thermodilution). Heart rate was continuously recorded and calculated from the electrocardiogram. Baseline hemodynamic status and response to the first 4 mu g of isoproteren ol were similar in the 10 patients treated with beta(1)-antagonists and the rest of the patients. In ail 20 patients, heart rate response to the three subsequent isoproterenol challenge doses decreased progressively by 28%. Conclusion:The standardized isoproterenol sensitivity test is unreliable fo r clinical monitoring of cardiac beta-adrenoceptor function. Copyright (C) 1999 by W.B. Saunders Company.