Monitoring of beta-receptor sensitivity in cardiac surgery

To determine the repeatability of the hemodynamic response to repeated isoproterenol challenge doses to validate the standardized isoproterenol sensitivity test as an index of cardiovascular beta-receptor function.

Prospective, single-blind, nonrandomized clinical trial.

University department of cardiothoracic anesthesia.

Twenty middle-aged men scheduled for primary elective coronary artery bypass surgery, 10 of whom had been treated with cardioselective beta1-antagonists for more than 3 months.

After induction of anesthesia and baseline hemodynamic evaluation, cardiac beta-receptor sensitivity was estimated from the chronotropic/inotropic responses to four intravenous 4-microg isoproterenol bolus doses.

Baseline cardiovascular function and pharmacodynamic 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 microg of isoproterenol were similar in the 10 patients treated with beta1-antagonists and the rest of the patients. In all 20 patients, heart rate response to the three subsequent isoproterenol challenge doses decreased progressively by 28%.

The standardized isoproterenol sensitivity test is unreliable for clinical monitoring of cardiac beta-adrenoceptor function.