The influence of anesthesia on myocardial oxygen utilization efficiency in patients undergoing coronary bypass surgery.

A maximum efficiency of myocardial oxygen utilization is desirable, especially in patients with limited coronary blood supply. Little is known about the effects of anesthesia on the efficiency of myocardial oxygen utilization. The aim of this retrospective study was to investigate the effects of different types of anesthesia on myocardial efficiency in patients undergoing coronary bypass surgery. Myocardial blood flow (Argon wash in technique), myocardial oxygen uptake, and standard hemodynamics were measured awake, after induction of anesthesia, and during sternal spread. Myocardial oxygen utilization efficiency was calculated from the ratio of external work divided by myocardial oxygen consumption. Sixty-five patients in eight groups with different anesthetic techniques were studied: 1) halothane/nitrous oxide, 2) enflurane/nitrous oxide, 3) high-dose morphine, 4) high-dose fentanyl, 5) fentanyl/midazolam, 6) high-dose sufentanil, 7) sufentanil/nitrous oxide, and 8) propofol. In all groups induction of anesthesia was associated with a decrease of cardiac work (from 86 +/- 17 to 55 +/- 16 J/min in pooled data) which resulted from a decrease of both stroke volume index and blood pressure. However, myocardial oxygen consumption did not decrease proportionally (from 11.2 +/- 3.0 to 8.5 +/- 2.3 mL.min-1 x 100 g-1 in pooled data) and myocardial oxygen utilization efficiency was therefore decreased in all groups (from 29.2% +/- 2.5% at awake state to 23.9% +/- 5.8% after induction of anesthesia in pooled data). Surgical stimulation by sternotomy and sternal spread was associated with different patterns of hemodynamic response between groups. Blood pressures and external work tended to be higher in the high-dose narcotic groups while it remained less affected in the other groups. However, myocardial efficiency remained depressed in all groups (22.2% +/- 8.2% in pooled data) and with respect to myocardial efficiency no differences between anesthetic techniques were found. We conclude that the specific anesthetic technique does not influence impairment of myocardial oxygen utilization efficiency by anesthesia.