MYOCARDIAL-ISCHEMIA - A COMPARISON BETWEEN ISOFLURANE AND ENFLURANE IN CORONARY-ARTERY BYPASS PATIENTS

Isoflurane may precipitate ischemia in patients with coronary artery d isease, presumably via ''coronary steal.'' We sought to examine whethe r myocardial ischemia is more common in patients with coronary artery disease receiving isoflurane (0.7%) than in a control group receiving enflurane (0.9%). Thirty-eight patients scheduled for coronary artery bypass surgery were randomly assigned one anesthetic and monitored for ischemia. All patients had ejection fractions of at least 45%. Extran eous causes of ischemia were controlled as much as possible: arterial blood pressure was maintained within 20% of baseline (primarily with p henylephrine), heart rate was maintained below 80 bpm, effects from en dotracheal intubation were monitored, and measurements were made befor e incision. Electrocardiogram, transthoracic echocardiography, and cor onary sinus lactate measurement were used to detect ischemia. Measurem ents were made after insertion of vascular catheters, after intubation , and after 20 min of breathing the inhaled anesthetic. During the awa ke period and after induction of anesthesia with fentanyl (25 mug/kg), there was no significant difference detected between the two groups i n incidence of ischemia: 20% in the enflurane group and 22% in the iso flurane group (P = 0.38). After 20 min of receiving the inhaled anesth etic, the incidence of ischemia in the isoflurane group increased to 5 0%, whereas the incidence in the enflurane group was unchanged at 20% (P = 0.02). These results show that, even with strict control of hemod ynamics, isoflurane is associated with more myocardial ischemia than i s enflurane.