Isoflurane may precipitate
ischemia in patients with
coronary artery disease, presumably via "coronary steal." We sought to examine whether
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%. Extraneous causes of
ischemia were controlled as much as possible: arterial blood pressure was maintained within 20% of baseline (primarily with
phenylephrine), heart rate was maintained below 80 bpm, effects from endotracheal intubation were monitored, and measurements were made before incision. Electrocardiogram, transthoracic echocardiography, and coronary sinus
lactate measurement were used to detect
ischemia. Measurements were made after insertion of
vascular catheters, after intubation, and after 20 min of breathing the inhaled
anesthetic. During the awake period and after induction of
anesthesia with
fentanyl (25 micrograms/kg), there was no significant difference detected between the two groups in incidence of
ischemia: 20% in the
enflurane group and 22% in the
isoflurane group (P = 0.38). After 20 min of receiving the inhaled
anesthetic, the incidence of
ischemia in the
isoflurane group increased to 50%, whereas the incidence in the
enflurane group was unchanged at 20% (P = 0.02). These results show that, even with strict control of hemodynamics,
isoflurane is associated with more
myocardial ischemia than is
enflurane.