Coronary Vascular Effects of Volatile Anesthetics
in Humans
Evaluation of the actions of volatile anesthetics on the human
coronary circulation is difficult because the methods used to determine coronary
blood flow in humans are limited and because the interpretation of clinical findings
during anesthesia is complicated by changes in hemodynamics, the impact of surgery,
and the use of adjuvant anesthetics or vasoactive drugs. Halothane decreases MVO2
[62]
[398]
and variably
alters coronary blood flow in patients with coronary artery disease, but metabolic
or electrocardiographic evidence of ischemia has not been observed during halothane
anesthesia.[62]
[398]
[399]
[400]
Coronary
blood flow may be reduced by halothane or enflurane[401]
in some patients concomitant with decreases in MVO2
,
but simultaneous declines in oxygen extraction[62]
[401]
reflect relative coronary vasodilation.
In 1983, a report by Reiz and colleagues[63]
described the occurrence of myocardial ischemia as indicated by new electrocardiographic
changes and abnormal myocardial lactate extraction in 10 of 21 patients anesthetized
with isoflurane undergoing major vascular surgery. Five patients were treated with
phenylephrine and pacing to return arterial pressure and heart rate to control values,
and after these interventions, electrocardiographic and metabolic derangements resolved
in two of five patients. Despite the apparent dependence of these new episodes of
myocardial ischemia on alterations in systemic hemodynamics, the investigators[63]
proposed that isoflurane had caused coronary steal in these patients, even though
no specific evidence of blood flow redistribution between normal and collateral-dependent
zones was presented. The data of Reiz and colleagues[63]
have not been uniformly supported by subsequent studies. Coronary blood flow remains
unchanged during isoflurane anesthesia in patients undergoing coronary artery bypass
graft (CABG) surgery, but coronary sinus oxygen content increases consistent with
modest coronary vasodilation.[402]
[403]
[404]
Isoflurane alone does not produce electrocardiographic
or metabolic evidence of ischemia.[403]
Instead,
myocardial ischemia occurring during isoflurane anesthesia is most often associated
with tachycardia or hypotension.[64]
[399]
[402]
[404]
Isolfurane
increases the tolerance to pacing-induced ischemia in patients with coronary artery
disease.[405]
Comparisons of studies examining
the effects of isoflurane on the incidence of intraoperative myocardial ischemia
are complicated by differences in patient age, surgical procedure, operative time,
and preoperative LV ejection fraction.[406]
[407]
Compelling evidence demonstrating redistribution of coronary blood flow away from
ischemic to normal myocardium in humans anesthetized with isoflurane has yet to appear.
The incidence of intraoperative myocardial ischemia in susceptible
patients has been difficult to define. Less than 50% of intraoperative ischemic
episodes have been linked to alterations in systemic hemodynamics.[408]
[409]
[410]
[411]
The strongest predictor of intraoperative ischemia remains preexisting ischemia
on arrival to the operating room and not anesthetic technique.[408]
[410]
The only hemodynamic event definitively related
to intraoperative ischemia in patients undergoing CABG surgery is tachycardia.[410]
Evidence[412]
[413]
advocating the perioperative use of β1
-adrenoceptor antagonists to
prevent myocardial ischemia strongly supports this contention. Sternotomy causes
greater increases in calculated indices of MVO2
,
[414]
myocardial lactate production,[415]
and the incidence of hypertension requiring treatment with vasoactive drugs[415]
during morphine compared with halothane anesthesia. In contrast, induction of anesthesia
with desflurane in patients undergoing coronary artery bypass surgery may be associated
with tachycardia, hypertension, and a greater incidence of ischemia than that occurring
during induction with sufentanil.[416]
Steal-prone
anatomy has been identified in 23% of patients with coronary artery disease enrolled
in the Coronary Artery Surgery Study.[417]
However,
patients with steal-prone coronary anatomy do not have a greater incidence of ischemia
during desflurane anesthesia compared with other forms of coronary artery disease.
[416]
The incidences of myocardial ischemia and
adverse cardiac outcomes have been similar for cardiac patients undergoing noncardiac
surgery during sevoflurane compared with isoflurane anesthesia.[418]
New electrocardiographic changes, incidence of postoperative myocardial infarction,
and mortality rates are similar for patients undergoing CABG surgery independent
of anesthetic technique[409]
[410]
[411]
[414]
[415]
[416]
[419]
[420]
[421]
or the presence of steal-prone anatomy.[421]
Despite the findings that volatile anesthetics are mild coronary vasodilators, these
agents do not cause abnormal redistribution of myocardial perfusion resulting in
ischemia when tachycardia and hypotension are avoided.
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