RISKS DIRECTLY RELATED TO THE ANESTHETIC DRUG
Numerous studies have evaluated the influence of choice of anesthesia
on outcome, a question that is discussed throughout this book. From a global perspective,
there does not appear to be one best anesthesia technique. In a multivariate analysis
by Cohen and coworkers[51A]
of 100,000 anesthesia
procedures performed in Canada, the choice of drug did not provide any additional
prognostic information for predicting mortality beyond that of patient disease and
the surgical procedure. In univariant analysis, monitored anesthesia care did appear
to be associated with worse outcomes, but this was attributable to its use for sicker
patients (see Table 24-13
).
One question that has plagued the anesthesia literature is the
issue of inherent toxicity of the anesthetics. There are important distinctions
between undesirable side effects of anesthesia and true toxicity. In the initial
reports of the mid-20th century, there was much concern about curare toxicity. Recent
discussions of anesthetic toxicity have focused on halothane and sevoflurane. The
issues for halothane were fulminant hepatic necrosis and death. The issue for sevoflurane
was whether its metabolite, compound A, was nephrotoxic. After several case reports
of hepatic necrosis after halothane anesthesia, a retrospective study of 856,500
anesthesia procedures at 34 institutions was undertaken.[156]
[157]
[158]
In
all
but nine cases, hepatic necrosis could be explained by other causes. Of the remaining
nine cases, only seven received halothane. Halothane could be associated with hepatitis
and hepatic failure, but the incidence was very low.
Despite concern about the renal toxicity of sevoflurane (see Chapter
8
), the overall safety of this drug has been sufficiently established for
the U.S. Food and Drug Administration to allow its continued sale in the United States.
Some laboratory studies have supported the contention that sevoflurane reacts with
soda lime to form compound A and that this metabolite can lead to renal toxicity.
[159]
[160]
However,
clinical studies have been unable to confirm this potentially detrimental effect.
[161]
[162]
Numerous studies have attempted to define the "safest" anesthetic
for high-risk patients. In the late 1980s, there was particular concern that isoflurane
caused coronary steal in patients with coronary stenosis and collaterals and that
this could result in myocardial ischemia.[163]
[164]
A series of studies was conducted to evaluate the rate of perioperative cardiac
morbidity and mortality in patients undergoing coronary artery bypass grafting to
determine the importance of the agent used for general anesthesia.[165]
[166]
[167]
[168]
[169]
All of these studies demonstrated no difference
in outcome, supporting the contention that there is no one safest anesthesia technique.
A series of randomized trials demonstrated improved outcome with
regional rather than general anesthesia.[5]
[6]
[170]
[171]
[172]
[173]
[174]
For
lower extremity and pelvic surgery, regional anesthesia was associated with a lower
incidence of graft thrombosis and deep vein thrombosis, as well as decreased bleeding.
For vascular surgery patients, the primary finding was a lower incidence of graft
thrombosis and need for reoperation in patients undergoing infrainguinal bypass surgery;
however, the largest of these studies was unable to demonstrate any difference in
outcome based on anesthesia technique.[5]
[6]
[173]
The rate of this complication was low in
the
total cohort in the largest trial, making it impossible to detect any difference
based on technique.
Rodgers and coworkers[175]
published
a large metaanalysis of regional versus general anesthesia. Neuraxial blockade was
found to reduce postoperative mortality and other serious complications. The size
of some of these benefits remained uncertain.
