would you anesthetize this patient for cardiac or noncardiac surgery?
Premedication in patients with AS has to be
carefully administered. Oversedation may lead to hypotension and decreased CPP,
while undersedation may result in an anxious, tachycardic patient who is prone
to myocardial ischemia. Patients with AS are critically sensitive to preload
and an appropriate intravascular volume status has to be assured prior to
anesthesia induction. Systemic vascular resistance (SVR) must be maintained at
all times. Thus, neuraxial anesthesia with the risk of sympatholysis is
rela-tively contraindicated in patients with AS. Dysrhythmias are poorly
tolerated, making maintenance of a sinus rhythm imperative. A defibrillator
should be readily avail-able in the operating room.
Perioperative monitoring should be according to
the rec-ommendations of the American Society of Anesthesiol-ogists. Patients
with AS are at increased risk for ischemia and dysrhythmias and monitoring
should include leads II and V5. The sensitivity of this lead
combination for detecting myocardial ischemia is approximately 80%. A pulmonary
artery catheter is routinely used to estimate left-sided filling pressures in
some centers, but this remains controversial.
The main goals for inducing anesthesia in
patients with AS are to avoid major alterations in preload, afterload, heart
rate, and contractility. Thus, etomidate opioids, and mida-zolam are reasonably
good choices, but should be titrated to effect. Vecuronium and cisatracurium
are neuromuscular blockers with favorable hemodynamic profiles. Drugs such as
ketamine and pancuronium may increase heart rate and should be avoided.
Thiopental may cause decreased preload and should probably be avoided.
Similarly, propofol is asso-ciated with hypotension and should probably be
Anesthesia can be maintained with many different tech-niques so
long as the preload, afterload, heart rate, and contractility are monitored to
avoid adverse hemodynamic responses. Opioids, benzodiazepines, potent volatile
anes-thetics, and nitrous oxide should all be titrated, paying careful
attention to maintaining perfusion pressure. Tachycardia, bradycardia, and loss
of sinus rhythm are all problematic. Stroke volume across the stenotic aortic
valve is relatively fixed and is lower than normal; thus, an α-agonist, such as phenylephrine, is the agent of choice for treating hypotension.