Anesthetic Regimens
The specific anesthetic objectives for patients undergoing cardiac
procedures are not dissimilar to those for patients undergoing noncardiac procedures
(i.e., rendering patients
Figure 50-30
One-week stroke rate as a function of atheroma grade
(N = 189). (Redrawn from Hartmann GS, Yao
FS, Bruefach M, et al: Severity of aortic atheromatous disease diagnosed by transesophageal
echocardiography predicts stroke and other outcomes associated with coronary artery
surgery: A prospective study. Anesth Analg 83:701–708, 1996.)
pain free, amnestic, and unconscious). However, the pharmacologic options available
to achieve these goals are constrained by the hemodynamic dictates of the patient's
underlying condition. Such dictates include heart rate control, coronary perfusion
pressure requirements, myocardial oxygen supply/demand determinants, and effects
on left ventricular function. Even so, significant advances in anesthetic pharmacology,
monitoring, and other aspects over the last 2 decades have resulted in the evolution
of much safer anesthetic techniques for patients undergoing cardiac surgery. The
anesthetic technique now most frequently used is a balanced anesthetic approach.
Opioids represent the core of this approach, mainly because they are associated
with stable hemodynamics. The vagotonic-induced bradycardia is actually desirable
in several conditions. No one specific opioid has been demonstrated to be superior
to any other. However, opioids are an incomplete anesthetic and do not provide adequate
lack of consciousness and amnesia. Thus, they are variously combined with low/moderate
doses of volatile anesthetics and/or benzodiazepines.
Volatile agents may have the additional advantage of inducing
preconditioning, a potentially extremely important phenomenon in patients either
certain (CPB with aortic cross-clamping) or likely (OPCAB, manipulation-associated
hypotension and decreased coronary perfusion pressure, occlusion of coronary vessels
for distal anastomosis) to be subjected to myocardial (and perhaps neurologic) ischemic
insults.[120]
[121]
[122]
[123]
[124]
The effects of volatile agents on coronary blood flow distribution in patients with
"steal-prone" anatomy has been exhaustively investigated.[181]
[182]
[183]
In
the
setting of appropriate control of hemodynamic variables, no convincing evidence has
shown that isoflurane increases the frequency of ischemic events. Most practitioners
avoid NO because of concern regarding its undesirable effect on pulmonary vascular
resistance and myocardial function and because of its ability to increase gaseous
bubble size. The latter is a risk of excessively rapid rewarming of blood and the
propensity for oxygen and carbon dioxide to come out of solution and form bubbles
as solubility decreases when temperature increases. Propofol is not generally used
as the primary induction agent because of hypotension secondary to decreases in systemic
vascular resistance and mild myocardial depression. Benzodiazepines are a central
component of the balanced anesthetic approach for cardiac patients. Midazolam is
the specific agent most frequently used, and it has minimal effects on coronary blood
flow autoregulation.[184]
[185]
All commonly used muscle relaxants have been used successfully in patients undergoing
cardiac surgery.
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