Other Anesthetics

Barbiturates, particularly sodium thiopental, are occasionally used as induction agents for open heart surgery. They significantly decrease ventricular function at large doses, by inhibiting calcium ion transport across the sarcolemma. In addition, sodium thiopental causes venodilitation. This venodilatory effect may be useful in situations where reductions in preload are essential, such as in congestive heart failure.

Etomidate, another induction agent, has a much less direct effect on the ventricle than do the barbiturates. It does, however, inhibit steroidogenesis, which generally has little consequence on cardiac function.

Benzodiazepines, including midazolam, do not in themselves have significant effects on cardiac function. However, the concomitant administration of benzo-diazepines and high dose fentanyl may result in myocardial depression, particularly if the patient is receiving calcium channel blockers. They cause some vasodilitation.

Propofol, an intravenous sedative-hypnotic anesthetic, is sometimes used as both an induction and maintenance agent for cardiac surgery. Propofol inhibits ionized calcium influx and thus depresses myocardial function. It also produces venous and arterial vasodilitation. Propofol, which has a chemical structure similar to that of the antioxidant vitamin E, has been found to inhibit lipid peroxidation in hepatic and cerebral cells in vitro. Its effects on lipid peroxidation in the myocardium have not yet been studied. Based on these studies, however, propofol, as a result of its antioxidant properties, may be a useful agent for attenuation of pos-tischemic reperfusion injury of various organs in the postcardiopulmonary bypass period of the surgery.

Ketamine, a phencyclidine derivative, is used primarily as an induction agent for children undergoing cardiac surgery. It maintains hemodynamic stability through its sympathomimetic properties and inhibition of the reuptake of norepinephrine. However, by itself, ketamine depresses myocardial function through inhibition of Ca2+ flux and may therefore result in severe cardiac decompensation in patients with autonomic failure. Ketamine does have hallucinogenic effects which can be attenuated with the prior use of a benzodiazepine.

Droperidol, a butyrophenone, is a sedative which produces mental detachment. It blocks the transmission of norepinephrine (which makes the agent useful for the control of blood pressure in hypertensive patients), dopamine (which precludes its use in patients afflicted with Parkinson's disease), serotonin and gamma aminobutyric acid in the central nervous system. Large doses of this drug may produce a delayed awakening.

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