Effect of anesthetics on the heart.

In man, high doses of the "group 1" inhalation anesthetics (diethylether, cyclopropane, and fluroxene) produce relatively minor depression of ventricular function, although it is possible to depress the heart if the dose is great enough. The "group 2" drugs (halothane, methoxyflurane, etc.) produce dose-related depression in cardiac function, but reasonable caridac outputs and blood pressure can be maintained at light anethetic levels. Much the same can also be said for the intravenous barbiturates and other hypnotics. If ventilation is supported and hypovolemia avoided, large doses of the narcotic analgesics appear to produce minimal cardiac effects. The only intravenous drug which stimulates the heart is the dissociative anesthetic ketamine, and this is probably an autonomic, reflex phenomenon (as with group 1 inhalation anesthetics). Regional anesthesia and the neuromuscular blocking drugs appear to have relatively little effect on ventricular function. Most of the work in man on the effect of anesthetics has been in healthy patients or volunteers. The effects on patients with severe heart or other systemic disease may well be different. In fact, low concentrations of fluroxene have been shown to produce significant depression of stroke volume in patients with aortic vavular disease in contrast to the effects on healthy volunteers. All potent central nervous system depressant drugs possess the potential for significant cardiac depression. If such depression is undersirable in a particular patient, the only safe way to administer anesthesia is by careful titration of the dose against the best measurement of cardiac function which is available. At the present time, this would mean measuring at least direct arterial pressure, central venous pressure, and a continuous electrocardiogram. The optimal management would prpbably include recording systolic time intervals, pulmonary capillary wedge pressure, and some measure of cardiac output as well. All the skill and pharmacologic knowledge available connot substitute for vigilant monitoring and carful tiration of drug dose in the clinical situation.