A clinical study of sensitivity to sodium nitroprusside during controlled hypotensive anesthesia in young and elderly patients.

Aging has important effects on the cardiovascular system; baroreceptor reflex function decreases and the elderly are more resistant to both beta-receptor agonists and antagonists. The purpose of the present clinical study was to determine the relationship between age and sensitivity to sodium nitroprusside in 16 patients during deliberate hypotensive anesthesia by determining the blood pressure changes in young and elderly patients to incremental increases in dose of sodium nitroprusside. A dose-response curve relating change in mean blood pressure to dose of sodium nitroprusside (microgram X kg-1 X min-1) was constructed for each patient; the slope of this line is a measure of "sensitivity." The change in mean arterial blood pressure per microgram X kg-1 X min-1 nitroprusside dose (i.e., slope), showed a significant correlation with age (r = 0.766, P less than 0.001), demonstrating that sensitivity to sodium nitroprusside increases with advancing years. The maximum change in heart rate produced by nitroprusside showed a reciprocal correlation with age (r = -0.791, P less than 0.001). There was no significant correlation between age and maximum change in plasma norepinephrine or epinephrine concentrations during nitroprusside infusion. The increased sensitivity to nitroprusside might have been due to diminished baroreflex activity, resistance of cardiac adrenergic receptors to catecholamine stimulation, or alteration in sensitivity to the direct vasodilating effects of sodium nitroprusside. Whatever the mechanism, however, this clinical study has shown that lower doses of nitroprusside should be used in elderly patients to achieve the same degree of hypotension achieved in younger patients.