Non-Nitrovasodilator Hypotensive Agents: Calcium Antagonists

CALCIUM ANTAGONISTS

Dihydropyridine calcium channel blockers (nicardipine, clevidipine) are arterial selective vasodilators routinely used for perioperative blood pressure control in patients undergoing cardiothoracic surgery. Clevidipine is a relatively new drug with a short half- life, which facilitates its rapid titration. Unlike verapamil and diltiazem, the dihydropyridine calcium channel blockers have minimal effects on cardiac conduction and ventricular contractility. Calcium channel block-ers bind to L-type calcium channel and impair cal-cium entry into the vascular smooth muscle. These L-type receptors are more prevalent on arterial ves-sels than venous capacitance vessels. Consequently, cardiac filling and preload is less affected by these agents than nitrates, which might dilate both arte-rial and venous systems. With preload maintained, cardiac output often increases when vascular tone is reduced by use of dihydropyridine calcium blockers. Nicardipine infusion is titrated to effect (5–15 mg/h).

Other intravenous agents that can produce hypotension perioperatively include the intravenous angiotensin-converting enzyme inhibitor enala-prilat (0.625–1.25 mg). The role of enalaprilat as a nondirect-acting agent in the acute treatment of a hypertensive crisis is limited.