MANAGEMENT OF HYPERTENSIVE EMERGENCIES
Despite the large number of patients with chronic hypertension, hypertensive emergencies are relatively rare. Marked or sudden elevation of blood pressure may be a serious threat to life, however, and prompt control of blood pressure is indicated. Most fre-quently, hypertensive emergencies occur in patients whose hyper-tension is severe and poorly controlled and in those who suddenly discontinue antihypertensive medications.
Hypertensive emergencies include hypertension associated with vascular damage (termed malignant hypertension) and hyperten-sion associated with hemodynamic complications such as heart failure, stroke, or dissecting aortic aneurysm. The underlying pathologic process in malignant hypertension is a progressive arte-riopathy with inflammation and necrosis of arterioles. Vascular lesions occur in the kidney, which releases renin, which in turn stimulates production of angiotensin and aldosterone, which fur-ther increase blood pressure.
Hypertensive encephalopathy is a classic feature of malignant hypertension. Its clinical presentation consists of severe headache, mental confusion, and apprehension. Blurred vision, nausea and vomiting, and focal neurologic deficits are common. If untreated, the syndrome may progress over a period of 12–48 hours to con-vulsions, stupor, coma, and even death.
The general management of hypertensive emergencies requires monitoring the patient in an intensive care unit with continuous recording of arterial blood pressure. Fluid intake and output must be monitored carefully and body weight measured daily as an indi-cator of total body fluid volume during the course of therapy.
Parenteral antihypertensive medications are used to lower blood pressure rapidly (within a few hours); as soon as reasonable blood pressure control is achieved, oral antihypertensive therapy should be substituted because this allows smoother long-term manage-ment of hypertension. The goal of treatment in the first few hours or days is not complete normalization of blood pressure because chronic hypertension is associated with autoregulatory changes in cerebral blood flow. Thus, rapid normalization of blood pressure may lead to cerebral hypoperfusion and brain injury. Rather, blood pressure should be lowered by about 25%, maintaining diastolic blood pressure at no less than 100–110 mm Hg. Subsequently, blood pressure can be reduced to normal levels using oral medica-tions over several weeks. The drug most commonly used to treat hypertensive emergencies is the vasodilator sodium nitroprusside. Other parenteral drugs that may be effective include fenoldopam, nitroglycerin, labetalol, calcium channel blockers, diazoxide, and hydralazine. Esmolol is often used to manage intraoperative and postoperative hypertension. Diuretics such as furosemide are administered to prevent the volume expansion that typically occurs during administration of powerful vasodilators.