Uncomplicated severe hypertension

Many more patients are seen with transient asymptomatic hypertension than with a hypertensive emergency or urgency. The hypertension is generally related to other conditions such as pain, anxiety, withdrawal symptoms, or as a compensatory response to mild intravascular volume loss. If the patients are asymptomatic, not perioperative, and without active bleeding, the prognosis is stable and the underlying disorder is the focus of care. Such patients are at greater risk from excessive hypotension resulting from the unnecessary use of antihypertensive agents than from the hypertension itself ( F.ag.§0 1989). The approach is to treat the patient, not the blood pressure. Close follow-up is important, rather than the immediate initiation of antihypertensive therapy.

Antihypertensive agents

Table 3 and Table 4 list by category agents most commonly used to treat severe hypertension. Table 2 gives medical conditions for which each agent is mainly used.

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Table 3 Parenteral agents for severe hypertension

Sodium nitroprusside is the gold-standard parenteral agent for hypertensive emergencies against which all others are compared. It is the most potent, consistently effective, and highly recommended agent for hypertensive emergencies. Its kinetics are almost ideal. Its use is complicated by the fact that it is photosensitive and so must be shielded by foil or other cover. Concerns regarding excessive side-effects and complications have been raised, including the development of cyanide toxicity, a metabolic product of nitroprusside. The cyanide is normally further metabolized by the liver and cleared by the kidneys; however, impairment of either of these organs predisposes the patient to this complication. It is seen most commonly, but not only, in patients on high dosages for longer than 48 h. If cyanide toxicity is suspected, arterial and venous blood gases are evaluated, seeking metabolic (lactic) acidosis with a decreased arteriovenous O 2 difference. When this is present, the infusion should be discontinued immediately. Cyanide antidote kits can be used for severe cases. Hydroxycobalamin also counteracts cyanide and can be given either prophylactically or as acute treatment in those countries where it is approved (not the United States). The other serious concern with nitroprusside is excessive hypotension, precipitating myocardial infarction or stroke. This complication can be seen with any agent used to treat severe hypertension, and may not be increased with nitroprusside.

Nicardipine hydrochloride is a relatively new intravenous agent in the dihydropyridine category of calcium-channel blockers. Its overall effects are similar to those seen with nifedipine, but with less reflex tachycardia and less negative inotropic properties. Its efficacy is generally similar to that of nitroprusside, but with a much longer half-life. It vasodilates cerebral vessels and can raise intracranial pressure. It is gaining acceptance for the treatment of acute perioperative hypertension (Halpern 1995).

Fenoldopam mesylate is another newly approved agent for use in severe hypertension. It is a pure dopaminergic agonist, causing vasodilation in the renal, mesenteric, and splanchnic beds. In clinical trials it appears to have an efficacy relatively equal to that of nitroprusside with similiar kinetics, but without concerns regarding cyanide toxicity or photosensitivity. Because it has positive inotropic properties and specifically increases renal perfusion, it may have particular application in subsets of patients. It could replace much of the use of nitroprusside in the future ( Panacek..199.4.).

Potent diuretics generally do not have a primary role in the management of patients with severe hypertension. Many of these patients are intravascularly volume depleted, particularly those with eclampsia or during the perioperative period. Subsets of patients with active congestive heart failure will require diuresis in addition to antihypertensives.

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