Hypertensive crisis is defined as a severe elevation in BP and is classified as either urgency or emergency. In
hypertensive urgency there is no end-organ injury and no evidence that acute BP lowering is beneficial. Indeed, rapid uncontrolled pressure reduction may be harmful. Therefore, in
hypertensive urgencies BP should be lowered gradually over 24 to 48 hours using oral
antihypertensives. When the cause of transient BP elevations is easily identified, appropriate treatment should be given. When the cause is unknown, an oral
antihypertensive should be given. The efficacy of available treatments appear similar; however, the underlying pathophysiological and clinical findings, mechanism of action and potential for adverse effects should guide choice.
Captopril should be avoided in patients with bilateral
renal artery stenosis or unilateral
renal artery stenosis in patients with a
solitary kidney.
Nifedipine and other
dihydropyridines increase heart rate whereas
clonidine, beta-blockers and
labetalol tend to decrease it. This is particularly important in patients with ischaemic
heart disease.
Labetalol and beta-blockers are contraindicated in patients with
bronchospasm and
bradycardia or
heart blocks.
Clonidine should be avoided if mental acuity is desired. In
hypertensive emergency there is an immediate threat to the integrity of the cardiovascular system. BP should be immediately reduced to avoid further end organ damage.
Sodium nitroprusside is the most popular agent.
Nitroglycerin (
glyceryl trinitrate) is preferred when there is acute coronary insufficiency. A beta-blocker may be added in some patients.
Loop diuretics,
nitroglycerin and
sodium nitroprusside are effective in patients with concomitant pulmonary oedema.
Enalaprilat is also theoretically helpful, especially when the
renin system might be activated. Initial treatment of
aortic dissection involves rapid, controlled titration of arterial pressure to normal levels using intravenous
sodium nitroprusside and a beta-blocker. If beta-blockers are contraindicated,
urapidil or
trimetaphan camsilate are alternatives.
Hydralazine is the
drug of choice for patients with
eclampsia.
Labetalol,
urapidil or
calcium antagonists are possible alternatives if
hydralazine fails or is contraindicated. For patients with
catecholamine-induced crises, an alpha-blocker such as
phentolamine should be given;
labetalol or
sodium nitroprusside with beta-blockers are alternatives. There are few, if any, comparative or randomised trials providing definitive conclusions about the efficacy and safety of comparative agents. Some investigators recommend decreasing the diastolic BP to no less than 100 to 110 mm Hg. A reasonable approach for most patients with
hypertensive emergencies is to lower the mean arterial pressure by 25% over the initial 2 to 4 hours with the most specific
antihypertensive regimen.