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A hypertensive emergency is severe hypertension with acute impairment of an organ system (especially the central nervous system, cardiovascular system and/or the renal system) and the possibility of irreversible organ-damage. In case of a hypertensive emergency, the blood pressure should be lowered aggressively over minutes to hours with an antihypertensive agent.
Several classes of antihypertensive agents are recommended and the choice for the antihypertensive agent depends on the cause for the hypertensive crisis, the severity of elevated blood pressure and the patients usual blood pressure before the hypertensive crisis. In most cases, the administration of an intravenous sodium nitroprusside injection which has an almost immediate antihypertensive effect is suitable but in many cases not readily available. In less urgent cases, oral agents like captopril, clonidine, labetalol, prazosin, which have all a delayed onset of action by several minutes compared to sodium nitroprusside, can also be used.
It is also important that the blood pressure is lowered not too abruptly, but smoothly. The diagnosis of a hypertensive emergency is not only based on the absolute level of blood pressure, but also on the individual regular level of blood pressure before the hypertensive crisis. Individuals with a history of chronic hypertension may not tolerate a "normal" blood pressure.
Terminology
Generally, the terminology describing hypertensive emergencies can be confusing. Terms such as hypertensive crisis, malignant hypertension, hypertensive urgency, accelerated hypertension and severe hypertension are all used in the literature and often overlap.
Hypertensive emergency as a specific term
The term hypertensive emergency is primarily used as a specific term for a hypertensive crisis with a diastolic blood pressure of 120 mm Hg and above plus end organ damage (brain, cardiovascular, renal) (as described above) in contrast to hypertensive urgency where as yet no end organ damage has developed. The former requires immediate lowering of blood pressure such as with sodium nitroprusside infusions (NOT injections) while urgencies (about 3/4 of cases with diastolic blood pressure of 120 mm Hg and above) can be treated with parenteral administration (NOT oral) of labetalol or some Ca-channel blockers! The former use of oral nifedipine, a Ca-channel antagonist, has been strongly discouraged or banned because it is not absorbed in a controlled and reproducible fashion and has led to serious and fatal hypotensive problems.
Hypertensive emergency as a generic term
Sometimes, although not very often, the term hypertensive emergency is also used as a generic term, comprising both hypertensive emergency as a specific term for a serious and urgent condition of elevated blood pressure and hypertensive urgency as a specific term of a less serious and less urgent condition (the terminology hypertensive crisis is usually used in this sense).