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 substantially lowered over minutes to hours with an antihypertensive agent.
During a hypertensive emergency uncontrolled BPs lead to progressive or impending end-organ dysfunction; therefore, it is important to lower the BP aggressively. Acute end-organ damage may occur including neurological, cardiovascular and other. Some examples of neurological damage include hypertensive encephalopathy, cerebral vascular accident/cerebral infarction, subarachnoid hemorrhage, and intracranial hemorrhage. Cardiovascular damages include myocardial ischemia/infarction, acute left ventricular dysfunction, acute pulmonary edema, and aortic dissection. Other end-organ damage include acute renal failure or insufficiency, retinopathy, eclampsia, and microangiopathic hemolytic anemia.Also, severe blood pressure leads to problems in the eye such as retinopathy or damage to the blood vessels in the eye.
It is also important that the blood pressure is lowered not too abruptly, but smoothly. The initial goal in hypertensive emergencies is to reduce the pressure by no more than 25% (within minutes to 1 or 2 hours) and then toward a level of 160/100 mm Hg within 2–6 hours. Excessive reductions in pressure may precipitate coronary, cerebral, or renal ischemia. 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.
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 patient's 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.