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Hypertensive emergency is defined as severely elevated blood pressure (typically >180/120 mmHg) with evidence of acute end-organ damage, requiring immediate IV antihypertensive therapy. It is distinguished from hypertensive urgency, which lacks end-organ damage.
Extreme elevations in blood pressure overwhelm cerebral and renal autoregulation, causing fibrinoid necrosis of arterioles. End-organ manifestations include hypertensive encephalopathy, hemorrhagic or ischemic stroke, aortic dissection, acute MI, acute decompensated heart failure, and microangiopathic hemolytic anemia.
The specific end-organ threatened determines the antihypertensive agent of choice: nicardipine or labetalol for hypertensive encephalopathy; nitroprusside or esmolol for aortic dissection (target SBP <120 within 20 min); nitroglycerin for acute pulmonary edema. BP reduction should be controlled — no more than 25% in the first hour to avoid hypoperfusion injury.