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A hypertensive emergency is a situation in which uncontrolled hypertension is associated with acute endorgan damage. Most patients presenting with hypertensive emergency have chronic hypertension, although the disorder can present in previously nortnotensive individuals, particularly when associated with pre-eclampsia or acute glomerulonephritis. The pathophysiological mechanisms causing acute hypertensive endothelial failure are complex and incompletely understood but probably involve disturbances of the renin-angiotensin-aldosterone system, loss of endogenous vasodilator mechanisms, upregulation of proinflammatory mediators Including vascular cell adhesion molecules, and release of local vasoconstrictors such as endothelin 1. Magnetic resonance Imaging has demonstrated a characteristic hypertensive posterior leucoencephalopathy syndrome predominantly causing oedema of the white matter of the parietal and occipital lobes; this syndrome is potentially reversible with appropriate prompt treatment. Generally, the therapeutic approach is dictated by the particular presentation and end-organ complications. Parenteral therapy is generally preferred, and strategies include use of sodium nitroprusside, beta-blockers, labetelol, or calcium-channel antagonists, magnesium for preeclampsia and eclampsia; and short term parenteral anticonvulsants for seizures associated with encephalopathy. Novel therapies Include the peripheral dopamine-receptor agonist, fenoldapam, and may include endothelin-l antagonists.
A hypertensive emergency is defined as a situation that requires immediate blood-pressure reduction (not necessarily to normal values) to prevent or limit targetorgan damage, and a hypertensive urgency is defined as a situation in which blood pressure should be lowered within a few hours.1 The distinction between emergencies and urgencies is important because it dictates management. Patients with target-organ damage, such as encephalopathy or aortic dissection, require emergency blood-pressure reduction with intensive monitoring and parenteral drug therapy. Patients presenting with significantly raised blood pressure but without evidence of target-organ injury need urgent, but not emergency, blood-pressure reduction. This aim can be achieved by use of oral agents and without intensive-care monitoring.
Epidemiology
About 20-30 % of adults in the more developed countries have hypertension. Blood pressure tends to increase with age in most societies, and hypertension is slightly more common in men than in women, especially in younger and middle-aged groups.2 In the USA, the incidence and prevalence of hypertension are about 1.5-2.0 times greater in African Americans than in the white population.3 The exact prevalence of hypertension depends on definition. In general, definite hypertension has been taken to be a blood pressure, on two or more...