Hypertensive emergencies

A hypertensive emergency is a situation in which uncontrolled hypertension is associated with acute end-organ damage. Most patients presenting with hypertensive emergency have chronic hypertension, although the disorder can present in previously normotensive individuals, particularly when associated with preeclampsia 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-1 antagonists.