Treatment
In a hypertensive emergency, treatment should first be to stabilize the patients airway, breathing, and circulation per ACLS guidelines. Patients should have their blood pressure slowly lowered over a period of minutes to hours with an antihypertensive agent. Documented goals for blood pressure include a reduction in the mean arterial pressure by less than or equal to 25% within the first 8 hours of emergency. If blood pressure is lowered aggressively, patients are at increased risk of complications including stroke, blindness, or kidney failure. Several classes of anti hypertensive agents are recommended, with the choice depending on the cause of the hypertensive crisis, the severity of the elevation in blood pressure, and the patients baseline blood pressure prior to a hypertensive emergency. Physicians will attempt to identify a cause of the patients hypertension, including chest radiograph, serum laboratory studies evaluating kidney function, urinalysis, as that will alter the treatment approach for a more patient-directed regimen.Hypertensive emergencies differ from hypertensive urgency in that they are treated parenterally, whereas in urgency it is recommended to use oral anti hypertensives to reduce the risk of hypotensive complications or ischemia. Parenteral agents are classified into beta-blockers, calcium channel blockers, systemic vasodilators, or other (fenoldopam, phentolamine, clonidine). Medications include labetalol, nicardipine, hydralazine, sodium nitroprusside, esmolol, nifedipine, minoxidil, isradipine, clonidine, and chlorpromazine. These medications work through a variety of mechanisms. Labetalol is a beta-blocker with mild alpha antagonism, decreasing the ability of catecholamine activity to increase systemic vascular resistance, while also decreasing heart rate and myocardial oxygen demand.
If the process is not stopped, homeostatic failure begins, leading to loss of cerebral and local autoregulation, organ system ischemia and dysfunction, and myocardial infarction. Single-organ involvement is found in approximately 83% of hypertensive emergency patients, two-organ involvement in about 14% of patients, and multi-organ failure (failure of at least 3 organ systems) in about 3% of patients.In the brain, hypertensive encephalopathy - characterized by hypertension, altered mental status, and swelling of the optic disc - is a manifestation of the dysfunction of cerebral autoregulation. Cerebral autoregulation is the ability of the blood vessels in the brain to maintain a constant blood flow. People with chronic hypertension can tolerate higher arterial pressure before their autoregulation system is disrupted. Hypertensives also have an increased cerebrovascular resistance which puts them at greater risk of developing cerebral ischemia if the blood flow decreases into a normotensive range. On the other hand, sudden or rapid rises in blood pressure may cause hyperperfusion and increased cerebral blood flow, causing increased intracranial pressure and cerebral edema, with increased risk of intracranial bleeding.In the heart, increased arterial stiffness, increased systolic blood pressure, and widened pulse pressures, all resulting from chronic hypertension, can cause significant damage. Coronary perfusion pressures are decreased by these factors, which also increase myocardial oxygen consumption, possibly leading to left ventricular hypertrophy.