TABLE 531 Classification of Blood Pressure for Adults Aged 18 Years and Older

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Hypertensive emergencies are those situations that require immediate blood pressure reduction to prevent or limit damage to target organs (i.e., brain, eyes, heart, or kidneys). The terms malignant hypertension or hypertensive crisis may also be used to refer to this category. Target-organ damage occurs in syndromes such as hypertensive encephalopathy, intracranial hemorrhage, acute left ventricular failure with pulmonary edema, unstable angina pectoris, acute myocardial infarction, dissecting aortic aneurysm, and eclampsia.1 A hypertensive emergency is not defined by any absolute pressure measurements but, instead, is contingent on the presence of relative blood pressure increases combined with injury to any of the so-called target organs. In fact, a patient with a low baseline pressure can present with "normal" or mildly elevated pressure and be considered to have a true hypertensive emergency, if there is evidence of concurrent related central nervous system (CNS), cardiovascular, or renal dysfunction.

The treatment goal in hypertensive emergency is the immediate reduction of mean arterial pressure (MAP = [1/3(SBP-DBP) + DBP]) in a controlled, graded manner, using improvement in the patient's condition as a guide. Blood pressures should not exceed a 20 to 25 percent reduction within the first 30 to 60 min. Although hypertensive emergencies are the most serious complications of hypertension, they occur in only 1 percent of all hypertensive patients.

Hypertensive urgency is less clearly defined in the literature. Most sources concur that hypertensive urgency occurs when the blood pressure elevation presents a risk for imminent target-organ damage. Although acute organ injury has not yet occurred in hypertensive urgency, the risk of injury is high if the elevated blood pressure is allowed to persist. In many cases of hypertensive urgency, elevated blood pressure in the presence of preexisting conditions (e.g., renal insufficiency, congestive heart failure, coronary artery disease, or CNS disorders) increases the likelihood of target-organ damage. As with hypertensive emergencies, in hypertensive urgencies, relative increases in blood pressure are more important than absolute values. The main challenge for the clinician is determining whether the asymptomatic hypertensive patient is experiencing a hypertensive urgency. The first priority in recognizing this condition is to determine whether target-organ dysfunction exists. If dysfunction does not exist, the clinician must determine whether damage to the CNS, cardiovascular, or renal system is impending, given the elevated blood pressure and relevant past medical history. If target-organ dysfunction exists, the emergency physician must identify whether the end-organ dysfunction is chronic and at risk of acute further impairment, or whether the dysfunction is acute and related to the hypertension (i.e., then to be considered an emergency rather than an urgency). This may be difficult without knowledge of the patient's past medical history, including prior laboratory values and clinical findings. In many cases, the clinician may be obligated to initiate antihypertensive treatment without being certain of the diagnostic classification.

The treatment goal in hypertensive urgencies is the gradual reduction of blood pressure within 24 h by using oral antihypertensive agents, although the recommended duration to reduce the blood pressure varies in the literature from a few hours to 48 h. Because a common cause of hypertensive urgency is noncompliance with medications, restarting a patient on a previously established regime is an acceptable strategy. Any patient with a diagnosis of hypertensive urgency should be started on an antihypertensive medication with follow-up in 24 h. Admission decisions depend on the patient's comorbid conditions, and the clinician's impression of the patient's anticipated response to therapy.

Acute hypertensive (nonemergency/nonurgency) episode occurs when a patient is found to have stage 3 hypertension (T§ble..,..53-1; systolic pressure of 180 mmHg or more, and diastolic pressure of 110 mmHg or more) with no signs or symptoms of evolving or impending target-organ damage.1 Although many of these patients receive treatment in an effort to prevent target-organ damage, there is some controversy regarding the need for immediate treatment. There is evidence to show that in some cases acute interventions may actually be harmful.4 In chronically hypertensive individuals, complications of acute blood pressure reduction can include altered sensorium, seizures, transient ischemic attacks, and amaurosis and other visual changes. In addition, there is no evidence of a beneficial effect of acute blood pressure reduction on long-term control or on the chronic effects of hypertension. In general, these patients require no acute intervention but should be referred to a primary care physician for follow-up and initiation of therapy. If these patients have previously been diagnosed as hypertensive but have been noncompliant with medications, a reasonable strategy would be to restart the patients on their previous treatment regimen and then refer for appropriate follow-up care within 24 to 48 h.

Transient hypertension occurs in association with other conditions such as anxiety, alcohol-withdrawal syndromes, and some toxicologic substances. One specific type of transient hypertension is white-coat hypertension,5 a phenomenon that occurs when a patient has an elevated blood pressure in a clinical setting but has a normal pressure at other times. White-coat hypertensive patients have elevated pressures only in a medical setting but are normotensive when followed over a 24-hour period with ambulatory blood pressure monitoring. A number of studies have shown that at least 20 percent of newly diagnosed hypertensive individuals are actually normotensive in their normal environment.5 The cardiovascular morbidity and mortality rates of individuals with white-coat hypertension correlate with their ambulatory blood pressure as opposed to their pressure measurements in the medical setting. Therefore, a single encounter in the Ed setting should not be the basis for diagnosis of new-onset hypertension, nor does it constitute an indication to initiate antihypertensive therapy. However, patients do require prompt and close follow-up care for repeat blood pressure testing.

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