Hypertensive Encephalopathy

The triad of severe hypertension, altered mental status, and (often) papilledema characterizes hypertensive encephalopathy, and it may be accompanied by lethargy, confusion, headache, visual disturbances, and seizures. Somnolence, stupor, and nausea or vomiting may also occur. Retinopathy may or may not be present. The mechanism of the disease is loss of autoregulation as a result of the cerebral overperfusion caused by profound hypertension; when the hypertension is controlled, the patient’s mental status improves. Persistent overperfusion results in vasodilation and increased permeability of cerebral blood vessels, which in turn leads to the development of cerebral edema. If not adequately treated, hypertensive encephalopathy can progress to cerebral hemorrhage, coma, and death.

Hypertensive encephalopathy is most likely to occur in previously normotensive individuals who experience a rapid rise in blood pressure, such as children with acute glomerulonephritis and young women with preeclampsia or eclampsia. Because chronically hypertensive patients usually experience a more gradual rise in blood pressure, cerebrovascular decompensation is less likely. Hypertensive encephalopathy produces characteristic findings on computed tomography (CT). Scans show a posterior leukoencephalopathy that predominantly affects the white matter of the parietooccipital regions bilaterally. CT is useful in excluding other causes of altered mental status such as intracranial bleeding.

Accelerated-Malignant Hypertension

Accelerated-malignant hypertension occurs most commonly in young African American males with underlying renal parenchymal disease or renovascular disease. It is most commonly found in patients with long-standing hypertension and usually occurs without encephalopathy.¹⁰ When endothelial vasodilator responses are overwhelmed, further hypertension and endothelial damage occur and lead to inflammatory vasculopathy. Marked elevation in blood pressure and characteristic eyeground findings make the diagnosis. Flame-shaped hemorrhages develop around the optic disk because of the high intravascular pressure, and soft exudates are caused by ischemic infarction of the nerve fibers secondary to occlusion of the supplying arterioles. Common symptoms include headache (85%), visual blurring (55%), nocturia (38%), and weakness (30%). Laboratory evidence includes azotemia, proteinuria, hematuria, hypokalemia, and metabolic alkalosis. Papilledema is considered the sine qua non of malignant hypertension. Accelerated hypertension is used to describe the same condition (hemorrhages and exudates) without papilledema. Because the absence of papilledema does not connote a different clinical prognosis or therapy, the term accelerated-malignant hypertension is now recommended.

Cerebrovascular Hypertensive Crisis

Hypertension frequently complicates the management of patients with cerebrovascular accidents (CVAs). After a CVA patients generally have focal neurologic deficits that are somewhat predictable based on the territory of the brain affected. A thorough neurologic examination can elucidate clues about the vessel in which flow has been disrupted either by occlusion or by hemorrhage. Ischemic strokes result from three major categories: thrombotic, embolic, and hypoperfusion. Compromised blood flow produces cell death at the center of the ischemic region and reversibly damaged neurons in the periphery, also known as the penumbra. The penumbra’s viability depends on its perfusion. Hemorrhagic stroke is caused by either intracranial or subarachnoid bleeding. Intracranial pressure (ICP) increases and cerebral perfusion pressure (CPP) is reduced at the site of the hematoma. Therefore, maintaining cerebral perfusion is key in both types of CVA, and an understanding of cerebrovascular physiology is helpful in determining the best treatment strategy.

Cerebral blood flow (CBF), a function of CPP, is equal to mean arterial pressure (MAP) minus ICP (CPP = MAP − ICP). The process of vasoconstriction and vasodilation of the cerebral vasculature maintains a steady CBF. However, cerebral autoregulation fails at approximately 25% above or below the patient’s usual MAP. In addition, changes in ICP or brain injury can result in loss of the brain’s ability to autoregulate blood flow. Increased ICP, commonly seen with hemorrhage or edema, decreases CPP and makes the brain more vulnerable to changes in MAP. In normal individuals, CBF remains fairly constant at MAP values of approximately 60 mm Hg up to 150 mm Hg. When MAP decreases to less than the lower limits of autoregulation, the brain becomes hypoperfused and cerebral hypoxia develops, with symptoms such as dizziness, nausea, and syncope. In chronically hypertensive individuals, the lower limit of autoregulation increases, and autoregulation might fail at MAP values that are well tolerated in nonhypertensive individuals. This suggests that chronically hypertensive patients cannot tolerate a rapid return to “normal” blood pressure and that MAP should be acutely decreased by no more than 20% to 25%.

Cardiovascular Hypertensive Crisis

Hypertensive emergencies involving the heart and great vessels include congestive heart failure, acute coronary syndromes, and aortic aneurysm or dissection. Blood pressure is frequently elevated in patients with acute pulmonary edema, particularly when a high-output state is the cause, such as volume overload with renal failure, thyrotoxicosis, or severe anemia. Transient diastolic dysfunction, which may or may not be a direct result of the elevated blood pressure, also causes acute pulmonary edema with hypertension and congestive heart failure. Symptoms include tachypnea, tachycardia, pulmonary rales, jugular venous distention, and an S₃ gallop.

Acute coronary syndromes are also frequently accompanied by hypertension. Reducing myocardial work by lowering blood pressure and the heart rate has been demonstrated to decrease infarct size in patients not receiving thrombolytic therapy. Classically, patients have symptoms of chest pain, dyspnea, diaphoresis, nausea, and light-headedness.

Acute aortic dissection is thought to occur as a result of aortic dilation or high blood pressure superimposed on a structural weakness of the arterial wall causing a tear in the intimal layer. Pulsatile pressure extends the dissection by separating the layers of the arterial wall. Historical series report a mortality of 1% to 2% per hour. The stresses that extend the dissection are thought to be related as much to the aortic pulse wave or pulse pressure (the difference between systolic and diastolic pressure over time) as it is to MAP. Heart rate, myocardial contractility, and MAP all contribute to increased pulse pressure. Affected patients include elderly persons with hypertension or atherosclerotic disease and individuals with connective tissue disorders. Hallmark symptoms are acute, severe retrosternal pain radiating to the back or intrascapular pain. Patients may have pulse deficits, neurologic symptoms, or ischemic symptoms in involved organs such as the gut, kidney, or heart.

Renovascular Hypertensive Crisis

The kidney is unique in being both a target organ and the cause of many hypertensive emergencies. Hypertension causes 30% of cases of end-stage renal disease, which makes it the second most common cause after diabetes. Nephrosclerosis may develop in chronically hypertensive patients after 10 to 15 years and is manifested as damage to the medial layer of capillaries, reduced kidney size, and nonnephrotic levels of proteinuria without hematuria. By contrast, malignant hypertension damages the intimal layer of the renal capillary bed and may result in enlarged kidneys, cellular urinary sediment, hematuria, and severe proteinuria.

Severe hypertension in a young patient raises the possibility of intrinsic acute renal disease, such as glomerulonephritis. IgA nephropathy has surpassed poststreptococcal glomerulonephritis in frequency, and Henoch-Schönlein purpura is the most likely cause of acute glomerular disease in children.

Renal artery stenosis is present in only 1% of unselected hypertensive patients but is seen in 4% of blacks and 32% of whites who have severe hypertension (diastolic blood pressure > 125 mm Hg with retinopathy). It is also more common in patients with a rapidly progressive course. Occasionally, devastating acute renal failure may occur as a result of intrarenal vasculitis. This is common in the setting of scleroderma and may be responsive to angiotensin-converting enzyme inhibitors (ACEIs).

Catecholamine Excess

The most familiar drugs found to cause hypertension in EDs today are sympathomimetic drugs such as phenylephrine, cocaine, and methamphetamine. Tyramine can induce a hypertensive crisis in patients taking a monoamine oxidase inhibitor, and hypertension can complicate withdrawal syndromes from alcohol, benzodiazepines, clonidine, and beta-blockers. Pheochromocytoma can cause intermittent hypertensive crisis and may be responsible for many clinical findings besides hypertension, such as headache, sweating, palpitations, pallor, nausea, and rarely, seizures. Some patients with pheochromocytoma may have paroxysms of low blood pressure as well.

Hypertension in Pregnancy

Third trimester emergencies are addressed separately in Chapter 121. Emergencies include eclampsia and preeclampsia. Pregnant women between 20 weeks’ gestation and 2 weeks postpartum who have any degree of hypertension (≥140/90 mm Hg) or an increase of more than 30/15 mm Hg above their baseline blood pressure, accompanied by peripheral edema and proteinuria, have preeclampsia. Hypertension is important mainly as a symptom of the underlying disorder rather than as a cause. Preeclampsia is essential to recognize because it can progress suddenly to eclampsia, defined by the occurrence of convulsions. Additional symptoms include headache, visual changes, epigastric pain, oliguria, facial and extremity edema, and HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet count). Eclampsia can rapidly progress to coma or death. Magnesium infusion is more effective than other anticonvulsants in this setting. Because definitive treatment consists of delivery of the fetus, the emergency physician (EP) usually collaborates with an obstetrician early in the patient’s course through the department.