HTN: Chapter 83

Marx: Rosen's Emergency Medicine: Concepts and Clinical Practice, 6th

ed.

Perspective

Perspective Medical management of hypertension has reduced stroke mortality by 50% on an age-

adjusted basis Probably partially responsible for the decline in mortality from coronary artery

disease. Although approximately 75% of patients with chronically elevated BP are aware of

their disease as few as one half to one quarter of these patients are adequately treated.

Anxiety and pain often cause transient hypertension, but evaluation of the patient for evidence of acute end-organ ischemia is important.

Even if the patient's BP does remain elevated without end-organ damage, urgent treatment is rarely beneficial, and an appropriate referral for long-term management should be made.

Principles of Disease

Definition In adults, a systolic pressure less than 140 mm Hg and a diastolic pressure

less than 90 mm Hg are considered normal. Prehypertension

If the systolic pressure is between 140 and 159 mm Hg or if the diastolic pressure is between 90 and 95 mm Hg, the term prehypertension is now applied. reflecting that the lifetime incidence of hypertension in these individuals is

twice that of individuals in the “normal” range.[2]

Hypertension The patient with a systolic pressure of 160 mm Hg or greater or a diastolic

pressure over 95 mm Hg is considered to be hypertensive.

Even isolated systolic hypertension in elderly patients is a significant risk factor for cardiovascular disease, especially when combined with other risk factors.

In older patients, an elevated pulse pressure (determined by subtracting diastolic from systolic pressure) is an equally significant risk factor for stroke and MI.

A single elevated BP does not necessarily mean that the patient has hypertension. This is especially true in children.[9] BP measurement should be repeated after the patient is in a reclining position for at least 10 minutes and should be checked in both arms.

If the second reading is also elevated or close to the hypertensive range, the patient should be advised of the potential for hypertension and referred for follow-up.

Pathophysiology

Essential hypertension. No specific cause of essential hypertension has been identified, although many

factors, including heredity, age, race, obesity, and the amount of dietary sodium, may contribute to the elevated BP

Two major theories exist: (1) hypertension results from alterations in the contractile properties of

smooth muscle in arterial walls (2) alterations of arterial smooth muscle are a response to chronically

elevated BP resulting from a primary failure of normal autoregulatory mechanisms.

Renin, Angiotensin, and Aldosterone

Renin An enzyme produced by the kidney that splits off angiotensin I from a plasma

globulin precursor.[11] Angiotensin I is converted by an enzyme in the lung to produce angiotensin II. Angiotensin II is a potent vasoconstrictor and also stimulates aldosterone production in the adrenal gland.

ACE inhibitors or angiotensin blockers are clearly the drugs of choice in hypertensive patients with diabetes or decreased left ventricular function, or both.

Renal Disease

All types of renal disease have been associated with hypertension Renovascular hypertension results from the overproduction of renin secondary

to reduced blood flow through the stenotic renal artery. The increased levels of renin lead to activation of the angiotensin pathway and resultant hypertension.

Another vascular lesion associated with arterial stenosis and hypertension is fibromuscular dysplasia of the renal arteries. This disease is predominant in young white women, and flank bruits are often present.

Up to 70% of patients with chronic pyelonephritis have elevated BP.

Arterial Disease

Coarctation of the aorta An important cause of secondary hypertension, and early surgical

intervention can greatly improve the patient's prognosis. triad of upper extremity hypertension, a systolic murmur best heard over the back,

and delayed femoral pulses should alert the examiner to the diagnosis of coarctation.

Loss of elasticity in the larger arteries associated with the aging process produces systolic hypertension as well as elevations in pulse pressure.

The current literature strongly suggests that isolated systolic hypertension is associated with an increased risk of stroke, heart disease, and renal failure and should be treated.

Thyroid and Parathyroid Disease

In thyroid storm, patients are usually hypertensive and tachycardic and β-blockade is a mainstay of the acute management.

Pheochromocytoma

Pheochromocytomas are responsible for less than 1% of cases of hypertension. The characteristic feature of pheochromocytoma is paroxysms of hypertension

associated with palpitations, tachycardia, malaise, apprehension, and sweating. These episodes may be related to physical and emotional stress, eating, position,

or even micturition. Because of the episodic nature of this syndrome, the patient is often dismissed, and a

diagnosis of hyperventilation syndrome or anxiety attack is made.

The diagnosis is confirmed with elevated urinary levels of catecholamines, metanephrines, and vanillylmandelic acid.

Treatment consists of α-blockade to control hypertension and subsequent β-blockade for the control of cardiac dysrhythmias.

Emergency Department Presentation

Hypertension is seen in the emergency department in the following four general ways:   

1.    “Hypertensive emergency” or “hypertensive crisis” with acute end-organ ischemia

2.   “Hypertensive urgency,” a historical term related to arbitrarily elevated BP with nonspecific symptoms

3.    Mild hypertension without end-organ ischemia 4. Transient hypertension related to anxiety or the primary complaint

CLINICAL PRESENTATION OF HYPERTENSIVE EMERGENCIES

BP is usually markedly elevated and there is evidence of acute dysfunction in the cardiovascular, neurologic, or renal organ system. These conditions are true medical emergencies and mandate reduction of BP within 1 hour.

Hypertensive Encephalopathy

Throughout the normal range of BP, cerebral blood flow is maintained by fluctuations in the vascular tone of the cerebral resistance vessels known as autoregulation.

Hypertensive encephalopathy is an uncommon syndrome resulting from an abrupt, sustained rise of BP that exceeds the limits of cerebral autoregulation of the small resistance arteries in the brain.

Hypertensive encephalopathy (1) acute in onset (2) reversible. Patients present with severe headaches, vomiting, drowsiness, and confusion.

Hypertensive encephalopathy is a true medical emergency; untreated patients develop increasing coma, and death may ensue within a few hours. The rapid measured reduction of BP is mandatory. The standard treatment regimen is intravenous (IV) nitroprusside with a careful reduction of the MAP by 25% or to a minimum diastolic pressure of 110 mm Hg over an hour.

Malignant Hypertension

Malignant (accelerated) hypertension is severe hypertension associated with evidence of acute and progressive damage to end organs.

The diastolic BP is usually greater than 130 mm Hg.

Patients with malignant hypertension appear ill and often present with complaints of severe headache, blurred vision, dyspnea, and chest pain or with symptoms of uremia.

In addition to elevated BP, these patients must demonstrate evidence of acute end-organ damage as a result of the hypertension.

Malignant hypertension is treated by the judicious lowering of MAP by 25% of pretreatment levels over the initial minutes to hours, then toward a target of 160/100 over 2 to 6 hours

Stroke Syndromes

In most of these patients, elevated BP is the physiologic response to the stroke itself and is not the immediate cause

Some have recommended careful antihypertensive treatment for patients with persistent, extreme elevations of BP after a stroke (e.g., diastolic pressure >140 or MAP >130 mm Hg), but data are lacking.

If BP reduction is pursued in these patients, labetalol is the

agent of choice.

Pulmonary Edema

Most patients with congestive heart failure have some degree of increased peripheral vascular resistance (PVR) and resultant hypertension; this is a normal response.

With standard treatment of pulmonary edema, including morphine, nitrates, oxygen, ACE inhibitors, and furosemide, catecholamine levels fall and BP returns rapidly toward normal.

Pregnancy

Any acute elevation of the diastolic BP above 100 mm Hg in the pregnant patient represents a true hypertensive emergency.

Although it may cause tachycardia and hypotension, the antihypertensive agent of choice in preeclampsia has classically been IV hydralazine.

Aortic Dissection

The goals of medical therapy are to lower the BP to a systolic level of 100 to 120 mm Hg and to reduce the ejection force of the heart.

The combined α/β-blocker labetalol has been used successfully

MANAGEMENT OF HYPERTENSIVE EMERGENCIES

Vasodilators Sodium Nitroprusside

Nitroprusside (Nipride, Nitropress) is a powerful vasodilator, with a direct effect on the smooth muscle of both resistance and capacitance vessels.

Cyanide is an intermediate metabolite, but cyanide toxicity is extremely rare

Vasodilators

Nitroglycerin Nitroglycerin is a vasodilating agent that acts

predominantly on the venous system, decreasing left ventricular end-diastolic pressure.

Hydralazine Hydralazine (Apresoline) is a direct arteriolar vasodilator that was widely

used in the past for the treatment of hypertensive emergencies of pregnancy. The usual starting dose of hydralazine is 5 mg IV, with repeated doses of 5

to 10 mg every 20 minutes as needed to keep the diastolic pressure below 110 mm Hg

β-Blockers

Labetalol Labetalol (Trandate, Normodyne) is a selective

α1-blocker and nonselective β-blocker with a

ratio of α/β-blockade between 1:3 and 1:7. Labetalol lowers BP by blockade of the α1-

receptors in vascular smooth muscle and the cardiac β-receptors.

α-Blockers

Phentolamine (Regitine) is an α-blocking agent used for the management of catecholamine-induced hypertensive crises (e.g., pheochromocytoma, MAOI crisis, cocaine overdose).

Nicardipine Nicardipine (Cardene) is a parenteral dihydropyridine

calcium channel blocker that has become very popular in the treatment of postoperative hypertension.

Nicardipine is administered as an infusion beginning at 5 mg/hr, increasing the infusion rate every 15 minutes until the desired reduction of BP has been achieved, to a maximum dose of 15 mg/hr.

Enalaprilat and Enalapril

Enalaprilat (Vasotec) is a parenteral active metabolite of the ACE inhibitor enalapril.

The acute dose is 0.625 to 5 mg administered as a single bolus.

Osteopathic Considerations

Sub-occipital release Normalizes the parasympathetics

Rib raising Normalizes the sympathetics