Hypertension

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Chapter 41 Hypertension

Stuart L. Linas, MD , Shailendra Sharma, MD

1 What are the hemodynamic determinants of blood pressure (BP)?

Arterial BP is the product of cardiac output (CO) and systemic vascular resistance (SVR).

image

Malignant hypertension is caused by increased SVR.

2 What is hypertensive crisis?

Hypertensive crisis is the turning point in the course of hypertension in which immediate management of the elevated BP has a decisive role in the eventual outcome. It is a condition of severe and uncontrolled increase in the BP. An acute increase in BP can occur in the absence or presence of acute or chronic target organ dysfunction.

3 What are the target organs affected by hypertensive crisis?

Four organs are the usual target of severely elevated BP:

image Kidneys: acute kidney injury caused by proliferative endarteritis and fibrinoid necrosis of afferent artery

image Brain: hypertensive encephalopathy, cerebrovascular accidents (CVA)

image Eye or retina: retinal hemorrhage or exudates or papilledema

image Heart: acute coronary syndrome, decompensated heart failure, aortic dissection, and acute intravascular hemolysis

4 What are malignant hypertension and accelerated hypertension?

Both are syndromes in which a markedly elevated BP is associated with hypertensive neuroretinopathy. In accelerated hypertension, there may be flame hemorrhages or cotton wool exudates. Malignant hypertension is diagnosed when papilledema occurs as well.

5 What are hypertensive urgency (HU) and nonemergent hypertension (NEH)?

When severe hypertension occurs in the absence of any acute end-organ damage, it is classified as HU-NEH. Because the complications from HU are not immediate, this condition can be treated safely outside the intensive care unit and hospital with gentle reduction in BP achieved over hours to days.

6 What is hypertensive encephalopathy?

Hypertensive encephalopathy occurs in the setting of sudden and sustained elevation in BP. It occurs in both benign and malignant hypertension. The clinical presentation is that of altered mental status and/or seizures, but focal neurologic findings are uncommon. This condition can be difficult to distinguish from a primary neurologic event.

7 What are the causes of malignant and accelerated hypertension?

In contrast to ambulatory hypertension (over 90% essential) as many as 50% of patients with malignant or accelerated hypertension have secondary causes. The most important of secondary causes are medications, chronic kidney disease, and renal artery stenosis (RAS).

8 What is the short-term treatment of hypertension and hypertensive emergency?

The short-term treatment of choice is intravenous (IV) sodium nitroprusside. The initial dose is 0.5 mcg/kg/min, and this should be increased by 0.5 mcg/kg/min every 2 to 3 minutes until a diastolic BP < 110 mm Hg has been attained. Further acute decreases in BP should be avoided to prevent hypoperfusion to vital organ(s) because blood flow autoregulation may have been altered to accommodate chronically elevated BP. Acceptable alternative parenteral drugs for the short-term treatment of malignant hypertension include labetalol, nicardipine, enalaprilat, or fenoldopam. Extreme caution should be taken while using agents known to cause or further worsen intravascular volume status because patients with hypertensive emergency often present with intravascular volume depletion.

9 Outline the typical long-term antihypertensive regimen after successful treatment of malignant hypertension or hypertensive crisisss

Because malignant hypertension is mediated by increased SVR, it is recommended that long-term therapy include a vasodilator such as hydralazine or minoxidil. Vasodilators cause reflex tachycardia and sodium retention; therefore it is usually also necessary to include a β-blocker (labetalol) and a diuretic agent. In some cases, long-term BP reduction may be achieved with less potent vasodilators, such as angiotensin-converting enzyme (ACE) inhibitors or calcium channel blockers.

10 What is the appropriate short-term treatment for hypertension in a patient with pheochromocytoma?

Hypertension from pheochromocytomas is caused by vascular smooth muscle α1-receptor activation, which results in vasoconstriction. Thus the best short-term treatment is IV administration of the α1-blocker phentolamine. Sodium nitroprusside is also a reasonable choice. β-Blockers should initially be avoided because they cause both unopposed peripheral α1-receptor stimulation and decreased CO.

11 Describe the short-term treatment of cocaine-induced hypertensive crisis

Cocaine-induced hypertensive crisis falls under “catecholamine-associated hypertension.” Cocaine causes hypertension by inhibiting catecholamine reuptake at nerve terminals. Therefore drugs that can block α1-receptors such as labetalol or phentolamine are effective. Selective β-blockers without α1 blockade such as propranolol are not recommended because of the risk of unopposed α1 action. If hypertension is severe, sodium nitroprusside is the drug of choice. In the setting of cocaine-related myocardial ischemia, nitroglycerin and benzodiazepines are effective against both cocaine-induced hypertension and vasoconstriction of the coronary arteries. Cocaethylene is a compound formed in vivo when cocaine and ethyl alcohol (EtOH) have been ingested simultaneously. It produces greater increases in heart rate, rate-pressure product, and euphoria compared with the effects of cocaine alone. Therefore the treatment of hypertension tends to pose greater therapeutic challenge in patients consuming EtOH as well as cocaine.

Cocaine-induced hypertension should be treated with extreme caution and treatment regimens reviewed with passage of time because the condition undergoes spontaneous resolution when cocaine is metabolized.

12 How is hypertension treated in the short term in patients with aortic dissection?

Aortic dissection begins with a tear in the intima of the aorta; this is propagated by the aortic pulse wave (dP/dt). Myocardial contractility, heart rate, and BP contribute to the aortic pulse wave. The goal of treatment is to decrease myocardial contractility and heart rate. This goal has traditionally been best achieved with sodium nitroprusside and esmolol. Labetalol alone is also effective in this setting.

13 Why is BP elevated in patients with CVA?

Patients with CVA often have a severe increase in BP potentially resulting from a central mechanism and/or compensatory increase in response to increased intracranial pressure. Stress responses to hospitalization, headache, urinary retention, or concomitant infection may lead to abnormal autonomic activity and raised levels of circulating catecholamines. Greater than 60% of patients with CVA will have an acute hypertensive response.

image Central mechanism

The primary cause is damage or compression of specific regions in the brain that mediate autonomic control. Increased sympathoadrenal tone and subsequent release of renin, each in isolation or together, can also contribute to high BPs.

image Failure of autoregulation of cerebral blood flow and response to increased intracranial pressure (ICP)

With acute brain injury, the ability of the brain to autoregulate and maintain cerebral blood flow is impaired. Autoregulation is a mechanism by which the brain can maintain a constant cerebral blood flow despite a wide fluctuation in cerebral perfusion pressure (CPP) (from the range of 60-180 mm Hg).

image

CPP is the difference between mean arterial pressure (MAP) and ICP. Under physiologic circumstances cerebral venous pressure (backflow in the cerebral venous system) is the primary determinant of ICP. In absence of any pathologic condition, cerebral venous pressure is zero; thus the arterial pressure determines CPP.

When the ICP goes up because of increase in cerebral venous pressure (as in CVA), MAP goes up in an attempt to maintain adequate CPP.

14 How should hypertension be treated in patients with CVA?

image Hypertensive encephalopathy

The goal is gradual and careful reversal of vasogenic subcortical edema. MAP should be cautiously reduced by no more than 15% over a 2- to 3-hour period. Severe neurologic complications have occurred with MAP reductions at 40% or more.

image Thromboembolic cerebrovascular disease

The goal is salvation of ischemic penumbra. For patients thought to be candidates for reperfusion therapy, systolic BP (SBP) > 185 mm Hg and diastolic BP (DBP) > 110 mm Hg warrant treatment. For the subset of patients who are not candidates for reperfusion therapy, the expert opinion is to treat SBP > 220 mm Hg and DBP > 120 mm Hg with a goal of 15% to 25% reduction in MAP over the first 24 hours.

image Subarachnoid hemorrhage

Poorly controlled BP increases the risk of rebleeding. The presence of blood in the subarachnoid space induces intense vasospasm and increases the risk of severe ischemia 4 to 12 days after the first bleeding. The goal is 20% to 25% reduction in BP over a 6- to 12-hour period but not less than 160 to 180/100 mm Hg.

image Intracerebral hemorrhage

The consensus guidelines on treatment of intracerebral bleeding:

image IV medications should be used to treat SBP > 200 mm Hg or MAP > 150 mm Hg with BP monitoring done every 5 minutes.

image In suspected intracranial hypertension, BP should be lowered with a parenteral agent if SBP is > 180 mm Hg or MAP > 130 mm Hg while maintaining CPP above 60 to 80 mm Hg.

image In the absence of elevated ICP, treat SBP > 180 mm Hg and MAP > 130 mm Hg with a target BP of 160/90 mm Hg or a MAP of 110 mm Hg.

image The rate of BP reduction should be slowed if the patient’s neurologic status deteriorates. Oral therapy should be instituted before parenteral treatment is discontinued. Clonidine or α-methyldopa should be avoided because of the risk of impaired cerebral function.

15 Describe the short-term treatment of hypertension in patients with ischemic heart disease and ongoing angina

Hypertension can precipitate ischemic chest pain in patients with severe coronary artery disease. Alternatively, hypertension can result from chest pain, which results in marked increases in catecholamines and secondary reactive hypertension. In either setting, hypertension is associated with an increase in SVR and increases in myocardial oxygen demand. Nitroglycerin and β-blockers are the initial agents of choice. Because nitroprusside increases heart rate and myocardial oxygen demand in this setting, it is considered a secondary agent.

16 How should hypertension associated with preeclampsia be treated?

The traditional treatments of choice are hydralazine or α-methyldopa. If these drugs are ineffective or poorly tolerated, labetalol is a reasonably safe and effective alternative. Medications to be avoided because of potential teratogenesis include sodium nitroprusside, trimethaphan, diazoxide, ACE inhibitors, β-blockers, and calcium channel blockers. Unfortunately, the safety profile of many antihypertensive drugs during pregnancy is unknown. Because preeclampsia and eclampsia may be life threatening, sometimes it may be necessary to prescribe potent antihypertensive agents (sodium nitroprusside or minoxidil) with unclear fetal toxicity potential.

17 What are the causes of RAS, and how should it be evaluated?

The major causes are fibromuscular dysplasia (especially in young women) and atherosclerosis (in those aged > 55 years in association with polycystic kidney disease). Although Doppler ultrasonography of the renal vasculature is an excellent noninvasive test to confirm RAS, it has not been standardized, and magnetic resonance angiography is recommended.

18 What is reactive hypertension?

Patients with stage 1 or 2 hypertension that is poorly controlled with medications can have marked elevation in BP to stressors such as pain or shortness of breath. Increases in catecholamines of stress lead to severe elevations in BP that should be distinguished from primary hypertension because the approaches to therapy differ. In reactive hypertension it is necessary to treat the cause of BP, for example, chest pain or pancreatitis, rather than the elevated BP.

19 Why does lowering of BP potentially result in a decline in glomerular filtration rate (GFR) in severe hypertension?

Normally, GFR is maintained despite decreases in BP by compensatory increases in efferent arteriolar tone (Fig. 41-1) Two major causes exist of loss of GFR after reduction of BP in the setting of severe hypertension:

image RAS: In a patient with a fixed atherosclerotic lesion of the main renal artery, a drop in BP can cause a fall in GFR because the fixed lesion limits afferent arteriolar flow to such an extent that even maximal elevation in efferent arteriolar tone cannot compensate and maintain GFR.

image Long-standing essential hypertension: In this setting, no macrovascular abnormalities are present; the problem is marked sclerosis of the microvasculature of the kidney, including the afferent artery. Because of afferent arteriolar sclerosis, the afferent artery is unable to vasodilate in response to a drop in BP. Hence, GFR falls when BP is lowered even with increases in efferent arteriolar tone that normally would offset, at least partially, decreases in BP.

image

Figure 41-1 Impaired autoregulation of glomerular filtration rate (GFR). BP, Blood pressure.

20 When should an evaluation for secondary hypertension be considered?

image At initial presentation of malignant hypertension (especially if the patient is white, younger than 30 years, or older than 50 years of age)

image When rapid onset of severe hypertension occurs within less than 5 years

image When an increase in serum creatinine level occurs after the initiation of ACE inhibitor treatment

image In compliant patients whose BP is difficult to control after an adequate trial with a combination of diuretic, β-blocker, and potent vasodilator

21 What are the important causes of secondary hypertension?

Secondary hypertension accounts for 5% of cases of hypertension.

image Renal: renovascular disease, renal parenchymal disease, polycystic kidney disease, Liddle syndrome, syndrome of apparent mineralocorticoid excess, hypercalcemia

image Endocrine: hyperthyroidism, hypothyroidism, primary hyperaldosteronism, Cushing syndrome, pheochromocytoma, congenital adrenal hyperplasia

image Drugs: prescription (e.g., estrogen, cyclosporine, steroids); over-the-counter (e.g., pseudoephedrine, nonsteroidal antiinflammatory drugs); illicit (e.g., tobacco smoking, ethanol, cocaine)

image Neurogenic: increased intracranial pressure, spinal cord section

image Miscellaneous: coarctation of aorta, obstructive sleep apnea, polycythemia vera

22 What are the causes of primary aldosteronism, and how should they be distinguished?

The major causes are unilateral aldosterone-producing adenoma (APA) and bilateral idiopathic adrenal hyperplasia (IAH). Primary aldosteronism should be suspected in a patient with hypokalemia and hypertension with metabolic alkalosis. It is necessary to first demonstrate renal potassium wasting (high urine K+ in association with low serum K+) followed by a decrease in renin and an elevated aldosterone level. The plasma aldosterone/renin ratio (> 40) is often used. If the ratio is elevated, the aldosterone response to either NaCl infusion or fludrocortisone is used and considered positive if the plasma aldosterone level remains elevated (> 10 pg/mL). Treatment of APA is surgical adrenalectomy, whereas mainstays of treatment of IAH are mainly medical. Adrenal imaging can sometimes distinguish between APA and IAH, but it is often necessary to pursue a more definitive study to verify the diagnosis of APA. By far, selective adrenal vein sampling is the most validated technique used to differentiate APA from IAH.

Key Points Hypertensionimage

1. Hypertensive crisis (or hypertensive emergency) is the turning point in the course of hypertension when the immediate management of elevated BP plays a decisive role in limiting or preventing target organ damage.

2. Hypertensive crises can damage four main target organ systems: eye, brain, heart, and kidney.

3. The short-term treatment of choice for malignant hypertension is IV sodium nitroprusside.

4. Long-term therapy for malignant hypertension should include a vasodilator such as hydralazine or minoxidil, a β-blocker, and a diuretic agent.

5. Nitroglycerin and β-blockers are the initial agents of choice for patients with ischemic heart disease and angina.

Bibliography

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2 Kaplan N.M. Pheochromocytoma. In: Kaplan N.M., ed. Clinical Hypertension. 7th ed. Philadelphia: Lippincott Williams & Wilkins; 1998:345–363.

3 Kelleher C.L., Linas S.L. Hypertensive crisis: emergency and urgency. In: Fink M.P., Abraham E., Vincent J.-L., et al. Textbook of Critical Care. 5th ed. Philadelphia: Saunders; 2005:879–888.

4 Kitiyakara C., Guzman N.J. Malignant hypertension and hypertensive emergencies. J Am Soc Nephrol. 1998;9:133–142.

5 Lange R.A., Hillis L.D. Cardiovascular complications of cocaine use. N Engl J Med. 2001;345:351–358.

6 Pohl M.A. Renal artery stenosis, renal vascular hypertension, and ischemic nephropathy. In: Schrier R.W., ed. Diseases of the Kidney. 7th ed. Philadelphia: Lippincott Williams & Wilkins; 2001:1399–1457.

7 Qureshi A.I. Acute hypertensive response in patients with stroke: pathophysiology and management. Circulation. 2008;118:176–187.

8 Qureshi A.I., Ezzeddine M.A., Nasar A., et al. Prevalence of elevated blood pressure in 563,704 adult patients with stroke presenting to the ED in the United States. Am J Emerg Med. 2007;25:32–38.

9 Vaughan C.J., Delanty N. Hypertensive emergencies. Lancet. 2000;356:411–417.

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