Malignant hypertension is characterized not only by very high blood pressure with swelling of optic nerve head, hemorrhages and retina exudates, but also by signs of hypertensive encephalopathy such as severe headache, vomiting, blurred vision, transient paresis, epileptic seizures, and in particularly serious cases, sopor and coma. These symptoms are caused by spasm of cerebral arteries and swelling of the brain. Autopsies sometimes diagnose multiple small blood clots in the cerebral arteries in such patients.
Rapidly progressive heart and renal failure are also possible. Oliguria is possible at the time of diagnosis. Fibrinoid necrosis of the walls of small arteries and arterioles is characteristic, however these changes are reversible with successful treatment. The pathogenesis of malignant hypertension is unknown. The clinical picture is caused by at least two independent processes: dilation of cerebral arteries and generalized fibrinoid necrosis of arteriole walls.
The dilation of cerebral arteries is caused by loss of the ability to self-regulate arterial tone with a strong increase in blood pressure. Cerebral blood flow becomes excessive, leading to hypertensive encephalopathy. As a rule, plasma renin activity and aldosterone secretion are high, and this may contribute to vascular lesions. Malignant hypertension develops in less than 1% of patients suffering from arterial hypertension. It is possible both with hypertension and symptomatic hypertension. In some reported cases it was the first sign of the disease.
If a patient receives treatment, malignant hypertension usually does not appear. The average age of such patients is 40 years, and men suffer from it more often than women. Before the appearance of antihypertensive drugs, patients with malignant hypertension died within 2 years – either from renal failure, hemorrhagic stroke or heart failure. With modern treatment, the five-year survival rate exceeds 50%.
Treatment of malignant hypertension and hypertensive crises
Hypertensive crisis and malignant hypertension are both emergency conditions requiring immediate medical attention. However, they must be distinguished from severe hypertension. Suffering from a sharp decrease in blood pressure with these diseases can result in ischemia of the myocardium and brain.
1. Treatment of complications.
2. Reduction of diastolic blood pressure by 30%, but not lower than 95 mm Hg.
The drugs used to treat malignant hypertension and crises are divided into two groups according to their speed of action.
1. Drugs designed to immediately lower blood pressure, e.g. with epileptic seizures. Such drugs are not suitable for long-term treatment.
Sodium nitroprusside, trimetaphan camsilate and nitroglycerin are injected intravenously, with constant monitoring of blood pressure.
The best emergency medication is Sodium Nitroprusside which effects arterial and venous channels. This drug should be infused at a rate of 0,25-8 mkg/kg/min. Unlike ganglionic blockers, it is not addictive, so it can be injected intravenously for several days with minimal risk of side effects.
Nitroglycerin is injected at a rate of 5-100 mkg/min. It is more effective in patients after coronary artery bypass surgery or in patients with myocardial infarction, left ventricular failure, and unstable angina.
It is easiest to use diazoxide with no need of individual dose selection, but its efficiency is less than with other drugs. Diazoxide mainly affects arterioles, it is rapidly infused intravenously at a dose of 50-150 mg, and lowers blood pressure in 1-5 minutes. The same dose, if necessary, is infused again in 5-10 minutes or in a few hours when blood pressure starts to rise. The total dose should not exceed 600 mg a day. Sometimes blood pressure drops too much, so the drug is contraindicated in cases of suspected dissecting aortic aneurysm and myocardial infarction. Diazoxide can increase myocardial contractility, which is why β-blockers are usually prescribed at the same time.
Enalaprilat (enalapril form for intravenous infusion) is especially indicated for left ventricular failure, and Labetalol IV is indicated for myocardial infarction and angina pectoris (as it prevents an increase in heart rate).
Labetalol can be ineffective if a patient has previously taken β-blockers, and it is contraindicated in case of heart failure, bronchial asthma, bradycardia, and AV-blockade. It is infused in patients with eclampsia, if hydralazine is ineffective.
Trimetaphan camsilate (0,5-5 mg/min IV) is rarely used. It affects arterial and venous channels. When infused, the patient must be in a sitting position, and the medical staff continuously monitors their blood pressure. Dosage is harder to determine than for sodium nitroprusside, however, Trimetaphan camsilate helps better with dissecting aortic aneurysm.
2. Longer-acting drugs lower blood pressure less quickly (peak effect occurs in no less than 30 minutes) but then they can be ingested.
If such a delay is possible, hydralazine IV is used. It often works after 10 minutes. 10 mg of hydralazine is infused every 10-15 minutes to achieve the desired blood pressure or total dosage of 50 mg. The whole dose of hydralazine, which was required for the initial lowering of blood pressure, can then be infused IM or IV every 6 hours. In patients with severe coronary artery disease, Hydralazine is used with great care; it is contraindicated during an angina attack and in dissecting aortic aneurysms. On the other hand, it is indicated for preeclampsia.
In addition, using sublingual Nifedipine can quickly reduce blood pressure, but it causes tachycardia.
Furosemide (ingested or IV) is an important part of treatment. It enables sodium uresis, helps with the elimination of hypertensive encephalopathy and heart failure, and increases sensitivity to the main antihypertensive drug.
Cardiac glycosides are also indicated for heart failure. Even at the slightest suspicion of pheochromocytoma, drugs leading to release of catecholamines are contraindicated (e.g. methyldopa, reserpine, guanethidine).
As a drug of choice, IV phentolamine (trade name Regitin) should be infused carefully to avoid a sharp decrease in blood pressure. If treatment does not help with malignant hypertension and renal failure progresses, peritoneal dialysis or hemodialysis can be used: a decrease in circulating blood volume can sometimes lower blood pressure and improve kidney function. If this is still insufficient and there is no response to antihypertensive therapy (including minoxidil), bilateral nephrectomy can reduce blood pressure, especially with very high plasma renin activity. Then, permanent hemodialysis or kidney transplantation are prescribed.
Bilateral nephrectomy is the last resort after all other options have been tried. It is used only in life-saving circumstances.
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