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When to use antihypertensives

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VOL: 97, ISSUE: 28, PAGE NO: 41

Nigel Davies, MSc, BSc, RN, CertEd, is deputy director of nursing, South Buckinghamshire NHS Trust, and visiting lecturer, South Bank University

Nigel Davies, MSc, BSc, RN, CertEd, is deputy director of nursing, South Buckinghamshire NHS Trust, and visiting lecturer, South Bank University

Many drugs may be used individually or in combination to lower blood pressure in patients with hypertension (Box 1). The choice depends to some extent on the cause of a patient's hypertension.

There are three broad determinants of blood pressure, so the pharmacological manipulation of one of these can lead to changes in blood pressure. Factors that affect blood pressure include:

- Peripheral vascular resistance, which is regulated largely by changes in vasodilation and vasoconstriction;

- Cardiac output, which involves the amount of blood ejected from the heart with each beat (stroke volume) and heart rate;

- The volume of blood in the circulation, which can be regulated by the kidneys.

Oral antihypertensives

Some drugs, which may routinely be given in oral form, can have a profound effect on blood pressure and may require close monitoring in high-dependency settings.

This is particularly likely to occur when the first dose is administered. For example, angiotensin-converting enzyme (ACE) inhibitors may cause rapid falls in blood pressure in some patients. In others, the administration of a combination of an antihypertensive, such as a beta-blocker and a diuretic, may lead to a marked reduction in blood pressure.

In such cases it is important to monitor whether the patient's condition becomes compromised by the fall in blood pressure. In addition to the assessment and monitoring of blood pressure, this situation requires assessment of a patient's cerebral and renal function.

Drugs for severe hypertension

Very severe hypertension (diastolic blood pressure greater than 140mmHg) requires urgent hospital treatment. However, blood pressure needs to be reduced gradually to prevent loss of organ perfusion as this can lead to cerebral infarction, blindness, poor renal function and cardiac ischaemia.

Blood pressure can therefore usually be successfully reduced with oral antihypertensive agents such as beta-blockers, for example atenolol or labetalol, or calcium channel-blockers, such as amlodipine or nifedipine.

Occasionally, it may be necessary to reduce a very high blood pressure rapidly in a high-dependency setting. Sodium nitroprusside is the drug of choice if intravenous treatment is warranted (Boxes 2 and 3).

Other intravenous drugs that are used include:

- Labetalol;

- Hydralazine;

- The vasodilator glyceryl trinitrate (Davies, 2001).

Other uses for antihypertensive drugs

In addition to the treatment of accelerated or very severe hypertension, intravenous drugs are sometimes needed during or after surgery to lower blood pressure in otherwise healthy patients. In such situations, the drugs may be used to help prevent complications such as bleeding at suture sites. Antihypertensive agents are also used for patients with heart failure.

High blood pressure in pregnancy

This is a special case that needs to be considered by health care professionals working in antenatal care. High blood pressure can lead to pre-eclampsia and eclampsia, which have serious implications for both the mother and baby.

Drugs used for the treatment of hypertensive crises in pregnancy include methyldopa, hydralazine, labetalol and, increasingly, magnesium sulphate. Knowledge of their pharmacological effects and the stage of pregnancy are essential to ensure foetal development is not harmed.

Further Reading

Davies, N. (2000) Cardiac care. In: Sheppard, M., Wright, M. Principles and Practice of High Dependency Nursing. London: Bailli[ep1]re Tindall.

Trouce, J., Gould, D. (2000) Clinical Pharmacology for Nurses. Edinburgh: Churchill Livingstone.

UKCC (2000) Guidelines for the Administration of Medicines. London: UKCC.

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