It is thought that at least 18% of the UK population suffers from hypertension; the majority, at least 95%, of unknown cause (Beevers et al 2001). Hypertension is present in 1–6% of women of childbearing age (Magee 2001). Hypertension has been termed the ‘silent killer’ because the sufferer commonly has no symptoms and is only diagnosed through screening or when the disease manifests itself in a complication of the disorder. Hypertension is present in up to 10% of all pregnancies either as a pre-existing disease (5–15% of the total) or as a disorder specific to pregnancy, pre-eclampsia (Lloyd 2003). Diagnosing and treating the hypertensive diseases of pregnancy is very challenging and may involve a balancing act between the health of the mother and the maturity of the fetus.

Aetiology

In the majority of cases, hypertension has no known cause. This is termed primary or essential hypertension. In a small number of cases however, hypertension is secondary to another disease process, such as renal disease, which accounts for one-third of cases, or other disease processes such as adrenal defects as found in phaeochromocytoma or Cushing’s syndrome, or as a complication of drug therapy.

Pathophysiology of hypertension

Essential hypertension

Although the exact cause of essential hypertension is not known, it is probable that many interrelated factors contribute to increased blood pressure. Normal blood pressure is dependent on a balance between cardiac output and peripheral resistance as described above. Most people with essential hypertension have a normal cardiac output but a raised peripheral resistance. The reason for this is unclear. Factors that may contribute to this may include a familial tendency, diet, obesity, insulin resistance, fetal development and neurovascular anomalies (Beevers et al 2001). Whatever the cause, the result is an inappropriate decrease in the diameter of the arterioles resulting in increased peripheral resistance. As a result, cardiac rate and/or stroke volume increases to produce a blood pressure sufficient to overcome this resistance and get sufficient blood with gases and nutrients to the cells of the body to enable metabolism to take place.

Secondary hypertension

Secondary hypertension is the result of an identifiable abnormality which causes increased peripheral resistance (Gutierrez & Petersen 2002). For example, renal disease may result in decreased renal perfusion stimulating the kidneys to release increased amounts of renin; an adrenal tumour or hyperthyroidism will stimulate increased amounts of catecholamines. Inappropriately increased levels of renin or catecholamines will cause vasoconstriction and thus increase peripheral resistance. Cardiac output will increase in order to raise blood pressure sufficiently to get sufficient gases and nutrients to all the cells of the body.

Signs and symptoms

Hypertension is generally asymptomatic. It is usually diagnosed during routine physical examination when an increased blood pressure is observed, or secondary to another disorder as described above. Diagnosis may result from examination of the eyes by the ophthalmologist in those with visual impairments. Should hypertension be undiagnosed during such examinations, the first evidence may be due to a complication of the condition such as cardiac or renal disease, or stroke.

Those who do experience symptoms complain of vague symptoms such as occipital headache, weakness, dizziness, epistaxis or visual disturbances.

Diagnosis

Diagnosis of hypertension is made when resting blood pressures >140 mmHg systolic and/or 90 mmHg diastolic are observed (Box 2.2).

Box 2.2 White coat hypertension

This is a condition in which patients display an increased blood pressure when in hospital or other clinical environment which is not apparent at home. No signs of stress such as tachycardia are presentand thus it is difficult to determine the true blood pressure from a single measurement. White coat hypertension therefore describes a situation in which anxiety increases blood pressure. In the absence of any other indicators of hypertension, the midwife should attempt to develop a good relationship with the woman and her family and reassure her that heranxiety is the likely cause of her rise in blood pressure. She should then arrange to see her, preferably in her own home, to repeat the test.

Treatment

The goal of successful management of both essential and secondary hypertension is to lower and maintain blood pressure below 140/90 in order to prevent complications or death by permanent damage to sensitive organs of the body such as the heart, brain, kidneys and eyes. Additionally, the patient will be investigated for secondary causes although these will only be present in a minority of cases.

Treatment will depend on the degree of hypertension and the presence of end organ damage. Inthe absence of an underlying pathology, treatment will include lifestyle changes as well as pharmacology if merited. Antihypertensive drug therapy is usually introduced when there is a sustained systolic of 160 mmHg or diastolic of 100 mmHg or more.

Lifestyle changes

All patients with hypertension will be advised about lifestyle. For those with mild hypertension, changes in diet, a reduction of stress and a decrease in salt intake may be all that is required to reduce blood pressure to a level that will prevent complications to body organs and tissues. Even in those with a more severe degree of hypertension, lifestyle changes may slow down the development of complications of the condition. Areas in which the patient will be advised and supported to make changes are:

• Diet including weight reduction if necessary, healthy eating, salt reduction, alcohol consumption

• Exercise once the hypertension is under control to help achieve and maintain a satisfactory weight

• Smoking cessation, as smoking confers an additional risk factor in the development of hypertension

• Stress management – although the relationship between stress and hypertension has not been proved, stress reduction and the use of relaxation techniques has been shown to be beneficial to health promotion.

Drug therapy

Severe hypertension will be treated pharmacologically in an attempt to prevent further damage to body organs and tissues. The medical practitioner has a range of oral medications that can be used in the treatment of hypertension:

• Vasodilators such as hydralazine, which act predominantly on the smooth muscle of arterioles

• Angiotensin converting enzyme (ACE) inhibitors such as captopril, which reduce peripheral resistance by blocking the conversion of angiotensin I to angiotensin II

• Diuretics such as thiazides and furosemide (frusemide), which reduce interstitial fluid causing vessel wall stiffness. Regular monitoring of serum potassium is essential as hypokalaemia can be a side-effect of these drugs (Kennedy 2002)

• Drugs which act on the central nervous system:

– Centrally acting drugs, such as methyldopa, which decrease sympathetic nervous system activity

– Beta blockers, such as propranolol, which block beta receptors in the sympathetic nervous system – these drugs reduce blood pressure but have the added advantage of being cardioprotective – they inhibit the rate and force of cardiac contraction as well as reducing the normal cardiac response to stress and exercise.

– Alpha blockers, such as prazosin, which result in vasodilation of peripheral arterioles

– Calcium channel blockers, such as nifedipine, which relax smooth muscle in arterioles.

Prognosis

Long-term hypertension is a serious condition resulting in vascular and organ damage. The higher the blood pressure, the higher the risk of complications. Arterial walls become thickened and sclerosed reducing blood supply to tissues. Areas of necrosis may develop which may rupture under pressure. Thrombosis is likely. The most vulnerable organs to damage from sustained hypertension are:

The heart

Increased workload results in hypertrophy of the myocardium, and the coronary arteries are unable to supply sufficient blood to this muscle. Angina pectoris or myocardial infarction may result.

The brain

Increased pressure in the narrowed and damaged cranial blood vessels may cause rupture or blockage of the vessels and death of brain tissue – a stroke.

The kidneys

Renal blood vessels will also become narrowed and weakened with resultant thromboses and dysfunction.

The eyes

Retinal capillaries may rupture causing degenerative changes.

HYPERTENSION IN PREGNANCY AND CHILDBIRTH

Overview

Hypertensive disorders occur in up to 10% of all pregnancies and contribute significantly to both maternal and fetal mortality and morbidity rates (Lloyd 2003). Caring for the pregnant women with hypertension is a considerable challenge for the multidisciplinary team. As in the general population, there are seldom any signs or symptoms of hypertension and as the midwife is the primary care giver in the majority of pregnancies, she must be alert for this condition. Screening early in pregnancy will identify women with pre-existing hypertension. Ongoing examination throughout pregnancy will identify women developing pregnancy-induced hypertension or pre-eclampsia. However, hypertension may be a late sign of pre-eclampsia and thus the health of both mother and fetus may be compromised before the condition is detected.