Hypertension

Published on 01/03/2015 by admin

Last modified 22/04/2025

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Hypertension

Hypertension is a common clinical problem. It is defined as chronically increased systemic arterial blood pressure. The definition of hypertension has changed over the years, as more effective treatments have become available. The WHO classification of hypertension is shown in Table 68.1. It is important not to base clinical decisions on a single blood pressure reading. Some patients have ‘white coat’ hypertension, where readings taken by doctors or other health professionals are misleadingly high. Ambulatory blood pressure measurement over a whole day provides the most detailed information (Fig 68.1).

Table 68.1

WHO classification of hypertension

Category	BP (mmHg)
Optimal blood pressure	<120/80
Normal blood pressure	<130/85
Mild hypertension	140/90–159/99
Moderate hypertension	160/100–179/109
Severe hypertension	≥180/110

Fig 68.1 24-hour ambulatory blood pressure monitoring.

If hypertension is left untreated, patients are at risk of several complications. These include:

stroke

left ventricular hypertrophy leading eventually to heart failure

chronic kidney disease

retinopathy.

Occasionally patients present with severe hypertension associated with a severe form of retinopathy known as papilloedema, and progressive renal failure. This is known as malignant hypertension and requires urgent treatment.

Causes of hypertension

Hypertension is related to genetic and environmental factors. Often it runs in families, more than would be expected simply on the basis of a shared environment; other associations include obesity, diabetes, and excess alcohol consumption. In many patients, the cause is not known, and in these patients it is referred to as ‘primary’ or ‘essential’ hypertension. So-called secondary hypertension is due to clearly identifiable causes (see below), some of which may be diagnosed or monitored biochemically. However, other modalities of investigation are at least as important in the investigation of hypertension. For example, imaging of renal arteries, or isotope renograms, may provide vital diagnostic information.

Renal parenchymal disease. This is strongly suggested by the finding of a reduced estimated glomerular filtration rate (eGFR) and/or proteinuria.

Renal artery stenosis. This should be suspected in refractory hypertension, especially if creatinine rises on treatment with angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs). This is best diagnosed with magnetic resonance angiography. It may be associated with grossly elevated renin concentrations.

Primary hyperaldosteronism. This is dealt with in more detail on page 99. It should be suspected if hypokalaemia (often with associated alkalosis) is present, especially if there is a failure to respond to potassium supplementation. The ratio of aldosterone to renin is characteristically elevated, although imaging studies (CT or MRI) are required to make the diagnosis.

Phaeochromocytoma. This is a relatively rare cause of secondary hypertension. It should be suspected if hypertension is paroxysmal, or if symptoms (like palpitations, headaches) are episodic. Urinary catecholamines are usually but not always raised, and there are often false positive results as well. Urine or, especially, plasma metadrenalines (catecholamine metabolites) are more sensitive and specific for diagnosis. Isotope (MIBG) scans are very specific and help to localize the tumour. The biochemical pathways involved in the production of catecholamines are illustrated in Figure 68.2.

Fig 68.2 Pathway for production of catecholamine metabolites.

Cushing’s syndrome. This is dealt with in more detail on pages 98–99. It is not usually a diagnostic dilemma, since the signs and symptoms of Cushing’s syndrome, and the association with hypertension, are well recognized. However, if there is doubt, a dexamethasone suppression test (p. 83) may be useful.

Obesity/sleep apnoea. Obesity is an increasingly common cause of secondary hypertension, especially if it is associated with sleep apnoea. The latter is likely in the presence of an increased neck circumference.

Other. Less common causes of secondary hypertension include acromegaly, hyperthyroidism and hypothyroidism, and coarctation of the aorta.

Treatment of hypertension

Various groups of antihypertensive drugs are used in the management of hypertension. When patients fail to respond to one or more agents, many physicians add in other drugs, on the grounds that increasing the dose of existing treatments often increases side effects without enhancing the efficacy. Thus many patients end up on multiple drugs for their hypertension. Commonly used groups of drugs include the following:

ACEIs/ARBs. ACEIs inhibit angiotensin-converting enzyme, and so reduce production of angiotensin II (a potent vasoconstrictor) and, ultimately, aldosterone (a potent mineralocorticoid). ARBs block angiotensin receptors (Fig 68.3). Both groups of drugs may in some patients reduce the renal damage induced by hypertension; this can be monitored by their effect on reducing proteinuria. In some patients with refractory hypertension, the introduction of ACEI/ARBs is associated with a rapid rise in creatinine. In this scenario, the drug should be stopped and renal artery stenosis suspected (see above; Fig 68.4).