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Managing hypertension: measurement and prevention

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VOL: 98, ISSUE: 38, PAGE NO: 38

Rose Hurst, MSc, BSc, DipSystPrac, DipHE, C&G NVQ Assessor, SRN, is cardiac nurse specialist, Brighton and Sussex University Hospitals NHS Trust and Mid Sussex Primary Care Trust

In the UK, 14% of deaths from coronary heart disease in men and 12% of deaths from CHD in women are related to raised blood pressure (National Heart Forum, 2002). Yet most people are unaware that they have a problem until they have a coronary event such as a stroke.

In the UK, 14% of deaths from coronary heart disease in men and 12% of deaths from CHD in women are related to raised blood pressure (National Heart Forum, 2002). Yet most people are unaware that they have a problem until they have a coronary event such as a stroke.

The levels of systolic blood pressure (SBP) - blood pressure during the contraction phase of the cardiac cycle - and diastolic blood pressure (DBP) - blood pressure during the relaxation phase of the cardiac cycle - are both related to the risk of developing cardiovascular disease. Sustained SBP 160mmHg and/or DBP 100mmHg requires drug therapy. Patients with an SBP of 140-159mmHg or a DBP of 85-99mmHg may require treatment depending on their overall risk of developing cardiovascular disease (Department of Health, 2000).

Optimal BP treatment targets are an SBP of less than or equal to 140mmHg and a DBP of less than 85mmHg, and even lower levels in people with diabetes (Ramsay et al, 1999) (Table 1).

The risk of having CHD within 10 years can be estimated using the Joint British Societies' Cardiac Risk Assessor software, available from the British National Formulary website (www.bnf.org/BNFExtraFrame.htm). Alternatively, multiplying coronary risk by 1.33 gives a reasonable estimate of cardiovascular risk over 10 years (Jackson, 2000).

Blood pressure management in primary care
All adults should have their BP measured at least every five years. Those with normal-to-high values (an SBP of 135-139 and a DBP of 85-89mmHg) and those who have had high readings at any time should have their BP measured annually. The risk of CHD should be recalculated at this time, as the risks of both high BP and CHD increase with age. All patients with hypertension should have a thorough history taken and a physical examination, with routine investigations (Box 1). Treating raised BP in an otherwise healthy person cuts the risks of death, myocardial infarction and stroke (Hampton, 1999).

It is vital to ensure the accuracy of BP measurement (Box 2). Consistently underestimating it by just 5mmHg could result in almost two-thirds of people with hypertension being denied potentially life-saving treatment.

Accepted good practice is to take two readings, several minutes apart, from the same arm. The lower of the two readings should be used. The SBP is palpated to avoid auscultatory gap, and the DBP is read using the fifth Korotkoff sound (disappearance of the sound), with no rounding off the pressure reading.

It is good practice to take readings from both arms on at least the first visit. Usually, there is no significant difference in pressures between arms and using the one that is nearest to the observer is reasonable. Occasionally, there is a consistent difference between the two arms, in which case BP should be routinely measured in the one with the highest pressure. If there are differences of more than 20mmHg for systolic or more than 10mmHg for diastolic present on three consecutive readings, the patient should be referred to a cardiovascular centre for further investigation. Older patients and those who have diabetes should also have their BP taken while standing to check for postural hypotension.

The cuff bladder should encircle the arm completely with its centre over the brachial artery. If it is too small or too large, it will give falsely high or low readings. Mercury sphygmomanometers and aneroid devices are commonly used. The principal clinical concerns are to ensure accuracy, reproducibility and reliability.

Ambulatory blood pressure measurement
Ambulatory blood pressure measurement (ABPM), where the patient's BP is measured intermittently over 24 hours, is valuable in diagnosing and treating older patients, and is also increasingly used in pregnancy. It provides an accurate and reproducible estimate of a patient's usual long-term BP. Taking a large number of measurements reduces the risk of misclassification, but the process is relatively expensive.

Treatment thresholds and targets must be adjusted downwards when making decisions based on ABPM. The average difference between BP taken in a clinic and daytime ABPM is approximately 12/7mmHg. The average daytime BP should be used for treatment decisions, not the 24-hour average. The level of ABPM may alter the way BP is managed when: the average clinic BP is 160/100mmHg; there is no target organ damage, or cardiovascular complications; and the estimated 10-year CHD risk is less than 30%. In this situation, elevated BP is the only indication for antihypertensive treatment, and normal values by ABPM may indicate that no treatment is required. Patients in this category must be followed up annually.

Blood pressure measurement in the home
There is less evidence for the value of self-measurement of BP than there is for ABPM. At present, it is performed mostly by patients on their own initiative, using devices bought over the counter, without medical supervision.

It is a means of gaining further insight into the effects of strategies for BP control in patients who are motivated and informed and who remain under medical supervision. The patient is more relaxed at home, so upward adjustment of 12/7mmHg is needed for comparison to measurements made in a clinical setting.

Medical reasons for hypertension
There is uncertainty about the pathophysiology of hypertension. A small proportion of patients (2-5%) have underlying renal or adrenal disease as the cause of hypertension. In the remainder there is no clear single identifiable cause and is labelled as essential hypertension.

Factors that may contribute to a raised BP include: salt intake, obesity and insulin resistance, the renin-angiotensin system, the sympathetic nervous system, genetics, endothelial dysfunction, low birthweight and intrauterine nutrition, and neurovascular anomalies.

Rarely, hypertension is secondary to an underlying condition that is usually suspected from physical examination and the results of routine tests.

The most challenging condition is so-called white-coat hypertension or isolated clinic hypertension, which occurs in 8-10% of patients with hypertension. While some people exhibit a physiological response to anxiety others have hypertension that normalises over time and repeated measurements. In yet others its history is undetermined.

The latter patients are at low risk and, while they can avoid medication in the short term, they need further investigation and repeated monitoring. The white-coat effect may be avoided if measurements are taken by the practice nurse, or if ABPM is used.

Health promotion
Changes in diet and lifestyle may: lower BP by as much as drug monotherapy; reduce the need for drug therapy, including multiple drug regimens; enhance the antihypertensive effects of drugs; and reduce overall cardiovascular risk.

Patients should be encouraged to make the necessary changes, especially those who have hypertension and those with a strong family history of CHD. Changes may include:

- Taking exercise: regular dynamic physical exercise such as brisk walking, tailored to the individual;

- Reducing weight: for each kilogram lost, BP falls by 2.5/1.5mmHg;

- Cutting down on alcohol: men should consume fewer than 21 units and women fewer than 14 units a week;

- Reducing salt intake: cutting daily intake from 10g to 5g reduces BP by 5/3mmHg, more so in older people and those with higher initial recorded BP levels;

- Eating more fruit and vegetables: increasing consumption from two to seven portions a day lowers BP in patients with hypertension by 7/3mmHg. If this is combined with a low-fat diet BP will fall by 11/6mmHg.

Further measures to reduce risk include smoking cessation and replacing saturated fat with polyunsaturated and monounsaturated fats, eating oily fish and cutting total fat intake. If patients have mild hypertension but no cardiovascular complications or target organ damage, the response should be observed in the initial four to six months. When drug treatment has to be introduced more quickly, lifestyle changes should be instituted in parallel.

Drug therapies and treatments
If repeated BP measurements are still greater than 140/85mmHg following non-pharmacological advice, drug therapy may be employed (Ramsay et al, 1999).

- The major classes of drug do not, on average, differ in effectiveness, frequency of side-effects or quality of life, although individual patient variation often occurs;

- A thiazide diuretic or beta-blocker is recommended as first-line treatment in most patients, as the evidence for reduction in cardiovascular events is strongest with use of these drugs;

- Preferential use of other antihypertensives is recommended in certain situations (where there are complications from another disease, for example).

Add-on antihypertensive treatment

Monotherapy controls hypertension in less than half of all patients and a third will require three or more drugs:

- Antihypertensives from different classes generally have an additive effect when prescribed together. Submaximal doses of two drugs may result in larger falls in BP and fewer side-effects than maximal doses of a single drug;

- It is rational to combine drugs with different modes of action, for example, diuretic with beta-blocker, diuretic with angiotensin-converting enzyme (ACE) inhibitor, beta-blocker with calcium-channel blocker (not verapamil), calcium channel-blocker with ACE inhibitor;

- For third-line drug therapy, common combinations are diuretic, ACE inhibitor and calcium-channel blocker; or diuretic, beta-blocker and calcium-channel blocker;

- Nifedipine in capsule form should not be prescribed for hypertension.

The older person

- The benefit of treatment is greater for older than for younger people, because of their higher overall risk;

- Where hypertension is first diagnosed after the age of 80 years, there is currently no firm evidence to guide policy;

- Antihypertensive treatment should be continued after patients reach the age of 80 years;

- Thiazides are the recommended first-line treatment for the elderly;

- A dihydropyridine calcium-channel blocker is the next choice, as there is evidence that these drugs are as effective as thiazides in improving outcome and beta-blockers are probably less effective in the elderly (Staessen et al, 1997).

Diabetes

- The national service framework for CHD (Department of Health, 2000) sets a target BP of less than 140/85mmHg, while the British Hypertension Society sets a target of less than 140/80mmHg. In type 1 diabetes with nephropathy, the BHS recommends a target BP less than 130/80mmHg, or 125/75mmHg if there is proteinuria of 1g in 24 hours. In patients with type 2 diabetes who have nephropathy there is less evidence to guide practice;

- In patients without nephropathy, the optimal first-line drug is yet to be established. At present, any of the major classes of antihypertensives are appropriate;

- In type 1 diabetes with nephropathy, ACE inhibitors may have a specific reno-protective action and are recommended as first-line treatment. BP control is important and combinations of antihypertensive drugs are usually required to achieve this;

- For patients with type 2 diabetes with nephropathy, the treatment evidence is less clear. ACE inhibitors have an antiproteinuric effect and delay progression to overt nephropathy, but it is unclear whether this is owing to a specific effect over and above any BP-lowering effect;

- The BHS states that calcium-channel blockers are safe to use in diabetes, although some studies suggest possible adverse cardiovascular outcomes.

Ethnic groups

- Thiazides and calcium-channel blockers are particularly effective in patients from the Afro-Caribbean community;

- Beta-blockers and ACE inhibitors are less effective in this group because their renin-angiotensin system is often suppressed. However, these drugs may be effective when given in combination with drugs that activate the renin-angiotensin system, for example diuretics, calcium-channel blockers or alpha-blockers.

- Other ethnic groups respond similarly to white Europeans when given antihypertensive treatments.

Prognosis

For a 5-6mmHg reduction in DBP, antihypertensive treatment reduces the relative risk of stroke and coronary events by 38% and 16% respectively. The absolute risk reduction depends on the initial level of cardiovascular risk.

- Seventy per cent of patients with type 2 diabetes have a BP 140/90mmHg. In type 1 diabetes, in the absence of nephropathy, the prevalence of hypertension is similar to that in the non-diabetic population;

- In the Afro-Caribbean population, prevalence may be 50% in those aged over 40;

- British Asians (from the Indian subcontinent) also have a high prevalence of hypertension and type 2 diabetes with insulin resistance.

Other measures to reduce cardiovascular risk
Primary prevention: aspirin

Aspirin is not recommended as a preventive measure in people at high risk of CHD but with no actual symptoms, as it is not clear whether the benefit outweighs the harm (DoH, 2000).

Although aspirin has been shown to reduce cardiovascular events in hypertensive patients (Hansson et al, 1998; Medical Research Council, 1998), the number of clinically significant bleeding episodes was similar to the number of cardiovascular events prevented by aspirin, suggesting the margin between benefit and harm is narrow.

- The BHS recommends 75mg of aspirin for hypertensive patients aged 50 years and over who have controlled BP (less than 150/90mmHg) and target organ damage or diabetes or a 10-year CHD risk greater than 15%;

- Lipid-lowering therapy is recommended with hypertensive therapy if cholesterol 5.0mmol/L and the 10-year CHD risk is greater than 30% (DoH, 2000).

Secondary prevention

When there is evidence of cardiovascular disease:

- Aspirin (75mg) is recommended unless contraindicated;

- Lipid-lowering therapy when cholesterol 5.0mmol/L.

Follow-up
Patients with stabilised BP should be followed up every three months, when the following should be done:

- Measurement of BP and weight;

- Reinforcement of non-pharmacological advice;

- Assessment of general health and drug side-effects;

- Urinalysis for proteinuria (annually).

Conclusion
Almost one-third of women aged 45-54 have hypertension, compared with more than half of those aged 55-64 and over three-quarters of those aged 75 and over.

The Health Survey for England (Erens and Primatesta, 1999) shows that 32% of men and 23% of women known to have hypertension were not having drug therapy to treat the condition. Most people are not aware that they have hypertension until they have a stroke or heart attack, so it is vital that patients' blood pressure is monitored regularly. An estimated 6% of deaths from CHD could be avoided if the number of people with hypertension were halved (National Heart Forum, 2002).

Although the level at which hypertension is diagnosed changes as more evidence becomes available on the risks and benefits of treatment, it is vital that practitioners keep up to date to enable them to follow the latest guidelines.

- The second National Blood Pressure Testing Week, titled Know Your Numbers! The Pressure's Rising, runs from September 16 to 22. For information contact the Blood Pressure Association on tel: 0208 772 4994; website: www.bpassoc.org.uk

- The British Hypertension Society provides information about blood pressure devices on tel: 0208 725 3412; e-mail: bhsis@sghms.ac.uk; website: www.hyp.ac.uk/bhs/information

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