Blood pressure measurement and routine hypertension investigations
THE CONTEXT
Accurate measurement includes appropriate technique and interpretation of ambulatory or home readings, alongside investigations for risk factors, causes and complications.
Clinic measurement technique
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Use a validated, well-maintained and properly calibrated machine.
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Measure sitting blood pressure routinely. Add standing measurements in older patients, diabetic patients and those with possible postural hypotension; rest the patient for 2 minutes.
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Remove tight clothing and support the arm at heart level.
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Use an appropriate cuff whose bladder encompasses more than two-thirds of the arm.
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Lower pressure at 2 mmHg per second and read blood pressure to the nearest 2 mmHg.
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Use phase V, the disappearance of sounds, for diastolic blood pressure and take two measurements at each visit.
Ambulatory monitoring
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Automated readings over 24 hours or longer provide a better blood pressure profile than a limited number of clinic readings and correlate more closely with target organ damage.
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Ambulatory readings are systematically lower than clinic readings by approximately 12/7 mmHg, so treatment thresholds and targets require downward adjustment.
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Use average ambulatory daytime blood pressure to guide management decisions, rather than the 24-hour or night-time average.
Home measurements and indications
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Patients can measure blood pressure at home using commercially available semi-automatic devices; the value of readings depends on their environment and timing.
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Home or ambulatory measurements are particularly helpful for unusually labile blood pressure, refractory hypertension, possible symptomatic hypotension and suspected white coat hypertension.
Routine investigations
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Investigations include urinalysis for blood, protein and glucose; blood urea, electrolytes and creatinine; blood glucose; serum total and high-density lipoprotein cholesterol; thyroid function tests; and a 12-lead electrocardiogram.
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Hypokalaemic alkalosis may indicate primary hyperaldosteronism but is usually due to diuretic therapy.
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The electrocardiogram is used to assess left ventricular hypertrophy and coronary artery disease.