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Ten tips on measuring blood pressure

Cardiology GPSI Dr Rubin Minhas offers tips on making sure BP monitoring in your practice is as accurate as possible

Cardiology GPSI Dr Rubin Minhas offers tips on making sure BP monitoring in your practice is as accurate as possible

1 Make sure all sphygmomanometers are regularly calibrated. Mercury devices should be checked at least once a year but aneroid devices – if used – need to be checked at least two or three times a year. Automated devices should only be used if they have been recalibrated according to the manufacturer's instructions. Consider delegating responsibility for calibration to the practice manager.

2 Some automated devices that measure BP at the wrist have been clinically validated. But ensure the arm is positioned at the level of the heart to reduce error.

3 Every consulting room needs to have both regular and large cuffs to minimise the chances of the wrong cuff being used. ‘Miscuffing' can introduce large errors in measurement. ‘Undercuffing' – using either too narrow or too short a bladder – can lead to overestimation of blood pressure, while ‘overcuffing' – using too wide or too long a bladder – may lead to underestimation.

4 If a patient appears nervous or stressed make sure that this is mentioned in the notes. Decisions to start treatment should not be based on readings that reflect a rise related to anxiety. Patients should not have their legs crossed and should not be talking while the reading is taken. The diastolic blood pressure can be expected to be about 5mmHg lower if the patient is lying down.

5 Measure BP on the same arm every time and record which arm has been used in the notes. It is good practice to tell the patient which arm they should have readings taken from so that they can tell others who might be measuring their BP. A difference in BP between arms can be expected in about 20% of patients. If differences between arms of greater than 20mmHg for systolic or 10mmHg for diastolic pressure are present on three consecutive readings, the patient should be considered for referral for further evaluation.

6 Arm support is very important. Muscle contraction in an unsupported arm can raise diastolic blood pressure by as much as 10%, and raising the arm above heart level leads to underestimation by as much as 10mmHg. The patient's arm should be horizontal at the level of the heart as denoted by the midsternal level.

7 Try to measure BP at the same time of day where practically possible. BP rises with waking and then tends to fall throughout the day. Current guidelines do not make specific recommendations regarding the time when blood pressure should be measured but it seems sensible to try to measure it at a consistent time.

8 If you suspect that readings seem unexpectedly high or variable consider a referral for ambulatory blood pressure monitoring (ABPM). Remember that ABPM readings will be lower than clinic readings by approximately 10/5mmHg.

9 Remember that BP variability is large. Studies have shown BP can vary from the mean by a standard deviation of 12/8mmHg in the same patient on different days. In one study 15 readings (over five different days, with three readings per occasion) were required to reduce variability by 80%.

10 Measuring BP in patients with arrhythmias can be a problem. This is because there can be large beat-to-beat variation in blood pressure when cardiac rhythm is irregular. Oscillometric devices may not provide acceptable levels of accuracy and precision and should not be used in these situations. If heart rate is extremely slow, for example 40 beats per minute, it is important that the deflation is performed more slowly than normal (normal rate 2-3mmHg per second) as rapid deflation will lead to underestimation of systolic and overestimation of diastolic pressure.

Dr Rubin Minhas is a cardiology GPSI in Kent currently working as a GP researcher for the US public-policy think tank the RAND corporation

Competing interests: none declared

BP monitoring

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