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Blood Pressure Measurement - Part 2: using automated devices.

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VOL: 103, ISSUE: 19, PAGE NO: 26

Phil Jevon, PGCE, BSc, RN, is resuscitation officer/clinical skills lead, Manor Hospital, Walsall, and honorary clinical lecturer, Birmingham Medical School

When automated blood pressure devices were first manufactured, their accuracy and reliability was questioned. However, better technology has resulted in more accurate and reliable devices (Beevers et al, 2001).

 

When automated blood pressure devices were first manufactured, their accuracy and reliability was questioned. However, better technology has resulted in more accurate and reliable devices (Beevers et al, 2001).

 

 

The British Hypertensive Society (2007) lists blood pressure devices that it has validated. Most measure blood pressure using one of the following:

 

 

- Oscillometry to detect arterial blood flow;

 

 

- A microphone to detect the Korotkoff sounds;

 

 

- Ultrasound to detect arterial blood flow.

 

 

Oscillometric blood pressure devices
Most modern devices use oscillometry, where blood pressure measurement is based upon variations of pressure in the cuff due to pulsing of the artery directly beneath it (Berger, 2001). Using an oscillometric device, even if CE marked, to diagnose hypertension is not recommended because a much greater accuracy and precision of measurement is required (Medicines and Healthcare products Regulatory Agency, 2005). Also, its reliability in the presence of a cardiac arrhythmia (particularly atrial fibrillation), pre-eclampsia and certain vascular diseases has been questioned; an alternative method of measurement (for example auscultation) should be used in these situations (MHRA, 2005).

 

 

Procedure for measurement
The principles for the accurate measurement of blood pressure using an automated electronic device will be similar to those for the manual recording of blood pressure using a sphygmomanometer in respect of patient preparation, patient position and cuff choice/placement. However, when using an automated electronic device, it is important to be familiar with its working and to follow the manufacturer’s recommendations.

 

 

The following generic principles apply when measuring blood pressure using an automated device:

 

 

- Ensure that the patient has been sitting or lying down for at least five minutes and is comfortably relaxed (Fig 1) (BHS, 2006);

 

 

- Explain the procedure to the patient and obtain her or his consent;

 

 

- Ask the patient to remove any tight clothing from around her or his arm (Fig 2);

 

 

- Ensure the patient’s arm is supported at the level of her or his heart;

 

 

- Select an appropriately sized cuff: the bladder of it should encircle at least 80% of the arm but no more than 100% (Fig 3);

 

 

- Place the cuff snugly onto the patient’s arm, with the centre of the bladder over the brachial artery - some cuffs have a ‘brachial artery indicator’, an arrow which needs to be aligned with the brachial artery;

 

 

- Ask the patient to refrain from talking or eating during the procedure as this can result in an inaccurate higher blood pressure;

 

 

- Switch on the automated device and press start to record the blood pressure measurement, following the manufacturer’s recommendations (Fig 4);

 

 

- Document the systolic and diastolic blood pressures on the patient’s observation chart following local protocols (Fig 5);

 

 

- Switch off the automated device and remove the cuff;

 

 

- Compare with previous readings and inform the nurse in charge/medical team;

 

 

- Ensure the device is correctly and safely stored; if necessary recharge the battery following the manufacturer’s recommendations and local policy (Fig 6).

 

 

Errors in automated measurement
Errors in measurement can be caused by:

 

 

- Defective equipment, for example leaking tubing or a faulty valve;

 

 

- Use of incorrectly sized cuff: if it is too small, the blood pressure will be overestimated and, if it is too big, the blood pressure will be underestimated;

 

 

- The cuff not being at the same level as the heart.

 

 

Checking automated devices
The devices should be regularly checked and calibrated in line with the manufacturer’s recommendations. It is also good practice to occasionally check the device against a mercury sphygmomanometer or another validated device. The cuff should be cleaned following local policy and the manufacturer’s recommendations.

 

 

Ambulatory blood pressure monitoring
Ambulatory blood pressure monitoring devices allow the recording of the patient’s blood pressure at regular intervals during normal living and working conditions. Indications for this monitoring include wide fluctuation of readings, multiple therapies which have failed to achieve the target blood pressure and when the symptoms suggest the possibility of hypotension (BHS, 2006). The routine use of automated ambulatory blood pressure monitoring is not recommended as its value has not been established (NICE and the BHS, 2006).

 

 

Professional responsibilities
This procedure should be undertaken only after approved training, supervised practice and competency assessment, and carried out in accordance with local policies and protocols.

 

 

This article has been double-blind peer-reviewed

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