Arterial blood pressure is taken frequently by healthcare professionals in a wide variety of patients. Many factors can influence the reading, including: fear; smoking; exercise; pain; the patient talking/being spoken to, having their legs crossed or having a full bladder; using a cuff of the incorrect size; and anxiety caused by the clinical environment (see “Measuring blood pressure: Parts 1 and 2”). It is important to try to reduce these effects and to take a standardised approach with each patient, to ensure that you obtain an accurate reading. Mercury sphygmomanometers are reliable but are being withdrawn for health and safety reasons—primarily the hazards of dealing with mercury spillages and the ultimate disposal of mercury (EA, 2014). Devices without mercury are now commonly used, but you are strongly advised to assess and evaluate published literature regarding their accuracy. The British and Irish Hypertension Society (BIHS) validates a list of sphygmomanometers (see https://bihsoc.org). Use aneroid sphygmomanometers if they are regularly calibrated according to local policy as they lose accuracy with use (BIHS, 2020). The performance of the device depends greatly on calibration (Tolonen et al., 2015). Before and after measuring blood pressure, decontaminate your hands by washing with soap and water or by using an alcohol-based hand sanitiser. Clean equipment used to measure blood pressure between patients, following local policy (NICE, 2020).

To reduce extraneous effects on blood pressure readings, a quiet, comfortable location at normal room temperature is optimal (NICE, 2019). If the environment is too noisy, it may also affect your ability to hear the Korotkoff sounds, if using the auscultatory method.

In clinical practice, you may need to record the blood pressure with the patient in various positions, such as sitting and standing. This is often the case for patients with postural hypotension. Always ensure that the patient’s arm is supported when taking the reading, whatever the position may be: e.g., a colleague may need to support the arm when the patient is standing. Identify the position, such as L (lying), St (standing), and so on, when recording on the chart.

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ObservationsAdults

Measuring blood pressure Part 3: The patientNaomi Stetson, formerly Lead Nurse, Peart-Rose Clinic, Imperial College Healthcare NHS Trust, London

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Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.Always first explain the procedure to the patient and obtain their consent, in line with the policies of your employer or educational institution.

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Ideally, the patient should not have had caffeine, smoked cigarettes or eaten for 30 minutes before measuring blood pressure (NICE, 2019). Caffeine can cause a small rise in blood pressure (Noordzij et al., 2005); smoking can also affect the reading (Ragueneau et al., 1999). Ensure that the patient has an empty bladder; systolic blood pressure measurements can increase by 10 to 15 mmHg when the bladder is full (Handler, 2009; O’Brien et al., 2003).

Explain the procedure and ask the patient for their consent. The patient should keep both feet flat on the floor; there is some evidence that having legs crossed at the knees can raise the blood-pressure reading (Adiyaman et al., 2007). Perform the procedure in silence; blood pressure may increase when a patient is spoken to or when talking (Le Pailleur et al., 2001; Thomas et al., 1992).

Eating, drinking, smoking and emptying bladder Body position and talking

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To obtain an accurate blood pressure assessment, the patient should have avoided exercise for about 30 minutes. Let the person rest for at least 5 minutes before taking their measurement to settle their blood pressure (NICE, 2019; BIHS, 2017); resting for up to 10 minutes may help produce an accurate reading for effective management (Nikolic et al., 2013).

Rest

The blood pressure in the left arm may differ from that in the right; occasionally this may be significant. Evidence suggests that a difference of 10 mmHg or more may help identify patients who need further vascular assessment (Clark et al., 2012). When diagnosing hypertension, take measurements in both arms (NICE, 2019; Mancia et al., 2013). If there is a significant and consistent difference (on a second reading) between the systolic pressures of more than 20 mmHg, use the arm that had the higher reading for subsequent measurements (NICE, 2019). Avoid measuring blood pressure in an arm affected by a cerebrovascular accident or a mastectomy/lymphoedema.

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Which arm? Arm position

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Avoid “terminal digit bias”

When taking the blood pressure of a patient who is sitting or standing, make sure that their arm is at the level of their heart, in line with their mid-sternum (NICE, 2019; Mancia et al., 2013). When a patient is lying flat on a bed, their arm is already at the same level as their heart.

Muscle contraction raises blood pressure and affects the reading (Frese et al., 2011). Make sure the patient’s arm is supported to avoid muscle tension, whatever position they are in.

Find a comfortable position for yourself when measuring blood pressure, so that you feel relaxed and can avoid rushing the procedure. It should take about 5 minutes to carry out. Deflating the cuff too rapidly will tend to underestimate systolic pressure and overestimate the diastolic reading (Frese et al., 2011). Deflate the cuff slowly by 2 mmHg per second (NICE, 2019).

Ensure that the dial is close enough to read the figures clearly; ideally it should be at eye level. Record the measurement as soon as possible, rather than trying to remember it.

There can be a tendency for healthcare professionals to record blood pressure readings with either “0” or “5” as the terminal digit (Wingfield et al., 1996). For an accurate reading, record the pressure to the nearest 2 mmHg. Use of an automatic device removes this effort, but potential errors relating to preparation of the patient remain (Handler, 2009).

Observations

Adults

Measuring blood pressure Part 3: The patient Page 2

Page 2 of 2

Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.Always first explain the procedure to the patient and obtain their consent, in line with the policies of your employer or educational institution.

Reading the scale