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Pre‐procedural considerations

Equipment

Sphygmomanometer

The device used to measure blood pressure is called a sphygmomanometer. It consists of a rubber cuff connected to a rubber bulb that is used to inflate the cuff and a meter that registers the pressure in the cuff (Tortora and Derrickson [199]). Sphygmomanometers that are uncalibrated or not working accurately can cause blood pressure measurement error (Benmira et al. [17]). If using a manual sphygmomanometer, check that the dial is set at zero prior to commencing (Chen et al. [40]). In addition, follow the manufacturer's recommendations and local policies regarding servicing and care of the device (NICE [132]).

Manual mercury sphygmomanometers have gradually been phased out of mainstream clinical practice and replaced with dial or electronic manometers (Environment Agency [60]). This is primarily due to potential mercury leaks, which are hazardous to both the environment and humans, and secondly because since April 2009 they have no longer been available to either members of the public or healthcare professionals (Environment Agency [60]).

Cuff

The cuff is made of an inelastic material that encloses an inflatable bladder and encircles the arm. It is important that the correct cuff size is selected for the individual patient as cuffs that are too small yield a reading that is falsely high and large cuffs give a falsely low reading (British Hypertension Society [28], MHRA [118]). With the correct size of cuff, the bladder should encircle 80% of the patient's arm (British Hypertension Society [28]).

Inflatable bladder, valve, pump and tubing

In a manual sphygmomanometer, the system used to inflate and deflate the bladder consists of a bulb attached to the bladder with rubber tubing. When the bulb is compressed, air is forced into the bladder; to deflate the bladder, there is a release valve. The rubber tubes have conventionally been placed so they are inferior to the cuff; however, it is now recommended that they are placed superiorly to prevent them impeding auscultation (British Hypertension Society [28]).

Stethoscope

It is recommended that the stethoscope, which should be of high quality with well‐fitting earpieces, should be placed over the brachial artery at the antecubital fossa (Bickley [18], Pan et al. [152]). The bell part of the stethoscope may capture the low pitch of the Korotkoff sounds better than the diaphragm but the diaphragm has a larger surface area and is easier to manipulate with one hand (Pan et al. [152], [151]).

Specific patient preparation

It is important to maintain a standardized environment in which to take the patient's blood pressure (NICE [132]). The patient should empty their bladder and be seated (unless thigh or orthostatic blood pressure measurements are required) in a relaxed, quiet and comfortable setting (RCP [172]). Their arm should be outstretched and supported (an unsupported arm may result in an increase of diastolic blood pressure by 10%) (NICE [132]). The brachial artery at the antecubital fossa should be positioned level with the heart, approximately level with where the fourth intercostal space meets the sternum (Bickley [18], Waugh and Grant [207]).

The patient's back should be supported and if they are in a chair their feet should be on the floor as systolic blood pressure can increase in people with their legs crossed (Privšek et al. [166]). Correct patient positioning can be seen in Figure 14.25.

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Figure 14.25 Correct blood pressure reading technique.

Blood pressure should initially be measured in both arms as often people have a significant difference in blood pressure measurement between their arms (NICE [132]). Patients who have a large and persistent disparity may have underlying conditions such as occlusive artery disease (Bickley [18]). Differences of up to 10 mmHg can be due to random variation (RCP [172]). The arm with the highest reading should be the one used for subsequent measurements (NICE [132]).

Procedure guideline 14.3

Blood pressure measurement (manual)

Table 14.5 Prevention and resolution (Procedure guideline 14.3)

Problem	Cause	Prevention	Action
The result is unexpectedly low or high	Poor technique, incorrect cuff size or faulty equipment Patient incorrectly positioned or recently having exercised	Check the sphygmomanometer prior to use to see when it was last serviced. Check all the components for signs of damage. Choose the correct size of cuff. Ensure the patient is correctly positioned and has rested prior to the procedure.	Wait 1–2 minutes before repeating the blood pressure measurement ( NICE [132]). If the measurement is still unexpected, consider changing devices or asking a colleague to repeat the procedure. If it remains abnormal, notify the medical team of the result.
On auscultation, the Korotkoff sounds disappear after the initial sound, then reappear and then disappear again	This is called the auscultatory gap – it may mislead the practitioner into obtaining an incorrect result ( Pan et al. [151])	Palpate the pulse as the cuff is being deflated to gain an approximation of the systolic blood pressure ( NICE [132]).	Document that the patient has an auscultatory gap and ensure other practitioners are aware to prevent future errors. Recheck using the correct procedure.
On auscultation, the Korotkoff sounds are inaudible or very weak	Poor placement of the stethoscope A noisy environment Venous congestion The patient may be in shock ( Bickley [18])	Find a quiet environment in which to measure the patient's blood pressure; listen with the bell of the stethoscope rather than the diaphragm; wait for venous congestion to resolve ( Bickley [18]).	If still inaudible, ask the patient to elevate their arm overhead for 30 seconds, then bring it back to the correct height to inflate the cuff and measure their blood pressure; this increases the loudness of the sounds ( Bickley [18]).