Blood Pressure Measurement OSCE Guide

Contents

1. Introduction
2. General Inspection and Equipment
3. Applying the Cuff
4. Palpatory Estimate of Systolic Pressure
5. Measuring Systolic and Diastolic Pressure by Auscultation
6. Automated Blood Pressure Measurement
7. Interpreting the Reading
8. Lying and Standing (Postural) Blood Pressure
9. Completing the Examination
10. Quiz

Introduction

Wash your hands and don personal protective equipment if appropriate.

Introduce yourself to the patient including your name and grade e.g. 3rd year medical student/junior doctor/consultant.

Confirm the patient’s details taking 3 points of identification usually; full name, date of birth and NHS/hospital number.

Briefly explain what the procedure involves and gain consent: “I’d like to measure your blood pressure, which involves wrapping a cuff around your upper arm and inflating it. It will feel tight for a few seconds but it shouldn’t be painful.”

Ask the patient if they have any pain anywhere before you begin, particularly in the arm you intend to use.

Position the patient seated and relaxed, ideally having rested for at least 5 minutes. The arm should be supported at the level of the heart (roughly the mid-sternum). If the arm is held above heart level the reading will be falsely low, and if it dangles below heart level the reading will be falsely high, because of the effect of hydrostatic pressure on the column of blood.

Ask the patient to expose the upper arm by rolling up or removing the sleeve. A tight rolled-up sleeve can act as a tourniquet and distort the reading, so make sure the arm is genuinely free.

General Inspection and Equipment

Before measuring, take a moment for a general inspection of the patient and the bedside. Note whether the patient appears comfortable or distressed, flushed, sweaty or pale, as anxiety, pain and recent exertion all transiently raise blood pressure. Look around the bed for clues such as fluid balance charts, an observation chart, antihypertensive medications or a GTN spray.

Choose the arm carefully. Avoid an arm with an arteriovenous fistula (used for dialysis), lymphoedema following axillary surgery such as a mastectomy, an intravenous cannula or infusion running, or any area of injury or infection. Inflating a cuff over these can cause harm or give an unreliable result.

Gather and check your equipment: a sphygmomanometer (manual aneroid or mercury column, or a validated automated device), an appropriately sized cuff, and a stethoscope if measuring manually.

Image - A clinical aneroid sphygmomanometer with its cuff and inflation bulb, used to measure blood pressure manually by auscultation

Creative commons source by Michael V Hayes [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Cuff size is critical and a common source of error. Match the cuff to the patient’s upper-arm circumference: the inflatable bladder inside the cuff should encircle at least 80% of the arm. A cuff that is too small requires more pressure to compress the artery and will overestimate blood pressure, whereas a cuff that is too large will underestimate it. Keep small, standard and large cuffs available and choose deliberately rather than defaulting to whichever is to hand.

Applying the Cuff

Palpate the brachial artery in the antecubital fossa. It lies just medial to the biceps brachii tendon and roughly in line with the medial epicondyle of the humerus. Identifying it accurately matters because the cuff and, later, the stethoscope must sit directly over it.

Wrap the deflated cuff snugly around the upper arm, with the lower edge around 2–3 cm above the antecubital fossa so it does not obstruct stethoscope placement. Most cuffs have an artery marker which should be lined up over the brachial artery. The cuff should be firm but not so tight that you cannot slide a finger underneath.

Keep the patient’s arm relaxed and supported throughout. Isometric muscle contraction from an unsupported arm raises the reading, and talking during measurement can elevate systolic pressure by several mmHg, so ask the patient to stay quiet while you take the reading.

Palpatory Estimate of Systolic Pressure

Before listening, it is good practice to make a palpatory estimate of the systolic pressure. Palpate the radial pulse with one hand and steadily inflate the cuff with the other. Note the pressure at which the radial pulse disappears — this gives an approximate systolic blood pressure.

This step serves two important purposes. First, it tells you how high to inflate the cuff for the auscultatory measurement so you do not cause unnecessary discomfort. Second, and more importantly, it guards against the auscultatory gap. In some patients, particularly those with stiff arteries or long-standing hypertension, the Korotkoff sounds temporarily disappear below the true systolic pressure and then reappear at a lower pressure. If you began listening within this silent gap you could seriously underestimate the systolic pressure. The palpatory method avoids this trap.

Once the radial pulse is no longer palpable, fully deflate the cuff and wait briefly before the auscultatory measurement to allow venous congestion to settle.

Measuring Systolic and Diastolic Pressure by Auscultation

Place the diaphragm of the stethoscope gently over the brachial artery in the antecubital fossa. Avoid pressing too hard or tucking the stethoscope under the cuff, as this can produce turbulent flow and artefactual sounds.

Re-inflate the cuff to around 20–30 mmHg above the palpated systolic estimate, then slowly deflate it at approximately 2–3 mmHg per second. Deflating too quickly will cause you to overshoot the true pressures and underestimate the reading.

As the cuff deflates you will hear the Korotkoff sounds. These arise because the cuff partially occludes the brachial artery, and as the pressure falls below systolic, blood begins to spurt through the narrowed vessel in turbulent, pulsatile bursts which are audible. The classification is as follows:

• Phase I – the first appearance of clear, repetitive tapping sounds. The pressure at this point is the systolic blood pressure.
• Phase II – softer, sometimes swishing sounds.
• Phase III – crisper and louder sounds as more blood flows through.
• Phase IV – an abrupt muffling of the sounds.
• Phase V – the point at which the sounds disappear completely. This is taken as the diastolic blood pressure.

The sounds disappear at diastole because, once cuff pressure falls below the lowest (diastolic) pressure in the artery, flow becomes continuous and laminar rather than turbulent, and laminar flow is silent. In most adults Phase V is taken as the diastolic value, but in situations where the sounds carry on almost to zero — classically in pregnancy and in children — the muffling at Phase IV is used instead.

Image - The principle behind manual measurement. The cuff pressure is shown falling over time; turbulent flow produces the Korotkoff sounds, which begin at systolic pressure and disappear at diastolic pressure

Creative commons source by Cmglee [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Record the result as systolic over diastolic, for example 120/80 mmHg, and note which arm was used and the patient’s position. Continue deflating fully and remove the cuff once finished.

Automated Blood Pressure Measurement

In day-to-day NHS practice, blood pressure is most often measured with a validated automated (oscillometric) device. Rather than detecting Korotkoff sounds, these devices measure the oscillations in cuff pressure produced by the pulsating artery. The point of maximal oscillation corresponds to the mean arterial pressure, and the device uses an algorithm to estimate the systolic and diastolic values from this.

The same principles still apply: the patient should be rested and seated, the cuff size must be correct, and the arm supported at heart level. Automated devices can be unreliable in atrial fibrillation and other irregular rhythms because the algorithm assumes a regular pulse; in these patients a manual measurement is preferred. If an automated reading is unexpectedly high or low, it should always be confirmed manually.

Image - An automated (oscillometric) blood pressure monitor, the type most commonly used on NHS wards and in general practice

Creative commons source by Belovaci [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Interpreting the Reading

A normal adult blood pressure is generally considered to be around 120/80 mmHg. Using current UK (NICE) thresholds for a clinic reading, hypertension is diagnosed when the blood pressure is persistently 140/90 mmHg or higher (with ambulatory or home monitoring used to confirm the diagnosis). Hypotension is broadly defined as a blood pressure below 90/60 mmHg, though what matters clinically is whether the patient is symptomatic or under-perfused.

Persistent hypertension is a major risk factor for stroke, ischaemic heart disease, heart failure and chronic kidney disease. The vast majority of cases are primary (essential) hypertension with no single identifiable cause, but it is important to remember secondary causes such as renal disease, primary hyperaldosteronism, phaeochromocytoma and coarctation of the aorta. Coarctation is worth bearing in mind in a younger patient, where it characteristically produces hypertension in the arms with relatively low pressures in the legs and a radio-femoral delay.

Image - Coarctation of the aorta: narrowing of the aorta beyond the arch raises pressure proximally (the arms) while reducing it distally (the legs), a recognised secondary cause of hypertension in younger patients

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Hypotension may reflect hypovolaemia, sepsis, cardiac failure, an arrhythmia, or the effect of medication. A single low reading in a well patient is often of little concern, but a low blood pressure in an acutely unwell patient is a red flag for shock and warrants urgent review.

It is also worth considering the pulse pressure, which is the difference between the systolic and diastolic values (normally around 40 mmHg). A wide pulse pressure can be seen in aortic regurgitation and in stiff, calcified arteries in the elderly, whereas a narrow pulse pressure can occur in aortic stenosis, heart failure or significant hypovolaemia.

Lying and Standing (Postural) Blood Pressure

If postural (orthostatic) hypotension is suspected — for example in a patient who reports dizziness, light-headedness or falls on standing — a lying and standing blood pressure should be performed.

Measure the blood pressure with the patient lying flat, having rested for a few minutes. Then ask them to stand and repeat the measurement, classically at 1 minute and again at 3 minutes after standing. Stay with the patient throughout in case they feel faint.

Postural hypotension is defined as a drop in systolic pressure of 20 mmHg or more, or a drop in diastolic pressure of 10 mmHg or more, on standing. Normally, standing causes blood to pool in the legs, but the baroreceptor reflex rapidly increases heart rate and vasoconstriction to maintain pressure. A significant postural drop indicates that this reflex is impaired, which may be due to dehydration or hypovolaemia, medications such as antihypertensives and diuretics, or autonomic dysfunction seen in conditions like diabetes and Parkinson’s disease.

Completing the Examination

Thank the patient, ensure they are comfortable and help them re-dress if needed.

Wash your hands and clean the equipment.

Document the reading clearly, including the value, the arm used, the patient’s position, and whether the measurement was manual or automated.

Summarise your findings to the examiner.

To complete the assessment, suggest that you would repeat the measurement to confirm an abnormal result, measure the blood pressure in both arms (a sustained difference of more than 15 mmHg can indicate peripheral vascular disease, while a large acute inter-arm difference — conventionally greater than 20 mmHg — may point to aortic dissection), perform a lying and standing blood pressure if postural symptoms are reported, and consider ambulatory or home blood pressure monitoring to confirm a diagnosis of hypertension. This also helps to identify white-coat hypertension, where the clinic reading is raised simply because the patient is being assessed, and masked hypertension, where the clinic reading is normal but the blood pressure is genuinely raised at home. Where appropriate, you would also perform a full cardiovascular examination, check the patient’s pulse, and arrange relevant investigations such as a urine dip for protein and blood, blood tests including renal function, and a 12-lead ECG to look for evidence of end-organ damage.

Quiz

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