Standard Operating Procedure

SOP ID C03

Version 1.0

Title Blood Pressure Measurement

Approved by Clinical Effectiveness Group

Date Issued 1st February 2013

Review Date 31st January 2015

Directorate Clinical

Clinical Publication Category

Mandatory - No deviation from document permissible

1. Scope 1.1 This Standard Operating Procedure (SOP) outlines the correct procedure for measuring

non-invasive blood pressure in according with NICE1 and European Hypertension Society Guidance.2 This SOP must be read in conjunction with Clinical Guideline (CG06) - Atrial Fibrillation and Hypertension: Screening and Referral.

2. Responsibility 2.1 It is the responsibility of all ambulance clinicians to adhere to this SOP.

3. Introduction 3.1 Blood pressure is the force exerted on the walls of the arteries by the volume of blood as

it circulates. Blood pressure is always measured as two numbers (Figure 1). The first number represents the systolic pressure; the pressure when it is at its highest, during the contraction of the heart. The second number, the diastolic pressure, records the pressure when the heart relaxes and refills with blood in between each beat.

3.2 Figure 1 - Systolic and Diastolic Pressure:

4. Measurement Protocol 4.1 The following procedure must be followed when measuring blood pressure:

1. The first step in blood pressure measurement is adequate explanation of the procedure, in an attempt to allay fear and anxiety. Those having blood pressure measured for the first time should be told that there may be some minor discomfort caused by inflation of the cuff.2

2. Rest their forearm at the level of the heart, as denoted by the mid-sternal level.

Dependency of the arm below heart level will lead to an overestimation of systolic and diastolic pressures, whilst raising the arm above heart level will cause an underestimation.2 Correct arm positioning is vital; the magnitude of positional errors can be as great as 10mmHg. The arm must be supported during measurement, as an un-supported arm causes isometric exercise to be performed, increasing the blood pressure and heart rate by as much as 10%.3

3. Remove any restrictive clothing that may impair blood flow and affect the reading. 4. Wrap the cuff around the arm. If the bladder does not completely encircle the arm,

its centre must be over the brachial artery (or as indicated by guidance printed on the cuff). The lower edge of the cuff should be 2-3 cm above the point of brachial artery pulsation. There is unequivocal evidence that a cuff that is too small will cause an overestimation of blood pressure, whilst one that is too large may lead to underestimation, although the magnitude of the error is likely to be smaller.

5. Palpate the brachial artery in the antecubital fossa (use radial artery where this is

not possible) whilst the cuff is rapidly inflated to about 30mmHg above the point at which the pulse disappears. Deflate cuff slowly, noting the pressure at which the pulse reappears; this is the approximate level of the systolic pressure. Palpatory estimation is important, because phase 1 Korotkoff sounds sometimes disappear as pressure is reduced and reappear at a lower level (the auscultatory gap), resulting in systolic pressure being underestimated unless already determined by palpation. Although the radial artery is often used for palpatory estimation of the systolic pressure, using the brachial artery is preferred as it establishes its location prior to auscultation.

6. Allow the cuff to deflate. 7. Wait 15-30 seconds. 8. Place the stethoscope gently over the brachial artery at the point of maximal

pulsation. The stethoscope should be held firmly and evenly but without excessive pressure, which may distort the artery, producing sounds below diastolic pressure. The stethoscope end piece should not touch clothing, the cuff or rubber tubes, to avoid friction sounds. On dual headed stethoscopes, the clinician’s thumb must not be placed over the opposite diaphragm or bell.

9. Inflate cuff rapidly to about 30mmHg above the palpated systolic pressure. 10. Deflate at a rate of 2-3mmHg per second.

11. As the pressure in the cuff falls five distinct Korotkoff sounds should be heard

through the stethoscope (Table 1 and Figure 1). 12. Note the systolic blood pressure. This occurs at the start of Phase I; the first

appearance of faint, repetitive, clear tapping sounds that gradually increase in intensity for at least two consecutive beats.

13. Note the diastolic blood pressure. This occurs at the start of Phase 5, the point at

which all sounds disappear completely. In rare instances where the Korotkoff sounds persist down to zero, phase 4 (muffling of sounds) should be recorded as diastolic pressure, and a note made to this effect.

14. When all sounds have disappeared, the cuff should be deflated rapidly and

completely to prevent venous congestion of the arm before the measurements is repeated.

15. If a clinician is in anyway unsure of a reading, the blood pressure should be

repeated by another clinician. 16. If an irregular pulse is detected, refer to Clinical Guideline (CG06) - Atrial

Fibrillation and Hypertension: Screening and Referral. 4.2 Table 1 - Korotkoff Sounds:

Phase Description

1 The first appearance of faint, repetitive, clear tapping sounds that gradually increase in intensity for at least two consecutive beats is the systolic blood pressure.

2 A brief period may follow during which the sounds soften and acquire a swishing quality. In some patients, sounds may disappear altogether for a short time.

3 The return of sharper sounds, which become crisper, to regain or even exceed the intensity of phase 1 sounds.

4 The distinct, abrupt muffling of sounds, which become soft and blowing in quality.

5 The point at which all sounds finally disappear completely is the diastolic pressure.

4.3 Figure 1 - Illustration of Korotkoff Sounds for a Blood Pressure of 120/80mmHg:

5. Limitations 5.1 Clinicians must recognise that blood pressure will always be a variable haemodynamic

phenomenon that is influenced by a wide range of factors.23 Variability in the pressure recorded may occur from moment to moment due to respiration, emotion, exercise, meals, tobacco, alcohol, temperature, bladder distension and pain. Blood pressure is also influenced by age, race and a diurnal variation, with the pressure being lowest during sleep.4 Arrhythmias such as atrial fibrillation can make the measurement of blood pressure particularly challenging due to marked beat-to-beat variability; stroke volume and therefore blood pressure depend on the preceding pulse interval.1,2

5.2 White Coat Hypertension (WCH) is a phenomenon where normotensive individuals

become hypertensive during assessment by a health professional, with pressures returning to normal outside of the medical environment. The phenomenon is reported to occur in as many as 15% to 30% of the population, although this may be inflated due to inadequate evaluation of patients.1 It is more common in pregnancy and with increasing age, although is generally poorly understood.1 One theory is that WCH is linked to the physiological ‘fight and flight’ reaction. Studies have demonstrated that anxiety can increase blood pressure by as much as 30 mmHg.5 The degree varies greatly from patient to patient, being absent in many, and it is not substantially influenced by reassurance or familiarisation with the technique of blood pressure measurement.4

5.3 The systolic pressure must always be estimated by first palpating the brachial pulse with slow deflation of the cuff. Termed the first pass, this stage is important as sometimes the initial sounds disappear as pressure is reduced (the auscultatory gap) leading to an underestimation of systolic pressure by auscultation alone. In a case series, 21% of 168 untreated hypertensive patients demonstrated an auscultatory gap.

5.4 The reading must be recorded exactly as it is measured. The tendency by clinicians to

round readings up or down, often to the nearest zero (digit preference), must be avoided.

6. Referral 6.1 Clinical Guideline (CG06) - Atrial Fibrillation and Hypertension: Screening and Referral

must be used to determine appropriate referral arrangements.

7. Documentation 7.1 In line with Trust Policy, a Patient Clinical Record must be completed and annotated

appropriately. Any deviation from this clinical guideline must be recorded, with any potential or actual adverse event reported through the incident reporting system.

7.2 When screening is delivered as part of either the Know your Blood Pressure or Health

Check programs the appropriate specific form for the program should be used, with a PCR only required if conveyance to hospital is necessary.

8. References

1. National Institute for Health and Clinical Excellence (2011) Hypertension: Clinical management of primary hypertension in adults. NICE

2. O'Brien E, Asmar R, Beilin L, Imai Y, Mallion JM, Mancia G, Mengden T, Myers M, Padfield P,

Palatini P, Parati G, Pickering T, Redon J, Staessen J, Stergiou G & Verdecchia P. (2003) European Society of Hypertension recommendations for conventional, ambulatory and home blood pressure measurement. Journal of Hypertension. 21. (5): 821-848.

3. Silverberg D.S, Shemesh E. and Jaina A. (1977) The unsupported arm: a cause of falsely raised

blood pressure readings. British Medical Journal. 2. 1331.

4. Parati G, Ulian L, Santucciu C, Omboni S and Mancia G. (1995) Blood pressure variability,

cardiovascular risk and antihypertensive treatment. Journal of Hypertension. 13. (Sup 4): S27-34.

5. Williams B, Poulter N.R, Brown M.J, Davis M, McInnes G.T, Potter J.F, Sever P.S. and Thom

S.McG (2004) Guidelines for management of hypertension: report of the fourth working party of the British Hypertension Society. Journal of Human Hypertension. 18. 139-85.