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Blood pressure
brachial artery
Joanna Trim, MPhil, BSc, RN, is nurse adviser,
University Hospital Birmingham NHS Foundation Trust.
Blood pressure measurements assist with assessment
of a patient’s cardiovascular status. They reflect the
pressure exerted by blood on the wall of blood vessels.
radial artery
Anatomy and physiology
The body relies on blood pressure to deliver essential
oxygen to – and remove waste products from – tissues,
cells and vital organs. It is maintained by a
combination of neural, chemical and renal controls.
Blood pressure is dependent on cardiac output, blood
volume in the cardiovascular system and peripheral
resistance. It is made up of two parameters:
l Systolic pressure – the higher pressure – is an
indication of the integrity of the heart, arteries and
arterioles, and reflects the higher pressure in the major
arteries after ventricular systole (contraction);
l Diastolic pressure – the lower pressure – indicates
blood vessel resistance and is the minimum pressure
after ventricular diastole (Dougherty and Lister, 2004).
ulnar artery
Fig 1. The anatomy of the arm
Korotkoff’s sounds
The various noises heard when taking a blood pressure
are known as Korotkoff’s sounds:
l Phase one is the appearance of faint yet clear
tapping sounds, which gradually increase in intensity;
l Phase two is the softening of sounds, which may
sound like blowing or swishing;
l Phase three is the return of sharper sounds that do
not regain the intensity of phase one;
l Phase four is a distinct muffled sound, which
becomes soft and blowing;
l Phase five is silence.
Fig 2. The patient’s arm is slightly flexed at heart level. The lower edge
of the cuff is placed 2cm above the antecubital fossa (inner elbow)
Preparation
The equipment – an electrical device or stethoscope
and sphygmomanometer – should be checked to ensure
it is in working order to minimise reading errors.
l The patient should be given an explanation of why
their blood pressure is being taken and the procedure
itself, so that informed consent can be obtained.
l It is also important to reassure the patient and allay
any anxieties, as these may affect the reading.
l Ensure the correct cuff size is used. Incorrect size may
result in inaccurate readings. Most national guidelines
advocate a large cuff for all patients (Mulrow, 2001).
l
The procedure
If possible, ensure the patient has rested in a quiet
environment before starting the procedure to minimise
inaccurate readings from recent exercise or exertion.
l
Fig 3. Estimating the systolic pressure using the pulse. Inflate cuff to
70mm of mercury (mmHg) and increase more slowly, until the pulse
can no longer be felt
NT 11 January 2005 Vol 101 No 2 www.nursingtimes.net
keywords n Observations n Assessment n Blood pressure
Remove any restrictive clothing that may impair
blood flow and affect the reading.
l Position the patient’s arm slightly flexed and support. Position the cuff 2cm above the antecubital fossa
and ensure the bladder’s centre covers the brachial
artery (Figs 1 and 2) (Mulrow, 2001).
l
Fig 4. The stethoscope bell (low frequency) is placed over the
brachial artery
Manual reading
l Estimate the systolic pressure (Fig 3). Allow the cuff
to deflate and wait 15–30 seconds.
l Place stethoscope bell over the brachial artery with
the pump valve closed (Fig 4).
l Re-inflate the cuff to 20mmHg or 30mmHg above
the estimated systolic pressure. Deflate the cuff by
releasing the valve at about 2mmHg/second (Fig 5),
noting the systolic pressure when Korotkoff’s sounds
are heard in phase one and phase five (Dougherty and
Lister, 2004). Round up to the nearest 2mmHg.
Electrical device
l Place the cuff on the patient’s arm and press start
(Fig 6). Remind the patient the cuff may tighten
considerably before starting to deflate.
References
Docherty, B. (2002)
Cardiorespiratory physical
assessment for the acutely ill: 1.
British Journal of Nursing
11: 11, 750–758.
McAlister, F., Straus, S. (2001)
Measurement of blood pressure:
an evidence based review.
British Medical Journal
322: 908–911.
Mulrow, C.D. (2001) Evidencebased Hypertension. London:
BMJ Books.
Dougherty, D., Lister, S. (2004)
The Royal Marsden Hospital
Manual of Clinical Nursing
Procedures. Oxford: Blackwell.
Recording the results
l Document the readings immediately and compare
against normal values, taking into consideration the
patient’s condition and any pre-existing factors.
l For first assessments, measure blood pressure from
both arms; the side with the higher reading should be
used thereafter (McAlister and Straus, 2001).
Contraindications
Fig 5. The pump and valve. Turn the valve anticlockwise to open,
clockwise to close
Patients with a side affected by stroke, mastectomy or
renal fistula should avoid having blood pressure
readings taken on this side.
If a patient has an IV catheter in one arm, use the
other arm to take the reading to prevent potential
damage to the catheter and interruption of administration of medication.
Common causes of error
Accuracy may be affected by patient anxiety and the
cuff position and size.
l Pressing down on the stethoscope bell can place too
much pressure on the brachial artery, which may affect
the reading.
l Poor understanding of Korotkoff’s sounds. The
practitioner needs to understand the different sounds
to take the reading at the appropriate time.
l
Professional responsibilities
Fig 6. Once the cuff is on the patient’s arm, press the start button.
When the procedure is complete the electrical device will take a
reading automatically
NT 11 January 2005 Vol 101 No 2 www.nursingtimes.net
Any health care worker measuring blood pressure
must receive approved training and complete
supervised practice. It is the individual’s responsibility
to ensure their theoretical and practical knowledge
and skills are maintained. Local protocols and
guidelines must be adhered to at all times. n
This article has been double-blind
peer-reviewed.
For related articles on this subject
and links to relevant websites see
www.nursingtimes.net
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