Chapter 17
BLOOD PRESSURE MEASUREMENT
Sharon Jones
Introduction
This presentation is concerned with taking
patients’ blood pressures and outlines the
procedure as well as potential causes for
error.
Part 1 – Blood Pressure Overview
Part 2 – Blood Pressure Measurement
Part 3 – Blood Pressure Measurement
Procedure
Part 4 –Factors that Influence Blood
Pressure
PART 1: Blood Pressure
Overview
Definition
Blood Pressure (BP) is the pressure exerted
by the blood against the walls of the blood
vessels (Tortora, 2006).
Blood Pressure is dependent on:
• strength of the heartbeat
• elasticity of arterial walls
• volume and viscosity of the blood
• person’s health, age and physical
condition
Systolic and Diastolic Pressures
Systolic Pressure
• The peak pressure of the blood in the
arteries caused by ventricular
contraction.
• Indication of the integrity of the heart,
arteries and arterioles.
Diastolic Pressure
• The minimum pressure of the blood
against the vessel wall following
closure of the aortic valve.
• Direct indication of blood vessel
resistance.
Korotkoff’s Sounds
1. Phase I The pressure level at which the
first faint, clear tapping sounds are heard,
which increase as the cuff is deflated
(reference point for systolic BP).
2. Phase II During cuff deflation when a
murmur or swishing sounds are heard.
3. Phase III The period during which sounds
are crisper and increase in intensity.
4. Phase IV When a distinct, abrupt muffling
of sound is heard.
5. Phase V The pressure level when the last
sound is heard (reference point for
diastolic BP).
PART 2: Blood Pressure Measurement
Measurement
BP is recorded in millimetres of mercury:
• mm Hg
The systolic reading is written first, followed
by the diastolic, for example:
• 140/80 mm Hg
Hypertension in
adults is defined as a
systolic pressure of
more than 140 mm
Hg
Hypotension in
adults is defined as a
diastolic pressure of
less than 100mm Hg
Methods of Measurement
Direct: intra-arterial
recording. Invasive
technique usually
performed in areas
where patients
continually
monitored, such as
high dependency
units and theatres.
Indirect: more
commonly
performed. Measure
the BP in the
brachial artery of the
arm.
Indirect BP Measurement
• Sphygmomanometer with stethoscope
• Sphygmomanometer with Doppler
• Sphygmomanometer with palpation
• Dinamap or automated device
PART 3: Blood Pressure Measurement Procedure
Sphygmomanometer with
stethoscope
You will need:
• Sphygmomanometer
• Stethoscope
• Observation chart
Q. As you read through the action points in
the next slide, work together in your
learning groups to identify the rationale
behind each step. You might want to refer
back to the printed book for help.
• Wash hands.
• Explain procedure to the patient and assess level of
understanding.
• Ensure the patient is positioned comfortably, and has
been rested for approximately 3 minutes if supine or
seated and 1 minute if standing.
• Remove tight clothing, support arm horizontally at
heart level.
• Avoid talking throughout the procedure.
• Apply a sphygmomanometer cuff that covers
approximately 80% of the circumference of the upper
arm, with the centre of the bladder positioned over the
line of the brachial artery approximately 2cm above
the elbow.
• Position the manometer at eye level, ensuring it can
be easily observed by the practitioner.
• Estimate the systolic pressure through palpation
Estimation of the systolic pressure:
• Palpate the brachial artery pulse
• Inflate the cuff until the pulsation
disappears.
• Deflate cuff
• Estimate systolic pressure
• Inflate the cuff 30mm Hg higher than the estimated
systolic pressure.
• Position the stethoscope over the brachial artery,
ensuring it does not come into contact with the
tubing of the cuff.
• Lower mercury column slowly (2mm per second),
observe the needle of the dial as it is lowered and
listen for Korotkoff sounds.
• Read blood pressure to the nearest 2mm Hg.
• Record the systolic and diastolic pressures, noting
which arm was used, and compare to previous
readings. Report irregularities to senior practitioner.
• Remove the cuff and ensure patient’s comfort.
• Clear away equipment and clean according to local
policy.
Cuff Size
If a cuff is too large or too small,
underestimation or overestimation of the
BP occurs.
• 12 x 26 cm
standard adult size.
• 12 x 40 cm
obese adult size.
• 10 x 18 cm
small adult size.
Monitors
Two main types:
• Auscultatory: use sound for
measurement.
• Oscillometric (automated): rely on
variations of pressure in the cuff,
caused by the pulse in the artery.
Equipment Checks
• Manometer: Visibility of meniscus;
calibration
• Cuff: Condition; length and width of
inflatable bladder
• Inflation/deflation device: Any
malfunctions; control valve
• Stethoscope: Condition & cleanliness
PART 4: Factors that Influence Blood Pressure
Factors that Influence the BP of
Adults
These include:
• Age, anxiety, smoking, meals, time of day,
temperature and sleep.
• ‘White coat’ hypertension – blood
pressure notably higher when recorded by
doctors and nurses. (O’Brien et al, 1997)
To minimise ‘white coat’ hypertension, try to
relax your patient through familiarising
them with their surroundings and using
good communication skills.
The healthcare practitioner responsible for
undertaking BP measurement must
ensure their practice is up-dated and their
competence with this skill maintained to
deliver safe, evidence based care at all
times.