An evidence based approach in BP reading

1. HOW TO MEASURE BLOOD
PRESSURE
Vital Signs in the Ambulatory
Setting:
An Evidence-Based Approach

2. ARTERIAL BLOOD PRESSURE
Guyton and Hall, pp 174
The pressure / force exerted by the blood against any unit
area of the vessel wall is called Blood Pressure.
Standard Units of Blood Pressure
Blood pressure is mainly measured in: Millimeters of mercury
(mm Hg). Occasionally, BP is measured in: Centimeters of water
(cm H2O)
One millimeter of mercury pressure equals 1.36 centimeters of
water pressure because the specific gravity of mercury is 13.6
times that of water, and 1 centimeter is 10 times as great as 1
millimeter.

3. Systolic Blood Pressure:
The force exerted by the blood against any unit area
of the vessel wall while heart is contracting (Systole)
is called Systolic Blood Pressure.
less than 120 mmHg
Diastolic Blood Pressure:
The force exerted by the blood against the unit area
of the vessel wall while heart is relaxing (Diastole)
less than 80 mmHg
ARTERIAL BLOOD PRESSURE
Average Normal Arterial Pressure:
90-119 mmHg systolic
60-79 mmHg diastolic Guyton and Hall, pp 174

4. MEAN ARTERIAL BLOOD PRESSURE
Mean Arterial Pressure:
The average of the arterial pressures measured in millisecond over a
period of time. It is responsible for driving blood into the tissues
throughout the cardiac cycle. It is better indicator of perfusion to
vital organs than systolic blood pressure. It is not equal to the
average of systolic and diastolic pressure.
To calculate a mean arterial pressure, double the diastolic blood
pressure and add the sum to the systolic blood pressure. Then divide
by 3.
For example, if a patient’s blood pressure is 83 / 50 mmHg, his MAP
would be 61 mm Hg.
MAP = SBP + 2 (DBP)
3
MAP = 83 +2 (50)
3
MAP = 83 +100
3
MAP = 61 Guyton and Hallm 183

5. Mean Pressure = diastolic P + 1/3 (systolic P - diastolic P)
Another way to calculate the MAP is to first calculate the pulse
pressure (subtract the DBP from the SBP) and divide that by 3,
then add the DBP:
MAP = 1/3 (SBP – DBP) + DBP
MAP = 1/3 (83-50) + 50
MAP = 1/3 (33) + 50
MAP = 11 + 50
MAP = 61 mm Hg
MEAN ARTERIAL BLOOD PRESSURE

6. Male > Female … (equal at menopause)
() Old age: Atherosclerosis
BP () due to neural & hormonal factors.
() BP due to  venous return.
Some hormones like adrenaline, noradrenaline & thyroid () BP.
BP is higher in lower limbs than upper limbs.
() stress)
BP () due to  venous return.
BP () due to  in metabolism.
■ Sex:
■ Age:
■ Emotions:
■ Exercise:
■ Hormones:
■ Gravity:
■ Stress:
■ Sleep:
■ Pregnancy:
■ Temperature: BP () with heat due to vasodilatation
() with cold due to vasoconstriction
PHYSIOLOGICAL FACTORS AFFECTING
ARTERIAL BLOOD PRESSURE
()
Obesity

7. Guyton and Hall, pp 183
PHYSIOLOGICAL FACTORS AFFECTING ARTERIAL BLOOD
PRESSURE

8. PHYSIOLOGICAL FACTORS AFFECTING
ARTERIAL BLOOD PRESSURE

9. PHYSIOLOGICAL FACTORS AFFECTING
ARTERIAL BLOOD PRESSURE

10. Factors determining CO:
1. Stroke volume
2. Heart rate
Cardiac Output = Stroke Volume X Heart Rate
Cardiac Output
(CO)
= Output of
ventricles / minute
 5 L/min
(av. 5-6 L/min)
Stroke Volume
(SV)
= Output of
ventricles / beat
70 ml/beat
(av. 70-80 ml/beat)
Heart Rate
(HR)
= beats/ minute
 70-75 beats/min
(av 60-100 beats/min)
Cardiac Output (CO)
This is the amount of blood
pumped by ventricles per minute
PHYSIOLOGICAL FACTORS AFFECTING ARTERIAL BLOOD
PRESSURE

11. Cardiac Output
PHYSIOLOGICAL FACTORS AFFECTING
ARTERIAL BLOOD PRESSURE

12. EFFECT OF RADIUS ON PRESSURE
23

13. Factors affecting vessel diameter
 Vasodilator agents:
 Nitric oxide.
 Histamine.
 Atrial natriuretic peptide (ANP).
 Prostacyclin; PGI2.
 Vasoconstrictor agents:
 Norepinephrine.
 Angiotensin II.
 Vasopressin.
 Endothelin-1.
 Thromboxane A2.

14. Two methods: Direct & indirect
Sphygmomanometer:
Types:
Mercury sphygmomanometer
Aneroid equipment
Automatic equipment
Blood Pressure Cuff Size:
Small – children & small adults
Average
Large – overweight & large adults
MEASUREMENT OF BLOOD
PRESSURE
14

15. Direct
Arterial catheter
Indirect
Stethoscope and
blood pressure
cuff
Measurement of Blood Pressure

16. MEASUREMENT OF BLOOD
PRESSURE
BP is measured by listening for Korotkoff sounds
produced by turbulent flow in arteries:
•Systolic pressure: When 1st sound is heard.
•Diastolic pressure: When last sound is heard.

17. MEASUREMENT OF BLOOD
PRESSURE
17

18. CLINICAL FEATURES-COMPLICATIONS OF HYPERTENSION
18
Headache
Nausea
Vomiting
Dizziness
Confusion
Shortness of breath
Chest discomfort
Visual disturbance
Sleepiness
May be asymptomatic

19. BLOOD PRESSURE – AN OVERVIEW
CAUSE SYSTOLIC BP CORRECTIVE ACTION
Sit without back support + 6 to 10 Support back (sit in chair)
Full bladder + 15 Empty bladder before BP taken
Tobacco/caffeine use + 6 to 11 Don’t use before clinic appointment
BP taken when arm is:
Parallel to body
Unsupported
Elbow too high
Elbow too low
+ 9 to 13
 + 1 to 7
 + 5
 False low
While seated in chair, patient’s arm
must be straight out and supported,
with elbow at heart level
“White coat” reaction + 11 to 28 Have someone else take the BP
Talking or hand gestures + 7 No talking or use of hands during BP
Cuff too narrow/small + 8 to 10
Right-sized cuff properly placed over
bare upper arm
Cuff too wide/large False low
Cuff not centered + 4
Cuff over clothing + 5 to 50 (Pickering et al., 2005; Perry & Potter, 2006)

20. BP – IT’S ALL ABOUT THE
NUMBERS!
Terminal Digit Preference
Some people may show a preference for certain numbers in
auscultated BP readings*
 Zeros, even numbers, odd numbers
 Research study on BP revealed 99% of auscultated SBP/DBP readings ended in zero
Be aware you might “like” certain numbers more than others!
(*Roubsanthisuk, W., Wongsurin, U., Saravich, S., & Buranakitjaroen, P., 2007)

21. BLOOD PRESSURE – AN
OVERVIEW
Automated BP machines give fast
& accurate blood pressure
measurement
Cannot be used in patients with:
Seizures, shaking, or shivers
Weak pulses
Agitation
Any situation where the arm cannot be
kept still

22. BLOOD PRESSURE – AN
OVERVIEW
Equipment for accurate BP measurement
Functional & calibrated machine
Right-sized cuff
Pen or pencil
Flowsheet, chart, or medical record
Clean hands and fingers!
Patient in a comfortable & relaxed position
Wait 5 minutes if patient was active

23. RIGHT CUFF IN THE RIGHT
PLACE
Cuff width = 20% more than upper arm diameter
Cuff width = 2/3 of upper arm length
Cuff bladder length encircles 80% of upper arm
Cuff arrow aligned with brachial artery
Inside of the elbow
http://connection.lww.com/products/evans-smith

24. BLOOD PRESSURE PROCEDURE
1.Wash hands & put
on gloves, if
appropriate
2.Provide privacy
3.Assist patient to a
comfortable &
relaxed position
4.Back supported,
legs uncrossed

25. BLOOD PRESSURE PROCEDURE
4. Unplug & roll machine near the patient
5. Ensure connecter hose will reach
6. Turn on machine to self-test
7. Select proper arm cuff size
 Small adult cuff
 Medium adult cuff
 Large adult cuff
 Pediatric cuff
http://www.pharmj.com/Hospital/Editorial/200501/meetings/p27ashp.html

26. BLOOD PRESSURE PROCEDURE
8. Expose upper arm completely
 Do not put cuff over clothing!
 Machine can’t “hear” the pulse with
clothing
9. Upper arm properly supported at 
level
10. Squeeze air from cuff & attach
connector hose
 Check for kinks
11. Wrap flat cuff snugly around the
upper arm
12. Arrow mark on cuff is at inside of
elbow

27. BLOOD PRESSURE
PROCEDURE
13. Set machine for adult or pediatric
BP
14. Press start button
15. No talking or hand gestures by you
or the patient
16. Check digital display for BP when
cuff is fully deflated
17. Repeat BPs may be taken if 2
minutes apart
18. Remove cuff and replace clothing

28. NORMAL BP MEASUREMENTS
AGE Normal BP
Newborn to 6 weeks * Systolic 50 - 70
Infant (6 weeks to 6 months) * Systolic 70 - 95
Toddler ( 1 to 3 years) * Systolic 80 - 100
Young Children ( 3 to 6 years) Systolic 80 - 110
Older Children (10 to 14 years) Systolic 90 - 120
Adults Systolic 90 - 120
Diastolic 80 or less
(Mosby’s Critical Care Nursing Reference, 2002; Perry & Potter, 2006)
(* BP is often not taken on children less than 3 years of age)

29. BLOOD PRESSURE
PROBLEMS
What if a BP cannot be
obtained?
What if the cuff doesn’t
fit?
What if a right-sized cuff
isn’t available?
Consult with RN or MD for
all troubleshooting issues

30. BLOOD PRESSURE
PROCEDURE
19. Inform RN or MD
for:
Very high or very
low BP
Difficulty taking a BP
Unable to get a BP
reading

31. BLOOD PRESSURE
PROCEDURE
20. Discuss BP with patient or
parent
21. Remove gloves & wash
hands
22. Clean cuff per facility
protocol

32. BLOOD PRESSURE
PROCEDURE
23. Document the Results
Flowsheet, clinic record, or clinic
chart
24. Communicate the
Results
RN
MD

33. WHAT’S WRONG WITH THIS
PICTURE?
More than one
thing may be
wrong.
Write down as
many wrong
things as you
can find!
Are you
ready for
your big
wedding? Not really, there’s so
much to do – I am very
nervous these days
(Blood Pressure Competency Questionnaire
Kaiser Permanente Southern California Region
June 2006)

34. WHAT’S WRONG WITH THIS
PICTURE?
Provider and patient are
talking
BP cuff applied over
clothing
Arm supported above
heart level
Patient legs are crossed
Selected size of the cuff
looks big for the patient
Are you
ready for
your big
wedding? Not really, there’s so
much to do – I am very
nervous these days
(Blood Pressure Competency Questionnaire
Kaiser Permanente Southern California Region
June 2006)

35. BP MEASUREMENT IN THE
CLINIC
YOU can make the
difference:
Welcoming presence
Decrease any anxieties & fears
Reassure patients & family
Accurate vital signs