Factors Causing Variations in Blood Pressure

Age: blood pressure is lower in children than in adults. Pressure gradually increases until 45 to 50 years, after that it accelerates sharply.

Sex: there is no difference in B.P. values between boys and girls until puberty. After that, females usually have a lower blood pressure than males of the same age until menopause when their pressure readings increase over man’s.

Body build: B.P. is higher in persons with overweight than in persons of the same age with normal weight. Weight reduction usually decreases the blood pressure.

Race: certain races e.g., Negroes will have higher B.P. readings than other races.

pressure norms are lower in tropical climates than temperate and highest in polar climate.

Time of the day: in all persons, B.P. is lowest in the early morning and then rises to a peak in the evening, and then it declines.

muscular exertion will raise the blood pressure.

Pain: severe pain may cause temporary and marked increase in the blood pressure.

Emotion: fear, worry, excitement and other emotional factors will raise the blood pressure to greater level. Blood pressure is more likely to be raised in persons who live in stressful urban environments or who have jobs with constant mental tension than in persons leading relaxed tranquil lives.

Posture: it is often stated that B.P. is lower when lying down than when sitting or standing. When the B.P. is decreased suddenly on standing posture, it is called orthostatic hypotension.

Disease conditions: diseases affecting the circulatory system and kidneys may increase the blood pressure. Disease that weakens the heart action may lower the blood pressure.

the drugs such as amyl nitrite and nitroglycerin cause a decrease in the blood pressure. Certain drugs increase the blood pressure.

haemorrhage causes a low blood pressure by decreasing the volume of blood in the blood vessels.

Increased intracranial pressure:
pressure in the cranium usually produces a rise in the blood pressure e.g., head injury and intra cranial tumors.


Instruments Used in Measuring the Blood Pressure

The standard instruments used to measure the blood pressure are called a sphygmomanometer. There are two types of pressure manometers – mercury and aneroid. Both give accurate readings when they are functioning properly. Experiments show that the mercury manometers are accurate and reliable than the aneroid manometers. To be accurate the mercury column should have no “zero error”, the mercury level should rest at zero before pressure is applied and it should, fall freely as cuff pressure is released.

The use of a proper size cuff is necessary to get an accurate reading. If the cuff is too narrow or not overlapping, the readings will be false. A cuff that is too wide for the extremity gives a low reading. The width of the cuff bladder should be 20% greater that the diameter of the extremity on which it will be used. It should be long enough to encircle the extremity.

For measuring the venous pressure, a water manometer is used. The manometer containing saline is attached by a shop cock to a venipuncture needle. The apparatus, because it comes in contact with the blood stream, should be sterile. In some settings, electronic equipments are used which eliminate the need of a stethoscope.

Check Defects in the B.P. Apparatus

Blocked air vent

Column not vertical

Air filter blocked

Tubing perished

Badly fitting connection

Release valve stuck/slack

Illegible scale/dirty glass

Unstable hinge

Inflation valve faulty

Velcro worn

Inappropriate Bladder size


Nurses Responsibility in the Measurement of B.P.

Preliminary Assessment

1. Identify the client

2. Check the diagnosis, reason for taking B.P. schedule frequency of obtaining blood pressure

3. Previous measurement and range of blood pressure

4. Physical and mental state of the client. Postpone blood pressure taking on a client who is angry, anxious or in pain or a crying child.

5. Assess the arm on which the blood pressure can be taken.


Do not take blood pressure reading on a client’s arm if:

1. The arm has an intravenous infusion on it.

2. The arm is injured or diseased.

3. The arm has a shunt or fistula for the renal dialysis.

4. On the same side of the body where the female client had a radical mastectomy.

5. Check defects in the B.P. apparatus.


Vital signs

Vital signs are a basic component of assessment of physiological and psychological health of a client. Body temperature, pulse, respiration and blood pressure are the signs of life.

Blood Pressure

Blood pressure is the force exerted by the blood against the walls of the blood vessels as it flows through them. Systolic pressure is the highest degree of pressure exerted by the blood against the walls of the blood vessels during the ventricular systole when the left ventricle if forcing the blood into the aorta. Diastolic pressure is the lowest pressure that occurs when the heart is in its resting period just before the contraction of the left ventricle. Pulse pressure is the difference between the systolic and diastolic pressure and represents the volume output of the left ventricle.

The average blood pressure for the healthy adult is usually about 120/80 mm Hg. A systolic pressure above 150 or below 90 mm Hg is regarded as abnormal. Venous pressure may vary from 40 to 110 mm of water.

Hypertension is a condition of abnormally high blood pressure. Hypotension is a condition of abnormally low blood pressure.

Preparation of the Articles

1. Sphygmomanometer

2. Stethoscope

3. Piece of paper

Preparation of the Client

Explain the procedure to the client to gain the confidence and cooperation of the client.

Place the client in a comfortable position either lying down with the arm resting on the bed or sitting with the arm supported on the table at heart level to ensure accurate reading. Client should be resting atleast 5 to 10 minutes prior to taking the blood pressure.



Steps of Procedure

1. Wash hands

Reasons: to prevent cross infection

2. Take the equipment to the bedside.

3. Apply deflated cuff evenly with rubber bladder over the brachial artery, the lower edge being ‘2’ inch above the antecubital fossa. The two tubes turning towards the palm.

Reasons: as uneven or too loose cuff gives a falsely high reading because excessive amount of pressure is needed to occlude brachial artery.

4. Palpate the brachial artery with the finger tips. Place the bell of the stethoscope on the brachial pulse. The stethoscope must hang freely from the ears.

Reasons: any rubbing of the tubes can mislead the sounds.

5. Close the valve on the pump by turning the knob clockwise. Pump up air in the cuff until the sphygmomanometer registers about 20 mm above the point at which the radial pulsation disappears.

Reasons: if the cuff is not inflated high enough, true systolic pressure may be missed. Inflating the cuff too high causes unnecessary pain and may produce pain and may produce vasospasm, which distorts pressure reading.

6. Open the valve slowly by turning the knob anti-clockwise. Permit the air to escape very slowly. Note the number on the manometer where the sound first begins. This is the systolic pressure.

Reasons: the first sound is heard when the blood organs begins to flow through the brachial artery again.

7. Continue to release the pressure slowly. The sound becomes louder and clearer. Note the point on the manometer where the sound ceases. This is the diastolic pressure.

8. Allow the air to escape and the mercury to fall zero. Wait for 1 minute with the cuff deflated.

Reasons: occlusion of blood during the pressure reading causes venous congestion in the forearm.

9. Repeat the procedure if there are any doubts about the reading.
Do not take blood pressure more than three times in succession on the same arm.

Reasons: venous blood must be allowed to drain or it will falsely elevate the succeeding blood pressure reading.


After Care of the Patient and the Articles

1. Remove the cuff by rolling it and replace it in the box.

2. Assist the client to cover the arm which is exposed.

3. Take the apparatus to the duty room and keep it safely in the cupboard.

4. Wash hands.

5. Record the reading immediately, with the date and time, e.g., 120/80 mm Hg.


Assessing Blood Pressure – Lower Extremity

The cuff may be wrapped around the thigh or above the ankle. Thigh pressure measurement required a larger cuff. Place the client in flat, prone or supine position with the cuff-centered mid thigh over the popliteal fossa. A systolic blood pressure measured at the thigh is generally 20 to 30 mm of Hg higher than that or measured in the arm.

To measure blood pressure in the ankle, place the client in a flat, supine position and place a standard arm cuff just above the malleolus. Auscultate  or palpate the posterior tibialis or dorsalis pedis artery as the cuff is deflated.

Cuff Size

Appropriate size of the cuff and its placement is crucial in obtaining a correct measurement. The width of the cuff bladder should be 40 % of the circumference of the midpoint of the limb. The bladder length should be 80% of the limb circumference or about twice the bladder width.


Acceptable Bladder Dimensions for Arms of Different Sizes

Cuff – Bladder width (cm) – Bladder Length (cm) and Arm circumference range at midpoint (cm)

Newborn – 3 – 6 – less than 6

Infant – 5 – 15 – (6-15)

Child – 8 – 21 – (16-21)

Small adult – 10 – 24 – (22-26)

Adult – 13 – 30 – (27-34)

Large adult – 16 – 38 – (35-44)

Adult thigh – 20 – 42 – (45-52)


Hypertension: it is blood pressure that is above normal for a sustained blood.

Primary/essential hypertension: it is hypertension without a known cause.

Secondary hypertension: it is one which is associated with a known pathology.

Hypotension: it is condition of abnormally low blood pressure.

Orthostatic hypotension (postural Hypotension):
it is a low blood pressure associated with weakness or fainting when rises to an erect position (either supine to sitting, supine to standing or sitting to standing). It is the result of peripheral vasodilation without a compensatory rise in cardiac output.


Common Sources of Instrument error in B.P. Measurement


1. Manometer

Cause: Loss of mercury

Effect: reading impaired

How to rectify: have mercury added till 0 (zero) mark

Cause: clogged air vent at top of manometer tube

Effect: mercury column responds slugglishly to pressure

How to rectify: clean or replace air vent

Cause: loose air vent nut

Effect: mercury column bounces

How to rectify: tighten nut

2. Bladder

Cause: too narrow

Effect: high reading

How to Rectify: determine proper bladder and cuff size

Cause: too wide

Effect: low reading

How to rectify: determine proper bladder and cuff size

Cause: not centered over artery

Effect: high reading

How to rectify: use proper technique

3. Cuff

Cause: applied too loose

Effect: high reading

How to rectify: use proper technique

Cause: applied over clothing

Effect: reading impaired

How to rectify: use proper technique

Cause: too narrow

Effect: high reading

How to rectify: use large adult cuff

Cause: too wide

Effect: low reading

How to rectify:  use pediatric cuff

3. Tubing

Cause: pressure leaks

Effect: reading impaired

How to rectify: check for leaks and replace

4. Stethoscope

Cause: ear tips forward

Effect: auditory impairment: low systolic, high diastolic

How to rectify: use proper technique

5. Sensory impairment


Effect: inaccurate reading: low systolic, high diastolic

How to rectify: hearing tests, correction of impairment if possible

Cause: sight

Effect: high or low reading

How to rectify: read top of meniscus of mercury column at eye level.

6. Stethoscope

Cause: heavy pressure on brachial artery

Effect: distorts artery and produces sound heard below diastolic pressure

How to rectify: use proper technique

7. Cuff deflation

Cause: too fast

Effect: systematic error; systolic too low, diastolic too high

How to rectify: deflate at 2 mm Hg/sec

8. Cuff inflation

Cause: excessive and unnecessary high pressure

Effect: painful to client; may result in falsely high reading

How to rectify: determine maximum inflation level

Cause: maximum inflation level not determined

Effect: may mistake onset of 3rd phase for onset of first. Systolic underestimated

How to rectify: preliminary palpation for systolic pressure maximum inflation level

9. Subconscious bias

Cause: digit preference

Effect: improper reading recorded

How to rectify: read mercury column accurately

9. Systolic recheck

Cause: system inflated after deflation has begun

Effect: blood trapped in forearm: inaccurate reading

How to rectify: completely deflate system/wait 1-2 min, begin again.


Other equipment used for assessing blood pressure are as following:

Non-invasive blood pressure monitor:

Electronic blood pressure monitors sense vibrations within the artery wall, record the pressure readings and display them in digital numbers.

Doppler ultrasound:

The B.P. may be taken with an ultrasound or Doppler apparatus, which amplifies sound. This is especially useful if the sounds are indistinct or are inaudible with a regular stethoscope.

Direct electronic measurement:

It is possible to measure blood pressure directly through the insertion of a thin catheter into an artery (arterial line). The tip of the catheter senses the pressure and transmits this information to a machine (transducers) that displays the systolic and diastolic pressure in a wave form. This technique is primarily used in intensive care units, operation theatres etc.


A device which convert non-electric parameters like temperature, pulse, respiration and blood pressure to corresponding electrical parameters.


Blood Pressure – Vital sign. Factors, instruments used, nurse’s responsibility and Procedure

blood pressure - vital sign, nurse's responsibility