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Blood Pressure monitoring

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Gail P. Mooney, MSc, PG Social Research Methods, RGN, lecturer, School of Health Science, University of Wales, Swansea.

What it is?

Blood Pressure (BP) is the pressure exerted by blood on the wall of a blood vessel (Tortora and Grabowski, 1993). When the ventricles are contracting the pressure is at its highest, this is known as ‘systolic’. ‘Diastolic’ is when the ventricles are relaxing and the pressure is at its lowest.

Normal/ideal values

Normal blood pressure ranges between 100/60 to 140/90 mmHg: BP can fluctuate within this range and still be normal (Mallett and Dougherty, 2000).

Hypotension (low blood pressure) is when the systolic is below the normal range. Low blood pressure could be an indication of hypovalemia, septic shock or cardiogenic shock.

Hypertension (high blood pressure) is when the systolic is above the normal range. High blood pressure could be an indication of cardiovascular disease, a side effect of drug medication or trauma.

Recording the blood pressure

The blood pressure is recorded for a number of reasons:

- To acquire a baseline;

- To monitor for fluctuation in blood pressure;

- To aid in diagnosis of disease;

- To aid in assessment of the cardiovascular system;

- To monitor medication e.g. anti-hypertensive drugs.

Blood pressure is usually measured in millimetres of mercury (mmHg) and can be measured in two ways, invasive or non-invasive.

Invasive measurement requires the insertion of a small cannulae into the artery, which is then attached to a transducer. The transducer transmits a waveform to a monitor - this allows continuous measurement of the blood pressure. This method is usually performed in critically ill patients and patients undergoing major operations.

Non-invasive measurement requires the use of a sphygmomanometer and stethoscope or an electronic sphygmomanometer.

Auscultation of sphygmomanometer blood pressure usually reveals five (‘Korotkoff’) sounds (Woodrow, 2000):

1. First sound heard, sharp thud - systolic pressure;

2. Soft, tapping, intermittent;

3. Loud (not as loud as phase 1);

4. Low, muffled, continuous: start - 1st diastole;

5. Disappears - 2nd diastole.

Equipment needed:

 - Stethoscope;

  • Sphygmomanometer.


- Explain to the patient what you are about to do - even if the patient is unconscious.

- Ensure that the patient is comfortable, as relaxed as possible and not distressed.

- Note if the patient has had any medication that may alter the blood pressure.

- Any tight or restrictive clothing should be removed from the patient’s arm.

- The position of the patient is not as important as the position of the arm; this should be supported and should be level with the heart (Jowett, 1997).

- Apply the cuff (inside the cuff is the bladder), make sure that the cuff is empty of air before applying; ensure the correct size cuff is used on the patients arm. The width of cuff should cover at least 40% of the arm circumference and the length should cover at least two-thirds of the arm (Jowett, 1997). The centre of the cuff should cover the brachial artery.

- Make sure that you can see the sphygmomanometer and that it is in line with the heart.

- Palpate the brachial pulse and inflate the cuff until the pulse can no longer be felt. This will give an estimate of the systolic pressure. Deflate the cuff and re-inflate to 30mmHg higher than estimated (Jowett, 1997).

- Position the stethoscope over the brachial artery and slowly deflate the cuff at 2-3mmHg per second.

- The first beating sound should be recorded; this is the systolic pressure.

- Continue to deflate the cuff; the last sound to be heard is the diastolic pressure.

- Record the blood pressure on the observation chart. Any abnormalities or irregularities should be documented and reported to the medical team.

- Before leaving the patient make sure any clothing removed is replaced and that the patient is comfortable.

Electronic sphygmomanometer - the same procedure is carried out as above without the use of the stethoscope. Manufacturer’s guidelines should be followed and appropriate training completed.

When and how often should the blood pressure be recorded?

The frequency of recording the blood pressure depends on the condition of the patient. Patients in a critical care environment will require their blood pressure to be recorded continuously.


- The blood pressure should be recorded to the nearest 2mmHg - to maintain accuracy.

- Nurses should wash their hands thoroughly between patients to eliminate the risk of cross infection.

- The correct size cuff should be used - the wrong size cuff will lead to an inaccurate measurements. 

  • The sphygmomanometer (electronic or mercury) should be calibrated and serviced regularly in accordance to manufacturers instructions.
  • Equipment should be cleaned and precautions against cross infection must be adhered to.


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