Procedure
Optimum conditions for blood pressure measurement
- dry air temperature 20-25 ºC
- quiet surroundings
- no heavy exertion or smoking during the 30 minutes prior to the measurement
- patient psychologically at rest, not talking, breathing quietly and with an empty bladder
- sitting (or lying)
- repetition at different times.
Which arm?
The blood pressure in the arteries of both arms is virtually the same. Blood pressure measurements in the right arm tend to give slightly higher values (2-10 mmHg, usually not more than 5 mmHg). Larger differences can usually be attributed to incorrect method, anatomical differences between the two arms or abnormalities of the aortic arch and large blood vessels.
For this reason it is wise when examining a patient for the first time to measure the blood pressure in both arms. If upon repetition a significant difference is found, the blood pressure should be read and measured in the future on the side where the highest value is found.
The application of the cuff [Figures 44, 45]
- remove tight clothing and jewellery.
- relax the arm, patient should not make a fist!
- the middle of the inflatable cuff should be placed at the height of the brachial artery.
- lower edge of the cuff about 2 cm above the elbow crease.
- apply cuff evenly around the arm so that it fits well (there should not be room for more than one finger between the cuff and the arm).
- cuff at the height of the patient’s heart.
- correct dimensions of the cuff. Standard is usually 30 x 13 cm. A wider and longer cuff (38 x 14 cm) is necessary if the circumference of the upper arm is more than 35 cm. A cuff which is too small will give falsely elevated blood pressure values and one which is too large will give falsely low blood pressure values.
Figure 44: The application of the cuff
Figure 45: The application of the cuff
Inflating and deflating the cuff and reading the blood pressure
- check whether the sphygmomanometer is on 0 [Figure 46].
Figure 46: The sphygmomanometer
- place a stethoscope on the medial side (inside) of the elbow crease (where the brachial artery passes!).
- palpate the radial artery on the thumb side of the wrist.
- then quickly inflate the cuff (to prevent congestion and pain in the patient) until the radial artery pulsations can no longer be felt (and therefore the artery is completely occluded!).
- after that quickly inflate the cuff by another 30 mmHg [Figure 47].
Figure 47: The inflation of the cuff
- now hold the stethoscope firmly so that it makes good contact with the skin of the elbow crease (not too lightly, but do not press too hard either).
- then without stopping allow the cuff to slowly deflate at a rate of 2 mmHg per second. If the deflation rate is too high then the start of phase 1 and phase 5 may be missed and a falsely low blood pressure may be read. If the deflation rate is too low, venous congestion may occur which may also lead to false (mostly too high) values being read.
- make sure that the sphygmomanometer is at the correct eye height.
- read off the systolic blood pressure at the start of phase 1 of the Korotkoff sounds and the diastolic blood pressure at the start of phase 5. In children, pregnant women, and pathology where there is increased cardiac output, the start of phase 4 should be read.
- read off to an accuracy of 2 mmHg [48].
Figure 48: Reading off the blood pressure
NB. 1
Doctors and nurses are often seen to inflate the cuff to about 200 mmHg without palpating the radial artery. This can lead to incorrect measurements in people with a very high pressure who have a so-called auscultatory gap (silent gap). In this situation there is a silence in the 2nd Korotkoff phase instead of a murmur and soft tones. For example, if the blood pressure of such a person were 230/95 mmHg and there were a silent Korotkoff phase 2 between 200 and 150 mmHg then the arbitrary inflation of the cuff to 200 mmHg would lead to a blood pressure of 150/95 mmHg being read! Therefore (as described above) the radial artery should be checked in everybody by means of palpation to ensure that the brachial artery is completely compressed before the blood pressure is read.
NB. 2
In the case of cardiac arrhythmias, a reading should not be taken during ectopic beats. In the case of atrial fibrillation, accurate reading of blood pressure is not possible and the best that can be done is to read blood pressure in a phase during which the heart rate comes as close as possible to 60 beats per minute.
Recording blood pressure
- the indirect (with the help of a sphygmomanometer and thus a non-invasive measurement) blood pressure measurement is often indicated with the acronym BP.
- first the systolic and then the diastolic blood pressure are noted. For example, BP 128/76 mmHg.
- if the blood pressure has to be read with the help of Korotkoff phases 1 and 4 then first the systolic blood pressure and then the Korotkoff phases 4 and 5 are noted. For example,
BP 126/82/20 mmHg or BP 134/84/0 mmHg in the case of phase 4 continuing to 0 mmHg. - if no position is noted then the sitting position is assumed. Record whether patient is standing or sitting!
Measurement frequency and intervals
When looking for hypertension:
- measure in both arms
- measure at least in duplicate per consultation with at least one minute in between (preferably 2-3 minutes)
- measure on at least 3 different occasions.