The blood pressure should be taken at a set point in the cardiovascular or general examination, so that it is not forgotten (figure 44). The upper limb is exposed up to the axilla. The patient sits or lies on a couch. The cuff should not impinge on the axilla or the cubital fossa and should be wrapped closely and evenly around the upper arm. Smaller cuffs are available for children. Too small a cuff can give a falsely higher reading, while too large a cuff prevents access to the brachial artery. The monometer should be at your eye level.
Palpate the radial pulse as the cuff is inflated – raise the pressure to 30mm of mercury above the level at which the pulse disappears. Apply your stethoscope lightly over the brachial artery on the medial aspect of the cubital fossa. Lower the cuff pressure 5mm of mercury at a time. The systolic blood pressure is the level at which you first hear the sound. The diastolic is the point at which the sound becomes suddenly faint or inaudible (Korotkoff sounds: I – appearance; IV – muffling; V – disappears).
In cardiovascular disease, take the blood pressure in both arms and, in hypertensive patients, in lying and standing positions. An initial falsely high reading may be obtained, together with an increased pulse rate. Repeat any reading that is abnormal, but allow the cuff pressure to drop to zero between measurements.
In peripheral vascular disease the blood pressure may also be measured in the lower limbs. A wider cuff is required for thigh compression and a Doppler probe is used to detect the presence or absence of a distal pulse. The systolic blood pressure is the point of detectable sound when letting down the cuff.