Precautions
It is a common observation that BP recordings are variable when taken by different individuals. To decrease this variability it is important that certain precautions are taken while BP is recorded.
Posture
The patient can be seated or lying, but must be comfortable and relaxed. This is important since the systolic pressure elevation due to anxiety ("white coat hypertension") can go up by 17 to 27 mmHg. In pregnant women BP must not be recorded lying down because of the possibility of the pressure on the Inferior Vena Cava diminishing the venous return.
Equipment
The standard mercury sphygmomanometer is still considered to be the best equipment. Instruments like the aneroid and electronic ones may show variations in readings and need to be calibrated (compared) with the mercury sphygmomanometer. When using the mercury sphygmomanometer, the following points must be adhered to the:
- lower edge of the cuff should be 2.5 cms above the antecubital fossa.
- stethoscope diaphragm must be just below the cuff edge.
- width of the cuff must be 40 per cent of the circumference of the arm (usually 12.5 cms in normal adults, 17 cms in obese adults, 7.5 cms in young children, 3.5 cms in infants).
- length of the rubber bag (usually 25 cms), must be enough to cover more than 80 per cent of the circumference of the limb.