Blood pressure measurement: Measuring blood pressure is a skill undertaken early in nurse training, Charlotte Alderman looks at the technique and what lies behind it

Abstract

Most devices for measuring blood pressure are dependent on one common feature, namely, occluding the artery of an extremity (arm, wrist, finger, or leg) with an inflatable cuff to measure blood pressure either oscillometrically, or by detection of Korotkoff sounds. Other techniques, which are not dependent on limb occlusion, such as pulse-waveform analysis, can also be used, but these have little application in clinical practice. The array of techniques available today owe their origins to the conventional technique of auscultatory blood pressure measurement, and these new techniques must indeed be shown to be as accurate as the traditional mercury sphygmomanometer. Since the introduction of sphygmo- manometry, mercury and aneroid sphygmomanometers have been the most popular devices for measuring blood pressures. This article has been adapted from the newly published 4th edition of ABC of Hypertension . The book is available from the BMJ bookshop and at http://www.bmjbooks.com/ Mercury sphygmomanometer No matter which device is used to measure blood pressure, it must be recognised that blood pressure is a variable haemodynamic phenomenon, which is influenced by many factors, not least being the circumstances of measurement itself. These influences on blood pressure can be significant, often accounting for rises in systolic blood pressure greater than 20 mm Hg, and if they are ignored, or unrecognised, hypertension will be diagnosed erroneously and inappropriate management instituted. These factors have to be carefully considered in all circumstances of blood pressure measurement—self measurement by patients, conventional measurement, measurement with automated devices whether in a doctor's surgery, an ambulance, a pharmacy, or in hospital using sophisticated technology. 1 2 The observer must be aware of the considerable variability that may occur in blood pressure from moment to moment with respiration, emotion, exercise, meals, tobacco, alcohol, temperature, bladder distension, and pain, and that blood pressure is also influenced …