Blood pressure measurement: we should all do it better!1
R.T. Netea, Th. Thien*
Department of Medicine (541), University Medical Centre St Radboud, PO Box 9101, 6500 HB Nijmegen, the Netherlands, tel: +31 (0)24-3618819, fax: +31 (0)24-3541734, e-mail: T.Thien@aig.umcn.nl, *corresponding author
‘Because blood pressure (BP) measurement is a simple procedure, it is taken forgranted that all graduates from medical training programmes have the ability to record accurate, precise and reliable BP readings. However, research since the 1960s has shown this assumption to be false. Most health professionals do not measure BP in a manner known to be accurate and reliable. If you doubt this statement watch as BPs are taken in your own clinical setting to determine whether theguidelines discussed herein are followed and then examine recorded readings for signs of observer bias.’ This citation is taken from a chapter by Carlene and Clarence Grim, both very experienced BP researchers and teachers, in a recent book.2 Earlier, these authors published a curriculum for the training and certification of BP measurements for the healthcare providers.3 BP measurement is nowadaysrecognised as probably the most commonly performed clinical procedure. Nurses, physicians, medical students and even patients measure BP routinely. BP can be measured directly (intra-arterially) or indirectly. The first method represents the ‘gold standard’ for BP measurements but is invasive, requiring arterial cannulation and is therefore only used in particular (research) circumstances. Theindirect method is widely used in both daily practice and research. Many BP measuring devices have been developed in the last decades. However, measurement of BP using a mercury sphygmomanometer and a stethoscope according to the Korotkoff’s auscultatory principle remains the cheapest and most accurate (when compared with intra-arterial readings), and is considered the noninvasive gold standard,providing that the measurement is performed correctly. The tendency to ban the use of mercury, a toxic substance, in clinical practice is leading to mercury sphygmomanometers being replaced by alternative instruments. Most of these
devices are based on the oscillometric principle. However, only a limited number of them have already been validated. Several factors affect indirect BP readings.
F AC T O R S R E L AT E D T O P AT I E N T
Some of the factors affecting the BP are related to the person in whom the BP is being measured, commonly referred in the literature as biological variation (table 1). Rest period It has been recommended that the BP should be measured after several minutes rest to allow the BP to stabilise.4-7 However it is not exactly known how long the rest periodshould be. Average drops in the systolic BP (SBP) of 9 and 14 mmHg, respectively, have been reported after a rest period of four and eight minutes prior to the BP measurement. The decrease was less evident in the diastolic BP (DBP), amounting to 3 and 4 mmHg, respectively, for the same rest intervals.8 These results are consistent with the results of other studies that also report a decrease ofsimilar magnitude within the first five to ten minutes of rest.9-13 A longer rest period of more than 25 minutes was found to further slightly decrease the BP values, especially the SBP, but the question remains whether such a long rest period is feasible in general practice.9,13 On the other hand, clinical experience shows that in a few patients the BP increases if they have to wait to have their BPmeasured. These patients can be traced by measuring the BP both immediately after assuming supine or sitting position and after the rest period. Based on this data, it has been recommended that at least five minutes of rest should be allowed before the measurement of BP.14
© 2004 Van Zuiden Communications B.V. All rights reserved.
SEPTEMBER 2004, VOL. 62, NO. 8