Measurement of blood pressure: an evidence based review.

This is the first in a series of five articles on the treatment of hypertension

The reasons for routinely measuring blood pressures in adults are evident. Raised blood pressure is a common condition that does not have specific clinical manifestations until target organ damage develops. It confers a substantial risk of cardiovascular disease (particularly in the presence of concomitant risk factors), much of which is at least partially reversible with treatment. Finally, screening adults to detect hypertension early and initiate treatment before the onset of target organ damage is highly cost effective.[1]

Accurate measurement is of paramount importance. For example, consistently underestimating the diastolic pressure by 5 mm Hg could result in almost two thirds of hypertensive individuals being denied potentially lifesaving--and certainly morbidity preventing-treatment[2]; consistently overestimating it by 5 mm Hg could more than double the number of individuals diagnosed as hypertensive (half of whom would be inappropriately labelled and treated).[2]

What can interfere with the accuracy of blood pressure measurement?

Most people's blood pressure varies substantially throughout the day. Lowest readings occur during rest or sleep, while a variety of activities cause an increase (table 1). Additionally, numerous factors can affect the accuracy of measurements (table 2).[3-9] A comprehensive literature search identified all studies describing potential sources of bias in measurement of blood pressure. The studies were evaluated using a standard hierarchy of evidence (that of the Centre for Evidence-Based Medicine; http://cebm.jr2.ox.ac.uk/docs/ levels.html), and table 2 shows those factors which evaluated satisfactorily against a "gold standard." Full listings of the search strategy and references, all factors which have been described, and the supporting evidence behind each factor are given in Evidence Based Hypertension.[10]

 
Table 1 Effects of routine activities on blood pressure (adapted from 
Campbell et al[2]) 
 
                            Effect on blood pressure (mm Hg) 
 
Activity              Systolic blood pressure  Diastolic blood pressure 
 
Attending a meeting        [up arrow] 20              [up arrow] 15 
Commuting to work          [up arrow] 16              [up arrow] 13 
Dressing                   [up arrow] 12              [up arrow] 10 
Walking                    [up arrow] 12              [up arrow] 6 
Talking on telephone       [up arrow] 10              [up arrow] 7 
Eating                     [up arrow] 9               [up arrow] 10 
Doing des-k work           [up arrow] 6               [up arrow] 5 
Reading                    [up arrow] 2               [up arrow] 2 
Watching television        [up arrow] 0.3             [up arrow] 1 
Table 2 Factors that can interfere with the accuracy of blood pressure 
measurement 
 
                         Measured v actual blood pressure(*) 
 
Factor                   Systolic blood pressure   Diastolic blood 
                                                   pressure 
 
Patient 
Talking                  [up arrow] 17 mm Hg       [up arrow] 13 mm Hg 
Acute exposure to cold   [up arrow] 11 mm Hg       [up arrow] 8 mm Hg 
Acute ingestion of       [up arrow] 8 mm Hg for    [up arrow] 7 mm Hg 
 alcohol                  [is less than or          for [is less than or 
                          equal to] 3 hrs           equal to] 3 hrs 
 
Technique 
Patient supine rather    No effect; [up arrow]     [down arrow] 2-5 mm 
 than sitting             3 mm Hg in supine         Hg in supine 
                          position                  position 
Position of patient's    [down arrow] (or          [down arrow] (or 
 arm                      [up arrow]) 8 mm          [up arrow]) 8 mm 
                          Hg for every 10 cm        Hg for every 10 cm 
                          above (or below) heart    above (or below) 
                          level                     heart level 
Failure to support arm   [up arrow] 2 mm Hg        [up arrow] 2 mm Hg 
Cuff too small           [down …