[Agreement in the measurement of blood pressure among different health professionals. Are mercury sphygmomanometers reliable?].

OBJECTIVES

To assess reliability in terms of inter-observer agreement of blood pressure (BP) readings. Various health professionals and measuring systems. Influence of observer's experience.

DESIGN

Observational, descriptive, cross-sectional study.

SETTING

Urban health centre, Córdoba.

PARTICIPANTS

131 hypertensive, randomised patients, belonging to a functional care unit. 11 were excluded.

MEASUREMENTS

To reduce variability: course on the right way to take blood pressure, otoscope and verification of visual sharpness of observers, calibration and validation of measuring devices, limited time and blinding of measurements. 4 BP measurements per patient: 3 with mercury sphygmomanometer (2 simultaneously, one individual) and one with an automatic device. Descriptive, clinical and somatometric variables were gathered. Inter-observer agreement was evaluated through the intraclass correlation coefficient (ICC), the mean of differences method (MDM) and the simple concordance index (CI). An ICC > 0.75 was thought acceptable. A difference > 5 mmHg was thought clinically relevant (MDM and CI).

MAIN RESULTS

Acceptable consistency for MDM: alone, systolic and diastolic pressure of OBS 1/ OBS 2, bi-auricular, -6.1/+8.9 mmHg and -6.8/+5.8 mmHg. Less favourable results: for systolic and diastolic pressure: OBS 1/AUTO -20.9/25.0 and -16.4/15.1; OBS 2/AUTO -22.8/24.4 and -16.6/15.2. Remaining intervals always > 10 mmHg; CI > 0.75 in all comparisons except diastolic pressure OBS 1/AUTO and diastolic pressure OBS 2/AUTO (0.69 in both cases). 41% of comparisons were > 5 mmHg. No differences in less expert professionals were found.

CONCLUSIONS

Inaccuracy of the standard BP measurement method (mercury sphygmomanometer) for MDM and CI. Contradictory conclusions according to method of measurement. Differences not clinically acceptable.