Cluster-randomized controlled trial of oscillometric vs. manual sphygmomanometer for blood pressure management in primary care (CRAB)

Abstract

Background: Although mercury sphygmomanometers are seen as the gold standard instrument for blood pressure (BP) measurement, they are being withdrawn due to safety concerns. CRAB was a cluster-randomized controlled trial in 24 family practices in Tasmania, Australia, which aimed to determine the effect of an oscillometric device on BP management. Methods: Cluster-randomized controlled trial. Intervention practices were supplied with automated monitors and control (usual care) practices used mercury or aneroid sphygmomanometers. They were subsequently audited by a research nurse. Usual care practice audit periods were matched to intervention practices. All analyses were intention-to-treat and adjusted for potential clustering. Differences in BP were analyzed using generalized estimating equations. All other outcomes were analyzed using multilevel mixed-effects Poisson regression. Post hoc analyses were performed to determine the mediators of changes in prescribing behavior. Results: A total of 3,355 records were reviewed (828 visits had BP recordings). The percentage of BP recordings ending in 0 was significantly lower in intervention vs. usual care practices (systolic BP (SBP) 18% (107/587) vs. 71% (233/329), diastolic BP (DBP) 20% (119/584) vs. 70% (229/328), P 0.001). The mean of SBP recordings in the intervention group was 7.5 mm Hg (95% confidence interval (CI) 5.2, 9.9 mm Hg, P 0.001) higher than in the usual care group. Patients taking BP lowering drugs were more likely (incidence rate ratio (IRR) 1.3, 95% CI 1.1, 1.7, P = 0.01) to have a BP lowering drug prescribed if they were in the intervention compared to the usual care. Conclusions: Although digit preference was largely eliminated by oscillometric measurement, prescribing behavior was mediated by SBP. © 2009 American Journal of Hypertension, Ltd.