Cluster-Randomized Controlled Trial of Oscillometric vs. Manual Sphygmomanometer for Blood Pressure Management in Primary Care (CRAB)

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mercury sphygmomanometers are seen as the gold standard instrument for blood pressure (BP) measurement, they are being withdrawn due to safety concerns.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 clusterrandomized 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.