Abstract 6265: A Cluster Randomised Controlled Trial of Oscillometric Versus Manual Sphygmomanometers for Blood Pressure Management in Primary Care (CRAB)
Although mercury sphygmomanometers are seen as the gold standard instrument for blood pressure (BP) measurement they are being withdrawn due to health and safety concerns. This has potential for changes in BP recording and management. CRAB aimed to determine the effect of an oscillometric device on digit preference, BP measurement and antihypertensive drug prescribing. Cluster randomized controlled trial in 24 family practices in Tasmania, Australia. Practices were excluded if they had oscillometric devices. Intervention practices were supplied with OMRON HEM-907 monitors for all clinical rooms and other BP measuring devices were removed. Three practices (2 control & 1 intervention) withdrew. Intervention practices had a 1 week run-in phase for familiarization and novelty reduction. Intervention practices were subsequently audited by a research nurse as prospective collection of data by a family physician may have influenced the outcome measures of interest. Control practice audit periods were matched to intervention practices. All analyses were ITT and adjusted for potential clustering. Differences in BP were analysed using generalised estimating equations. All other outcomes were analysed using multilevel mixed-effects poisson regression. Post hoc analyses were performed to determine the mediators of changes in prescribing behaviour. 3355 records were reviewed with 828 visits having BP recordings. The percentage of BP recordings ending in “0” was significantly lower in intervention vs. control practices [SBP 18% (233/329) vs. 71% (107/587), DBP 20% (229/328) vs. 70% (119/584) p<0.001]. The mean of systolic BP recordings in the intervention group was 7.5 mmHg (95% CI 5.2, 9.9 mmHg) higher than in the control group. Patients taking BP lowering drugs were more likely (IRR 1.3 95% CI 1.1, 1.7) to have a BP lowering drug prescribed if they were in the intervention compared to the control. Post hoc analyses identified systolic BP and not terminal digit preference as mediators of changes in prescribing behaviour. Oscillometric BP devices led to increases in overall prescribing of antihypertensive drugs. This was most likely mediated by reductions in measurement error leading to higher BP recordings.