Despite the use of gold standard equipment such as mercury sphygmomanometers in primary care for the measurement of blood pressure, accuracy remains a problem. This is due to a combination of system (eg, lack of calibration of instruments), physician (eg, observer error) and patient (eg, sympathetic drive) factors. Programmable automatic and semiautomatic oscillometric devices are likely to replace such devices because of occupational health concerns with the use of mercury.
This is a cluster randomised controlled study of an automated oscillometric blood pressure device method of determining blood pressure (intervention) versus usual manual measurement (control) in primary care. Both arms ambulatory blood pressure (ABP) measurements were also taken. The study included 555 patients with systolic hypertension (treated and untreated) and no serious comorbidities under the care of 88 primary care physicians in 67 Canadian primary care practices. The intervention was an automated oscillometric blood pressure device (BpTRU) programmed to take six recordings at 2 min intervals. Physicians and practice staff were instructed to observe the first measurement to check whether the device was correctly fitted and then exit the room to minimise white coat effect.
Two outcomes were assessed: the difference in systolic blood pressures (SBPs) between (1) awake ABP minus automated blood pressure measurement and (2) awake ABP minus manual blood pressure measurement. Practices were cluster randomised to intervention or control although the mechanism of randomisation was not specified. Randomisation was stratified by the four cities where the study took place. Neither the timeframe of this study nor the period of follow-up was stated.
The estimated mean difference for the intervention group between the awake ambulatory SBP/diastolic blood pressure (DBP) and automated clinic blood pressure (−2.3, 95% CI −0.31 to −4.3/−3.3, −2.7 to −4.4) was less (p=0.006/p=0.26) than the difference in the control group between the awake ABP and the manual clinic blood pressure (−6.5, 95% CI −4.3 to −8.6/−4.3, −2.9 to −5.8). Automated clinic SBP/DBP showed a stronger (p<0.001) within group correlation (r=0.34/r=0.56) with awake ABP after enrolment compared with manual clinic blood pressure versus awake ABP before enrolment (r=0.10/r=0.40); the mean difference in r was 0.24 (0.12 to 0.36)/0.16 (0.07 to 0.25). The between-group correlation comparing automated clinic DBP and awake ABP (r=0.56) was stronger (p<0.001) than that for manual clinic blood pressure versus awake ABP (r=0.30); the mean difference in r was 0.26 (0.09 to 0.41). The net reduction in blood pressure that can be attributed specifically to the automated clinic blood pressure intervention was −5.4/−2.1 mm Hg.
This study had a high level of physicians consenting to participate (43% of those approached) and providing enough patients (41%). No practice inclusion or exclusion criteria were described. It would seem reasonable that practices should not have oscillometric devices in situ to avoid contamination. Patient eligibility was SBP ≥160 mm Hg and DBP <95 mm Hg (untreated) and SBP ≥140 mm Hg and DBP <90 mm Hg (treated) on last prestudy visit. These criteria seem to have been chosen to allow investigation of the white coat effect. By doing so, however, it has not allowed assessment of effects on reverse white coat or masked hypertension, or differences between the two methods over a broader range of blood pressure measurements.
There were unequal clusters in each arm (36 oscillometric devices and 31 manual devices) and therefore physicians (52 vs 36) and patients (303 vs 252). This was attributed to chance by the authors. It could have been avoided if practices were stratified by number of physicians in the study rather than region. The intervention was described as ‘automated office blood pressure using the BpTRU device’. However, it was more than this, as this arm was also instructed to take multiple measures in an isolated room with the observer absent after the initial measurement. No direct observation seems to have been made for compliance checking purposes.
Implementation of the study findings will be facility dependent. The authors report that, in Canada, primary care physicians generally use several examination rooms. This is likely not to be the case elsewhere, especially, in healthcare systems where primary care is not financially well supported. Our own cluster randomised study has shown that simply replacing the manual machines with oscillometric devices leads to improved blood pressure management.1
The net reduction in blood pressure measurement in the intervention arm versus the control was −5.4/−2.1 mm Hg. This can be seen as validating its correlation with awake ABP measurements, and this is an additional value of the intervention. It may be a surrogate method of establishing measures representative of those made away from the clinic where such facilities are not available to the clinician. In our study of 8529 individuals from 11 hypertension referral centres with a mean clinic SBP/DBP of 142/82 mm Hg, average clinic measurements by trained staff were 6/3 mm Hg higher than daytime ABP.2 This is very similar to the 5/2 mm Hg in this group with an average 141/80 mm Hg in the manual measurement arm.
In summary, this study adds further evidence for the adoption of oscillometric devices in primary healthcare.
Source:Evidence Based Medicine.