The challenge of measuring blood pressure in low-resource settings
Authors: James M Roberts, Vanessa Assibey-Mensah
Journal: The Lancet Global Health (2019)

The two leading causes of maternal mortality worldwide are haemorrhage and hypertension in pregnancy.1Say L Chou D Gemmill A et al.Global causes of maternal death: a WHO systematic analysis.Lancet Glob Health. 2014; 2: e323-e333Summary Full Text Full Text PDF PubMed Scopus (2852) Google Scholar The care of both requires assessment of blood pressure, a challenge that has been difficult to meet in low-resource settings. For the past several years, the CRADLE Trial Collaborative Group has worked to meet this challenge. In The Lancet Global Health, Nicola Vousden and the CRADLE Trial Collaborative Group2Vousden N Lawley E Nathan HL et al.Effect of a novel vital sign device on maternal mortality and morbidity in low-resource settings: a pragmatic, stepped-wedge, cluster-randomised controlled trial.Lancet Glob Health. 2019; 7: e347-e356Summary Full Text Full Text PDF PubMed Scopus (24) Google Scholar report on the latest and most definitive step of this quest, the ability of their efforts to reduce maternal mortality. The progress towards their goal and the challenges of demonstrating its efficacy provide valuable lessons in how to address a technological challenge and assess the proposed solution. WHO, in recognition of the problems with blood pressure measurement in low-resource settings, presented several requirements for a successful device.3WHOAffordable technology : blood pressure measuring devices for low resource settings. World Health Organization, Geneva2005Google Scholar The first, of course, was accuracy. In addition, it was proposed that the ideal device would be sturdy, inexpensive, and require minimal training to use. The CRADLE group has developed and tested a device, CRADLE Vital Sign Alert, to meet these requirements. They established accuracy of a semi-automated oscillometric device during pregnancy and postpartum, with both high and low blood pressure.4Nathan HL de Greeff A Hezelgrave NL Chappell LC Shennan AH Accuracy validation of the Microlife 3AS1-2 blood pressure device in a pregnant population with low blood pressure.Blood Press Monit. 2015; 20: 299-302Crossref PubMed Scopus (27) Google Scholar, 5Nathan HL de Greeff A Hezelgrave NL Chappell LC Shennan AH An accurate semiautomated oscillometric blood pressure device for use in pregnancy (including pre-eclampsia) in a low-income and middle-income country population: the Microlife 3AS1-2.Blood Press Monit. 2015; 20: 52-55Crossref PubMed Scopus (57) Google Scholar The device is hand inflated but with automatic readout so that the only power required is for the screen. The resulting low power consumption allows thousands of uses per battery charge. Batteries are rechargeable using a USB port. The device is simple, sturdy, and light (300 g) and costs less than €20 per device.6de Greeff A Nathan H Stafford N Liu B Shennan AH Development of an accurate oscillometric blood pressure device for low resource settings.Blood Press Monit. 2008; 13: 342-348Crossref PubMed Scopus (32) Google Scholar An extremely useful feature is the traffic-light readout that allows a minimally trained individual to obtain interpretable data.7Nathan HL Seed PT Hezelgrave NL et al.Early warning system hypertension thresholds to predict adverse outcomes in pre-eclampsia: a prospective cohort study.Pregnancy Hypertens. 2018; 12: 183-188Crossref PubMed Scopus (18) Google Scholar Preliminary qualitative studies indicated that both users and patients approved of the device.8Nathan HL Boene H Munguambe K et al.The CRADLE vital signs alert: qualitative evaluation of a novel device designed for use in pregnancy by healthcare workers in low-resource settings.Reprod Health. 2018; 15: 5Crossref PubMed Scopus (28) Google Scholar The ultimate step in the development was determining in the present study whether the use of the device in low-resource centres improved outcomes. The study design was a stepped-wedge, cluster-randomised controlled trial.9Brown CA Lilford RJ The stepped wedge trial design: a systematic review.BMC Med Res Methodol. 2006; 6: 54Crossref PubMed Scopus (626) Google Scholar This design randomly allocates the sequential crossover of each cluster from control to intervention at fixed times. It is especially appropriate when, as in this study, the proposed intervention is safe and likely to improve care, since no cluster is deprived of the intervention. The clusters chosen were intentionally diverse, to increase generalisability, with ten clusters in eight countries, comprising 286 centres. The outcome was definitive, a composite of maternal death, eclampsia, or emergency hysterectomy. The intervention was the combination of training and the use of the Cradle Vital Sign Alert. The statistical approach was to compare the event rates of all-cause maternal mortality or major morbidity during the post-intervention and pre-intervention phases, while accounting for the clustered design and variability between and within clusters over time. The results before adjustment indicated a reduction in the primary outcome (79·4 per 10 000 deliveries pre-intervention to 72·8 per 10 000 deliveries post-intervention [odds ratio 0·92, 95% CI 0·86–0·97; p=0·0056]). However, with a priori planned adjustments, there was insufficient evidence to suggest that a significant benefit or harm could be attributed to the intervention (OR 1·22, 95% CI 0·73–2·06; p=0·45). In prespecified secondary analyses, only emergency hysterectomy remained significantly reduced after adjustment (OR 0·21, 95% CI 0·07–0·66; p=0·0072). In the current analysis, there was no explanation for the marked variability between centres, which was much greater than expected, but further assessment is in progress. Despite the negative results of the study, there is much to be learned from this approach to the resolution of a clinical problem addressing technological challenges. WHO clearly defined blood pressure measurement as a problem needing resolution and identified the components necessary for a successful solution. The CRADLE group logically and inclusively addressed and resolved these challenges with careful assessment of outcomes at each step. The current study demonstrated that the device was sturdy (less than 5% were damaged) and a defined secondary outcome, the rate of emergency hysterectomy, was reduced as might be anticipated with earlier recognition of haemorrhagic shock. Nonetheless, when adjusted for a much greater than anticipated between-centre variability, there was no evidence for the efficacy of the intervention to reduce the primary outcome. However, there are also valuable lessons to be learned from this finding. One of the major challenges facing clinical investigators is the need to avoid trying to resolve more questions than is possible in one study. The authors conclude that future studies of this type should perhaps be initially carried out in a single country with extensive pilot data to determine the impact of clinical care pathways, resource availability including staffing needs, and in individual centres to inform power analysis. The summary of the results of the group's approach to a complex technological challenge is that such a solution is possible. To accomplish this, assessment at each step is mandatory. However, to demonstrate ultimate success with their current approach is more complex than can be handled in a very diverse group of centres. However, perhaps their ongoing studies might resolve even this major challenge. JMR is a consultant on a grant/project on which Andrew Shennan is the Chair of the Data Monitoring Committee. VA-M declares no competing interests. Effect of a novel vital sign device on maternal mortality and morbidity in low-resource settings: a pragmatic, stepped-wedge, cluster-randomised controlled trialThere was an absolute 8% reduction in primary outcome during the trial, with no change in resources or staffing, but this reduction could not be directly attributed to the intervention due to variability. We encountered unanticipated methodological challenges with this trial design, which can provide valuable learning for future research and inform the trial design of future international stepped-wedge trials. Full-Text PDF Open Access