For accurate BP measurement, one cuff size does not fit all

The medical community has in recent years upped the attention it gives to the crucial preparatory and positioning steps in accurate blood pressure measurement. Nevertheless, millions of patients may still be getting mismeasured because their care teams continue to overlook one all-important detail: using an appropriately sized BP cuff.

For a randomized crossover trial published in JAMA Internal Medicine, researchers looked at the effects of using a regular adult BP cuff compared with one that was appropriately sized for an individual’s measured mid-arm circumference on automated readings. Their key finding: A one-size-fits-all approach produces “strikingly inaccurate” BP measurements.

“While higher or lower BP readings with too-small or too-large BP cuffs have been described in previous studies using BP devices that rely on auscultation, this issue has not been rigorously studied with automated oscillometric BP devices, which estimate blood pressure by a fundamentally different technique than auscultatory devices,” wrote the study’s authors, who include Tammy M. Brady, MD, PhD, vice chair for clinical research in the pediatrics department at Johns Hopkins University School of Medicine.

The 195 adult participants underwent four sets of triplicate BP measurements: three sets randomized to appropriate, too-small and too-large cuff application and a fourth repeating measurements using an appropriately sized cuff.

Each participant had their mid-upper arm circumference measured by research staff trained and certified in the procedure. The appropriate cuff was then determined according to manufacturer instructions and the four cuff sizes available: small, 20–25 cm; regular ,25.1–32 cm; large, 32.1–40 cm; or extra-large, 40.1–55 cm.

The authors found that use of a regular BP cuff resulted in a 3.6 mm Hg lower systolic BP reading among individuals who needed a small cuff. It also resulted in a 4.8 mm Hg and a 19.5 mm Hg higher systolic BP among those who needed a large or an extra-large cuff, respectively.

They also analyzed the measurement differences when using too-small cuffs across cuff sizes.

“Interestingly, the magnitude of measurement error increased with increasing cuff size,” the study says. “For example, BP was approximately 3 mm Hg higher when a small BP cuff was used for those requiring a regular BP cuff but was approximately 10 mm Hg higher when a large BP cuff was used for those requiring an extra-large BP cuff.”

The reasons for the errors are uncertain, they noted, but could be related to the algorithms manufacturers use to estimate BP from brachial arterial oscillations or to cuff fit, as many individuals who need an extra-large cuff have short humerus length relative to upper arm circumference.

“Regardless of cause, the potential clinical effect among those requiring larger cuff sizes includes overdiagnosis of not just hypertension, but also stage 2 hypertension,” the authors wrote, adding that the mean BP in those requiring an extra-large cuff was 144/87 when a regular BP cuff was used, whereas an appropriately sized cuff gave a mean blood pressure of 125/79.

“With misdiagnosis to this degree comes additional, likely unnecessary, clinical testing (laboratory and imaging) and treatment, leading to increased cost, psychosocial harm and risk for adverse events,” they wrote.

The AMA is  working  to improve health outcomes associated with cardiovascular disease through efforts such as the AMA MAP™ Hypertension program, which helps physicians, care teams and health systems boost BP-measurement accuracy, increase the use of evidence-based treatment, and work with patients in self-management of their blood pressure.

In addition, the AMA helped create the US Blood Pressure Validated Device Listing (VDL™), which identifies the BP-measurement devices that have been independently validated for clinical accuracy. Validated cuff sizes are noted for each device.