One Size Doesn't Fit All for Automated BP Measurement Cuffs, Trial Finds

Using a "regular" size arm cuff with an automated blood pressure (BP) device for all adults resulted in inaccurate BP readings regardless of arm size, but especially in individuals with larger arms, the randomized Cuff(SZ) trial found.

With individuals who needed a small cuff, use of a regular size cuff resulted in a 3.6-mm Hg lower systolic BP reading (P<0.001) than with an appropriately sized cuff, Tammy M. Brady, MD, PhD, of Johns Hopkins University School of Medicine in Baltimore, and co-authors reported in JAMA Internal Medicine.

On the other hand, for adults who needed a large or extra large cuff size, the use of a regular size cuff resulted in 4.8-mm Hg and 19.5-mm Hg higher systolic BP readings than with an appropriate size cuff (both P<0.001).

The discrepancies also consistently appeared in readings of diastolic BP for adults who had cuffs that were one size too large, one size too small, and two sizes too small, with differences of -1.3, 1.8, and 7.4 mm Hg, respectively.

Altogether, the researchers called these wrong-size measurements "strikingly inaccurate."

Previous studies have found similar problems from inappropriate cuff size used for manual auscultation, but "this issue has not been rigorously studied with automated oscillometric BP devices, which estimate BP by a fundamentally different technique," Brady's group wrote.

It's a widespread issue, Brady suggested. "Oftentimes, screened blood pressures are done with the cuff that's already attached to the device," Brady told MedPage Today. "Some of this is due to lack of resources; some of this is just due to the need for clinical efficiency."

Indeed, LaPrincess C. Brewer, MD, MPH, of the Mayo Clinic College of Medicine in Rochester, Minnesota, and co-authors wrote in an invited commentary, "These findings are especially relevant for under-resourced clinics, such as federally qualified health centers, that are often not adequately equipped and instructed to measure BP correctly."

These clinics "predominantly serve marginalized populations, such as racial and ethnic minority groups and socioeconomically disenfranchised individuals, who face CVD [cardiovascular disease] disparities," Brewer's group continued, so enabling them to correctly measure BP "is a key strategy to achieving health equity."

Even where resources may be available to do so, prior studies have found that clinicians may not follow proper protocol, noted Brady and colleagues. Only 74% of medical students in one study selected the appropriate cuff size for their patients. In another, staff at an academic health science center never measured arm circumference for cuff sizing.

In terms of the impact of "miscuffing," the study authors pointed out that most home-use BP monitors come with a regular size cuff. Thus, the 40% or more of U.S. adults who might require a large arm cuff size would obtain home BP readings overestimated by almost 5 mm Hg, they cautioned.

Misdiagnosis of hypertension could lead to overtreatment or undertreatment of serious medical conditions, the authors continued. Overtreatment could result in adverse effects of medications or extra healthcare costs, and undertreatment could lead to complications from preventable conditions like heart or kidney disease.

Secondary findings showed differences were greater when the cuff was two sizes versus one size different. With the number of sizes "off" held constant, the differences also increased as the appropriate size arm cuff increased.

In the Cuff(SZ) trial, the 195 participants were recruited with screening events at a public food market and a senior housing facility, as well as via targeted mailings to prior research participants and placement of study brochures in hypertension clinics at Johns Hopkins University. Mean participant age was 54. Of the participants, 34% were male and 68% identified as Black persons.

Of the group, 51% had hypertension, 20% had diabetes, and mean BMI was 28.8. Small, regular, large, and extra large cuffs were appropriate for 35, 54, 66, and 40 participants, respectively. Researchers determined appropriate size by measuring mid-arm circumference and following manufacturer instructions based on available U.S. cuff sizes.

Participants had their BP measured three times with each of the four cuff sizes in random order, except the fourth time, where their BP was taken with the appropriately sized cuff. All participants had their BP taken with the "regular" sized cuff at least once. Measurements were taken between 9 a.m. and 5 p.m. with other parameters held constant: participants had empty bladders, a 2-minute walk before each set followed by 5 minutes of rest, and 30 seconds between each of the three measurements in a set.

Authors noted that study limitations included insufficient subgroup sample size in some groups (like too few participants with hypertension and obesity in the small-cuff group); heterogeneity of magnitude and direction of BP misreadings between individuals; the rigorous training researchers had, which might not be seen in a clinical setting; and a lack of applicability for individuals with "extreme arm circumferences," for example <20 cm or >55 cm.

Comment