Certain Arm Positions Can Lead to Inaccurate Blood Pressure Readings

Certain arm positions — supported on a lap or hanging by the side of the body — led to significant overestimation of blood pressure readings compared with standardized positioning, a randomized trial in JAMA Internal Medicine showed, raising concerns about misdiagnosis or overestimation of hypertension.

In this video interview, researcher Tammy Brady, MD, PhD, of Johns Hopkins University School of Medicine in Baltimore, discusses the findings and implications.

The following is a transcript of her remarks:

Cardiovascular disease is a leading cause of death worldwide. And in fact, in the United States, cardiovascular disease accounts for approximately 800,000 deaths per year. Really key to preventing cardiovascular disease is screening for hypertension, and key to hypertension screening is getting accurate blood pressure measurements.

Now, many people don’t recognize that there are various patient preparatory steps and positions that are recommended in the guidelines for measurement. Many of these steps take time and occasionally require additional resources to comply with. In fact, several studies have shown that healthcare providers don’t always adhere to these steps.

So with this in mind, my co-investigators and I were really interested to see how important arm support and position is to blood pressure measurement accuracy.

For context, the guidelines state for a blood pressure measurement that the arm needs to be supported on a desk or a table, with the arm position in such a way that the middle of the cuff is at mid-heart level. Now, many settings don’t have a desk or other support for the arm, so they often make due by either having their arm rest in their lap or hang at their side. So again, we were curious to know if either of these two other positions had an impact on blood pressure accuracy.

To answer this question, we recruited 133 adults from the community to participate in a crossover randomized clinical trial. What we did is we took each of those participants and sorted them at random into one of six possible groups that differed by order of the three seated arm positions. Again — on the desk, in their lap, or at the side.

Everything else about the blood pressure measurement was standardized, specifically before each measurement was taken, we made sure all the participants emptied their bladders and then we had them walk for 2 minutes to mimic a typical scenario of them walking into the clinic or to the office before the screening takes place. Then they each underwent 5 minutes of seated rest periods with their back supported, their feet supported, and then each person wearing an upper arm blood pressure cuff that was selected in size based on their upper arm size.

[They] had three sets of triplicate measurements taken with a digital blood pressure device 30 seconds apart. After they finished each set of three measurements, the cuff was removed and then they walked for another 2 minutes to wash out any potential effect of embedded rest and then rested again for 5 minutes.

Now, because blood pressure varies from minute to minute B2B, all participants underwent a fourth set of triplicate measurements with their arms supported on a desk. This was done to account for those well-known variations in blood pressure readings, and then we used this in our difference-in-differences analyses.

What we found was that a lack of arm support and suboptimal arm positioning in fact significantly impacted blood pressure readings. Blood pressure measurements obtained when the arm was resting in the lap overestimated systolic blood pressure by 3.9 mm Hg and diastolic blood pressure by 4 mm Hg, and measurements obtained with the arm hanging at the side overestimated systolic blood pressure by 6.5 mm Hg and diastolic blood pressure by 4.4 mm Hg.

When screening for hypertension, it shows that it’s really essential to make sure you properly position your arm. By not doing so, you run the risk of having a falsely elevated blood pressure and potentially misdiagnosing a patient.

I think this work also highlights how important it is to not only educate healthcare providers, but also patients who conduct home blood pressure measurements to make sure they position their arms properly. One of the important parts of our guidelines states that prior to diagnosing someone with hypertension, patients need out-of-office blood pressure measurements. Again, we’re looking to exclude the white-coat effect that could falsely elevate a clinic blood pressure measurement. The findings from our study regarding arm position apply regardless of setting, whether they’re in the home or clinic. So if patients don’t know that they need to support their arms and position them properly, they may be providing their healthcare providers with inaccurate readings, contributing to a misdiagnosis.

It’s my hope that our paper reaches patients for this very reason, since I think so much rides on home blood pressure measurements.

While it may take an initial investment in time and resources to make sure that the blood pressure measurement setting is set up for proper measurement, I really think the return on investment has the potential to be significant in terms of not only better patient care with fewer misdiagnoses, but in savings and time. Patients having to return for measurements takes time, resources with repeat appointments and needing healthcare staff for those appointments, and money. Patients are going to lose time at work, they have to spend time in an evaluation and on medications. So again, the initial investment I think will have a big impact.

My hope is that this study alerts healthcare providers and patients alike to the importance of arm position and support to measurement. It’s really more than just putting on a cuff and pushing the button, and I hope patients will feel empowered to ask for repeat measurement in ideal conditions, which includes this arm support and positioning, if their blood pressure reading is ever elevated.

I also hope that healthcare providers recognize that it’s really important not only to train and certify those individuals in charge of measuring blood pressure in the clinic, but you need to retrain and recertify every 6 months to make sure that there’s no skill decay. And if you’re prescribing an out-of-office blood pressure measurement, taking the time to educate patients on the proper steps is really key to making sure you get the right diagnosis.

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