Getting the hypertension Dx right: Patient positioning matters

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Original Research

Getting the hypertension Dx right: Patient positioning matters

J Fam Pract. 2018 April;67(4):199-201,206-207

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References

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DISCUSSION

In this study, 27 subjects (13.2%) were misclassified as prehypertensive or hypertensive as a result of deviating from the standard position in obtaining BP. Although the standard position is universally recommended, the guideline is not always followed in clinical practice.¹⁴

One study by Villegas et al found that 60% of physicians and nurses working in a major hospital were measuring BP inaccurately.¹⁵ In our initial observational study, 60% of primary care practices visited did not adhere to the recommended patient positioning. These medical offices are located in the community surrounding our facility and are operated by the same health care organization. The misclassification of prehypertension and hypertension observed in our prospective comparison of BP recordings in table and chair positions is, therefore, likely to occur to some degree at these practices, as well.

Similar diagnostic misclassifications have been reported in other medical settings. In a published survey of 114 medical offices, McKay and coworkers noted frequent inconsistencies with published guidelines in measuring BP.¹⁶

Common clinical demographic data obtained during this study showed no association with the positional BP change. Increased muscle tension due to lack of body support while sitting on the edge of the examination table could be the cause of elevated BP for this subgroup of individuals. Measuring muscle tension of the arms and back while seated on an exam table and chair was beyond the scope of this study.

In clinical practice, different types of BP measuring devices are used. Calibration and quality control of these devices is often lacking.¹⁷ Before starting our study, we determined the statistical variance of the aneroid sphygmomanometers and found it to approximate the manufacturer’s precision specification. Guidelines recommend using the mean of 2 BP readings as representing the patient’s BP for a given clinic visit. Additional readings are recommended if there is more than a 5 mm Hg difference between the initial 2 readings.⁴

In our study, we used sampling statistics of the BP readings and clinical guideline BP ranges in making diagnostic determinations. The inability to identify those patients whose BP will be affected by positional change highlights the importance of following standard BP measurement guidelines for all patients.

Study limitations. Positional change in BP from examination table to chair lacks a comparison to BP changes in positioning from chair to table. If similar BP changes in the reverse sequence were to be observed, this would add support to the hypothesis that muscle tension of the unsupported body is a cause of BP elevation in certain individuals. We believe, however, that the sequence of BP measurements (from table to chair) did not have a significant impact because all patients were allowed to rest in each position before the BP was measured. The BP was therefore measured in a steady-state in both positions.

Increased muscle tension due to lack of body support while sitting on the edge of the examination table could be the cause of the elevated BP.

Additionally, BP measurement by aneroid sphygmomanometry is highly dependent on observer skill and hearing ability. Furthermore, a disproportionate number of BP measurements recorded in the study ended in zero, suggesting terminal digit bias by the observer. These sources of error may be avoided using an automated oscillometric measuring device.¹⁸ Automated devices also allow for repeated independent measurements that minimize the white-coat effect. However, there are also limitations to the accuracy of oscillometric equipment. This is especially true when recording BP in the elderly, a group whose stiff arterial walls may cause erroneous measurements.¹⁹

Guideline justification. Nonadherence to standard positioning when measuring BP leads to certain individuals being misclassified as prehypertensive or hypertensive. Misclassification in turn leads to unnecessary medical encounters, testing, and treatment. Misdiagnosis is also likely to increase the cost of an individual’s insurance coverage and out-of-pocket health care expenses.

CORRESPONDENCE
Roy N. Morcos, MD, St. Elizabeth Family Medicine Residency Program, 8423 Market Street, Suite 101, Boardman, Ohio 44512; roy_morcos@mercy.com.