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American Heart Association journal report: American Heart Association calls for check-up on modern blood pressure instruments
DALLAS, Feb. 16 -- The "gold standard" mercury manometer should not be replaced by electronic or aneroid devices used to take blood pressure measurements, according to an editorial in Hypertension: Journal of the American Heart Association.
"For more than a century, the mercury gravity sphygmomanometer has been the gold standard for indirect measurement of blood pressure," says Daniel W. Jones, M.D., lead author of the editorial. "It is a simple, gravity-based unit with easy calibration, infrequent need for repair, and it has been validated against intra-arterial blood pressure measurement."
Electronic instruments include in-home blood pressure monitoring devices as well as the small counters often seen at drug stores where a person places his or her arm through a mechanical cuff. Aneroid devices are commonly used in physician offices and have a round compass-like face attached to a cuff that is wrapped around the upper arm and inflated while a nurse or medical assistant listens to the cuffed area with a stethoscope.
The concerns brought up in the editorial don't necessarily mean that these devices should be done away with all together. "There is a place for the newer instruments, particularly as home monitoring devices. They are easy to use and are portable, which makes them ideal for some situations," says Jones.
The editorial authors, all members of the American Heart Association's Council for High Blood Pressure Research, say decisions by hospitals and clinics to replace mercury-gravity based instruments with these newer models have been made without consideration for the health risks of using less accurate devices to measure blood pressure.
About 50 million, or one in five Americans age 6 and older have high blood pressure, or hypertension. High blood pressure was listed as a primary or contributing cause of death on about 210,000 death certificates in 1998, the most recent year for which statistics are available. The cause of 90-95 percent of cases of hypertension isn't known. However, the condition is easily detected with proper instrumentation and technique, and it is treatable. High blood pressure is defined as systolic pressure (top number) of 140 or higher, and diastolic pressure (bottom number) of 90 or higher for most people.
The editorial notes that some facilities justify the replacement of mercury manometers with concerns about the safety and use of mercury in the workplace. However, Jones says modern mercury instruments are available in models that prevent breakage and accidental spillage of mercury. "This essentially eliminates those safety concerns."In considering the reliability of aneroid or electronic instruments, the editorial authors say a crucial issue is calibration. Calibration is a way to make sure measurements begin from zero - like when a scale is balanced or "zeroed" before you step on it to measure body weight. If the starting mark is above or below zero, the final measurement will be inaccurate.
The editorial says that neither electronic nor aneroid devices are calibrated regularly in many health care settings. "Most manufacturers of these instruments recommend calibration against a mercury manometer every six months. However, few hospitals and clinics have a regular program of evaluation and calibration," says Jones. He also notes that most of these instruments must be returned to the manufacturer for calibration.
Another concern with the new devices is validation. This ensures that the instrument can take accurate measurements over a wide range of blood pressures, ages and clinical conditions. "Most of these instruments have not been adequately validated to warrant routine use in hospitals and outpatient settings," says Jones.
The bottom line is that accurate blood pressure measurement is important, he says. Repeated overestimation of blood pressure can be associated with costly over treatment of hypertension; while continuous underestimation of blood pressure can cost many lives in failing to prevent cardiovascular disease. Hypertension is a major risk factor for cardiovascular disease, the number one killer in the United States.
The authors maintain that there is a "constant need for caution in the selection of blood pressure measuring devices. New is not always better."
They list nine specific recommendations in the editorial:
-- That clinicians educate themselves on the instruments available-- That doctors work with hospital administrators and committees to select instruments-- Encourage general use of mercury manometers as the instrument of choice until other devices are better validated-- Where aneroid or electronic instruments are used, ensure that they are validated -- Ensure a program of regular maintenance and calibration of all instruments-- Where aneroid or electronic devices are used exclusively, and mercury instruments cannot be reintroduced for regular use, insist on using mercury instruments for calibration-- Ensure a regular training program for those who measure blood pressure-- Encourage studies to validate the safety and reliability of all instruments used for blood pressure determination-- Use evidence in determining both safety and reliability of any instrument
Co-authors include Edward D. Frohlich, M.D.; Carlene M. Grim, R.N., M.S.N.; Clarence E. Grim, M.D.; and Kathryn A. Taubert, Ph.D.
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NR01-1258 (Hyper/Jones)
Media Advisory: Dr. Jones can be reached by phone at (601) 984-1010. (Please do not publish contact information.)
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