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Synopsis: In the presence of a protocol of annual maintenance, aneroid sphygmomanometers in regular clinical use were accurate to within 0.5 mm Hg (95% CI, < 1 mm Hg) when tested using a device calibrated against a mercury sphygmomanometer.
Source: Canzanello VJ, et al. Arch Intern Med. 2001; 161:729-731.
Because of increasing concerns over the personal and environmental hazards of mercury, mercury sphygmomanometers have been replaced by aneroid devices in many health care settings. Previous studies have shown that aneroid sphygmomanometers tended to be less accurate than their mercury counterparts, particularly with frequent or rough use. Because of this, Canzanello and colleagues undertook this study to determine whether the aneroid devices in their institution remained acceptably accurate under their existing maintenance program.
The study was done at the Mayo Clinic’s 2 principal inpatient facilities in Rochester, Minn. During a 4-month period, as part of the institutions’ routine maintenance program, 248 aneroid sphygmomanometers (17%) out of approximately 1500 devices that had replaced mercury sphygmomanometers over the previous 6 years were selected for study. Each device was visually inspected for damage and was replaced if it did not read 0 prior to testing. Canzanello et al used a digital pressure and vacuum meter, calibrated against a mercury sphygmomanometer, to test each aneroid device at 20 mm Hg intervals between 60 and 240 mm Hg.
Pressure values from the aneroid device were virtually identical over the pressure range tested (r = 0.99; P < .001), underestimating those of the reference device by a mean of 0.5 mm Hg (95% CI, 0.3-0.7 mm Hg). Virtually 100% of the values from the aneroid sphygmomanometers were within 4 mm Hg of those obtained on the reference device, which is the range recommended by the Association for the Advancement of Medical Instrumentation. Only 1 sphygmomanometer was replaced because of a resting reading different from 0. Canzanello et al concluded that the aneroid sphygmomanometers in clinical use at their institution, maintained according to institutional protocol, provided accurate pressure determinations when compared with a digital pressure and vacuum meter.
Although aneroid sphygmomanometers are widely used in clinical settings, including the ICU, the mercury sphygmomanometer has remained the gold standard for accuracy. Several studies have documented inaccuracies of potential clinical importance with aneroid devices that are not properly maintained.1,2 In one survey of general practitioners,3 only about half had serviced their sphygmomanometers within 1 year and one-fourth of the devices had never been serviced at all during a mean of 6 years of use. I am unaware of published studies of sphygmomanometers in use in the critical care setting, although there is no reason that use in that environment would not pose the same problems as elsewhere.
The good news is that, with a program of regular inspection and maintenance (in the case of Canzanello et al’s institution, once a year), aneroid sphygmomanometers are plenty accurate for clinical purposes. It is important to point out that only fixed, wall-mounted devices were included in this study, and one might expect more portable devices to receive more jars and jolts and hence be more likely to become inaccurate. Despite widespread direct monitoring of systemic arterial blood pressure via catheter-connected pressure transducers, indirect measurement using a sphygmomanometer remains an indispensable tool in the ICU. It is reassuring to know that replacement of mercury sphygmomanometers with their aneroid counterparts has not meant sacrificing accuracy, at least when the devices are properly inspected and maintained.
1. Bailey RH, et al. Arch Intern Med. 1991;151:1409-1412.
2. Mion D, Pierin AMG. J Hum Hypertens. 1998;12:245-248.
3. Hussain A, Cox JG. Br J Clin Pract. 1996;50:136-137.