Aneroid sphygmomanometers are comparable to mercury sphygmomanometers in cost, technique and performance. However, some medical professionals hesitate to adopt aneroid blood pressure devices because of conflicting statements they have heard about aneroid gauge performance. This fact sheet addresses common perceptions about aneroid sphygmomanometers.
What are the concerns about aneroid sphygmomanometers?
Obtaining accurate blood pressure measurement is a foremost concern in the selection of sphygmomanometers. Once calibrated, there is no expected difference in performance between aneroid and mercury sphygmomanometers manufactured by reputable companies. All sphygmomanometers need routine calibration checks and regular preventive maintenance. The procedures are different for mercury and aneroid sphygmomanometers, but are otherwise equivalent in frequency, complexity and the amount of attention required. In practice, aneroid and mercury sphygmomanometers require different calibration techniques but otherwise proportionate amounts of attention.
Some medical professionals have concerns that aneroid sphygmomanometers are easily damaged during use, resulting in inaccuracy due to the device being dropped or bumped and knocked out of calibration. This is perceived to be less of a concern for mercury sphygmomanometers due to the mercury column's rigid mounting requirements. Because the mercury column must be perfectly vertical in its mounting and the mounting perpendicular to the floor for accuracy, most mercury devices are either wall mounted or mounted on robust mobile stands. Concerns about dropping aneroid devices can be alleviated by purchasing aneroid sphygmomanometers as either wall-mounted units or mounted on mobile stands, comparable to the mercury sphygmomanometers, rather than selecting portable aneroid devices. One manufacturer has also responded to these concerns by developing and introducing a gear-free aneroid sphygmomanometer that purportedly can fall 30 inches onto a hard surface and still remain accurate. (Welch Allyn)
Comparative Characteristics of Sphygmomanometers
Sphygmomanometers are introduced to the marketplace only after thorough testing and evaluation. Sphygmomanometers sold in the United States are regulated and must be approved by the Food and Drug Administration (FDA). The FDA approval process requires companies to show that new sphygmomanometers are substantially equivalent to models already on the market and to demonstrate accuracy through a clinical validation study. The FDA recognizes ANSI/AAMI SP-9 (a voluntary standard) as a performance standard and both aneroid and mercury sphygmomanometers meet this standard. This Standard covers functionality, accuracy and safety, including requirements and suggested tests to verify compliance.
Many United States hospitals have eliminated mercury sphygmomanometers. Hospitals interviewed in a recent survey reported that the alternatives perform satisfactorily. There are many more hospitals that have not completely eliminated mercury sphygmomanometers but have phase out programs underway. (EPA, HCWH)
Both mercury and aneroid sphygmomanometers require routine maintenance. Key issues for mercury gauges include: verify (and adjust if necessary) the zero level of mercury, replace air filter, verify that column is perpendicular in its unit and vertical to the ground, check for oxidation of mercury (making column appear dirty and difficult to read) and clean tube if necessary. Key issues for maintenance of aneroid gauges include: check needle for smooth rotation, and test accuracy at several intervals against a reference meter.
In addition to managing the maintenance and calibration of the sphygmomanometers themselves, hospitals that use mercury gauges must also maintain the capability to safely handle mercury and respond to a mercury spill. Mercury spill capability includes personnel trained to respond to a spill on a 24-hour, 7 day per week basis, a mercury spill kit, hazardous waste resources for decontaminating a spill area and removing the mercury, and the financial resources for the spill response and liability associated with mercury exposure.
Increasingly hospital Group Purchasing Organizations (GPOs) are voluntarily supporting pollution prevention efforts. Premier, a healthcare alliance collectively owned by more than 200 independent hospitals and healthcare systems in the United States (representing more than 1,500 hospitals and healthcare sites) recently announced it will no longer allow products containing mercury to be offered through any group contract, unless no viable alternative exists. This means that mercury sphygmomanometers will no longer be offered. Consorta, Inc, (a cooperative health care resource management and GPO, whose shareholders are Catholic-sponsored, faith-based or non-profit health systems) also has an effort underway to obtain shareholder approval to take mercury containing medical devices off their contracts.
Conclusions from National Medical Associations on Sphygmomanometers
- American Heart Association: "The aneroid manometer is also widely used and can provide accurate measurements if properly calibrated". (Perloff et al)
- American Heart Association: "… because of the risk of the toxic effects of mercury spills, mercury manometers must be handled carefully and their use has been discouraged in some areas of high traffic where accidental spills are more prone to occur." (Perloff et al)
- American Medical Association: "When in proper functioning condition, both mercury and aneroid sphygmomanometers are acceptable instruments for blood pressure measurement." (Bailey and Bauer)
- American Medical Association: "However, least clinicians be lulled into a false sense of security about the accuracy of the mercury column manometer, frequent examination of the instrument is necessary to eliminate it as a source of blood pressure measurement error." (Bailey and Bauer)
- Working Meeting on Blood Pressure Measurement: "…there is no reason to fear replacing mercury manometers with manual aneroid devices. The issue is ensuring validation, calibration, and regular maintenance." (Summary Report: National High Blood Pressure Education Program, "Equipment Calibration" discussion by Dr. Bruce Morgenstern, April 19, 2002)
References and Supplemental Information
Richard H. Bailey and John H. Bauer, "A review of common errors in the indirect measurement of blood pressure sphygmomanometry", Archives of Internal Medicine, December 27, 1993
This document reviews three sources of error in indirect measurement of blood pressure (observer bias, equipment, and lack of measurement standardization) and the effect of these errors on accuracy. It also reviews techniques for proper for blood pressure measurement.
EPA Region 1 Mercury Challenge Program
http://www.epa.gov/region01/assistance/neeat/mercury/Directory2000.pdf (accessed 1/13/03)
http://www.epa.gov/region1/pr/2001/apr/010428.html (accessed 1/13/03)
These references highlight mercury reduction activities in the New England region under the EPA's Region 1 Mercury Challenge program. About a year ago, the Mercury Challenge program was merged with EPA nationwide efforts under the Hospitals for a Healthy Environment Program (H2E).
"Guidance for Industry: Non-Automated Sphygmomanometer (Blood Pressure Cuff) Guidance Version 1", November 19, 1998
http://www.fda.gov/cdrh/ode/blprcuff.pdf (accessed 1/13/03)
This is the FDA requirement for manufacturers to obtain approval to introduce new sphygmomanometers.
Health Care Without Harm (HCWH), "A New Era: The Elimination of Mercury Sphygmomanometers"
http://www.h2e-online.org/pubs/news/sphygmo.pdf (accessed 1/13/03)
This publication discusses elimination of mercury sphygmomanometers in hospitals. It includes a table of hospitals that had eliminated mercury sphygmomanometers as of January 2002.
Dorothee Perloff; Grim, Carlene; Flack, John; Frohlich, Edward D.; Hill, Martha; McDonald, Mary; Morgenstern, Bruce, "Special Report: Human Blood Pressure Determination by Sphygmomanometry" [AHA Medical/Scientific Statement]
American Heart Association, Volume 88(5), November 1993, pp 2460-2470
http://www.americanheart.org/presenter.jhtml?identifier=3000894 (accessed 1/13/03)
This is the American Heart Association's recommendation for indirect measurement of blood pressure. It is a useful resource that includes potential errors in measuring blood pressure and ways to correct or avoid them.
"The Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure", National Institutes of Health, National Heart, Lung, and Blood Institute, NIH Publication No. 98-4080, November 1997
http://www.nhlbi.nih.gov/guidelines/hypertension/jnc6.pdf (accessed 1/13/03)
This document provides guidance for primary care clinicians.
Summary Report: National High Blood Pressure Education Program (NHBPEP)/National Heart, lung, and Blood Institute (NHLBI) and American Heart Association (AHA) Working Meeting on Blood Pressure Measurement. National Institutes of Health, April 19, 2002
http://www.nhlbi.nih.gov/health/prof/heart/hbp/bpmeasu.htm (accessed 1/13/03)
This working group meeting examined the science supporting current blood pressure measurement policies and sought to identify additional research needed to develop policies to improve blood pressure measurement.
Welch Allyn DuraShock Sphygmomanometer
http://rcs.welchallyn.org/productpg.nsf/intro/durashock?opendocument (accessed 1/14/03)
This web reference is a link to product information on a gear free aneroid sphygmomanometer that is more shock resistant than traditional aneroid sphygmomanometers. (There is no implied endorsement of the product).