BRIEF COMMENTS
Assessment of sphygmomanometers: a proposal for excellence in blood pressure measurement
Fernando Nobre; Eduardo Barbosa Coelho; Maria Eulália Lessa do Valle Dallora; Pio Antonio de Figueiredo; Ana Beatriz Fernandes Ferreira; Maria Alice Oliveira Ferreira da Rosa
Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto - Universidade de São Paulo, Ribeirão Preto, SP, Brasil
Mailing address
Key words: Measurement, Blood Pressure; Arterial Hypertension; Sphygmomanometers.
Introduction
Systemic hypertension is known to be a risk factor for cardiovascular events. Its high social burden accounts for approximately 40% of early retirements and work absenteism, and is a highly prevalent health problem in Brazil. Surveys conducted in some Brazilian cities show a 22.3% to 43.9% prevalence of hypertension (>140/90 mm Hg)1.
Diagnosis of hypertension is mandatory, since failure to treat hypertensive individuals is associated with increased cardiovascular morbidity and mortality, whereas antihypertensive treatment reduces the risks posed by hypertension2.
Indirect measurement, first described by Riva Rocci3, is the most frequently used technique for blood pressure (BP) measurement in the clinical practice; however, it depends on several factors in order to reflect the real behavior of this variable.
Despite the importance and standardization of techniques for BP measurement, studies show low health professional compliance to the systematization recommended3. Aspects related to the patients, health care professionals and conditions of the sphygmomanometers used - such as calibration, conditions and size of cuffs and inflatable bladders, conservation and functioning of bulbs, are fundamental for correct BP measurement4.
In light of these considerations, we believe the assessment of calibration and functioning of the sphygmomanometers in use at Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da Universidade de Sao Paulo (HCFMRPUSP) is necessary so that we can learn their current functioning conditions and further propose a continuous maintenance policy.
Objectives
To evaluate calibration and functioning of the sphygmomanometers in use at HCFMRPUSP.
Materials and Methods
First the Centro de Engenharia e Manutenção de Bio-equipamentos - CEMB (Bioequipment Maintenance and Engineering Center) made an inventory of the total number of sphygmomanometers in use in HCFMRPUSP. Next, their components and functioning conditions were analyzed: calibration; state of preservation of inflation bulbs and valves; sizes and characteristics of cuffs and lining fabric of the inflatable bladders. The ideal standard for the characteristics and functioning of sphygmomanometers was based on the guidelines of the American Heart Association5.
The assessment of calibration of the devices was made at CEMB, using a Y-tube against a K. Takaoka mercury-column manometer with scale from 0 to 300 mmHg. The assessment was made twice. Devices were considered out of calibration whenever a > 3 mmHg difference was found when the technique described above was used.
Results
All 358 sphygmomanometers in use at HCFMRPUSP were mercury-column devices. Seven of them (2%) were out of calibration. As regards the cuff size, 345 (96.3%) were only adequate for normal adults, whereas only three (0.8%) were adequate for small adults and nine (2.5%) for large adults. A total of 114 (32%) inflatable bladders were perforated.
The fabric that encases the cuff was torn in 103 (29%) of the 358 devices assessed. A total of 114 (32%) inflation bladders had defects and required replacement. As regards the inflation bladder valves, 64 (18%) were not working properly and required repair or replacement. The characteristics and functioning conditions of the 358 sphygmomanometers assessed are shown in Table 1.
Discussion
This study demonstrates that the calibration and functioning conditions of the sphygmomanometers in use at HCFMRPUSP are worse than desired.
All sphygmomanometers used at HCFMRPUSP are mercury-column devices, and this is consistent with the literature that suggests that this type of device is less susceptible to decalibration. Likewise, decalibration is known to be more easily detected in them. Mion et al6 evaluated 524 sphygmomanometers in use at Hospital das Clínicas da Faculdade de Medicina da Universidade de Sao Paulo (HCFMUSP) and in private medical offices in the city of Sao Paulo, and found 204 (49%) aneroid devices and 320 (51%) mercury-column devices. At HCFMUSP, of the 351 sphygmomanometers assessed, 315 were mercury-column devices. However, in private offices, of the 173 sphygmomanometers assessed, only five were mercury-column devices.
One aspect that should be pointed out in our study was the small number - only 2%, of devices out of calibration. In other studies, the percentage of sphygmomanometers out of calibration was higher, although almost all were aneroid devices7,8.
In order to keep the equipment in perfect functioning conditions, after this assessment we created a calibration seal and routine assessment of the general conditions of the components, with established dates for the next calibration and assessment. Thus, a regular policy for calibration and assessment of the sphygmomanometers in use at HCFMRPUSP is now effective.
Concurrently, we created a policy for users' awareness of the importance of sending the devices for checks even before the pre-established deadline, if necessary, aiming to have 100% of the equipment in ideal functioning conditions. To achieve this goal efficiently, we elaborated an assessment form for each piece of equipment, describing all their components (Table 2).
The use of a cuff smaller than necessary for the patient examined results in blood pressure overestimation, whereas the opposite situation will lead to blood pressure readings lower than real2. In this study, the size of 345 (96.3%) cuffs was adequate for "normal adults" (arm circumference between 27 and 34 cm). Only nine (2.5%) were adequate for "large adults" (arm circumference between 35 and 45 cm) and three (0.8%) for "small adults" (arm circumference between 20 and 26 cm)1. Considering the importance of the size of the cuff used, we supplied all areas of the hospital with sets of three cuffs to be used in normal, large and small adults. Thus, we ensured that proper cuffs were available in all sectors of this institution.
Defects were found in 68 valves (18%), 114 (32%) inflatable bladders, and also in inflation bulbs; these rates are unacceptable and lead to inadmissible BP reading errors. Other authors8,9 evaluated the functioning of sphygmomanometers in different situations and also found inadequate conditions. For this reason, assessment of calibration and functioning of these devices is mandatory.
None of the studies previously cited proposed the creation of systematic and continuing programs for the assessment and maintenance of these devices to ensure accurate BP measurements.
Our study encouraged and was used as a reference for the elaboration of the HCFMRPUSP's "Programa de Excelência em Medida da Pressão Arterial" - PEMEPA (Excellence in Blood Pressure Measurement Program), which we suggest be applied in other institutions, clinics and medical offices, with the following guidelines:
1. Determination of device characteristics
2. Continuing assessment of equipment calibration
3. Permanent assessment of functioning conditions of the sphygmomanometer components
4. Creation of an identification seal bearing the current and next assessment dates
5. Users' awareness for constant observation of the functioning of all components, regardless of the date scheduled for assessment.
6. Acquisition and use of cuffs with adequate characteristics for the arm size of the individual examined.
Equally important for blood pressure measurement are the procedures carried out by health care professionals. For this reason, as part of PEMEPA, regular updating courses on procedures for BP measurements were created.
In conclusion, this study demonstrated decalibration and other functioning problems in the sphygmomanometers in use at HCFMRPUSP, and this could lead to inaccurate BP measurements. These data were useful to find solutions for the defects identified, and also to create an excellence program for blood pressure measurement for HCFMRPUSP which could be further used as a reference for other health services in the country.
Acknowledgements
We thank the Administrative Board of Hospital das Clínicas da Faculdade de Medicina and HCFMRPUSP's Centro de Engenharia e Manutenção de Bio-equipamentos (CEMB) for their invaluable help.
Potential Conflict of Interest
No potential conflict of interest relevant to this article was reported.
Sources of Funding
There were no external funding sources for this study.
Study Association
This study is not associated with any post-graduation program.
References
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- 6. Mion D Jr, Pierin AMG. How accurate are sphygmomanometers? J Human Hypertens. 1998; 12: 245-8.
- 7. Bayle RH, Knaus VL, Bauer JH. Aneroid sphygmomanometers: an assessment of accuracy at a University Hospital and Clinics. Arch Intern Med. 1991; 151: 1409-12.
- 8. Cady CE, Pirralo RG, Grim CE. Ambulance sphygmomanometers are frequently inaccurate [abstract]. Am J Hypertens. 1996; 9: 107A.
- 9. Mion D Jr, Pierin AMG, Alavarce D, Vasconcelos JHC. The results of the campaign for evaluating sphygmomanometers accuracy and their physical conditions. Arq Bras Cardiol. 2000; 74 (1): 35-8.
Publication Dates
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Publication in this collection
13 Oct 2009 -
Date of issue
Aug 2009
History
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Accepted
13 Nov 2008 -
Received
15 July 2008 -
Reviewed
12 Nov 2008
