Accuracy with
without mercury

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The fact that blood pressure is still measured in units of millimeters of mercury shows how entrenched this unit is in clinical practice. The World Health Organization has permitted its continuing use at a time when the SI units have displaced other traditional units from quantitative measurement.

The millimeter of mercury remains, but what about the mercury sphygmomanometer? A recent report from the Medical Devices Agency in the United Kingdom allowed the continuing use of mercury, but recommended that alternatives be considered when blood pressure devices were being purchased. The Agency saw no clear successor to the traditional instrument, and required hospitals to introduce health and safety measures to deal with mercury spills.

The lack of a clear successor to mercury lay in the question of accuracy. Alternatives did exist, these being the aneroid and the automated devices. Aneroid devices are mechanical and can suffer from being knocked out of calibration. Automated devices are still far from perfect, as is illustrated by the main validation protocol which will accept devices that are in error by more than 10 mmHg in 25 percent of patients at a time when clinicians are asked to measure blood pressure to within 2 mmHg. Further, the joint publication from the European Society of Cardiology, European Society of Hypertension and European Atherosclerosis Society recommends that automated devices are not to be used when deciding clinical treatment.

A solution to the problem has arrived, the Accoson greenlight 300 sphygmomanometer This innovative device has been developed with technical and scientific support from the Regional Medical Physics Department in Freeman Hospital and Newcastle University.

The traditional mercury display has been replaced by a series of bright green LEDs clearly displaying pressure in steps of 2 mmHg, and for the first time the clinically important cuff pressure deflation rate is indicated. Most importantly the device self-calibrates to zero each time it is switched on, thus ensuring reliable accuracy and mimicking the comfort factor clinicians have been used to when a mercury column is on zero before taking a blood pressure measurement.

The Accoson greenlight 300 sphygmomanometer provides a highly accurate and reliable clinical instrument, eliminates the use of mercury, and enables the United Kingdom medical device industry to take a lead in this important area.


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