In praise of mercury sphygmomanometers

BMJ 2001; 322 doi: https://doi.org/10.1136/bmj.322.7296.1248 (Published 19 May 2001) Cite this as: BMJ 2001;322:1248

Appropriate sphygmomanometer should be selected

  1. Alan Murray, professor of cardiovascular physics
  1. Freeman Hospital, Newcastle upon Tyne NE7 7DN
  2. Moulton, Northamptonshire NN3 7QP

    EDITOR—Users of mercury sphygmomanometers are being advised to consider alternatives, but this is causing problems. 1 2 Currently there is confusion over the advantages and disadvantages of the alternatives. The mercury sphygmomanometer, when used by trained staff, is the gold standard. Aneroid devices are also in widespread use, but they can be knocked out of calibration easily. These devices can be used, provided they are recalibrated every six months, but indications are that this advice is rarely taken.

    Automated devices are now readily available. The British Hypertension Society states that for these devices to be acceptable, no more than 25% of measurements should be in error by more than 10 mm Hg and no more than 10% by 15 mm Hg.3 Automated devices have a well accepted role in monitoring changes in blood pressure but a more limited one in determining absolute blood pressure. The combined recommendation of the European Society of Cardiology, the European Society of Hypertension, and the European Atherosclerosis Society is quite clear—automated devices are unsuitable as a routine substitute for the measurement of clinic blood pressure in the diagnosis of hypertension and not appropriate for determining the need for treatment and for assessing treatment efficacy.4

    Concerns have been expressed to the European Standards Committee for sphygmomanometers that the current degree of clinical accuracy required by the standard for automated devices is inadequate. Some would like to see noticeable improvements, but manufacturers will resist this strongly, simply because better accuracy cannot yet be achieved and, as O'Brien points out, the oscillometric techniques cannot measure blood pressure in all situations.5 Clinical users must decide when automated devices are appropriate and when they are not. We should not allow the argument that clinical staff are poor at taking manual measurements to influence decisions. Clinical staff can be trained.

    The looming difficulties over the measurement of blood pressure have been clear for some years. Recognising this, at the Freeman Hospital and the University of Newcastle, we developed a manual device in collaboration with a manufacturer of traditional sphygmomanometers. This modern electronic device is an accurate alternative to the mercury sphygmomanometer, with features to improve measurement technique and to provide automatic recalibration when switched on.

    Standards can help by weeding out poor quality devices but they do not recommend which devices should be used. A clinical decision must be made when selecting between manual and automated devices.


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    Electronic readings of blood pressure seem to be higher than readings obtained with mercury sphygmomanometers

    1. Jonathan Ireland, general practitioner (Jonathan.Ireland{at}gp-k83009.nhs.uk)
    1. Freeman Hospital, Newcastle upon Tyne NE7 7DN
    2. Moulton, Northamptonshire NN3 7QP

      EDITOR—Lawes writes of how he prefers mercury sphygomanometers to other blood pressure measuring devices.1 In view of the forthcoming rules regarding the use of mercury devices I performed a trial of a mercury compared with an electronic (Omron) device.

      Patients' blood pressure was checked with the electronic device followed by a mercury sphygomanometer to avoid the electronic reading influencing the observer. The left arm was used for all readings. Fifty one patients were checked in this way. In three cases the electronic device could not be made to record a measurement.

      In the remaining 48 patients the results were as follows. The mean (SD) readings with the mercury thermometer were: systolic 136.8 (23.7) mm Hg and diastolic 70.6 (11.1) mm Hg. The mean readings with the electronic device were: systolic 150.0 (23.1) mm Hg and diastolic 82.5 (13.7) mm Hg

      My partners and I are concerned that the electronic readings are higher than the readings obtained with the mercury sphygmomanometer. Blood pressure recording and the treatment of patients with pressures above 140/80 mm Hg occupy a considerable amount of our time and effort. If we switch to electronic measurement of blood pressure will we be increasing the amount of drug treatment used, and how valid will this be?

      I would be interested to hear if others have found that electronic devices give higher readings.


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