Accuracy of aneroid sphygmomanometers in clinical usage: University of Michigan experience

Aneroid manometers are frequently used to measure blood pressure. Aneroid manometers have moving parts that are subject to fatigue. The accuracy duration of the aneroid devices, like most digital devices, is unstudied. It has been accepted that if the aneroid device does not rest at '0' it is inaccurate, but how often is the device inaccurate when it does rest at '0'?

A Universal Biometer DPM-III measuring unit was used for all of the measurements at 10 University of Michigan Health System sites. A total of 136 aneroid manometers were tested. Two additional aneroid devices were not tested, as the needle did not start within '0'. Static pressure measurements were made at nine levels for all devices: 50, 80, 90, 100, 120, 150, 200 and 250mmHg.

The average difference of the nine pressure settings of the whole group was 0.2+/-0.31 (95% confidence interval 0.1-0.2) mmHg. The largest number of devices that were not calibrated within +/-3mmHg was seen at the 150mmHg setting with six (4.4%) of the devices failing. If an accuracy standard of +/-2mmHg was used, the largest number of devices failed at 250mmHg (22 devices, 16.2%). The largest number of devices that were inaccurate was manufactured 6 years prior to testing and was from two sites.

Aneroid devices were accurate. A yearly calibration programme should be performed and a +/-2mmHg standard should be used. Portable aneroid manometers may need to be more frequently calibrated due to the trauma associated with dropping.