Equipment Errors: A Prevalent Cause for Fallacy in Blood Pressure Recording - A Point Prevalence Estimate from an Indian Health University

BACKGROUND: Blood pressure (BP) recording is the most commonly measured clinical parameter. Standing mercury sphygmomanometer is the most widely used equipment to record this. However, recording by sphygmomanometer is subject to observer and instrumental error. The different sources of equipment error are faulty manometer tube calibration, baseline deviations and improper arm bladder cuff dimensions. This is further compounded by a high prevalence of arm bladder miss-cuffing in the target population. OBJECTIVES: The study was designed to assess the presence of equipment malcalibrations, cuff miss-matching and their effect on BP recording. MATERIALS AND METHODS: A cross-sectional check of all operational sphygmomanometers in a health university was carried out for the length of the manometer tube, deviation of resting mercury column from “0” level, the width and length of arm bladder cuff and extent of bladder cuff-mismatch with respect to outpatient attending population. RESULTS: From the total of 50 apparatus selected, 39 (78%) were from hospital setups and 11 (22%) from pre-clinical departments. A manometer height deficit of 13 mm was recorded in 36 (92.23%) of the equipment in hospital and 11 (100%) from pre-clinical departments. Instruments from both settings showed significant deviation from recommended dimensions in cuff bladder length, width and length to width ratio (P < 0.001). Significant number of apparatus from hospital setups showed presence of mercury manometer baseline deviation either below or above 0 mmHg at the resting state (χ(2) = 5.61, D. F. = 1, P = 0.02). Positive corelationship was observed between manometer height deficit, baseline deviation and width of arm cuff bladder (Pearson correlation, P < 0.05). Bladder cuff mismatching in response to the target population was found at 48.52% for males and 36.76% for females. The cumulative effect of these factors can lead to an error in the range of 10-12 mmHg. CONCLUSION: Faulty equipments and prevalent arm bladder cuff-mismatching can be important barriers to accurate BP measurement.