Discrepancies Between Direct and Indirect Blood Pressure Measurements Using Various Recommendations for Arm Cuff Selection

Abstract

Objective. The current recommendation for choosing an appropriate size cuff for measuring blood pressure (BP) is a bladder width to equal 40% of the upper arm circumference (UAC). However, most physicians use the older two-thirds or three-fourths upper arm length (UAL) recommendations to choose a cuff. The aim of this study was to verify the disparity in cuff size by using two-thirds UAL, three-fourths UAL, and 40% UAC criteria for cuff selection and to compare the indirectly measured BP by these criteria with directly measured radial intra-arterial BP. Methods. A prospective, cross-sectional, observational study was conducted in 65 hemodynamically stable patients, aged 5 days to 22 years. Direct BP measurements were obtained from a radial intra-arterial catheter. Indirect BP measurements were taken from the same arm as the arterial catheter with a mercury sphygmomanometer and standard-size arm cuffs. UAL and UAC of each patient were measured, and the 3 cuffs closest to two-thirds and three-fourths UAL and 40% UAC were used. For each cuff, 3 direct and 3 indirect BP measurements were taken. Student t test was used to compare mean systolic and diastolic BP for direct and indirect measurements. Results. A total of 172 observations were recorded, including 56 by two-thirds UAL, 55 by three-fourths UAL, and 61 by 40% UAC criteria. There was no significant difference between the means of the ideal cuff size by 40% UAC criterion and the actual cuffs used from the available standard cuffs. However, because of an unavailability of the larger cuffs for UAL criteria, the actual cuffs used were significantly smaller than ideal. Comparison of direct and indirect BP measurements revealed no significant difference in systolic BP when the latter was obtained by 40% UAC criterion. However, the difference in diastolic BP was significant. With available cuffs, a significant difference in systolic as well as diastolic BP was seen with both UAL criteria. Conclusions. Practitioners are likely to use significantly larger arm cuffs when following the two-thirds and three-fourths UAL criteria than when following the 40% UAC criterion. Of the 3 criteria for cuff selection, systolic BP by 40% UAC criterion most accurately reflects directly measured radial arterial pressure. However, the 40% UAC cuff significantly overestimates the diastolic pressure. Using available cuffs for indirect measurements by two-thirds and three-quarters UAL criteria significantly underestimates systolic as well as diastolic BP when compared with radial intra-arterial BP.