Determining the reliability of ultrasound measurements and the validity of the formulae for ultrasound estimation of postvoid residual bladder volume in postpartum women

Abstract

Aims: To determine the reliability and validity of ultrasonic assessment of the postvoid residual bladder volume (PVRBV) in postpartum women.

Methods: Ultrasound estimated PVRBVs were performed on 99 consecutive women with postpartum urinary retention, to validate 12 published bladder volume-estimation formulae. This ultrasound-predicted volume was compared with the immediately collected catheterized volume. Comparison of individual formula with the catheterized volumes was performed by using the Intraclass Correlation Coefficient (concordance), and difference plots (bias, linearity of the difference). All volumes were transformed logarithmically to ensure a normal distribution.

Results: The postpartum bladder maintained its ellipsoid appearance. One-way analysis of variance showed the variance of the individual formulae ranged from 83.42 to 3463.66 (SD 9.13 to 58.85). The four formulae with the least variance had an intraclass correlation coefficient ranging from 0.93 to 0.96, and a mean difference between volume estimated by the formula and catheterized volume ranging from -0.05 to -0.11 (SD 0.09 to 0.11). The error between the value predicted by the formulae and that of the catheterized volume was linear in only one formula: Volume = (pi x W x Dl x H) / 6.

Conclusions: The results of this study have shown that ultrasonic assessment of the PVRBV in the postpartum period is accurate, and it can be used as a guide to whether transurethral catheterization is necessary.