Measurement of residual urine volumes in women: Urethral catheterization or transvaginal ultrasound?

Abstract

The most practical and accurate method to measure residual urine volumes in women is yet to be determined. The practicality of transvaginal ultrasound in measuring the range of residuals typically encountered in a group of 100 symptomatic women attending for urodynamic investigations was tested and compared with urethral catheterization. Transvaginal ultrasound was found to be more comfortable, less invasive and quicker. In ideal circumstances for both techniques, mean time from voiding until residual assessment was 47 seconds for transvaginal ultrasound and 270 seconds for urethral catheterization. Transvaginal ultrasound was applicable to 99% of women, with accurate assessment of residuals possible in 96% (100% for urethral catheterization). Eighty-five percent of women were found to have a residual under the level of likely clinical significance (30 ml). Transvaginal ultrasound permits the avoidance of catheterization in these women. Transvaginal ultrasound allows for immediate retesting of the residual, a feature not possible if there is bladder drainage by urethral catheterization. Of the 22 women with residuals initially over 30 ml, 11 (50%) were able to lower this by an average of 69%, 7 (32%) of these to under 30 ml, with an immediate further attempt at voiding. In terms of practicality, transvaginal ultrasound is the method of choice for residual determination in the vast majority of women attending for urodynamic investigations. While it is not possible to directly compare the accuracy of the two techniques, a theoretical comparison is possible by summation of their respective sources of error. This comparison showed that the two techniques, in ideal circumstances, have similar accuracies over the range 0–175 ml. In non-ideal circumstances, urethral catheterization has more potential sources of error.