Ultrasound assessment of postoperatpive residual urine volume improving accuracy through a new calculation method

ABSTRACT

Postmicturition catheterization is the usual method for assessment of postoperative residual urine volume. Ultrasonography, though non-invasive, comfortable and safe compared with catheterization, is still accused as being inaccurate. The present study attempted to revive the ultrasound method by improving its accuracy through the usage of the combined formulae for volume estimation of the ellipsoid utilizing the most reliable measurement parameters. One hundred and fifty postoperative female patients were investigated. The ultrasound-estimated volumes were compared with the actual volumes measured following catheterization. Nonsignificant differences were detected at volumes between 100 cc. and 300 cc. [P > 0.05]. Significant differences were detected at urine volumes below 100 cc. [P < 0.01]. Such error was not due to missing positive cases [sensitivity 100%], but was due to underestimation in 8.9% of cases with urine volumes larger than 100 c.c. [specificity 91.1%]. Similarly, though the sensitivity of ultrasound was 100% at volumes above 300 c. c, significant differences were detected between ultrasonography and catheterization [P < 0.05]. This was due to overestimation in 2.1% of cases with urine volumes less than 300 cc [specificity 57.9%]. Through the usage of the present calculation method, ultrasonography may, therefore, be considered an accurate method of estimation of postoperative residual urine volume