A statistical study of the effects of urethral instrumentation on urine flow in women

Abstract

Data were obtained from a retrospective review of the records of 125 women who had undergone full urodynamic studies for a variety of clinical indications, to determine whether urethral instrumentation has an adverse effect on the parameters of urine flow in women. All patients had an initial urine flow study with a spontaneous void of at least 100 ml, after which they were catheterized to measure the postvoid residual urine. All patients then underwent urethral pressure studies, complex filling cystometry, pressure-flow voiding studies and urethrocystoscopy, after which they underwent another spontaneous non-instrumented urine flow study. Peak and mean flow rates were analysed statistically by blocked analysis of variance. The data were corrected for the effects of the volume voided by converting the flow rates into a nomogram percentile ranking using a computer program.

Statistical analysis indicated that peak flow rates increased from an average of 21.7 ml/s (SD±10.8 ml/s) before instrumentation to 24.3 ml/s (SD±10.5 ml/s) after instrumentation (P=0.0045). Mean flow rates also increased from 12.0 ml/s (SD±7.3 ml/s) before instrumentation to 13.3 ml/s (SD±7.3 ml/s) after instrumentation (P=0.0365). However, when these data were corrected for the effects of the volume voided, both the average peak nomogram percentile and the average mean nomogram percentiles were reduced, from 29.1% to 24.2% for the peak flow rate (P=0.0426) and from 32% to 27.9% for the mean flow rate (P=0.1019).

The corrected data indicate that both peak and mean flow rates are reduced in women following urethral instrumentation. The reduction in flow for peak flow rates is statistically significant. The reduction in mean flow rates did not reach this level of significance. This must be kept in mind when female patients are being evaluated for possible voiding disorders. Further prospective studies of the effect of urethral instrumentation on urine flow in women would seem to be indicated.