Changes in urethral resistance after surgery for stress urinary incontinence.

Seventy women with stress urinary incontinence underwent simultaneous voiding-urethrocystometry using microtip transducers and an 8-channel recorder, before and three to twelve months after either the modified Burch (48/70) or the modified Pereyra (22/70) retropubic urethropexy. Increase in urethral resistance (p less than 0.005) was more marked following the Pereyra procedure (0.042 +/- 0.039 to 0.07 +/- 0.061) and 30 percent experienced postoperative voiding difficulties, compared with the Burch procedure (0.035 +/- 0.029 to 0.055 +/- 0.03) where 20 percent experienced postoperative voiding difficulties. Of those patients who voided without a detrusor contraction prior to surgery (35/70), in 50 percent a detrusor contraction component developed to their voiding mechanism postoperatively (p less than 0.05) and overcame the increased urethral resistance with no postoperative voiding difficulties. In the remaining 50 percent a detrusor contraction failed to develop during postoperative voiding and 90 percent of them demonstrated reduced flow rates and increased use of Valsalva maneuver, and needed prolonged postoperative bladder drainage prior to resumption of spontaneous voiding (p less than 0.005). Inability to develop a detrusor contraction during voiding in face of increased urethral resistance promoted by the incontinence surgery provided a suitable explanation for post surgery voiding difficulties in 20 to 30 percent of patients.