Similar maximum flow rate decreases seen with two sling procedures

Beijing-Recent analyses of urodynamic testing data indicate that both autologous fascial pubovaginal sling and synthetic midurethral sling procedures decrease maximum flow rate and increase bladder outlet resistance, but the pubovaginal sling was found to create more bladder outlet resistance.

The analyses, based on data collected during Urinary Incontinence Treatment Network studies, provide insight into the mechanism of action of autologous fascial pubovaginal and synthetic midurethral sling procedures for improving stress urinary incontinence and highlight differences between them. Data were presented by first author Stephen R. Kraus, MD, at the 2012 International Continence Society annual meeting in Beijing.

The analyses were done using data collected in the SISTEr (Stress Incontinence Surgical Treatment Efficacy Trial) and TOMUS (Trial of Mid-Urethral Slings) studies. In SISTEr, women underwent pubovaginal sling (PVS) surgery with autologous fascia or Burch colposuspension and had urodynamic testing preoperatively and at 24 months after surgery. In TOMUS, women were randomized to undergo a retropubic or transobturator midurethral sling (MUS) procedure and had urodynamic testing preoperatively and at 12 months after surgery.

For the current analyses, statistical methods were used to control for possible bias associated with comparing urodynamic changes in two different patient populations enrolled in separate clinical trials.

Both the PVS and MUS procedures were found to decrease maximum flow rate during noninvasive uroflow (–5.7 mL/sec and –4.7 mL/sec, respectively) and during pressure flow study (–5.1 mL/sec and –2.1 mL/sec), and there was no significant difference between the procedures for either parameter.

However, analyses of data on voiding pressure at maximum flow and for bladder outlet obstruction index showed that while both

parameters were increased after PVS (11.8 cm H₂O and 20.5 cm H₂O, respectively) and after MUS (3.7 cm H₂O and 6.2 cm H₂O, respectively), the changes were significantly greater after the PVS procedure (p<.001 for both variables).

“Although we as urologists think we know about how sling procedures work in improving SUI, the real mechanism of action remains unclear. Comprehensive urodynamic testing using standardized methods was performed in both SISTer and TOMUS, allowing for analyses to investigate the mechanism of action of each sling procedure and also to compare the different sling procedures,” said Dr. Kraus, professor and vice chairman of urology at the University of Texas Health Science Center at San Antonio.

“The findings from the urodynamic analyses indicate that both PVS and MUS surgery increase bladder outlet resistance, but that the PVS procedure creates more bladder outlet resistance than MUS surgery.”

Statistically significant differences between the surgical groups were also found in analyses of cystometrogram volumes for first desire and strong desire. These parameters were also increased after both procedures, but the changes were 2.5- to 3-fold greater after PVS compared with MUS.

The analyses also showed that neither procedure was more likely to cause de novo detrusor overactivity (DO) or to resolve existing DO.

“The finding on de novo DO was a little bit of a surprise, as I would have expected the PVS procedure to be associated with more de novo DO,” Dr. Kraus told Urology Times.

He also noted that while the analyses show there are differences between PVS and MUS surgery in their effects on voiding function and storage, the study was not designed to explore how these differences impact clinical results.UT