Can Urodynamic Studies Identify Patients at Risk for Voiding Difficulty After Pubovaginal Sling? The “Voiding Quality Index”

INTRODUCTION

The role of urodynamic testing in the evaluation of women with symptoms and signs of “uncomplicated” stress urinary incontinence (SUI) is debatable. A large part of this debate focuses on the shortcomings of urodynamics in evaluating the storage phase and impacting treatment, particularly if a pubovaginal sling procedure is performed. A successful outcome following sling surgery is not just dryness. Patients should be able to void without obstruction and pain. To this end, a more critical evaluation of the urodynamic voiding phase is needed.

The predictive value of urodynamics in the determination of voiding dysfunction following pubovaginal sling is unknown. Several reports have implicated detrusor pressure (1) and/or poor urinary flow (2) as risk factors for voiding dysfunction. The results vary, perhaps as a result of different testing techniques or data analysis. An objective measurement assessing the quality of the voiding cycle that combines all parameters of the voiding phase may provide a more accurate reflection of emptying capacity. A “Voiding Quality Index” (VQI) calculated by a cumulative grade of each voiding parameter may enhance the predictive value and be more useful in identifying patients at higher risk of postoperative voiding dysfunction. Our objective was to determine if the VQI, a combination of voiding parameters, can predict prolonged catheter dependence after pubovaginal sling.

RESULTS

Sixty-six patients completed the study (mean age 61.5 years), while nine were excluded because of inadequate documentation. Multiple ancillary procedures included 17 anterior repairs, 6 vault suspensions, 5 hysterectomies, 5 anteroposterior repairs, and 1 posterior repair. There were no intraoperative sling-related complications.

The average catheter time following surgery was 11.1 days (range 1–106). The 50 patients who voided normally within 14 days were identified as the NR group and the 16 who experienced prolonged catheter dependence as the R group. Two patients who underwent sling incision at postoperative week 10 and 12, respectively, had good results. The other 14 resumed spontaneous voiding after 2 weeks. Table 3 shows the number of patients for each VQI score and number with urinary retention; a higher VQI score reflects better voiding quality.

When each voiding parameter was individually analyzed between groups with respect to catheter time, the mean values in each group demonstrated no predictive value. When analyzed between groups, the VQI was significantly lower for the patients who developed voiding difficulty (R) (Table 4). A questionnaire answered by these patients demonstrated an apparent discrepancy in the postoperative satisfaction (Table 5). Patients in the NR group were more likely to be satisfied.

DISCUSSION

Most pelvic surgeons would agree that a successful outcome after an anti-incontinence procedure is not achieved just by attaining dryness. Dryness must be achieved with minimal morbidity and normal urinary tract function. Voiding dysfunction following pubovaginal sling surgery can be a troublesome complication. Impaired contractility, Valsalva voiding, and decreased urinary flow rates have been associated with prolonged dependence on postoperative catheterization (5). Although most patients will resume normal voiding following anti-incontinence procedures, as many as 50% may experience some degree of postoperative voiding dysfunction (6). Thus, it is important to determine if preoperative urodynamic testing may predict postoperative voiding dysfunction by analyzing how patients void prior to surgery.

Carlson et al (7) reported on the value of urodynamics in women presenting with lower urinary tract symptoms (LUTS). Storage phase abnormalities were common in women with LUTS. Adding fluoroscopy detected additional voiding phase abnormalities in 33% of patients studied. This study revealed that women with LUTS are likely to have urodynamic abnormalities, particularly if fluoroscopic pressure-flow studies are performed. Voiding dysfunction may co-exist with stress urinary incontinence. Bradley and Rovner (8) reviewed the urodynamics in women with SUI and reported that 18% of women had urodynamic parameters for bladder outlet obstruction. The co-existence of voiding dysfunction and SUI is significant, as preoperative urodynamics may detect patients at risk for postoperative voiding dysfunction. Bhatia and Bergman (2,9) emphasized that urodynamics can be utilized to predict recoverability of normal voiding following Burch urethropexy. They demonstrated that uroflow and post-void residual urine cannot be relied upon to screen patients at risk for prolonged voiding difficulty (2). Patients voiding without detrusor contraction were at an increased risk. When the absence of a detrusor contraction was associated with impaired uroflow, the risk was magnified, as all patients exhibited voiding dysfunction (9). Similar findings have been reported in patients undergoing pubovaginal sling (10). Women who void without a detrusor contraction or with a weak detrusor contraction (less than 12 cm H₂O) are at risk for prolonged catheterization or retention (1). Patients categorized as Valsalva voiders had decreased subjective and objective cure rates following pubovaginal sling (11,12). These patients were also more likely to require pad usage postoperatively than patients who were not categorized as Valsalva voiders (13). These findings suggest that the preoperative voiding mechanics may facilitate identification of patients who are likely to be less satisfied following sling procedures. We devised the VQI with the rationale that a more objective assessment of voiding, combining all individual voiding parameters, may enhance the predictive value in detecting postoperative voiding dysfunction. As reflected in Table 4, when each voiding parameter was compared statistically with respect to catheter time, there was no statistical difference. However, when the VQI was applied to the urodynamic findings in these patients, there was a statistically significant difference. The average VQI in groups with prolonged catheter dependence was significantly lower than in those who did not develop retention (Table 4). The rate of prolonged catheter dependence ranged from 75%-100% in patients with a VQI of 0-1, and was approximately 10% in patients with a VQI of 4-5.

Catheter dependence is not the only symptom of voiding dysfunction in many patients. Those with catheter dependence greater than 14 days were less satisfied (81%) compared to those who used a catheter less than 14 days (98%). Although catheter free, women may be highly bothered by urgency symptoms or obstructive symptoms after a period of prolonged catheter dependence. Thus, patients with abnormal voiding mechanics appear more likely to have voiding dysfunction after sling surgery.

We note several limitations of this study. Many ancillary procedures were performed, and all were done by a single surgeon. However, many sling procedures are accompanied by prolapse repairs, making this relevant to the pelvic surgeon. The main limitations to this study are that reference values for “normal” female voiding are not clearly established by the literature. The authors chose to use data directly retrievable from the pressure-flow analysis, and the use of this formula compensates for this lack of normative voiding data by utilizing multiple components of the voiding cycle. Also, these data have not been applied to “mid-urethral” sling procedures, which are associated with less postoperative voiding dysfunction (13). Despite these limitations, we feel that the data suggesting that a VQI may be a more accurate measure predicting postoperative voiding dysfunction are compelling.

Presently, there is not enough evidence to suggest that urodynamic testing is necessary to identify stress urinary incontinence that will improve following surgical repair. A clinical evaluation, including a positive stress test, appears sufficient (14). Recent findings have revealed the potential of urodynamics to identify patients at risk for voiding dysfunction after pubovaginal sling. As we continue to develop our understanding of how women void, this predictive value of urodynamic testing ultimately may become more standardized. Considerable research is warranted in this area before the use of routine urodynamic testing is devalued in these patients.