Introduction

Changes in pelvic floor as well as urethral anatomy and function occur with aging, which can result in prolapse and urinary incontinence. With more than 10,000 baby boomers turning 65 each day for the next 18 years, our health care system will be flooded with women presenting with pelvic floor prolapse and incontinence for years to come. Rates of incontinence and pelvic organ prolapse (POP) in women of this age demographic is estimated to be 30% to 94%, and 1 in 8 women may require surgical repair for POP or incontinence by their eighth decade, with a reoperation rate of 30%. Similarly, rates of stress urinary incontinence (SUI) range from 30% to 50% in the same age demographic. Urinary incontinence is reported to alter the quality of life (QOL) in 15% to 35% of adult American women. Aside from the socially debilitating impact incontinence has on patient’s lives, it also comes at a significant cost to health care systems. Urinary incontinence is thought to be responsible for at least 12.4 billion dollars of health care spending with about 400 million dollars attributable to urodynamics (UDS), at a cost of approximately 1000 US dollars per study. For many, UDS has become part of the standard workup for a woman presenting with incontinence although it is often not clear that the information gleaned from the study will contribute to determining treatment options, assist in patient counseling, or help predict outcomes. This article reviews the role of UDS in the evaluation of urinary incontinence and POP.

Historical background

In 1999, as an initiative of the National Institute of Diabetes and Digestive and Kidney Diseases and the National Institute of Child Health and Human Development, the Urinary Incontinence Treatment Network (UITN) was formed. The UITN is a group of 9 independent sites comprising Urologists and Urogynecologists at each site with a single coordinating center. The primary task of the UITN was to develop trials to evaluate treatment of urinary incontinence in women, with the major focus being on surgical treatment. Emerging from the UITN were 3 level-I randomized controlled trials dedicated to the treatment of SUI; the SISTEr trial (Stress Incontinence Surgical Treatment Efficacy Trial), TOMUS (The Trial Of Mid-Urethral Slings), and the ValUE (Value of Urodynamic Evaluation) trial. The primary aim of the SISTEr trial was to assess the efficacy of the Burch colposuspension (BC) compared with that of the pubovaginal sling (PVS), whereas TOMUS, designed as an equivalence study, compares the efficacy and safety of 2 minimally invasive midurethral slings: the retropubic transvaginal tape (RMUS) and the transobturator tape (TMUS). The ValUE trial was designed to examine the role of preoperative UDS in women undergoing anti-incontinence procedures. These trials are, today, among the most solid data available to urologists in the diagnosis and treatment of SUI and that is why their importance is stressed in this review although other critical articles in this arena are also equally emphasized.

Historical background

In 1999, as an initiative of the National Institute of Diabetes and Digestive and Kidney Diseases and the National Institute of Child Health and Human Development, the Urinary Incontinence Treatment Network (UITN) was formed. The UITN is a group of 9 independent sites comprising Urologists and Urogynecologists at each site with a single coordinating center. The primary task of the UITN was to develop trials to evaluate treatment of urinary incontinence in women, with the major focus being on surgical treatment. Emerging from the UITN were 3 level-I randomized controlled trials dedicated to the treatment of SUI; the SISTEr trial (Stress Incontinence Surgical Treatment Efficacy Trial), TOMUS (The Trial Of Mid-Urethral Slings), and the ValUE (Value of Urodynamic Evaluation) trial. The primary aim of the SISTEr trial was to assess the efficacy of the Burch colposuspension (BC) compared with that of the pubovaginal sling (PVS), whereas TOMUS, designed as an equivalence study, compares the efficacy and safety of 2 minimally invasive midurethral slings: the retropubic transvaginal tape (RMUS) and the transobturator tape (TMUS). The ValUE trial was designed to examine the role of preoperative UDS in women undergoing anti-incontinence procedures. These trials are, today, among the most solid data available to urologists in the diagnosis and treatment of SUI and that is why their importance is stressed in this review although other critical articles in this arena are also equally emphasized.

The role of UDS in the prediction of SUI severity

Aside from using history and clinical examination to determine the presence of SUI, clinicians rely heavily on UDS to help in not only determining the presence of SUI but also attempting to quantify its severity. Urethral dysfunction has been traditionally assessed with urethral pressure profile (UPP) (with maximal urethral closure pressure [MUCP] being the most common measure of UPP) and more recently by valsalva leak point pressure (VLPP). UPP may be a technically difficult parameter to measure consistently. VLPP may be easier to measure clinically; however, there is a lack of standardization of the types of provocative maneuvers used and the timing of VLPP assessment. In addition to the acknowledged technical difficulties in performing VLPP and MUCP, there have been concerns regarding their reliability and correlation with symptom severity. VLPP has only modest correlations at best with several incontinence questionnaires and with voiding diaries.

Data from the SISTEr trial indicated that VLPP did not correlate with several presumed (physical examination) indices of SUI severity, such as POP-Quantified stage, POP-Quantified Aa measurement, Qtip angle at rest and strain, and change in angle. Also, VLPP failed to correlate with UDS parameters (volume of first leakage, volume at first sensation, presence of detrusor overactivity [DO], maximum cystometric capacity [MCC], maximum flow rate [Q _max ], and detrusor pressure at maximum flow rate [pdet.Q _max ]). However, lower VLPP was associated with higher Q _max suggesting that although VLPP does not measure symptom severity, it may accurately assess urethral function. In this same study, higher body mass index was associated with a higher VLPP, thereby suggesting that over time, more patients who are obese may have compensated by strengthening their pelvic floor.

The supine empty bladder stress test (SEBST), which indicates a low threshold for leakage in the supine position and with an empty bladder, was expected to correlate with more severe forms of incontinence, lower VLPP, and MUCP. In 2010, data from TOMUS demonstrated that VLPP and MUCP showed only a moderate correlation to each other (r = 0.36, P <.001), and little to no correlation to the SEBST. Overall, the majority of the available data suggest that the ability of urodynamic urethral function tests to predict incontinence symptom severity must be questioned.

Urodynamic predictors of SUI outcome

MUCP and VLPP may not reliably predict SUI severity; however, their usefulness in predicting outcomes after treatment of SUI has been suggested for years. Historically, lower preoperative MUCP has been associated with higher failure rates, specifically when vaginal bladder neck suspensions or BC are performed. However, in a prospective randomized trial comparing the results of a modified BC with PVS for the treatment of SUI in women with urethral hypermobility and low pressure urethra (MUCP <20 cm H ₂ O), Sand and colleagues reported that MUCP does no affect the success of a PVS or modified BC, and overall, the 2 procedures had equivalent outcomes at 3 months. Similarly, MUCP testing was not found to predict treatment outcome in a randomized study of 60 women undergoing tension-free vaginal tape (TVT) or PVS procedures.

There is conflicting data regarding the role of VLPP in predicting stress-specific success of incontinence procedures, be it a vaginal suspension, PVS, or synthetic midurethral slings (MUS). For example, Chaiken and colleagues reported that VLPP findings were of little prognostic significance in predicting the surgical success of PVS (using VLPP to differentiate between intrinsic sphincteric deficiency [ISD] and urethral hypermobility). Rodriquez and colleagues investigated the ability of VLPP to predict outcomes after a distal urethral sling procedure. The questionnaire-based outcomes revealed similar success, bother, and symptoms regardless of preoperative VLPP. Conversely, other studies have shown that women with very low VLPP (<60 cm H ₂ O) were less likely to have a successful outcome after a MUS procedure compared with those with higher VLPP.

In the SISTEr trial, the impact of the presence of urodynamic SUI and VLPP on surgical success was studied. Patients with urodynamic SUI (which represented about 89% of patients) were 2 times more likely to have overall success compared with those who did not; however, this difference did not reach statistical significance. For both treatment groups (BC and PVS), there was no difference between mean VLPP values between surgical successes and failures, demonstrating that lower VLPP values did not portend worse overall outcomes. This finding is in contrast to results from TOMUS in which patients with more severe urethral dysfunction, as determined by lower VLPP, were more likely to have treatment failure following either TMUS or RMUS. Overall, women with a VLPP or MUCP in the lowest quartile were 2 fold more likely to have SUI 1 year after TMUS or RMUS procedures.

Although both VLPP and MUCP did seem to be predictive of treatment success, their role in determining which MUS procedure to recommend was not clarified in TOMUS. Rechberger and colleagues compared the efficacy of the RMUS with that of TMUS for SUI, specifically investigating the influence of preoperative VLPP on outcome. Using the Stamey incontinence questionnaire, the investigators reported that the efficacy of the 2 procedures is comparable; however, at 18 months, patients who have ISD, defined as a VLPP of up to 60 cm H ₂ O, fared better with an RMUS compared with a TMUS. Thus, although the role of urethral function testing remains somewhat speculative about determining which incontinence operation to recommend for SUI, credible available data suggest that patients with more severe sphincteric function seem to fare worse after MUS procedures.

Several investigators have studied the ability of pressure-flow studies (PFS) to predict the outcome after surgery for SUI. Wang and Chen conducted a study on 79 women undergoing TVT for SUI and concluded that women with normal preoperative PFS were more likely to have better QOL and pad test results compared with those with abnormal PFS as determined by Q _max less than 12 mL/sec and pdet.Q _max of 20 cm H ₂ O or more. This finding is in contrast to the findings of the UITN in which, among 280 women with PFS before BC or PVS procedures, opening detrusor pressure, pdet.Q _max , and closing detrusor pressures had no impact on improvement in SUI after surgery.

The presence of DO on preoperative UDS may affect surgical planning and preoperative counseling. Some investigators have reported that patients having both DO and SUI on preoperative UDS had a lower success rate (69% vs 97%) than those with only SUI following TVT. In contrast, Duckett and Tamilselvi also reported outcomes of patients undergoing TVT who had DO and SUI and found that both subjective and objective cure rates were similar to cure rates found in patients with SUI only. The investigators concluded that the presence of preoperative DO does not negatively affect efficacy. Similarly, in the SISTEr trial and TOMUS, baseline DO did not predict stress-specific treatment failure. As with most aspects of the field, the definition of success varied greatly between studies, making comparisons between studies quite difficult. Although conflicting data exist, the majority of evidence seems to suggest that, regarding SUI outcomes, the presence of preoperative DO does not predict treatment failure.

UDS predictors of retention and voiding dysfunction

One of the most disappointing outcomes of anti-incontinence procedures is the development of postoperative urinary retention and/or voiding dysfunction. Miller and associates sought to predict patients who would develop urinary retention after PVS for SUI. They found that 19% of patients who voided without a detrusor contraction developed urinary retention, compared with 0% of those who had a contraction preoperatively. Of the 655 participants in the SISTEr trial, 57 participants (8 BC and 49 PVS) developed voiding dysfunction (defined as the need for surgical revision to facilitate bladder emptying or the use of any type of catheter after the 6-week visit), with 19 (all PVS) requiring surgical intervention. There were no preoperative UDS findings that were associated with an increased risk of voiding dysfunction. In particular, preoperative voiding pressures and degree of abdominal straining were not associated with postoperative voiding dysfunction. Results from TOMUS showed a statistically significant difference in the development of voiding dysfunction between treatment groups at both the 12- and 24-month time points. At 12 months, patients who underwent RMUS procedure had a higher incidence of voiding dysfunction compared with those who underwent a TMUS procedure (2.7% vs 0%, P = .004). This disparity became even greater at 24 months with 3% of patients in the RMUS group reporting voiding dysfunction requiring surgical intervention compared with 0% of patients in the TMUS group ( P = .002). To date, no data have been published from TOMUS regarding preoperative UDS predictors of voiding dysfunction. Others have noted that patients with abnormal, preoperative noninvasive PFS (Q _max <15 mL/sec) and abnormal flow pattern can predict voiding dysfunction after TVT.

Urodynamic predictors of de novo or persistent urge urinary incontinence

Another disheartening outcome of anti-incontinence surgery is the development of urge de novo urinary incontinence. Panayi and colleagues found that opening pressure may play a role in the development of postoperative DO after TVT. The investigators found that median preoperative opening detrusor pressure was higher in women who developed postoperative DO. Alperin and colleagues studied clinical and UDS parameters of 200 women undergoing MUS procedure for treating SUI. In the final analysis, including 92 patients, 56% of patients with filling pdet greater than 15 cm H ₂ O (indicating abnormal compliance) developed de novo urge incontinence compared with 21% in patients whose pressure was lesser than 15 cm H ₂ O (odds ratio [OR] 4.6). The investigators concluded that preoperative UDS is necessary because it might identify those patients who have altered compliance and therefore, might be at increased risk of developing de novo urge incontinence after a MUS procedure. A secondary analysis from the SISTEr trial reported on the risk of urge urinary incontinence (UUI) after surgery for SUI. Overall, the presence of preoperative DO increased the odds of developing UUI. Specifically, patients with preoperative DO had an OR of 2.20 ( P = .030) of developing symptoms of UUI and an OR of 2.41 ( P = .008) of requiring treatment of those symptoms. Duckett and Tamilselvi reported that in patients undergoing TVT, an objective cure (as determined by cystometry) of DO was achieved in 47%, whereas a subjective cure of urgency symptoms was achieved in 63%, based on King’s Quality of Life Questionnaire in women with MUI who underwent TVT.