Preoperative voiding detrusor pressures do not predict stress incontinence surgery outcomes

This study is a secondary analysis of data from the Stress Incontinence Surgical Treatment Efficacy Trial (SISTEr). In the original trial, 655 women were enrolled from February 2002 to June 2004. Details of the SISTEr study methods have been published previously [3] and are briefly outlined here. Inclusion criteria for enrollment included: (1) predominant SUI: stress > urge score on the Medical, Epidemiological and Social Aspects of Aging Questionnaire (MESA) [4], (2) positive stress test (observed leakage from the external urethral meatus coincident with a cough or Valsalva maneuver with a bladder volume ≤300 ml), (3) urethral hypermobility as evidenced by resting or maximum straining Q-tip angle >30° [5], (4) maximum cystometric capacity (MCC) ≥200 ml, and (5) postvoid residual (PVR) <150 ml. All study procedures were approved by the institutional review board of each participating clinical center and the Biostatistical Coordinating Center with written informed consent obtained from all women prior to enrollment.

Baseline urodynamic testing (free uroflowmetry, filling cystometry, and pressure-flow studies) were performed on all participants prior to surgery based on a standardized protocol implemented by all 20 urodynamic testers at the nine continence treatment centers. The SISTEr UDS protocol complied with terminology from the Standardization Committee of the International Continence Society [6] and technical recommendations from the Good Urodynamic Practice guidelines [7]. Standardized interpretation guidelines were used by on-site (local) physician reviewers. The details of our specific UDS Protocol and Interpretation Guidelines are available on the Urinary Incontinence Treatment Network website at http://​www.​uitn.​net/​resourcesforphys​icians.​htm. A Urodynamics Working Group supervised all aspects of urodynamic protocol development, procedural performance, and interpretation reliability [8, 9].

After standing filling cystometry, study participants sat to void for pressure-flow studies (PFS). For PFS pressure data to be considered valid, they had to satisfy the following criteria: (1) legible signals, (2) subject voided, (3) bladder pressure (p _ves) and abdominal pressure (p _abd) measuring systems properly functioning at PFS baseline and Q _max, (4) p _det at PFS baseline greater than −5 cm H₂O, (5) p _det at PFS baseline no more than 15 cm H₂O greater than p _det at MCC (insuring that change of position and transducer adjustment did not cause artifact in pressure measurement), (6) prevoid cough spikes demonstrated at least 70% agreement between the p _ves and p _abd signals (smaller spike at least 70% of the larger spike) [10] to demonstrate that the bladder and abdominal pressure transducers were functioning well, and (7) the local reviewer found no other reason to invalidate the study. For this analysis to be consistent with our other plausibility criteria, we also excluded all PFS with voiding detrusor pressure measures (ODP, p _det Q _max, or CDP) less than −5 cm H₂O.

We followed the methods used by Panayi et al. 2009 [2] to determine ODP and CDP, defining them as the detrusor pressure 1 s prior to the onset of flow and 1 s prior to cessation of flow, respectively, as recorded by the uroflowmeter. For ODP, to evaluate the appropriateness of the 1-s delay for the urine to flow through the urethra, emerge from the patient, and register on the uroflowmeter, we also recorded the highest detrusor pressure in the 1 to 5 s preceding the onset of flow on the uroflowmeter and how many seconds prior to flow it occurred. In more than 90% of the signals, the highest detrusor pressure in the 1 to 5 s preceding the onset of flow was equal to ODP at 1 s prior to onset of flow, and therefore, we only report ODP at 1 s for this analysis. Detrusor pressure at maximum flow (p _det Q _max) was recorded from the Q _max auto-annotation on each UDS signal. The reviewers were blinded to all outcome measures when the urodynamic data were extracted.

After-contractions are sometimes found as a pressure increase after flow ceases at the end of micturition [11]. The significance of this event is not understood, and there is no universally accepted definition. For the purpose of this review, we defined after-contractions as any detrusor pressure within 5 s of the end of flow greater than any detrusor pressure during flow.

Fifty arbitrarily selected urodynamic signals were jointly reviewed by the first and second authors for education, training, and clarification of definitions. Subsequently, a statistician (HL) randomly selected 22 signals for independent review to evaluate inter-rater reliability. A priori, 80% agreement was determined to be acceptable inter-rater reliability, and pressure measures with a numerical difference of 10% or less were considered the same since ≤10% differences in pressure are seldom clinically important. It was determined a priori that, if acceptable reliability could be established, a single interpreter would perform the remainder of the data extraction.

Success was evaluated at 24 months. Overall treatment success was defined as no self-reported SUI symptoms, a negative provocative standardized 300-ml stress test, no re-treatment for SUI, less than 15 g of urine on a 24-h pad test, and no leakage on a 3-day diary. Stress-specific success was defined as no SUI symptoms, a negative stress test, and no SUI re-treatment [12].

DO was defined as a urodynamic observation of involuntary detrusor contractions during the filling phase [6]. Preoperative DO was DO during the baseline UDS and postoperative DO was DO during UDS at the 24-month urodynamic visit. Since preoperative DO is likely to be associated with postoperative DO, in our analysis of postoperative DO, we performed two analyses, one excluding and one including subjects with preoperative DO.

Treatment of postoperative UUI was defined as treatment of clinically diagnosed new-onset or persistent UUI after the 6-week follow-up visit with any clinically acceptable treatment for OAB. This parameter was assessed at 3, 6, 12, 18, and 24 months.

Pelvic organ prolapse was assessed during preoperative physical examination using POPQ definitions [12, 13]. For this secondary analysis, we excluded subjects with pelvic organ prolapse past the introitus (stage 3 or 4) because prolapse could artificially increase pressures by causing urethral obstruction, and exclusion of prolapse subjects is consistent with previous literature evaluating the role of preoperative voiding detrusor pressures [1, 2].

The distributions of preoperative voiding detrusor pressure measures were assessed for normality. There was no strong evidence of deviation from normality, so independent sample t tests were used to test for differences in detrusor pressures by overall and stress success status, DO status, and UUI treatment status. Based on the number of subjects with and without postoperative UUI, there was at least 80% power to detect a difference in mean ODP values of 5 cm H₂O assuming that mean ODP of subjects with postoperative UUI was 13 with a standard deviation of 10 [14]. Pearson chi-square tests were used to test for relationships between categorical variables (e.g., after-contractions). Analyses were carried out using SAS statistical software Version 9.2 (SAS Institute, Inc., Cary, NC).