Pelvic organ prolapse can result in kinking of the bladder neck and bladder outlet obstruction. Surgical correction of anterior and/or apical prolapse results in an anatomic unkinking of the bladder outlet by realigning the bladder with the bladder neck and urethra, which in theory corrects anatomic outlet obstruction. The most commonly cited female obstruction nomogram was published by Blaivas and Groutz (2000) [1], which classified women into three grades of obstruction, based on the voiding detrusor pressure cutpoints of 57 and 107 cmH2O for differentiating mild, moderate and severe obstruction. However additional nomograms have identified much lower pressure cutpoints (20-25 cmH2O), and have included the addition of flow cutpoints (11-15 mL/s) and fluoroscopic criteria [Chassagne (1998), Nitti (1999) [2], Lemack and Zimmern (2000) [3], Defreitas (2004)]. What is not defined by these nomograms is the influence of large bladder capacity on voiding efficiency in the setting of bladder outlet obstruction and pelvic organ prolapse. To improve patient counseling in women with large capacity bladder considering prolapse repair, we sought to describe urodynamic (UDS) factors associated with the large capacity bladder in women who subsequently underwent anterior and/or apical prolapse repair at our institution over a 6-year period.

After obtaining IRB approval, we identified 592 sequential patient records, which contained anterior and/or apical prolapse repair CPT codes from the years 2009 to 2015. We identified 358 records from this group with possible pre-operative UDS CPT codes. Our data core exported additional demographics and ICD codes (28,744 data rows). A two-reviewer case-by-case retrospective chart review was performed for: additional demographics; UDS parameters; UDS tracings; pre-operative POP-Q stage; date of surgery; operation; date and volume of all post void residuals (PVR) after surgery. This revealed 266 women with verified pre-operative UDS followed by prolapse repair.

Our primary variable of interest was pre-operative bladder capacity at time of UDS.  Women were stratified by capacity, with the third tertile used to define large bladder capacity. Voiding efficiency (VE = voided volume / bladder capacity) was estimated before and after surgery using PVR and capacity. Our secondary variable of interest was longest follow-up PVR >200 mL, which was used to define elevated PVR after surgery. Comorbid covariates were identified by ICD code: any instance of diabetes, hyperlipidemia, neuropathy, obesity and urinary tract infection (UTI). Data were analyzed in SAS (Cary, NC, USA) using chi-square test, t-test, univariate and multivariate logistic regression, and Kaplan-Meier methods. A p-value <0.05 was defined as significant.

All 266 women (mean age 61 years) had preoperative UDS tracing, surgical and follow-up data available for analysis. Preoperative UDS revealed a mean: Pdet@Qmax 22 cmH2O (IQR 12-30), Qmax 18 mL/s (IQR 11-23), capacity 529 mL (IQR 370-659, σ=207), PVR 120 mL (IQR 5-160). The third tertile cutpoint for large capacity bladder was >600 mL (33%, n=88). Women with prolapse [POP-Q Stage: I (n=14), II (n=120), III (n=118), IV (n=14)] underwent anterior-only (n=115), apical-only (n=41) or combination anterior-apical (n=110) prolapse repair. Sling placement was performed in 56% (n=150) patients at time of prolapse repair. Comorbid conditions included diabetes (14%), hyperlipidemia (34%), neuropathy (6%), obesity (17%), and UTI (45%). Following prolapse repair, 239 out of 266 patients had a follow-up PVR recorded. There were a total of 519 PVR values recorded at up to 2,949 days (mean 395, σ=659) and 9 time points (median 2, IQR 1-3) after surgery. Mean PVR at longest follow-up was 66 mL (σ=120).

On univariate analysis, large capacity bladder >600 mL was associated with a younger age (mean 57 vs. 63 years; p<0.001) at time of prolapse repair. There was no significant difference in the proportion of large bladders with diabetes (p=0.508), hyperlipidemia (p=0.259), neuropathy (p=0.206), obesity (p=0.613) and UTI (p=0.387). POP-Q stage 3+ prolapse tended to occur in large bladders (57 vs. 46%; p=0.099). On UDS, large capacity (vs. <600 mL) had a mean: capacity of (763 vs. 413 mL; p<0.001), Pdet@Qmax (22 vs. 21 cmH2O; p=0.611), Qmax (20 vs. 17 mL/s; p=0.065), PVR (208 vs. 76 mL; p<0.001), VE (73 vs. 81%; p=0.027). There was no difference in prolapse stage or type of repair for large versus <600 mL capacity bladders. A similar proportion of large (vs. <600 mL) bladders underwent sling placement at time of prolapse repair (n=44/88 vs. 106/178; p=0.139). Follow-up PVR revealed a significantly elevated PVR in all patients with large bladder (23% >100 mL, p=0.038; 15% >200 mL, p=0.003; 11% >300 mL, p=0.001), however 44% of patients with a large (vs. <600 mL) bladder had a PVR improvement of >100 mL (n=39/88 vs. 50/178; p=0.008) on longest follow-up when compared to their pre-operative PVR.

In order to characterize changes in PVR over time and identify pre-operative patient characteristics associated with incomplete emptying after prolapse repair, longest follow-up PVR >200 mL was used to define elevated PVR after surgery. The 27 women with no recorded follow-up PVR were excluded from PVR analysis. On univariate logistic regression (Figure 1) for the response variable longest follow-up PVR >200 mL, the following factors were associated with elevated follow-up PVR:  UTI (OR 3.85; CI 1.36-10.90; p=0.011), capacity >600 mL (OR 3.74; CI 1.48-9.46; p=0.005), and pre-operative PVR >100 mL (OR 3.01; CI 1.21-7.47; p=0.018), >200 mL (OR 2.82; CI 1.10-7.28; p=0.031), >300 mL (OR 4.44; CI 1.54-12.90; p=0.006). Specific thresholds for pre-operative factors associated with longest follow-up PVR >200 mL included increased capacity (mean 647 vs. 518 mL), elevated pre-operative PVR (mean 231 vs. 105 mL), and poor VE (mean 66 vs. 80%). On stepwise backward logistic regression, our final multivariate model identified UTI (OR 3.74; CI 1.31-10.72; p=0.014) and capacity >600 mL (OR 3.64; CI 1.42-9.34; p=0.007) as independent factors associated with longest follow-up PVR >200 mL (AUC=0.727). Pre-operative capacity was assessed as a continuous variable, for the outcome longest follow-up PVR >200 mL, with a capacity cutpoint of 600 mL located at the left upper corner of the ROC (AUC=0.673). As a categorical value, the AUC was 0.658. To look at the association between time and longest follow-up PVR, we applied Kaplan-Meier cumulative incidence function methods (event = longest follow-up PVR >200 mL). Using this approach, UTI was associated with a higher proportion of patients with a PVR >200 mL at most recent follow-up, however the confidence interval included the null association (HR 1.81; CI 0.69-4.75). On Kaplan-Meier analysis for pre-operative capacity (Figure 2), a capacity >600 mL was significantly associated with a higher proportion of patients with PVR >200 mL at most recent follow-up (HR 3.60; CI 1.50-8.63).

Large bladder capacity >600 mL was associated with worse pre-operative PVR (mean 208 vs. 76 mL), poor VE (73 vs. 81%) and elevated PVR at longest follow-up (>100-300 mL). On multivariate regression, independent factors associated with longest follow-up PVR >200 mL were UTI (OR 3.74) and capacity >600 mL (OR 3.64). On Kaplan-Meier analysis, a capacity >600 mL was associated with a higher proportion of patients with PVR >200 mL at longest follow-up (HR 3.60).

In a woman considering anterior and/or apical prolapse repair, a large pre-operative bladder capacity >600 mL should raise the clinician's index of suspicion for ongoing incomplete bladder emptying following surgery.

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Lemack GE, et al (2000) Identifying women with outflow obstruction. J Urol 163:1823–1828