Introduction: Bladder capacity (BC) is an important metric in the management of patients with classic bladder exstrophy (CBE) and is used to clinically estimate likelihood of continence and determine eligibility for continence procedures, such as bladder neck reconstruction. The Koff equation, which estimates BC from patient’s age has limited applicability in the exstrophy population. We sought to develop a model of maximum bladder capacities for those with CBE using readily available clinical variables.
Methods: An institutional database of CBE patients was reviewed for those who have undergone annual gravity cystogram 6 months after bladder closure. Linear mixed effects models with random intercept and slope were used to construct models predicting log transformed BC and were compared with adjusted R2, Akaike Information Criterion, and cross-validated mean square error. The final model includes outcome of primary closure, sex, log-transformed age at successful closure, time from successful closure, and interaction between outcome of primary closure and log-transformed age at successful closure as the fixed effects with random effect for patient and random slope for time since successful closure.
Results: In total, 369 patients (107 female, 262 male) with CBE had at least one BC measurement after bladder closure. Patients had a median of 3 annual measurements (range 1-10). The log bladder capacity increases with the age at cystographic evaluation. Other factors associate with capacity include sex, outcome of primary bladder closure, age at successful bladder closure and age at evaluation. A web based interactive CBE bladder growth nomogram (Figure 1) may be found at https://exstrophybladdergrowth.shinyapps.io/be_app/.
Conclusions: Using readily accessible patient and disease related information, the bladder capacity model in this study provides an accurate prediction of bladder capacity. Using clinical factors specific for the exstrophy population should be considered over age-based Koff equation estimates.
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