Hypothesis / aims of study
Voiding dysfunction can be due to bladder outlet obstruction (BOO) or detrusor underactivity (DU). In male above 50 years, BOO owing to Benign Prostatic Hyperplasia is the most frequent cause of voiding dysfunction. Nevertheless, there is not unusual that some of these patients have DU alone or coexisting with BOO. Up to now there is no treatment for DU. A complication of DU is urinary retention, either acute (AUR) or postmicturition voiding residual (PVR). The treatment of this complication is bladder catheterisation.
However, experimentally it has been demonstrated that BOO removing can improve bladder function (1). Moreover, in human Hamman et al (2). have shown that temporarily suprapubic bladder catheterization decreases PVR and increases urinary flow.
We hypothesize that bladder catheterization is not only a mean to overcome urinary retention, but that it may improve bladder contractility. Therefore, our aim is to investigate urodynamic changes during the voiding phase of male with DU undergoing bladder catheterization for urinary retention
Study design, materials and methods
Study design. Longitudinal prospective study
Material and methods.
We carried out a prospective study in a cohort of 64 males submitted to bladder catheterization because of urinary retention. The patients were submitted to a urodynamic study and we withdraw from the study 20 patients without DU. Other 6 patients were excluded for having neurogenic dysfunction and 4 for taking active drugs over lower urinary tract. It was offered to the remained 34 patients to continue with bladder catheterization and to undergo a second urodynamic study 12 months later. Seventeen patients, aged 77 ± 7,6 years (mean± standard deviation), accepted and were submitted to a second urodynamic study.
Sample size was calculated based on the data provided by OU et al (3). Assuming an increase in Pdetmax of 8 cm H2O, a standard deviation of 10 cm H2O, a statistical power of 80%, and alpha level of 5%, the minimum sample size was calculated at 16 patients.
Urodynamic study was performed in accordance with the specifications of the ICS and guidelines for Good Urodynamic Practice. Detrusor contractility was calculated using the Bladder Contractility Index (BCI) (PdetQmax + 5. Qmax), and urethral resistance using the Bladder Outlet Obstruction Index (BOOI) (PdetQmax – 2. Qmax). DU was defined as a BCI < 100
Interpretation of results
The increment of BCI confirm our hypothesis that bladder catheterization improves bladder contractility.
We also found an increment of BOOI. Although we cannot reject that the cause of this BOOI increase might be in relation with the catheter maintenance, the absence of a significantly opening pressure increasing, the increase of the Pdetmax and the significantly number of patients who urinated in the second study, allows us consider that the cause may be a masked BOO as a consequence that the underactive detrusor is not able to reach a sufficient bladder pressure to demonstrate a BOO.