Defining bladder outlet obstruction and detrusor underactivity in females with overactive bladder: Are we forgetting about the free uroflowmetry?

ABSTRACT

INTRODUCTION: Both detrusor underactivity (DU) and bladder outlet obstruction (BOO) can coexist in patients with overactive bladder. Definitions of both DU and BOO are based on pressure-flow study (PFS) data. However, invasive urodynamics study can differ from a natural micturition, in fact, discrepancies between free uroflowmetry (UFM) and PFS have been largely described. Our goal is to assess the correlation of free-flowmetry and PFS among patients with OAB and to evaluate how different definitions of DU/BOO are able to discriminate patients with different free UFMs. METHODS: A retrospective review of urodynamics performed at a single institution was conducted. Females with OAB who voided more than 150 mL in both UFM and PFS were included. Parameters from both voiding episodes were compared with nonparametric test. Two definitions of DU were applied; PIP1 Pdet@Qmax+Qmax < 30 and Gammie Pdet@Qmax < 20 cmH2 O, Qmax < 15 mL/s, and BVE < 90% (Bladder voiding efficiency). Also, two definitions of obstruction were chosen; Defretias Pdet@Qmax ≥25 cmH2 O and Qmax ≤ 12 mL/s and Solomon-Greenwell female BOO index ≥ 18. Patients who matched with each definition were compared to those who did not, to assess if any definitions were able to discriminate different noninvasive uroflowmetries. RESULTS: A total of 195 patients were included. Overall, mean age was 55 ± 12 years, 90.8% had mixed urinary incontinence, and 39% complained of at least one voiding symptom. Globally, Qmax and BVE correlated poorly between UFM and PFS, showing that most of the variation corresponded to a systematic error. Twenty-two individuals were found to have DU, they had a difference of 13 mL/s on both maximum flows. Fifty-four patients showed BOO, with a difference between their Qmax of 19 mL/s. Among the four definitions analyzed, only PIP1 and Defreitas were able to discriminate patients with actually a lower Qmax on the free UFM. CONCLUSIONS: Patients with overactive bladder seem to have a systematic discordance between the urine flow of the free and invasive studies. Current definitions of DU and BOO, which are based on the PFS parameters, are not consistently able to discriminate patients who actually void deficiently on the free UFM.