RESUMO
BACKGROUND: Little is known about the effect of catheterization during pressure-flow studies (PFS) on voiding efficiency in children. Our objective was to determine the effect of urethral catheterization on Qmax and flow index (FI) during PFS compared to the free flow of uroflowmetry (UF). METHODS: We retrospectively reviewed 63 consecutive children who underwent UF and PFS at our center on the same day (2019-2022). Voiding data was available for 46 patients. Patients first underwent a UF with full bladder, then PFS after urethral catheter insertion. Patients with urethral pathologies (n = 6), on clean intermittent catheterization (CIC) (n = 2) and with major comorbidities (n = 2) were excluded. Indications for UF/PFS were LUTS, recurrent UTIs, incontinence or neurosurgical pre-operative evaluation. Data was collected from the UF and the PFS and compared using paired t-test. The idealized Qmax and flow index (FI) were calculated for UF and PFS using the formulas described by Franco et al.: Male Qmax = 11.26 + 0.0701(TBC [total bladder capacity]) - 0.0000513(TBC); Female Qmax = 10.723 + 0.073(TBC) - 0.0000423(TBC), FI = Actual Qmax/Expected Qmax (Franco and et al., 2016; Franco et al., 2018; Franco and et al., 2016). RESULTS: Median age was 7 years old (IQR 5-11). Twenty-one (40%) patients were male and 32 (60%) patients were female. Of the 53 patients, 3 boys and 4 girls (n = 7; 13%) were unable to void with the catheter in place during PFS but able to void after its removal. Of the remaining 46 cases, the Qmax during PFS was 5 mL/s slower than the Qmax recorded on the UF without catheter, representing a decrease of 29% (12.3 vs 17.3 mL/s; p < 0.0001). The impact of urethral catheter during PFS was more important in males vs females (Qmax decreased by 7.7 vs 3.3 mL/s, or 45 vs 19%). The mean FI during PFS was 44%, which was a 30% reduction compared to the 74% FI obtained with UF (p < 0.00001). In males, the FI decreased by 37% on PFS, whereas it decreased 26% in females, similar to the Qmax decrease. CONCLUSIONS: Voiding efficiency, as assessed by Qmax and FI, is decreased during PFS compared to uroflow studies. Our data documents for the first time the impact of urethral catheterization on pediatric voiding efficiency. Abnormal flow rates and elevated PVRs should be used to guide patient management only if obtained by uroflow. Prospective validation comparing free flow with PFS studies will help characterize the impact of urethral catheter relative to bladder pathology, age, gender and catheter size used.
