Quantifying the effect of urodynamic catheters on urine flow rate measurement

Voiding efficiency in children is significantly impaired by the presence of the urethral catheter during pressure-flow studies

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.

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

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.

Piezoresistor-Embedded Multifunctional Magnetic Microactuators for Implantable Self-Clearing Catheter

Indwelling catheters are used widely in medicine to treat various chronic medical conditions. However, chronic implantation of catheters often leads to a premature failure due to biofilm accumulation. Previously we reported on the development of a self-clearing catheter by integrating polymer-based microscale magnetic actuators. The microactuator provides an active anti-biofouling mechanism to disrupt and remove adsorbed biofilm on demand using an externally applied stimulus. During an in vivo evaluation of self-clearing catheter, we realized that it is important to periodically monitor the performance of implanted microactuators. Here we integrate gold-based piezoresistive strain-gauge on our magnetic microactuators to directly monitor the device deflection with good sensitivity (0.035%/Deg) and linear range (±30°). With the integrated strain-gauge, we demonstrate the multi-functional capabilities of our magnetic microactuators that enable device alignment, flow-rate measurement, and obstruction detection and removal towards the development of chronically implantable self-clearing smart catheter.

A quantitative comparison between free uroflow variables and urodynamic data, and the effect of the size of urodynamic catheters on its interpretation

Objective

To assess the effect of the urodynamic catheter on the urinary flow rate and residual volume in various urodynamic diagnoses, and compare the outcome when using a smaller catheter, as the effect of this catheter on free uroflow variables is mostly studied in patients with bladder outlet obstruction (BOO) and little is known about its effect in other urodynamic diagnoses.

Patients and methods

In all, 319 men undergoing a pressure-flow study (PFS) with a 5 F filling and 5 F measuring bladder catheter were subdivided into three groups based on a urodynamic diagnosis, i.e. normal PFS (group 1), BOO (group 2) and detrusor underactivity (DU, group 3). Another group (4) comprised 61 patients who had a PFS with the filling catheter removed before the voiding phase. The effect of the catheters on the maximum urinary flow rate (Q_max) and the postvoid residual volume (PVR) was analysed statistically and compared among the groups. We also compared the free-flow variables with the clinical and urodynamic variables.

Results

Groups 1–3 (with two catheters) had a significantly lower Q_max and higher PVR than those voiding with one catheter (group 4). The reduction in Q_max was highest in group 3 (41.9%) and least in group 2 (21%). Group 4 showed no significant change in Q_max in cases with BOO and a normal PFS but a significant decline in those with DU (19.6%). The PVR was positively associated with the bladder capacity and negatively with detrusor contractility, but no association with a urodynamic diagnosis of BOO or any specific symptom.

Conclusion

Detrusor contractility was the strongest predictor of the obstructive effect caused by the catheter. This study justifies the use of a single 5 F catheter at the time of voiding, although that can also cause a reduction in flow in patients with DU.

The evidence for urodynamic investigation of patients with symptoms of urinary incontinence

Urodynamic studies are the gold standard to objectively diagnose dysfunction of the lower urinary tract. The widely available evidence for the clinical relevance is, however, fragmented. This article summarizes the published knowledge supporting the use of urodynamic studies in urinary incontinence in female, male and frail patients, as well as patients with relevant neurological disease. Five technological innovations are discussed briefly. Standard urodynamic cystometry can, on the basis of a solid body of evidence, objectively unveil the entire function of the lower urinary tract in all patients with urinary incontinence, regardless of the patients' perception of (ab-)normality of signs and or symptoms.