Hypothesis / aims of study
The thinnest transurethral catheter compliant with international guidelines for good urodynamic practices is the 6F dual lumen. Although widely used, no consensus exists in the published literature regarding its impact on urinary flow parameters. Multiple other parameters including underlying patient pathology, voided volumes, position of void and patient inhibition may also affect flow rate. We have assessed the effect on flow rate of a 6Ch urodynamic catheter.
Study design, materials and methods
A prospectively collected database of video-urodynamic (VUDS) tests performed with a 6Ch dual lumen urethral catheter in a tertiary centre between 2016-2018 was screened for adult patients who voided a minimum of 150ml on free flow immediately before their VUDS. Data including demographics, position of voiding, free flow and video urodynamics parameters were collected. Participants were categorised according to their VUDS results into 4 groups:
1) normal pressure, normal flow void (N)
2) detrusor underactivity (DU)
3) bladder outlet obstruction (BOO)
4) impaired detrusor contraction with associated obstruction (DU/BOO).
Patients who voided off detrusor overactivity (DO), had non-diagnostic VUDS or incomplete data were excluded.
Paired samples t test and One-way ANOVA were used and statistical significance was determined as p<0.05.
Results
413 patients met the inclusion criteria. 39 (9.4%) were excluded as they did not have a representative void during their VUDS due to inhibition (36) or catheter related pain (3). A further 19 (4.6%) were excluded, as they were unable to void with the catheter in situ. Results were analysed for all patients as well as separately for male and female patients.
The remaining 355 patients (221 women and 134 men, mean age 52± 15y had a significantly higher mean maximum flow rate (Qmax) on their free flow Qmax= 21.7±10.9 ml/s compared to a Qmax= 14.9±8.3 ml/s with the 6F catheter in situ (p<0.001).
The mean voided volume on free flow was 298±137 ml, which was significantly smaller than the mean volume of 405±161 ml voided during their VUDS (p<0.001). 65 (18.3%) voided sitting during their VUDS, with a significantly reduced Qmax of 17.4±9ml/s compared to 22.4±9ml/s on the free flow.
Only minor differences were noted in the residual volumes at the beginning and end of VUDS, mean 90 and 86 ml respectively (p=0.57). Statistically significant differences were also noted in Qmax before and after catheterisation in 3 of the 4 patient groups in both women and men as detailed in Table 1.
Interpretation of results
The 6F catheter significantly influences urinary flow and might lead to inability to void in 5%. Overall, it lead to Qmax reduction of 32% compared to the free flow. Statistically significant differences were noted 3 of the 4 patient groups: normal pressure, normal flow void, detrusor underactivity (DU) and bladder outlet obstruction (BOO). The p value for the impaired detrusor contraction with associated obstruction group was 0.401, but only 3 patients were identified.