The aims of this study were twofold. A) To compare uroflowmetry parameters obtained during free uroflowmetry with those obtained during urodynamic pressure flow studies. B) To evaluate the effects of different size transurethral urodynamic catheters on pressure flow study parameters.

This was a prospective, randomized, comparative study. Inclusion criteria: Consecutive adult males ≥18 years presenting to urology outpatient with lower urinary tract symptoms who, after initial work up were planned for urodynamic pressure flow study. Exclusion criteria: i) Patients with active UTI, hematuria, Bladder stones. ii)) Any positive history of stricture urethra, neurological illness, bladder/ prostatic malignancy. iii) Any prostate, bladder, urethral, meatal surgery or any endourolgical intervention or prior pelvic surgery. iv) If taking drugs likely to affect micturition, which could not be stopped, v) failure to void or voided volume less than 150 ml on free uroflowmetry, vi) refused to give informed consent 
Eligible patients were randomized into one of two groups (Group 1, Group 2) using a computer-generated randomization table. No crossover was allowed after group allocation. Patients in group 1 underwent two urodynamic studies 45 minutes apart, one with a  5Fr catheter and the other with an 8Fr catheter. Patients in group 2 also underwent two urodynamic studies 45 minutes apart, but one with a 6Fr catheter and the other with an 8 Fr catheter. The order of catheter in group 1 (5Fr vs 8Fr) and 2 (6Fr vs 8Fr) were decided randomly. All urodynamic studies were performed in accordance with “Good Urodynamic Practice” recommendations of the International Continence Society. Those patients who i) could not void or voided less than 150 mL on urodynamic pressure flow study or ii) whose voided volumes in the free uroflowmetry and urodynamic pressure-flow studies varied by more than 30%, were subsequently excluded from study/analysis. Primary outcome measures for analysis included i)maximum flow rate (Qmax) ii) Pdet Qmax iii) Bladder outlet obstruction index (BOOI) and bladder contractility index (BCI). Statistical analysis was done with SPSS 20.0 (IBM SBSS20).

Of 184 patients screened, 128 patients were found eligible and were randomized to group 1 and 2 (64 each). Fourteen patients in each group were subsequently excluded leaving 50 patients in each group for analysis. The results are summarized in table 1 and 2.

All sizes of catheters used during pressure flow study (5Fr/6Fr/8Fr) significantly decreased Qmax when compared to Qmax obtained during free uroflowmetry. The impact of an 8Fr catheter was significantly more than a 5Fr or a 6Fr catheter with no significant difference between 5Fr and 6Fr catheter (Table 1) Similar results were noted for PdetQmax. An 8Fr catheter significantly increased PdetQmax when compared to either a 5Fr or a 6Fr catheter with no significant difference between 5Fr and 6Fr catheter. However, no significant upstaging was seen in terms of the number of patients who would be classified as true obstructed (BOOI index > 40) on using an 8Fr catheter when compared to a 5Fr or a 6Fr catheter. Similar findings were recorded using a cut off of 150 for BCI. (Table 2)

While catheters of different sizes significantly decrease Qmax when compared to free Qmax from a statistical standpoint, the catheter size (between a 5/6/8Fr) did not significantly alter the BOOI / BCI index and so all three catheter sizes would provide similar information to the clinician from a “urodynamically” obstructed or not obstructed standpoint.