Impact of different sized catheters on pressure‐flow studies in women with lower urinary tract symptoms

Aims This study assessed the impact of two catheters on urinary flow in women undergoing a pressure/flow (P/F) study for lower urinary tract symptoms (LUTS). Materials and Methods Women who agreed to undergo urodynamic testing were assigned prospectively to a 7 or 9 Fr catheter in P/F study according to a balanced randomized block design. Exclusion criteria: urinary tract infection, bladder stone or tumor, neuropathy, complete urinary retention, inability to void with catheter in place, free flowmetry volume below 150 ml, and urine volume varying by more than 20% on both free and P/F studies. We compared free flowmetry and P/F flowmetry with a 9 Fr catheter in 126/239 patients (Group A) and with a 7 Fr catheter in 113/239 (Group B). We determined the differences in the P/F results in terms of pre‐voided bladder volume, clinical and urodynamic categories, and age groups in the two groups. We compared the diagnosis of obstruction based on Q max during the P/F study and on Q max in free uroflowmetry. Results In Groups A and B, the Q max rate was significantly less ( P < 0.001) in P/F studies. Catheter size did not impact significantly. In patients with cystocele, post‐void residue or obstruction flow was reduced more than in the other categories. Q max diminished with age, by about 15% in women aged 50–60 and by 21% in women over 70 years old. Conclusions Q max in P/F studies is always reduced independently of catheter size, volume of urine, age, and clinical or urodynamic category. This may have clinical implications when interpreting P/F results and in accurately diagnosing obstruction.