Obstructive effect of a urethral catheter during voiding: Myth or reality?

Introduction: Whether or not the presence of a urethral catheter can provoke an obstructive effect during voiding remains a controversial subject. Using the Valentini-Besson-Nelson (VBN) mathematical micturition model, the purpose of this study was to compare the geometric effect of the urethral catheter in regards to the effect of other mechanical parameters likely to influence the voiding phase during a urodynamic study. Methods: The VBN mathematical micturition model was used to compute theoretical voidings. Starting from defined voiding conditions (Q°_max) such as V_ini = 300 ml, no catheter, normal detrusor contractility, and no urethral compression, we searched for relationships between changes in Q_max and the studied parameters: catheter diameter (F), detrusor contractility (k), and urethral compression (urac). results: A linearized approximation was obtained for both genders. The geometric obstruction due to the catheter was almost negligible for nonobstructed individuals compared with the volume effect up to a 6 Fr catheter size. Large decreases in Q_max resulted from impaired detrusor contractility or urethral compression. Higher effects resulted from concomitant decrease in detrusor contractility and urethral compression. Geometric effect of the catheter could lead to overestimation of bladder outlet obstruction in men. conclusion: A decrease in Q_max during voiding cystometrogram was found to be more often related to causes other than the catheter size, which, based on the VBN model, appeared to have a weak (almost negligible for nonobstructed individuals) effect, especially for small sizes (≤ 6 Fr).