Decreased maximum flow rate during intubated flow is not only due to urethral catheter in situ

We used the Valentini-Besson-Nelson (VBN) mathematical micturition model to analyze the potential obstructive effect of a 7-F transurethral catheter on the voiding process during intubated flow (IF) in women. Our hypothesis was that incomplete sphincter relaxation leads to residual sphincter pressure.

We reviewed a urodynamic database of women referred for evaluation of lower urinary tract dysfunction. Exclusion criteria were neurological disease or grade ≥2 prolapse. Eligible women underwent free uroflow (FF-1) before cystometry, an IF (7-F urethral catheter), and a second FF (FF-2) at the end of the session. Interpreted flows were restricted to voided volumes ≥100 ml and continuous flow patterns. Analysis of FF and IF was made using the VBN model.

Among 472 women, 157 met the inclusion criteria. The effect of the urethral catheter was geometric only in 60 (38.2 %) patients. An additional effect, identified as incomplete sphincter relaxation, was observed in 97 (61.9 %) patients. Among this second group, the same residual sphincter excitation was found for 30 (30.97 %) patients during FF-2.

When comparing IF with FF with the VBN model, the decrease in maximum flow rate (Q(max)) did not appear to result only from the geometric effect of the catheter but from incomplete sphincter relaxation during voiding, possibly because of patient's anxiety or a urethral reflex induced by the presence of the catheter. These findings emphasize the need to perform an FF before the IF to strengthen the reliability of conclusions of a urodynamic investigation.