Quantifying the effect of urodynamic catheters on urine flow rate measurement

The effect of urodynamic catheters on urine flow rate (Q max ) is well documented but under‐researched. Several studies show reduced Q max but methodologies and patient demographics differ. The aims of this study were to further quantify the effect of urodynamic catheters on Q max and to explore if this was consistent across different urodynamic diagnoses. Methods Four groups of 50 consecutive men attending for urodynamic studies (UDS) were retrospectively analyzed: Group 1 comprised 50 men with normal UDS, Group 2 was 50 men with BOO, and Group 3 contained 50 men with detrusor underactivity. Groups 1–3 had UDS performed using both 10 Fr filling and 4 Fr measuring catheters in situ. Group 4 comprised 50 men who had UDS performed with a smaller catheter assembly (8 Fr dual‐lumen). Values of Q max with and without catheters present were compared using paired Student's t ‐tests. Differences between groups were compared using ANOVA. Results Q max measured during UDS in men from Groups 1–3 showed a mean reduction of 38% compared to Q max from “free” uroflowmetry. ANOVA indicated this reduction was significantly greater among men with normal UDS. Interestingly the group who underwent UDS with a smaller catheter assembly showed no significant reduction in Q max measured with catheters in situ. Conclusion Our findings are in line with previous work suggesting that smaller calibre urethral catheters do not cause a significant obstructive effect during voiding. In addition it would appear that the reduction in Q max with larger urethral catheters in situ is greatest in those with normal urodynamics. Neurourol. Urodynam. 31:139–142, 2012. © 2011 Wiley Periodicals, Inc.