Quantifying the effect of urodynamic catheters on urine flow rate measurement.

INTRODUCTION 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.