Free Uroflow Versus Pressure-Flow Urodynamic Outcomes: Does the Transurethral Catheter Cause a Measurement Artifact?

Abstract

INTRODUCTION:The effect of a transurethral catheter on urodynamic pressure-flow studies has been questioned, especially for patients with bladder outlet obstruction (BOO). The purpose of this retrospective study was to compare urodynamic outcomes measured during free uroflowmetry with pressure-flow studies using a transurethral catheter. METHODS:We retrospectively reviewed the records of 22 adult patients who had voided volume that did not differ by more than 20% during 2 assessments: free uroflow and pressure-flow with a transurethral 5 Fr catheter in situ. The outcome measures were maximum flow (Qmax), average flow rate, voiding time, time to Qmax, and flow acceleration. Free uroflow and pressure-flow outcomes were compared using paired t tests. A Bonferroni adjustment was applied; probability < .01 was considered statistically significant. RESULTS:There were 17 males and 5 females. The mean age was 39.9 years (range, 18-80 years). The urodynamic findings were reported as: normal (n = 6), hypocontractile detrusor (n = 5), BOO (n = 5), overactive bladder symptom complex (n = 4), and low pressure-low flow system (n = 2). Qmax was significantly higher during free uroflow than during pressure-flow recordings (P = .001). Average flow rate was also significantly higher during free uroflow (P < .001). Voiding time was significantly slower and acceleration was significantly faster during free uroflow (both with P = .001). There was no significant difference between recording conditions in the time to Qmax.CONCLUSION: There appears to be a significant decrease in some uroflow measurements with a 5 Fr urethral catheter in situ during pressure-flow studies, which is contrary to the previous claim that any catheter smaller than 6 Fr does not alter the results. This measurement artifact needs to be considered when interpreting urodynamic studies, particularly if the patient has BOO. To compensate for differences between the free uroflow rate and uroflow rate with a catheter, the free uroflow rate and detrusor pressure may need to be considered when evaluating the degree of BOO.UroToday International Journal ® UI J