Hypothesis / aims of study
Urodynamic evaluation is often performed in the work-up of patients with lower urinary tract symptoms (LUTS). During filling cystometry, urethral pressure variations (UPV) can be observed if continuous intra urethral pressure measurement is performed. Continuous intra urethral pressure is technically not easy to measure, since the closed urethra during filling phase has no lumen like the bladder, the vagina or the rectum. In the period 1978-1996 various studies have described urethral pressure variations, and discussed whether this is an entity on its own, apart from detrusor overactivity. The International Continence Society (ICS) defined urethral instability in 1981 as urinary incontinence due to a sudden drop of urethral pressure. This definition is abandoned shortly after because this is a rare phenomenom. In a recent review was concluded that studies on this subject have a diversity in measurement techniques and materials. Urodynamic catheters with variation of one to six sensors in the urethra have been used in the literature. In the studies performed with multiple urethral pressure sensors, all sensors registered the urethral pressure variations simultaneously, they have however been best recognized at the point of maximal urethral pressure. If clinical relevance of urethral pressure variations is to be further examined, the demonstrating of this condition has to be widely applicable and research is needed to validate if single urethral sensor is as representative as multi sensor urethral catheters in diagnosing urethral pressure variations. Continuous urethra pressure measurement is usually performed with the use of dual microtip sensor urodynamic catheter with only sensor in the urethra. In our center, urodynamic studies have been performed with both the “standard” dual sensor catheter, as with a catheter with three urethral sensors. We present the results of a prospective study to compare the results of measurements with a single urethral sensor catheter with measurements with a triple urethral sensor catheter in demonstrating urethral pressure variations during filling cystometry.
Study design, materials and methods
This prospective observational intervention study was performed at the outpatient urology department of Leiden University Medical Centre between May 2016 and July 2018. All adult female patients, mentally fit to consent and requiring urodynamic evaluation for analysis of their LUTS were asked to participate in this study. All patients provided written informed consent. All patients underwent two series of filling and voiding cystometry. One serie was performed with the regular dual-microtip sensor urodynamic catheter positioned at the side of maximum urethral pressure. The other serie with was performed with a urodynamic catheter with three urethral sensors. At random was decided which type of catheter was used for the first filling series, the second measurement series was performed with the other type. Cystometry was carried out in a semi-upright sitting position with a continuous filling rate of 30-50ml/min. All urodynamic investigations were performed by the same specialized nurse according to ICS standard good urodynamic practices and terms 2016. Urethral instability (UI) in the measurement with single urethral sensor catheter was defined as urethral pressure drop exceeding 40 cmH2O. In the measurement with the triple urethral sensor catheter, urethral instability was defined as urethral pressure drop present in all three sensor measurements, with a pressure drop exceeding 40 cmH2O in at least one sensor measurement. Confidence intervals for correlation were calculated to a sample size of 76 patients.
Between May 2016 and July 2018, seventy-five consecutive patients enrolled in this study. The patients’ mean age was 54 years with a range of 19-90 years. In our study, the prevalence of UI is 33.3% (25 out of 75 patients). In 8 patients UI was seen in both single and triple urethral sensor catheters, in 14 patients only in the triple urethral sensor catheter and in 3 patients only in the single urethral sensor catheter. Prevalence of detrusor overactivity (DO) alone was in 17,3% (13 out of 75 patients). In 8 patients this was demonstrated in both filling cystometries, in 5 patients only during cystometry with single urethral sensor catheter. The combination of UI and DO was seen in 5 patients (6.7%).
Interpretation of results
Both urodynamic catheters are useful in the measurement of continuous urethral pressure during filling cystometry. The prevalence of UI is greater than the prevalence of DO in this series. If continuous urethral pressure measurement is omitted, a potential pathofysiological phenomenon is missed in 26,7% (20 out of 75) patients. The use of a triple urethral sensor catheter during filling cystometry was non-inferior to the single urethral sensor catheter in first sensation of filling.