Pressure-flow studies in the diagnosis of bladder outlet obstruction: a study comparing suprapubic and transurethral techniques

Influence of transurethral catheters on urine pressure-flow relationships in males: A computational fluid-dynamics study

BACKGROUND AND OBJECTIVE

In the field of urology, the pressure-flow study (PFS) is an essential urodynamics practise which requires the patient's transurethral catheterization during the voiding phase of micturition to evaluate the functionality of the lower urinary tract (LUT) and reveal the pathophysiology of its dysfunctionality. However, the literature evidences confusion regarding the interference of the catheterization on the urethral pressure-flow behaviour.

METHODS

The present research study represents the first Computational Fluid-Dynamics (CFD) approach to this urodynamics issue, analysing the influence of a catheter in the male LUT through case studies which included the inter-individual and intra-individual dependence. A set of four three dimensional (3D) models of the male LUT, different in urethral diameters, and a set of three 3D models of the transurethral catheter, diverse in calibre, were developed leading to 16 CFD non-catheterized either catheterized configurations, to describe the typical micturition scenario considering both urethra and catheter characteristics.

RESULTS

The developed CFD simulations showed that the urine flow field during micturition was influenced by the urethral cross-sectional area and each catheter determined a specific decrease in flow rate if compared to the relative free uroflow.

CONCLUSIONS

In-silico methods allow to analyse relevant urodynamics aspects, which could not be investigated in vivo, and may support the clinical PFS to reduce uncertainty on urodynamic diagnosis.

The effect of a 6 Fr catheter on flow rate in men

Background:

The pressure-flow study (PFS) is considered the gold standard for the detection of bladder outlet obstruction (BOO) in men. However, several studies have raised the possibility that transurethral catheterization might have an obstructive effect on PFS while others did not.

Objectives:

To evaluate the effect of a 6 Fr transurethral catheter on the pressure-flow study and to evaluate its clinical implication in men.

Materials and Methods:

A retrospective chart review study of 515 men referred for an evaluation of lower urinary tract symptoms and who underwent an urodynamic study (UDS). Of those, 133 met our inclusion/exclusion criteria. Non invasive free-flow studies (NIFFS) were performed before every UDS. Cystometrogram and PFS were performed through a 6 Fr transurethral catheter.

Results:

The maximal flow rate (Q_max) was significantly higher (P < 0.001) in the NIFFS (15.0 mL/s (range 9.0-23.0)) than in the PFS (11.0 mL/s (range 7.0-18.5)). This difference became greater (18.5 mL/s (range 10.0-30.3) vs. 13.0 mL/s (range 6.0-25.0), in favor of the NIFFS) when we analyzed only the patients (n = 34) who voided a similar volume. According to the International Continence Society (ICS) nomogram, the use of the PFS alone would have resulted in the upstaging of 14% of cases (10/71) in the overall population and 24% (4/17) in the sub-analyzed group.

Conclusion:

A 6 Fr transurethral catheter significantly lowers the maximal flow rate by 4 mL/s. Its presence resulted in an upstaging on the ICS nomogram. However, further studies will be necessary to confirm this upstaging.

[Quantification of bladder-outlet obstruction in males: standard method vc VBN method]

GOAL

To compare the merits of two methods, standard (Abrams-Griffiths number, Schafer's classification, etc.) and VBN, to study bladder-outlet obstruction in men with benign prostatic hyperplasia (BPH).

MATERIAL AND METHODS

The parameters deduced from both methods and from repeated pressure-flow studies were computed for a population of patients with BPH. Correlation coefficients between standard and VBN parameters were systematically evaluated. Test-retest reliability and inter-rater reliability of the VBN parameters were investigated.

RESULTS

The VBN obstruction parameter was linearly corelated to the A-G number (R = 0.992) and thus is related to the provisional ICS obstruction nomogram. A simple modification to the standard index projected isometric pressure (PIP) yields an mPIP parameter strongly correlated with the VBN detrusor contraction-strength parameter (R = 0.962). VBN analysis reveals minor phenomena such as premature fading of the detrusor contraction to be responsible for much of the void-to-void variability of pressure-flow studies. Consequently, the primary VBN obstruction and contraction-strength parameters exhibit better test-retest and inter-rater reliability than the standard parameters and are less sensitive to changes in testing circumstances (bladder volume, urethral catheter size and psychological factors).

CONCLUSION

With the standard approach to test bladder obstruction, two values: A-G and mPIP, derived from pressure-flow studies, best qualify the patient's voiding status. These parameters are simple to calculate but are sensitive to testing variations and minor phenomena. The VBN approach is more complicated, but its parameters for obstruction and detrusor contraction strength are less dependent on testing variations.

A Novel, Inexpensive, Double Lumen Suprapubic Catheter for Urodynamics

PURPOSE

We describe a novel, double lumen, intravesical, suprapubic catheter designed to meet the requirements of pediatric urodynamics that is easy to use and has minimal complications.

MATERIALS AND METHODS

A commercially available 10Fr pediatric suprapubic pigtail catheter forms the outer lumen for instilling filling media. A 16 gauge epidural catheter is inserted through the outer catheter providing an inner lumen for measuring intravesical pressures. The resultant double-lumen catheter is inserted suprapubically using a peel away needle supplied with the 10Fr catheter, with the patient under general anesthetic.

RESULTS

The catheter has been used for 15 years in more than 700 patients with good reliability and few complications. The concentric construction of the double lumens and the rigidity of the inner intravesical pressure channel ensure there is no transmission of pressure from the filling channel to the inner lumen. The catheter has a circular cross section and a pigtail distal end which help to retain it within the bladder. There is low resistance to filling that allows adequate filling rates to be achieved by gravity rather than necessitating a pump. The catheter is easily made from readily available components and is less expensive than other double-lumen catheters suitable for suprapubic use.

CONCLUSIONS

A reliable, double lumen catheter that fulfills criteria not found in commercially available alternatives can be inexpensively made for urodynamics.

Effect of 6F urethral catheterization on urinary flow rates during repeated pressure-flow studies in healthy female volunteers

OBJECTIVES

To prospectively examine the effect of a 6F urethral catheter on the urinary flow rate in healthy women without lower urinary tract symptoms undergoing pressure-flow studies.

METHODS

Women between the ages of 30 and 70 years, without lower urinary tract complaints and without a history of surgery for incontinence, were recruited. All women completed the Urogenital Distress Inventory-6 questionnaire, and only women with mild or no symptoms were enrolled. After a free flow rate was determined, cystometry and pressure-flow studies were performed once and then repeated using a 6F urethral catheter. The peak flow rates during the first and second studies were compared with one another and with the nonintubated values.

RESULTS

Of the 59 women that applied, 20 volunteers (mean age 41.7 years) met the entry criteria and were evaluated. The mean nonintubated flow rate was 22.65 mL/s. With a 6F urethral catheter in place, our cohort had a mean peak flow rate of 16.25 mL/s on the first study and 15.25 mL/s on the second. A significant difference was demonstrated between the free and intubated peak flow rates for both the first (P = 0.0006) and the second (P = 0.0001) study. No significant difference was detected between the two intubated peak flow rates (P = 0.262).

CONCLUSIONS

Our data suggest that the presence of a 6F urethral catheter significantly reduces the maximal flow rate compared with free flow studies. Whether these findings represent a truly obstructive effect of the catheter, detrusor fatigue, or other possible effect of the catheter remains to be elucidated.

Evaluation of female lower urinary tract symptoms: overview and update

Female lower urinary tract symptoms are nonspecific, and a thorough clinical evaluation is required to establish the correct diagnosis. Such evaluation should consist of a structured micturition history or questionnaire, physical examination with full bladder, micturition diary, pad test and urodynamic evaluation. The urodynamic evaluation should consist at least of cystometry, detrusor pressure/uroflow study, simple ('free') uroflowmetry, assessment of the relative contribution of urethral hypermobility and intrinsic sphincter deficiency, and estimation of postvoid residual urine by ultrasound or catheterization. Recent studies regarding the role of pad tests, micturition diaries and urodynamic studies in the evaluation of female voiding dysfunction are presented. Factors that are associated with the use of transurethral catheter during pressure-flow studies and current controversies regarding the diagnosis of female bladder outlet obstruction are reviewed and discussed. Although the urodynamic study is considered to be the best diagnostic tool in assessment of lower urinary tract function, some practitioners believe that urodynamic evaluation is not routinely warranted and prefer to employ a symptom-based empirical management strategy. Lower urinary tract symptoms are nonspecific, however, and should be used mainly to identify what bothers the patient. Urodynamic studies define the underlying pathophysiology. We believe that treatment of the underlying pathophysiology facilitates better treatment of symptoms.

Pressure flow study data in a group of asymptomatic male control patients 45 years old or older

PURPOSE

The role of pressure flow studies in the routine evaluation of patients with benign prostatic hyperplasia remains a controversial issue in urological practice. There are little data on age matched asymptomatic control groups. We evaluated pressure flow findings in such a group.

MATERIALS AND METHODS

A total of 24 male patients 47 to 80 years old (mean age 62.5) attending a general surgical clinic were recruited for study after ethical committee approval. The volunteers had never sought medical attention for urinary symptoms and did not perceive themselves as having a urological problem. Volunteers were assessed by International Prostate Symptom Score (I-PSS) and Madsen symptom score, clinical examination, free uroflowmetry, post-void residual ultrasound, repeat pressure flow studies and transrectal ultrasonography. Pressure flow tracings were manually analyzed for standard urodynamic values and the degree of bladder outflow obstruction according to recognized International Continence Society, Abrams-Griffith nomogram, linear passive urethral resistance relation and urethral resistance factor classifications.

RESULTS

Median I-PSS was 2.0 (interquartile range 1.2 to 5.7). For I-PSS quality of life the median was 1.0 (interquartile range 0.75 to 2.0). On pressure flow studies 3 patients (13%) had unequivocal obstruction, 7 (29%) were in the equivocal area and 14 (58%) had no obstruction, while 15 (63%) had unstable contractions on medium fill cystometry.

CONCLUSIONS

The data show that a surprising number of apparently normal men are obstructed by commonly used criteria. This finding confirms asymptomatic obstruction, suggesting that obstruction may be less important in the development of symptoms than previously thought. Also, until the natural history of obstruction is more clearly defined surgery in obstructed asymptomatic patients is probably unwise.

Is there a clinically significant change in pressure-flow study values after urethral instrumentation in patients with lower urinary tract symptoms?

OBJECTIVE

To determine the effect of urethral instrumentation on pressure-flow study values and subsequent grading of bladder outflow obstruction (BOO) in men with lower urinary tract symptoms (LUTS) using suprapubic intravesical pressure monitoring.

PATIENTS AND METHODS

Seventy-two men with LUTS underwent pressure-flow study using suprapubic intravesical pressure monitoring. The urethra was then instrumented successively with a 12 F catheter and a 17 F cystoscope, and a further pressure-flow study recorded after each procedure. Standard pressure-flow variables were measured for the three recordings. The presence and degree of obstruction were determined using commonly recognized grading systems, i.e. the Abrams-Griffiths nomogram. the linear passive urethral resistance ratio (LPURR) and the urethral resistance algorithm (URA).

RESULTS

There were statistically significant differences in the detrusor pressure at maximum flow and detrusor opening pressure between the uninstrumented and instrumented studies (12 F and 17 F) but no difference in peak flow rates between the groups or in the Abrams-Griffiths number or URA value between studies. Using the LPURR, there was a tendency to a lower obstruction class after urethral instrumentation, ranking as 17 F > 12 F > no instrumentation.

CONCLUSIONS

The changes seen after urethral instrumentation represent no more than the biological intra-individual variation normally seen in pressure-flow studies and do not lead to a clinically significant change in obstruction class.