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ORIGINAL RESEARCH |
From the Division of Urogynecology, Department of Obstetrics and Gynecology, Brown University School of Medicine, Providence, Rhode Island.
Address reprint requests to: Deborah L. Myers, MD 100 Dudley Street Providence, RI 02905 E-mail: dmyers{at}wihri.org
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Abstract |
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Methods: One hundred seventy-three women with urinary incontinence were evaluated prospectively by complete urodynamic studies. After catheterization, the pediatric Foley catheter test was performed on an empty bladder by withdrawing the inflated bulb of an 8-French Foley catheter through the urethra. The test was considered positive if the inflated catheter bulb could be withdrawn completely through the urethra. Women with grade 3 genital prolapse or higher were excluded. Intrinsic sphincter deficiency was defined as the presence of genuine stress incontinence and low maximum urethral closure pressure (at most 20 cm H2O).
Results: Seventy-six of 173 women (44%) had positive tests and 97 (56%) had negative tests. Seventy-six percent of those with positive tests were diagnosed with intrinsic sphincter deficiency, compared with 19% in women with negative tests (P < .001). All women with positive tests and negative cotton swab tests had intrinsic sphincter deficiency. The sensitivity, specificity, and positive and negative predictive values for diagnosing intrinsic sphincter deficiency were 76, 81, 76, and 81%, respectively.
Conclusion: A positive pediatric Foley catheter test in the absence of urethral mobility strongly suggests intrinsic sphincter deficiency. The pediatric Foley catheter test may be useful in screening for intrinsic sphincter deficiency.
Intrinsic sphincter deficiency is defined as the presence of a urethral sphincter mechanism that fails to maintain sufficient resistance for urinary continence either at rest or in the presence of minimal physical exertion.1 Its diagnosis can be difficult because standardized criteria to define the condition have not been established. Both low urethral closure pressure2 and low leak point pressure3 have been used; however, precise cutoff values have not been established and there is no correlation between the two measurements.4 In patients with low urethral closure pressure, standard anti-incontinence surgical procedures such as retropubic urethropexies are associated with a higher failure rate compared with patients who have normal closure pressure.5 Therefore, when evaluating women with stress urinary incontinence in the office, it is important that providers who do not have direct access to urodynamic testing be able to screen women for intrinsic sphincter deficiency and refer them to a physician specializing in the management of female urinary incontinence.
Identification of high-risk clinical factors has been used as a screening test for intrinsic sphincter deficiency.6 However, only one clinical characteristic, age over 50 years, was identified as an independent risk factor for intrinsic sphincter deficiency. The empty supine stress test7 is also useful in screening, but its precise relationship to urodynamic measures of urethral resistance, urethral closure pressure, and Valsalva leak point pressure is not clear.8 Another test described in the literature to assess the function of the urethral sphincter uses pull-through of the inflated bulb of a pediatric Foley catheter through the urethra.9 However, the efficacy of the test was not reported. The purpose of the present study was to evaluate the pediatric Foley catheter test as a screening method for intrinsic urethral sphincter deficiency.
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Materials and Methods |
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Each subject was evaluated by history, focused neurologic and urogynecologic examination, cotton swab test, urine culture and sensitivity, and multichannel urodynamics. Complex urodynamic assessment was performed using a Dantec UD 5500 (Dantec Inc., Copenhagen, Denmark). After uroflowmetry and catheterization of the bladder, the transurethral pediatric Foley catheter test was performed in the following manner. With the subject in the supine position, an 8-French pediatric Foley catheter was placed into the empty bladder and the bulb inflated to 1 mL using a tuberculin syringe. No anesthesia was used. Using gentle manual traction, one attempt was made to pull the bulb through the urethra. Two criteria were used to standardize the pull strength: subjects should report minimal discomfort as the catheter was being withdrawn, and the elastic rubber catheter should not stretch as it was being pulled. The pediatric Foley catheter test was considered positive if the catheter could be withdrawn completely through the urethra. The reproducibility of the test was assessed in 53 women randomly selected using a table of random numbers. A second observer who was unaware of the results of the first pediatric Foley catheter test performed retesting. The reproducibility for the pediatric Foley catheter test in determining a positive test as measured by the kappa statistic was 0.78 [95% confidence interval (CI) 0.68, 0.83].
Then multichannel cystometry, urethral profilometry, and Valsalva leak point pressure measurement were done. All testing was performed in the sitting erect position in a Century birthing chair (Century Mfg. Co., Tampa, FL). A Millar 8-French dual microtip transducer (Millar Instruments, Houston, TX) was used for the multichannel urethrocystogram and urethral profilometry. The urethrocystogram was performed using sterile water at 22C at a filling rate of 50 mL/min. Provocative measures such as water stimulation and cough were used to provoke detrusor instability. Urethral profilometry was performed with the dual microtip sensor positioned at 9 o’clock using a mechanical puller at a rate of 1 mm/second. Both static and dynamic (coughing at maximum effort) profiles were performed at cystometric capacity (with a minimum bladder volume of 200 mL). Maximum urethral closure and functional urethral length was assessed by averaging over three profiles. Leak point pressure measurements11 were recorded at maximum bladder capacity with an 8-French Millar catheter placed in the bladder. The resting vesical pressure was recorded. Then, the periurethral area was swabbed dry, and the subject was asked to "bear down while holding your breath, as if you were trying to make a bowel movement." The precise instant that fluid was observed at the external urethral meatus was recorded as the straining vesical pressure. The difference between the resting and the straining vesical pressure was designated the Valsalva leak point pressure. If the Valsalva alone did not cause leakage, the subject was asked to cough incrementally, and the lowest vesical pressure to cause leakage was recorded as the leak point pressure. The average of two Valsalva leak point pressure measurements was obtained.
Genuine stress urinary incontinence was diagnosed if the woman had involuntary leakage of urine concurrent with cough or Valsalva maneuver, in the absence of detrusor contraction.12 Intrinsic urethral sphincter deficiency was diagnosed if the woman had genuine stress urinary incontinence and a maximum urethral closure pressure of 20 cm H2O or less.5 Detrusor instability was diagnosed if a woman had symptoms of urge incontinence and objective demonstration of a bladder contraction and urinary leakage, spontaneously or on provocation, during cystometry when she was attempting to inhibit micturition.12 Low Valsalva leak point pressure was defined as a Valsalva leak point pressure less than 45 cm H2O in the sitting position with a subjectively full bladder.13
Demographic data on age, parity, weight, prior surgery, and estrogen status were collected. Women were classified as hypoestrogenic if they had undergone spontaneous or surgical menopause, were not on hormone replacement therapy, and had vaginal atrophy. Subjects were divided into two groups based on the result of the pediatric Foley catheter test. Data were analyzed using SAS (SAS Institute Inc., Cary, NC). We summarized age, weight, parity, and testing results using means and standard deviations and then compared the two groups using the two-sample t test for independent samples. Estrogen status, prior surgeries, and diagnoses were summarized using proportions, then the 
2 test was used to compare the two groups. Two-by-two contingency tables were constructed based on the results of the pediatric Foley catheter test and measurement of maximum urethral closure or Valsalva leak point pressure, and test indices calculated. Exact 95% confidence intervals (CI) for proportions were calculated.
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). There was no significant difference in parity, weight, estrogen status, or proportion of prior hysterectomies.
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). There was no significant difference in maximum cystometric capacity and mean Valsalva leak point pressure measurements between the two groups. The range of maximum cystometric capacities in all women was 411–502 mL.
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). There was no association between a positive pediatric Foley catheter test and the presence of genuine stress incontinence and low Valsalva leak point pressure. The number of women with detrusor instability was similar in the two groups.
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Based on maximum urethral closure pressure values and presence of genuine stress incontinence, 76 of the 173 women (44%, 95% CI 37%, 51%) were diagnosed as having intrinsic urethral sphincter deficiency. All test indices (sensitivity and positive predictive value of a positive pediatric Foley catheter test and specificity and negative predictive value of a negative test) were higher when we used maximum urethral closure pressure to define intrinsic sphincter deficiency compared with Valsalva leak point pressure. For the diagnosis of intrinsic sphincter deficiency, the false-positive (a positive pediatric Foley catheter test in the absence of intrinsic sphincter deficiency) rate was 18.5% (95% CI 11%, 26%) and the false-negative (a negative pediatric Foley catheter test in the presence of intrinsic sphincter deficiency) rate was 24% (95% CI 14%, 34%).
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Discussion |
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There are also no standardized criteria for measuring leak point pressure.14,15 In the absence of standardized criteria and for the purpose of this study, we defined intrinsic sphincter deficiency as the presence of genuine stress urinary incontinence with a maximum urethral closure pressure of 20 cm H2O or less.2,5 This definition has its limitations because some studies have reported that patients with maximum urethral closure pressure of 20 cm H2O or less may not be at risk for failure of standard anti-incontinence procedures.17,18 Nevertheless, using this definition, we found a correlation between the pediatric Foley catheter test and intrinsic sphincter deficiency. This correlation is similar to the findings reported by Lobel and Sand7 for the empty supine stress test, who also used the same definition for intrinsic sphincter deficiency. Similar to the supine stress test, presence of a positive pediatric Foley catheter test and lack of bladder neck mobility was almost diagnostic of intrinsic sphincter deficiency.7
We also examined the association of the pediatric Foley catheter test with leak point pressure, because some recent studies favored defining intrinsic sphincter deficiency in terms of leak point pressure.19,20 When we considered the diagnosis of intrinsic sphincter deficiency based on presence of genuine stress urinary incontinence and low leak point pressure, an association with the pediatric Foley catheter test results was not seen. This lack of an association may have been due to our technique of measuring leak point pressure. We measured leak point pressure at capacity using the technique of Swift and Ostergard.11 We defined low Valsalva leak point pressure as 45 cm H2O or less based on values reported by Versi13 for a full bladder. However, our technique of measuring leak point pressure may not have been optimal because maximum bladder capacity can vary from patient to patient. In our study, the range of measurement of maximum bladder capacity was small (400–500 mL) with a narrow standard deviation (73 mL). Nevertheless, this may have accounted for the lack of association of the pediatric Foley catheter test with leak point pressure. Another explanation for this finding is that the leak point pressure is a dynamic measure of urethral opening pressure under stress (such as Valsalva or cough),4 whereas the pediatric Foley catheter test (similar to the maximum urethral closure pressure) may represent an indirect measure of urethral resistance at rest.
For a woman to remain continent, intraurethral pressure must be greater than intravesical pressure under both resting and stress conditions. At rest, urethral resistance is generated by the interaction of urethral smooth muscle, urethral wall elasticity and vascularity, and periurethral striated muscle.21 This mechanism may explain why in women with intrinsic sphincter deficiency, relatively little resistance is encountered when the inflated bulb of a Foley catheter is withdrawn through the urethra. In a similar study using urethrography, Frewer22 showed that in incontinent women with normal urethrovesical angles, lower resistance was encountered from the urethral walls when dilating a Foley bulb in the urethrovesical junction compared with continent women.
Subjective criteria are used when performing the pediatric Foley catheter test. These include determination of the strength of the pull exerted on the catheter, the extent of stretch of the catheter by the person conducting the test, and patient evaluation of discomfort. For example, a forceful pull may cause the inflated bulb of the catheter to be pulled through a competent urethral sphincter, yielding a false-positive result, whereas an inadequate pull might result in a false-negative result. It is difficult to standardize these criteria even though we attempted to do so by stating that the subject should have only minimal discomfort during the test and the elastic rubber of the catheter should not stretch as it is being pulled. These subjective criteria likely account for the high false-positive and false-negative rates of the test. These limitations occur because the pull is being exerted manually by the person conducting the test and not a mechanical device as in traditional urethral pressure profilometry. These subjective criteria may limit the validity of the test to physicians who will perform the test on a regular basis. Although these features of the test adversely affect its reproducibility, they also make the test simple and easy to perform in the office.
It is also possible that the results of the pediatric Foley catheter test could have been biased by the values of the maximum urethral closure pressure or the Valsalva leak point pressure. Such an observer bias is unlikely because we performed the pediatric Foley catheter test before measurement of the maximum urethral closure and Valsalva leak point pressures.
With a sensitivity of 76% and specificity of 81%, the pediatric Foley catheter test may be a useful screening method for intrinsic sphincter deficiency. It is easy to perform, involves minimal patient discomfort, and requires only a catheter and a tuberculin syringe. Another screening method, the empty supine stress test, is also simple and inexpensive, but reported sensitivity ranges from 36% to 65%, with a specificity of 76%.7,8 The correlation of this test with urodynamic indices is also not clear. Whereas Lobel and Sand7 reported good correlation of the empty supine stress test with maximum urethral closure pressure, a later study8 reported poor correlation with maximum urethral closure pressure and better correlation with Valsalva leak point pressure. If screening for intrinsic sphincter deficiency were based on identification of high-risk factors6 alone (age greater than 50 years, prior incontinence surgery, myelodysplasia, radical pelvic surgery), we would have identified only 55 of the 173 (32%) women. To evaluate the best screening test, a study in which all screening methods are performed together with urethral pressure profilometry and leak point pressures is required.
In addition to sensitivity and specificity, another important characteristic of a screening test is its predictive value, which is dependent on the prevalence of the disease in the population. An office screening test for intrinsic sphincter deficiency should have a high negative predictive value (the probability that a patient does not have the disease if she has a negative test) because this finding would help a physician to reliably exclude the disease.7 In our referral population with a high prevalence of intrinsic sphincter deficiency, the negative predictive value of the pediatric Foley catheter test was only 81%. In a low-risk population with a prevalence of intrinsic sphincter deficiency of only 11%,23 we calculate that the negative predictive value of the test would increase to 96%, thus improving its usefulness.
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Footnotes |
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Received August 31, 2000. Received in revised form December 26, 2000. Accepted February 8, 2001.
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References |
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2. McGuire EJ. Urodynamic findings in patients after failure of stress incontinence operations. Prog Clin Biol Res 1981;78:351–60.[Medline]
3. McGuire EJ, Fitzpatrick CC, Wan J, Bloom D, Sanvordenker J, Ritchey M, et al. Clinical assessment of urethral sphincter function. J Urol 1993;150:1452–4.[Medline]
4. Bump RC, Elser DM, Theofrastous JP, McClish K. Valsalva leak point pressures in women with genuine stress incontinence: Reproducibility, effect of catheter caliber, and correlations with other measures of urethral resistance. Am J Obstet Gynecol 1995;173: 551–7.[Medline]
5. Sand PK, Bowen LW, Paganiban R, Ostergard DR. The low pressure urethra as a factor in failed retropubic urethropexy. Obstet Gynecol 1987;69:399–402.[Medline]
6. Horbach NS, Ostergard DR. Predicting intrinsic sphincter dysfunction in women with stress urinary incontinence. Obstet Gynecol 1994;84:188–92.
7. Lobel RW, Sand PK. The empty supine stress test as a predictor of intrinsic urethral sphincter dysfunction. Obstet Gynecol 1996;88: 128–32.[Abstract]
8. McLennan MT, Bent AE. Supine empty stress test as a predictor of low Valsalva leak point pressure. Neurourol Urodyn 1998;17: 121–7.[Medline]
9. Nichols DH, Randall CL, eds. Vaginal surgery. 4th ed. Baltimore: Williams & Wilkins, 1996:351–83.
10. Bump RC, Mattiasson A, Bo K, Brubaker LP, DeLancey JO, Klarskov P, et al. The standardization of terminology of female pelvic organ prolapse and pelvic floor dysfunction. Am J Obstet Gynecol 1996;175:10–7.[Medline]
11. Swift SE, Ostergard DR. A comparison of stress leak point pressure and maximum urethral closure pressure in patients with genuine stress urinary incontinence. Obstet Gynecol 1995;85:704–8.[Abstract]
12. Abrams P, Blaivas JG, Stanton SL, Anderson JT. The standardization of terminology of lower urinary tract function recommended by the International Continence Society. Int Urogynecol J 1990;1: 45–58.
13. Versi E. The significance of an open bladder neck in women. Br J Urol 1991;68:42–3.[Medline]
14. Swift SE, Utrie JW. The need for standardization of the Valsalva leak-point pressure. Int Urogynecol J 1996;7:227–30.
15. American Urogynecologic Society. Diagnosis of the incompetent urethral sphincteric mechanism. Quarterly report, no. 2. Washington, DC: American Urogynecologic Society, 2000.
16. Bump RC, Coates KW, Cundiff GW, Harris RL, Weidner AC.Diagnosing intrinsic sphincteric deficiency: Comparing urethral closure pressure, urethral axis, and Valsalva leak point pressures. Am J Obstet Gynecol 1997;177:303–10.[Medline]
17. Sand PK, Winkler H, Blackhurst DW, Culligan PJ. A prospective randomized study comparing modified Burch retropubic urethropexy and suburethral sling for treatment of genuine stress incontinence and low-pressure urethra. Am J Obstet Gynecol 2000;182:30–4.[Medline]
18. Maher CF, Dwyer P, Carey M, Gilmour D. The Burch colposuspension for recurrent urinary incontinence following retropubic continence surgery. Br J Obstet Gynaecol 1999;106:719–24.[Medline]
19. Nitti VW, Combs AJ. Correlation of Valsalva leak point pressure with subjective degree of stress urinary incontinence in women. J Urol 1996;155:281–5.[Medline]
20. English SF, Amundsen CL, McGuire EJ. Bladder neck competence at rest in women with incontinence. J Urol 1999;161:578–80.[Medline]
21. DeLancey JOL. Anatomy of the female bladder and urethra. In: Ostergard DR, Bent AE, eds. Urogynecology and urodynamics: Theory and practice. 3rd ed. Baltimore: Williams & Wilkins, 1991:3–18.
22. Frewer WK. Foley catheter urethrography in stress incontinence. J Obstet Gynaecol Br Commonwealth 1971;78:660–3.[Medline]
23. Richardson DA, Ramahi A, Chalas E. Surgical management of stress incontinence in patients with low urethral pressure. Gynecol Obstet Invest 1991;31:106–9.[Medline]
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