Evaluation of Female Urinary Incontinence

, , University of Texas Medical School

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Urodynamic Evaluation of the Bladder

Compliance assessment. Prior to any evaluation of urethral sphincter function, it is necessary to evaluate detrusor function. The relationship between high detrusor pressure (and high detrusor pressure at the point of urethral leakage) and upper tract deterioration was identified by McGuire and coworkers[17] in 1981. The therapeutic implications were developed further at the University of Michigan.[18,19] A cystometrogram (CMG) is an easy-to-perform and important urodynamic test in evaluating bladder compliance.

To test compliance, the pressure in the catheter is zeroed with flow "on." The patient is then catheterized, and the bladder is filled with warmed saline, water, or contrast at a rate of 60cc/min. If compliance is impaired, the volume at which high pressure occurs is the critical parameter to observe. It is important that the detrusor pressure during filling does not reach a level that would interfere with ureteral urine transport (i.e., > 40cm H2O). During compliance testing, the bladder is filled to the volume typical for the bladder being tested. For example, in a myelodysplastic child, the volumes recovered when catheterizing may be 200 to 300cc. If the detrusor pressures when the bladder is filled to this typical volume are less than 40cm H2O, the upper tracts are not at risk. However, if the patient does not typically catheterize himself or herself until the bladder contains 500cc and if the pressure is above 40cm H2O at this volume, this pressure predisposes to upper tract deterioration.

Other aspects of detrusor assessment. Uninhibited detrusor contractility may occur during the CMG. In the presence of neurologic disease, this disorder is referred to as detrusor hyperreflexia. In the absence of neurologic disease it is referred to as detrusor instability. Because uninhibited detrusor contractions may be the cause of incontinence in patients with urge incontinence even if they do not occur during a CMG, such uninhibited detrusor activity may be termed "CMG negative" detrusor instability; that is, the condition "detrusor instability" still exists although it has failed to manifest during the testing period.

Ambulatory cystometric monitoring appears to be a more sensitive method of detecting detrusor instability.[20] When overtly unstable activity occurs during standard test circumstances, the CMG may be termed "positive." However, urge incontinence is a detrusor motor phenomenon even if it is "CMG negative" during testing. This issue and recommended therapy are discussed more fully by McGuire.[5]

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