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Chapter: Medical Surgical Nursing: Assessment of Renal and Urinary Tract Function

Urodynamic Tests - Renal and Urinary Tract Function

Urodynamic tests provide an accurate evaluation of voiding problems, thus assisting in diagnosis.



Urodynamic tests provide an accurate evaluation of voiding prob-lems, thus assisting in diagnosis. Urodynamic studies are useful in evaluating changes in bladder filling and bladder emptying. Chart 43-4 outlines patient education for all basic urodynamic tests. The following urodynamic test procedures and measure-ments are the most common and are often performed simultane-ously (Albaugh, 1999; Appell, 1999).




Uroflowmetry (flow rate) is the record of the volume of urine passing through the urethra per time unit (milliliters per second). The flow rate reflects the combined activity of the detrusor mus-cle and the bladder neck and the degree of relaxation of the ure-thral sphincter. Because this test depends on the amount voided, the patient is instructed to arrive for the test with a strong urge to void, but not have an overly full bladder (EMG). When urethral sphincter competency is being evaluated, uroflowmetry is com-bined with electromyographic measurement of the external ure-thral sphincter via surface wire or needle electrodes placed at the level of the sphincter, on either side of the urethra. Uroflowme-try is often combined with cystometrography, in which case the bladder is filled as the intravesical pressure is being monitored be-fore the voiding phase of the study.




A cystometrogram (CMG) is a graphic recording of the pressures in the bladder during bladder filling and emptying. It is the major diagnostic portion of urodynamic testing. During the test, the amount of fluid instilled into the bladder and the patient’s sen-sations of bladder fullness and urge to void are recorded. These are then compared with the pressures measured in the bladder during bladder emptying. A urethral catheter is connected to a water manometer, and sterile solution of either normal saline or water is allowed to flow into the bladder, usually at the rate of 1 mL/sec. The patient informs the examiner when the first sen-sation of bladder filling is felt, when mild urgency is noted, and again when the bladder feels full. The degree of bladder filling at these points is recorded. The pressures above the zero level at the symphysis pubis are measured, and the pressures and volumes within the bladder are plotted and recorded. This test measures bladder sensation, compliance of the bladder wall during filling, and functional capacity. It also evaluates any phasic or sharp in-creases in bladder pressure, which may or may not be associated with incontinence of the infused fluid.


Throughout and at the end of bladder filling, the degree of abdominal pressure against the bladder, which could potentially cause leaking (stress incontinence), is measured. This measure-ment is referred to as the Valsalva leak-point pressure (VLPP). The terms VLPP and abdominal leak-point pressure can be used interchangeably.


While in a sitting or standing position, the patient is asked to cough or perform a Valsalva maneuver to assess whether urine leaks. Before this test is performed, it is important to determine if the patient is prone to vasovagal reactions and to alert the uro-dynamicist. A competent sphincter will not allow for any loss of urine, even with a full bladder and maneuvers such as a cough, laugh, or position change. 

When minimal weakness of the ure-thral sphincter causes a small amount of incontinence (currently considered leakage at or above a bladder pressure of 100 cm H2O), urethral hypermobility is the cause. When leakage occurs with a cough or the Valsalva maneuver at bladder pressures less than 100 cm H2O, intrinsic sphincter deficiency is believed to contribute to the incontinence. During the cystometrogram por-tion of the urodynamic study, if any urine leakage is noted when the patient coughs or performs a Valsalva maneuver, regardless of the amount of abdominal force that caused the leaking, a diag-nosis of “genuine stress urinary incontinence” is made. The VLPP determines the severity of SUI.


Urinary Pressure Flow


Urinary pressure flow is a study that is performed immediately after the filling phase of the CMG and simultaneously with the voiding CMG. Bladder pressure, urine flow, and sphincter electro-myography are measured simultaneously. This allows for a de-tailed picture of voiding function.




Electromyography (EMG) involves the placement of electrodes in the pelvic floor musculature or over the area of the anal sphinc-ter to evaluate the neuromuscular function of the lower tract. It is usually performed simultaneously with the CMG.


Videofluorourodynamic Study


The videofluorourodynamic study is considered the optimal uro-dynamic evaluation. This test combines a study of the filling and voiding phases of the CMG and the EMG with a simultaneous visualization of the lower urinary tract via a radiopaque filling agent in place of sterile water or saline. It allows for a complete and detailed assessment of the voiding dysfunction, which may be due in part to anatomic dysfunction.


Urethral Pressure Profile


The urethral pressure profile measures the amount of urethral pressure along the length of the urethra needed to maintain con-tinence. Gas or fluid is instilled through a catheter that is with-drawn while the pressures along the urethral wall are obtained.


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