First desire to void occurs between 150 and 250 mL infused
Strong desire to void does not occur until after 250 mL
No uninhibited detrusor contractions during filling, despite provocation
No stress or urge incontinence demonstrated, despite provocation
Voiding occurs as a result of a voluntarily initiated and sustained detrusor contraction
Flow rate during voiding is >15 mL/sec with a detrusor pressure of <50 cm H2O
From Wall LL, Norton P, Delancey J. Practical urogynecology. Baltimore, MD: Williams & Wilkins, 1993, with permission.
Figure 26.5 Detrusor overactivity on filling cystometrography. The patient begins to sense urgency, accompanied by an unstable bladder contraction, when 88 mL of water are instilled into the bladder. The detrusor pressure rises, and when 96 mL of water are instilled, she leaks. Pabd, abdominal pressure; Pves, vesical pressure; Pdet, detrusor pressure.
failure using standard retropubic urethropexy (Fig. 26.6). Cutoff values for these tests are poorly defined and remain controversial. Although women with stress urinary incontinence have, on average, significantly lower maximal urethral closure pressures than those without incontinence, there is wide overlap in the values between such women, and no lower limit of urethral closure pressure or leak point pressure is established that diagnoses stress urinary incontinence.
The urethral pressure profile is a test designed to measure urethral closure. Because continence requires the pressure in the urethra to be higher than the pressure in the bladder, it was believed that measuring the pressure differential between the two would provide useful clinical information. The urethral pressure profile is determined by slowly pulling a pressure-sensitive catheter through the urethra from the bladder.
The urethral closure pressure (Pclose) is the difference between the urethral pressure (Pure) and the bladder pressure: (Pves): Pclose = Pure − Pves.
It was suggested that women with stress incontinence with low urethral closure pressure (<20 cm H2O) have a poorer prognosis for surgical outcome than women who do not have this condition; however, this area is the subject of considerable debate (3,39,40). Because stress incontinence, by definition, occurs during increases in intra-abdominal pressure that are generated by some kind of physical activity, it is not obvious why measurement of resting urethral pressure should be relevant to stress-related leakage, which is a dynamic event. One review concluded that urethral pressure profilometry is not a useful diagnostic test for stress incontinence in women and that its use in clinical management is unsupported by current evidence (41).
Leak-point pressure (LPP) is a urodynamic measure of the minimum intra-abdominal or intravesical pressure required to cause incontinence during abdominal strain or cough.
Figure 26.6 Open and scarred bladder neck in an elderly woman who has undergone three anterior colporrhaphies for stress urinary incontinence in the past.
There is no consensus about whether it should be measured from the resting supine baseline (generally near 0) or from the standing resting baseline (which increases depending on body mass). Other factors that may affect the results include the catheter’s type, caliber, and placement (vaginal, rectal, or intravesical), the bladder volume at which the measurement is obtained, the mechanism by which intra-abdominal pressure is increased (coughing versus straining), and patient position (42).