Upright cystography at a moderate bladder volume demonstrates an open bladder neck and proximal urethra (O Fig. 7.5). A cystometrogram, preferably with iodinated contrast material under fluoroscopic monitoring, provides information on bladder compliance, as well as on capacity, which is essential to planning a reconstructive surgical procedure. In this context, bladder capacity is defined by a detrusor pressure of 40 cm, or just under that pressure. Any storage pressure above this value is associated with real risk. Compliance testing is unreliable in the presence of vesicoureteral reflux or urethral leakage, and
fluoroscopy is very useful to determine if either of those variables is present (O Fig. 7.6). Abdominal and detrusor leak point pressures are also useful here to demonstrate that stress incontinence is present, and to define the variable that directly determines risk: the detrusor pressure (P det) at the instant of urinary leakage.
If poor compliance is present no urethral procedure is safe until the abnormal compliance is corrected. In such cases, part of the expulsive force driving the incontinence is Pdet, and that must be treated at the source, not by an achieved elevation in urethral resistance. Increased ure-thral resistance will lead to higher detrusor pressures and more incontinence, albeit at higher pressures.
While any bladder will respond to increased outlet resistance, this is an invariable and accentuated response in a decentralized or hyperreflexic bladder. Slings used to close a nonfunctional proximal urethra raise abdominal leak point pressures quite dramatically, but do not change detrusor leak point pressures very much, if at all . These are thus safe procedures. That is not true for the artificial sphincter, placed at the bladder neck. That device raises both the abdominal and detrusor leak point pressure. Thus a bladder response must be anticipated, after a sphincter is implanted, and steps taken to prevent the development of abnormal compliance in the face of the change in outlet resistance. This can be done with medication and intermittent catheterization, a bladder enlargement procedure, for example an augmentation cystoplasty, or myectomy, or Botox injections, for example.
7.5 • Surgical Techniques for Creation of a Competent Proximal Urethral Sphincter
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