Материал: Oxford American Handbook of Urology ( PDFDrive )
102 CHAPTER 3 Bladder outlet obstruction
High-pressure chronic retention (HPCR)
HPCR is maintenance of voiding, with a bladder volume of >800 mL and an intravesical pressure above 30 cmH2O, accompanied by hydronephrosis.1,2 Over time, this leads to renal failure. When the patient is suddenly unable to pass urine, acute-on-chronic high-pressure retention of urine has occurred.
A man with high-pressure retention who continues to void spontaneously may be unaware that there is anything wrong. He will often have no sensation of incomplete emptying and his bladder may be insensitive to the gross distension. Often the first presenting symptom is that of bedwetting. This is such an unpleasant and disruptive symptom that it will cause most people to visit their doctor.
Visual inspection of the patient’s abdomen may show marked distension due to a grossly enlarged bladder. The diagnosis of chronic retention can be confirmed by palpation of the enlarged, tense bladder, which is dull to percussion.
Acute treatment
Catheterization relieves the pressure on the kidneys and allows normalization of renal function. A large volume of urine is drained from the bladder (often on the order of 1–2 L, and sometimes much greater).
The serum creatinine is elevated and an ultrasound will show hydronephrosis with a grossly distended bladder if the scan is done before relief of retention.
Anticipate a profound diuresis following drainage of the bladder. This is due to the following:
•Excretion of salt and water that has accumulated during the period of renal failure
•Loss of the corticomedullary concentration gradient, due to continued perfusion of the kidneys with diminished flow of urine through the nephron (this washes out the concentration gradient between the cortex and medulla)
•An osmotic diuresis caused by elevated serum urea concentration
A small percentage of patients have a postural drop in blood pressure. It is wise to admit patients with HPCR for a short period of observation, until the diuresis has settled.
A few patients will require intravenous fluid replacement if they experience a symptomatic fall in blood pressure when standing.
Definitive treatment
Treatment is with TURP or a long-term catheter. In those unable to void who have been catheterized, a trial without catheter is clearly not appropriate in cases where there is back-pressure on the kidneys.
Very rarely, a patient who wants to avoid a TURP and does not want an indwelling catheter will be able to empty their bladder by intermittent self-catheterization, but such cases are exceptional.
1 Mitchell JP (1984). Management of chronic urinary retention. BMJ 289:515–516.
2 Abrams P, Dunn M, George N (1978). Urodynamic findings in chronic retention of urine and their relevance to results of surgery. BMJ 2:1258–1260.
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104 CHAPTER 3 Bladder outlet obstruction
Bladder outlet obstruction and retention in women
In women this condition is relatively rare (~5% of women undergoing pressure-flow studies have BOO, compared with 60% of unselected men with LUTS).1
It may be symptom-free, present with LUTS or as acute urinary retention. In broad terms, the causes are related to obstruction of the urethra (e.g., urethral stricture, compression by a prolapsing pelvic organ such as the uterus, post-surgery for stress incontinence) or have a neurological basis (e.g., injury to sacral cord or parasympathetic plexus, degenerative neurological disease, e.g., MS, diabetic cystopathy).
Voiding studies in women
Women have a higher Qmax (maximal flow), for a given voided volume than that of men. Women with BOO have lower Qmax than those without BOO. There are no universally accepted urodynamic criteria for diagnosing BOO in women.
Treatment of BOO in women
Treat the cause (e.g., dilatation of a urethral stricture; repair of a pelvic prolapse). Where this is not possible (because of a neurological cause such as MS or spinal cord injury), the options are as follows:
•Intermittent self-catheterization (ISC) or intermittent catheterization by a caregiver
•Indwelling catheter (preferably suprapubic rather than urethral)
•Mitrofanoff catheterizable stoma
Where urethral intermittent self-catheterization is technically difficult, a catheterizable stoma can be constructed between the anterior abdominal wall and the bladder, using the appendix, Fallopian tube, or a narrowed section of small intestine, known collectively as the Mitrofanoff procedure. It is simply a new urethra that has an abdominal location, rather than a perineal one, and is therefore easier to access for ISC.
For women with a suprasacral spinal cord injury with preserved detrusor contraction and urinary retention due to detrusor-sphincter dyssynergia (DSD), sacral deafferentation combined with a Brindley stimulator can be used to manage the resulting urinary retention.
Fowler syndrome
Fowler syndrome is a primary disorder of sphincter relaxation (as opposed to secondary to, for example, SCI). Increased electromyographic (EMG) activity (repetitive discharges on external sphincter EMG) can be recorded in the external urethral sphincters of these women (which on ultrasound are of increased volume) and is hypothesized to cause impaired relaxation of external sphincter.
It occurs in premenopausal women, typically aged 15–30, often in association with polycystic ovaries (50% of patients), acne, hirsutism, and menstrual irregularities. It may also be precipitated by childbirth, gynecological or other surgical procedures.
BLADDER OUTLET OBSTRUCTION AND RETENTION IN WOMEN 105
Patients report no urgency with bladder volumes >1000 mL, but when attempts are made to manage their retention by ISC, they experience pain, especially on withdrawing the catheter.
Pathophysiology
Fowler may be due to a channelopathy of the striated urethral sphincter muscle leading to involuntary external sphincter contraction.
Treatment
Treatment is with ISC, sacral neuromodulation with Medtronic InterStim (90% void post-implantation and 75% are still voiding at 3-year follow-up). The mechanism of action of sacral neuromodulation in urinary retention is unknown.
Further reading
Swinn MJ, Fowler C, et al. (2002). The cause and treatment of urinary retention in young women. J Urol 167:151–156.
1 Madersbascher S, Pycha A, Klingler CH, et al. (1998). The aging lower urinary tract: a comparative urodynamic study of men and women. Urology 51:206–212.
106 CHAPTER 3 Bladder outlet obstruction
Urethral stricture disease
A urethral stricture is an area of narrowing in the caliber of the urethra due to formation of scar tissue in the tissues surrounding the urethra. The disease process of anterior urethral stricture disease is different from that in the posterior urethra.
Anterior urethra
The process of scar formation occurs in the spongy erectile tissue (corpus spongiosum) of the penis that surrounds the urethra (spongiofibrosis). Causes include the following:
•Inflammation (e.g., balanitis xerotica obliterans [BXO]), gonococcal infection leading to gonococcal urethritis (less common today because of prompt treatment of gonorrhea)
•Trauma
• Straddle injuries—blow to bulbar urethra (e.g., cross-bar injury)
•Iatrogenic—instrumentation (e.g., traumatic catheterization, traumatic cystoscopy, TURP, bladder neck incision)
The role of nonspecific urethritis (e.g., Chlamydia) in the development of anterior urethral strictures has not been established.
Posterior urethra
Fibrosis of the tissues around the urethra results from trauma—pelvic fracture or surgical (radical prostatectomy, TURP, urethral instrumentation). These are essentially distraction injuries, where the posterior urethra has been pulled apart, and the subsequent healing process results in the formation of a scar, which contracts and thereby narrows the urethral lumen.
Symptoms and signs of urethral stricture
•Voiding symptoms—hesitancy, poor flow, post-micturition dribbling
•Urinary retention—acute, or high-pressure acute-on-chronic
•Urinary tract infection—prostatitis, epididymitis
Management of urethral strictures
When the patient presents with urinary retention, the diagnosis is usually made following a failed attempt at urethral catheterization. In such cases, avoid the temptation to blindly dilate the urethra. Dilatation may be the wrong treatment option for this type of stricture—it may convert a short stricture that could have been cured by urethrotomy or urethroplasty into a longer and denser stricture, thus committing the patient to more complex surgery and a higher risk of recurrent stricturing. Place a suprapubic catheter instead, and image the urethra with retrograde and antegrade urethrography to establish the precise position and the length of the stricture.
Similarly, avoid the temptation to inappropriately dilate a urethral stricture diagnosed at flexible cystoscopy (urethroscopy). Arrange retrograde urethrography so appropriate treatment can be planned.