The artificial urinary sphincter (AUS), a device used to treat urinary incontinence, has undergone five revisions since first being described in use in 1972. All types of artificial sphincters perform similar functions: to open partially when bladder pressure exceeds physiologic limits, to equalize pressures of stress, to open fully when operated, to fail in the open position, and to allow catheterization without further operations on the device. 8 The most current model, the AS-800 (American Medical Systems, Minnetonka, MN), introduced in 1982, consists of three parts: an inflatable cuff, a pressure-regulating balloon, and a pump. The cuff is typically placed around the urethra and is filled with fluid, via a pump/reservoir mechanism, providing continence through encircling compression of the urethra. For a patient to urinate, the fluid is pumped from the cuff to the reservoir. The fluid may then be pumped back into the cuff to provide continence or left in the reservoir leaving the cuff in the "open" position. All models enable catheterization without open modification of the device. The AS-800 is equipped with a deactivation button, which allows the device to be left in the "open" state. The device is reactivated by a sharp squeeze on the pump, opening a valve, which enables fluid transfer from the balloon to the cuff.
As subsequent versions of the AUS have been developed, reliability has improved. Mechanical failure rates range between 8 and 20 percent. 9 Examples of mechanical failure include fluid leaks, tube kinking, and pump failure. Fluid leaks present as the sudden onset of incontinence, with the cuff often being the source of the leaking fluid. Tube kinking is often the result of excessive tube length. These patients present in acute urinary retention, as they are unable to deflate the urethral cuff. Pump failure also manifests as a decreased ability or total inability to deflate the urethral cuff. This is usually the result of obstruction of the device's tubing by blood or other debris. Urologic consultation is necessary in these cases to further evaluate the source of the mechanical failure and treat the patient for urinary retention. These patients tend to require only replacement of the defective portion of the apparatus. Another complication, particularly seen in the use of AUS in the pediatric population, is bladder hypertonicity, which occurs after initial placement of the device. Hypertonicity may lead to renal failure, so these cases require close monitoring by nephrology and urology.10 When the clinical presentation warrants, patients in the emergency department who have a history of AUS implantation should be evaluated for the possibility of renal failure.
Cuff erosion, which is the most common cause of total sphincter failure, tends to occur more commonly in female patients, especially when either the bladder or the vagina has been injured during the implantation procedure. The incidence ranges between 1.3 and 18 percent but has decreased in recent years. After implantation, the device is left in the deactivated state postoperatively for 8 to 12 weeks to allow perivesicular inflammation to decrease as well as to allow the urethra to restore vascularity before regular use of the AUS. Further risk factors for cuff erosion include increased cuff pressure, decreased cuff size, and urethral catheterization, all of which may lead to cuff erosion secondary to pressure necrosis. Patients with cuff erosions tend to present several months postoperatively and may present with any of the following: perineal pain, urethral discharge, gross hematuria, dysuria, urinary urgency or frequency, or recurrent incontinence. Urologic consultation is necessary, with the diagnosis being confirmed by retrograde urethrography and cystourethroscopy. Treatment includes cuff removal with possible reimplantation at a later date, antibiotics, and catheterization.
Infection is infrequent with the AUS, especially in the more recent models. Recent studies report an incidence of infection in the range of 1.2 to 2.7 percent. Like any foreign body, the AUS causes a tissue reaction, which may facilitate infection if bacteria are present. S. epidermidis and coliform bacteria tend to be the most common etiology for bacterial infection of the device. A patient's presentation may be subtle in cases of infection and requires a thorough history and physical examination, as well as a heightened degree of suspicion. Patients may be afebrile, lack an elevated white blood cell count, and have sterile blood and urine cultures. Others may have pain, swelling, erythema, or induration around the mechanism. In male patients, there may be thinning of the scrotal skin overlying the pumping mechanism (the most common site of infection), and induration or tenderness along the length of tubing may be palpable in the patient. Treatment of this complication includes urgent removal of the apparatus, with the possibility of reimplantation of a new device after healing.
Patients who present with recurrent urinary incontinence may have difficulties at a variety of sites in the urinary tract. Problems involving the cuff of the AUS include erosion or urethral atrophy and/or rigidity, all of which interfere in the compressibility of the urethra and lead to further incontinence. Treatments involve exchanging various parts of the AUS device itself and may be done electively. Occasionally, detrusor instability leads to increased bladder pressures that overwhelm the urethral cuff. This instability may be treated with medication. Mechanical failure of the urethral cuff may be treated with urologic follow-up and elective replacement of the defective component.
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