Mechanical Occluder Devices for Urinary Incontinence

Chapter 202


Mechanical Occluder Devices for Urinary Incontinence



Urinary incontinence is a common and serious problem in dogs. Acquired urethral sphincter mechanism incompetence (USMI) occurs in up to 20% of dogs after ovariohysterectomy, with ureteral ectopia, pelvic bladder, and other urogenital malformations contributing to the overall incidence of incontinence in dogs. Although urinary incontinence is not directly life threatening, the resultant house soiling is a major cause of euthanasia or abandonment of indoor pets. As a result, small animal practitioners often are pressured to provide effective options for the treatment of urinary incontinence that will produce a rapid and permanent resolution of clinical signs.



Therapeutic Options


Pharmacologic therapy is the standard of care for initial treatment of dogs with acquired urinary incontinence. Although treatment with α-agonists or estrogenic compounds (see Chapter 201) is effective in the majority of animals with acquired urinary incontinence, in approximately 20% of dogs with USMI the disorder is refractory to medical therapy. Male dogs with USMI and dogs with congenital malformations are far less likely to respond to drug therapy. Endoscopic or surgical procedures are considered as a means to improve control of urinary incontinence when the disorder shows no response to medical therapy or when clients feel that the lifelong administration of drugs is undesirable. Historically, endoscopic application of urethral bulking agents has provided a minimally invasive method for the treatment of USMI in female dogs (see Web Chapter 71). Although this procedure is effective in the majority of dogs (66% rate of complete continence; Byron et al, 2011), the durability of this effect is poor, with the mean duration of continence ranging from 5.2 to 16.4 months. In addition, the length of the male canine urethra makes endoscopic urethral bulking techniques impractical for use in male dogs. Because of the need for repeated injections over time and the limited availability of suitable bulking agents, many referral practices are actively seeking out other means of therapy for refractory incontinence.



Artificial Urethral Sphincter


The canine artificial urethral sphincter (AUS; Figure 202-1) is a modification of an inflatable silicone hydraulic vascular occluder that was intended for use in the temporary constriction of blood vessels in laboratory animals (Adin et al, 2004; Sereda et al, 2005). The device is similar in concept to an artificial urethral sphincter used in human beings with urinary incontinence (AMS 800), although that device requires manual deflation before each act of urination—a feature that prevented its direct application in dogs. Instead, the canine AUS is designed to produce a low level of static urethral compression, similar to the effect of urethral bulking agents. After the device was evaluated in cadavers, it was determined that these inflatable cuffs could be placed around the canine urethra through a caudal abdominal approach. Actuating tubing from the cuff is connected to a permanent subcutaneous injection port (Le Grande CompanionPort vascular access port) that is placed under the skin on the caudoventral abdomen. Incremental injections of fluid into the port created corresponding increases in urethral pressure in the cadaver study (Adin et al, 2004). Mechanical studies showed that devices that were inflated with sterile 0.9% NaCl remained inflated over a 5-month period of immersion in simulated body fluid (Sereda et al, 2006). Based on the success of these initial investigations and a subsequent pilot study in four client-owned dogs with refractory USMI (Rose et al, 2009), we now have performed the procedure in over 30 dogs with an expanding list of acquired and congenital causes of urinary incontinence.




Indications


In human beings, the AUS is used almost exclusively to treat men with urinary incontinence resulting from radical prostatectomy. Because of the severity of incontinence in affected men, significant urethral compression and a dynamic (deflatable) cuff are required to achieve continence and intermittent bladder emptying, respectively. In contrast, the canine AUS has been applied to treat the more commonly encountered female USMI—a condition that is more responsive to the mild, static increases in urethral pressure produced by this device. After experiencing initial success in treating female dogs with USMI, we now have expanded our criteria to include female dogs with pelvic bladder and urethral hypoplasia as well as those with continued incontinence after conventional or laser surgery for ureteral ectopia. Because of the extremely poor efficacy of alternative therapies, the canine AUS device has proven to be particularly useful in the treatment of male dogs with USMI.



Diagnostic Evaluation


Diagnostic screening of candidates for AUS implantation is similar to evaluation of any animal with urinary incontinence. Testing should include a complete blood count, serum biochemistry panel, urinalysis, and urine bacterial culture to rule out concurrent metabolic or infectious diseases that may be contributing to clinical signs of incontinence. Animals with a current urinary tract infection or with active pyoderma are treated with appropriate antibiotics to resolve any infection before implantation of a permanent implant such as the AUS is considered. Baseline urinary tract ultrasonography also is performed to screen for urolithiasis, ureteral dilation, renal parenchymal changes, or abnormalities in the bladder wall that may indicate preexisting urinary tract disease. In our practice, the medical history regarding the onset of incontinence is crucial in determining whether advanced imaging (computed tomographic excretory urography) or uroendoscopy are required to rule out concurrent anatomic abnormalities that should be corrected before AUS implantation is considered. A dog that has acquired USMI after gonadectomy is not subjected to advanced imaging, whereas an animal that has been leaking urine from birth is more likely to have concurrent ureteral ectopia, ureterocele, or other anomalies, and advanced imaging is recommended. Although urodynamic evaluation is a standard part of the screening of human patients with incontinence, it does not predict response to surgical therapy accurately and is not currently used as a standard screening test before AUS implantation.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Mechanical Occluder Devices for Urinary Incontinence
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