Urethral obstruction in cats: Catheters and complications (Proceedings) - Veterinary Healthcare
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Urethral obstruction in cats: Catheters and complications (Proceedings)


CVC IN BALTIMORE PROCEEDINGS


Post Obstructive Issues

• Indwelling urethral catheters: With acute, easily removed urethral plugs, an indwelling catheter is unlikely to be necessary. Indwelling catheters are indicated to prevent reobstruction 1) in cases of difficult catheterization where significant urethral trauma has occurred, 2) when large amounts of crystalline debris remain even after bladder flushing, 3) in severely ill cats with metabolic compromise. Indwelling catheters also are used to monitor urine output and to manage detrusor atony or functional obstruction. Non-irritating 5Fr red rubber catheters or infant feeding tubes are preferred. All urinary catheters can be considered irritating to the urethra, which can worsen inflammation or urethrospasm, but this disadvantage must be weighed against the probability of reobstruction, multiple catheterizations, and additional client cost or frustration.

• Indwelling catheters are left in place 24 – 72 hours depending on the individual circumstances. When the urine flowing is fairly clear of crystalline debris, haziness and blood, the catheter is removed. The cat is monitored during the day to ensure he can void normally.

• Ins and outs: Post-obstructive diuresis can lead to remarkable amounts of fluid loss (may exceed 2 liters/day). Tailoring the fluid administered "in" to meet the urine coming "out" helps clinicians meet variable fluid needs for the first couple of days. In this situation, insensible fluid needs can be calculated at 10 – 20 ml/kg/day, and then urine volume measured and replaced as measured. Over time, fluids will need to be slowly tailored so that the animal can be weaned off fluid therapy. Most cats will need potassium supplementation during the post-obstructive diuresis.

• Urethrospasm is a challenging complication of feline obstruction. Short term administration of smooth muscle relaxants (prazosin), striated muscle relaxants (diazepam) and/or analgesics (NSAIDs, Opioids) are minimally helpful. Diazepam may transiently aid bladder expression in some cats. All of these drugs have potential adverse effects as well. "Tincture of time" is the most reliable treatment for urethrospasm; however the urinary bladder must be kept small with urinary catheterization or gentle manual expression in the meantime.

• Detrusor atony is also possible following urinary obstruction and bladder overdistension. A cat whose bladder remains larger than a golf ball following a voiding attempt may require placement of an indwelling catheter for a variable period of time (usually 1-3 days) to maintain a small bladder size. Recovery of normal detrusor function will be enhanced by preventing excessive detrusor stretch or strain in the days following relief of the obstruction.ing. Atony can be managed with manual bladder expression if urethral resistance is low and expression is not difficult or painful. Manual expression of urine, especially in the face of any increased outlet resistance, can create further bladder wall trauma and may delay return to normal function. Bethanechol can also be useful in the recovery of acute detrusor atony,: however urethral outlet resistance must be lowered (typically with pharmacologic means) before introducing bethanechol.

• Urinary tract infection: Iatrogenic infection is common after alleviating lower urinary tract obstruction, or after prolonged urine retention. Ideally, antimicrobials (chosen based on urine culture and susceptibility) are withheld until the urinary catheter has been removed and the animal is urinating adequately. However, if signs of fever, renal pain, or sepsis are evident, urine should be cultured and antimicrobials administered immediately.

• Urethral tear or rupture: With proper technique, urethral damage is unlikely during urinary catheterization. Partial tears or ruptures can be confirmed by urethrography and usually are managed with an indwelling urinary catheter or cystostomy tube placement.

• Perineal urethrostomy is avoided during acute obstructive episodes except as a salvage procedure.

Tips for Preventing Catheter Complications

• Leave only soft, non-irritating catheters such as silicone or Teflon catheters or soft infant feeding tubes in the urethra. Tomcat catheters (polypropylene) are extremely irritating when left in contact with the urethral mucosa, and are more likely than softer catheters to cause bladder trauma when left indwelling. When using an indwelling urinary catheter, always use a closed collection system to decrease the odds of ascending bacterial infection.

• Consider the use of a urethral relaxant during and after the period of catheterization. See Table 1 for medications and doses.

• Consider the one-time use of a nonsteroidal anti-inflammatory such as ketoprofen at the time of catheterization. This may be contraindicated in animals where renal azotemia is suspected or confirmed.

• Ensure patency of the indwelling catheter at all times and monitor urine output. The bladder should not distend at all while the catheter is in place.

• Consider the use of anxiolytic and/or mildly tranquilizing medication during and immediately after the period of indwelling catheterization. See Table 1 for medications and doses. These medications may reduce straining and sympathetic tone resulting from stress. Although amitryptyline has been described to promote urethral relaxation and propulsion of urethral plugs in cats, and offers slightly earlier relief of hematuria and straining in non-obstructed cats, its use in acute situations may increase the likelihood of urine retention and early recurrence of bladder inflammation in cats.

The prognosis for voiding disorders in cats depends on the initiating cause and the duration of dysfunction. Most cats with post-obstructive voiding difficulty will improve with time and proper management. Several days to a week may be necessary before normal voiding returns. With reversible neurologic lesions, return of urinary function usually accompanies recovery of other motor functions; however, pharmacologic treatments may be required during the recovery time period. Medical treatments are usually continued for several days after voiding function has returned, then tapered. Cats with chronic or irreversible neurologic lesions may not improve significantly with treatment, or may require lifelong management. Surgical salvage (urethrostomy) may be necessary in cases of permanent urethral damage.


Table. Key Pharmacologic Agents Used for Urinary Obstruction in Cats
Long term preventive care should be initiatied for cats following urethral obstruction.For cats with struvite crystalluria or mineralized plugs, struvite preventative dietary management can be used. Uroliths should be analyzed quantitatively (most are calcium oxalate) and preventive strategies applied according to mineral composition. Cats with non-crystalline, inflammatory plugs should be managed as for idiopathic cystitis. Owners should be advised of the high likelihood of recurrence for any of these etiologies.

References

Bartges JW (1996), "Pathophysiology of urethral obstruction," Vet Clin North Am Small Anim Pract 26:255-64.

Lane IF (2000), "Diagnosis and management of urinary retention," Vet Clin North Am Small Anim Pract 30:25-57.

Lees GE (1994) " Management of voiding disability following relief of urethral obstruction," in John August, ed, Consultations in Feline Internal Medicine, 2 nd ed. Philadelphia, WB Saunders.

Olby N, (2006), "Neurogenic micturition disorders," in John August, ed, Consultations in Feline Internal Medicine, 5 th ed, Philadelphia, Elsevier.

Fischer JR, Lane IF (2007). Incontinence and urine retention. In Elliott and Grauer, eds. BSAVA Manual of Canine and Feline Nephrology and Urology, 2nd ed.

Drobatz, K. (2008) Emergency management of the critically ill cat with urethral obstruction. In Bonagura and Twedt, eds, Kirk's Current Veterinary Therapy XIV.

Achar et al (2003). Amitriptyline eliminated calculi through urinary tract smooth muscle relaxation. Kidney Int 64:1356.


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