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Feline Lower Urinary Obstruction

by Andrea Jensen
Spring 2008


Feline lower urinary obstruction is an acute blockage of urethral outflow which commonly occurs in cats of all ages, with an increased prevalence in adult cats.  It may begin as idiopathic cystitis, or may develop independently with no other apparent urinary disease.  While lower urinary tract disease is approximately equal in likelihood between the male and female cat, the male is far more likely to develop an acute obstruction.  Male cats have a longer urethra which narrows as it passes into the region of the penis, unlike the shorter female urethra that terminates at the wide open vestibule of the vagina.

Whether the patient is male or female, urinary obstruction is a life threatening emergency with a rapid progression.  It is acutely painful, and progresses to uremic crisis in as little as 24 hours post obstruction.  Signs of discomfort may not be apparent for as much as 12 hours post obstruction, but the progression thereafter is so rapid that this condition is considered one of the most important for feline guardians to be aware of.  A knowledgeable guardian that recognizes signs of obstruction and immediately takes action can save the life of a cat that could potentially be in a coma or dead by the next day.  Urinary obstruction should not be taken lightly, and time is of the essence to save the life of the suffering cat.

What exactly is blocking urine flow?

Contrary to popular belief, feline urethral obstruction is not usually due to uroliths (stones).  Uroliths are common in other species, but may only account for as little as 10-20% of all documented urethral obstructions in male cats.  In the relatively few cases that the obstruction is due to uroliths, they are most often struvite or calcium oxalate.  These types of stones are brightly radiopaque and easily visualized on radiographs as bright white dots in any part of the urinary tract from the kidneys to the urethra.

dwg The most common cause of obstruction in male cats is a urethral plug.  Plugs do have some mineral content, and are therefore variably detectable on radiographs.  The mineral component is often magnesium ammonium phosphate (struvite), but in far less quantity than in the struvite urolith, and therefore will not show nearly as brightly on radiographs, if at all.  Plugs are not as rigid as stones, and tend to mold in shape to the urethra.  They have a firm core made up of a matrix mucoprotein and embedded minerals, and are packed with other components such as exudates, red blood cells, cellular debris, sloughed epithelial cells, fibrin, and sometimes viral or bacterial pathogens.  Plugs may be formed at any location in the urethra, and usually become lodged in the penile segment.  A plug that is lodged in this location may continue to collect debris and become even larger.

What are the clinical signs of blocked outflow?

Lower urinary tract urgency is the first sign of outflow obstruction.  As the bladder fills and the cat is unable to relieve the pressure, he will keep trying to urinate.  In some cases, the obstruction may not be complete, and small quantities of urine may be expelled.  A partial obstruction often leads to a full obstruction, as the plug continues to collect debris.  In fact, the body's inflammatory response to a partial obstruction results in an increased amount of exudates and cells, which only speeds the growth of the obstructing plug.  Even if there is urine found in the litter box or wetness under the tail, any signs of pollakuria or stranguria (increased frequency or difficulty in urination) should be treated as a medical emergency.

Typically, uremia begins to develop if the obstruction is not relieved in the first 24 hours.  This is the stage when the cat will begin to appear systemically ill, and may even begin showing a "drunken" gait and signs of dehydration.  This is the stage of post renal azotemia and uremic crisis due the body's inability to eliminate waste products.  BUN, creatinine, and phosphorous dramatically increase.  Severe hyperkalemia (increased potassium) and metabolic acidosis can be fatal, often from sudden cardiac arrest.  Possible decreases in calcium compound the cardiac risk.  The pressure within the bladder by day two is already backing up to the kidneys and causing potentially irreversible damage to the kidneys.  A large number of obstructed cats do not survive past day two.  Some will continue to progress into day three, and may enter a uremic coma.  It is highly unusual for a cat to survive longer than three days without treatment.

What can we do about it?

In light of the rapid progression and high mortality rate, the most important thing a cat guardian can do is pay attention to litter box habits and take any signs of stranguria seriously.  Medical care within the first 24 hours of a partial or complete obstruction could mean the difference between life and death for the cat.  The guardian should also be alert to any unusual behaviors, such as attempting to urinate outside the litter box.  Since urinary obstruction is a painful experience for the cat, he may quickly associate his discomfort with the litter box and attempt to relieve himself someplace else.  Any time a cat is observed in a urination stance repeatedly in a short period of time, whether or not any urine is being expelled, the immediate action should be to call a veterinary emergency service.

Veterinary diagnostics and management of urethral obstruction are performed simultaneously.  If a distended bladder is palpated by the veterinarian, one of the first steps is to perform a cystocentesis (tap the bladder with a needle), both for diagnostic and therapeutic purposes.  The relief in pressure will provide the patient with instant relief and reduce the pressure backing up in the ureters and kidney, which allows the kidneys to once again function to clear waste products into the urinary bladder if the patient has not advanced to multi-systemic disease.

Once the pressure has been relieved, further diagnostics can be performed and a therapeutic plan can be determined.  Some common diagnostics include blood chemistry and hematology to check for kidney and liver function, as well as signs of other systemic disease.  Potassium and calcium should be evaluated to assess cardiac risk.  Hydration status and signs of shock are evaluated and treated.  Radiographs may reveal the type and location of the obstruction.  A Urinary catheter may facilitate dislodging of the obstruction, and is often left in place to maintain a constant outflow.  The catheter is both therapeutic and diagnostic, because it is used not only to keep the bladder draining, but also to measure urine output, particularly once IV fluids are started.  During placement, urethral irrigation may also be performed to flush and dilate the urethra and possibly flush the plug out.  Hydropulsion (reverse flushing) may be attempted for stubborn plugs.  After a plug is relieved, a well lubricated catheter is usually left in place for the reasons noted above, as well as to treat underlying problems that could predispose to rapid re-obstruction.

Following treatment and relief of an obstruction, the patient may experience temporary bladder atony.  This results from the muscular layer of the bladder wall being stretched excessively, which temporarily disables the ability to contract and express urine even after the blockage is cleared.  Clinically, this resembles a condition of urinary bladder paralysis.  If a catheter is kept in place for a day or two, which prevents the bladder from filling, bladder atony usually subsides and function is returned to normal.  However, if an overdistended bladder is not relieved for two or three days after a total obstruction, permanent atony is possible.

The prognosis for urinary obstruction is favorable if it is noticed and medical attention is provided in the first 24 hours.  Beyond the first 24 hours, the prognosis rapidly progresses from good to poor to grave.  Feline guardians must be aware of this life threatening medical emergency, and are urged to act quickly when faced with signs of pollakuria or stranguria.  Guardians should also be aware that a blockage is present several hours before signs are apparent.  If a cat appears to be straining to urinate, it should be realized that the clock has been ticking for several hours, and waiting until the next day could be too late.  At the time of stranguria, the cat is already suffering extreme discomfort, and could be only a few hours from a uremic crisis.  Medical attention should be immediate.

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