The term “blocked tomcat” or “blocked tom” refers to the obstruction of normal urine output from the urinary bladder through the urethra. Because of differences in male cats’ urethral anatomy, this condition occurs more frequently in tomcats and is thusly named; but it can sometimes occur in female cats as well. When urine cannot be eliminated from the body, the bladder becomes painfully distended and post-renal kidney failure occurs. Toxins are left to accumulate in the bloodstream causing subsequent harmful effects on the brain, heart, and other organ systems. Urine obstruction is a life-threatening condition and can result in permanent kidney damage or death if not quickly corrected. This is truly a medical emergency!
Abnormal urine sediments in the form of inflammatory cells, blood, mucous, bacteria, and urinary crystals can become clumped together and collect at a narrowing in the urethra. Male cats’ urethras taper toward the opening at the prepuce making them especially susceptible to forming a “plug” which obstructs normal urination. All of the constituents of a urinary plug can be the result of a true bacterial infection or a complicated disorder called Feline (Idiopathic) Lower Urinary Tract Disease, or FLUTD. More than half of cats over 10 years of age with FLUTD will have an undetermined, or idiopathic, cause of the disease. Nonetheless, a blocked urethra is a serious possible consequence.
The term “blocked tom” has been replaced for the most part by the “obstructive form of FLUTD” to describe any cat, male or female, with this life-threatening problem.
To understand all of the harmful consequences of urine obstruction, it is important to realize the normal function of the urinary tract. The kidneys’ primary purpose is to eliminate waste while conserving water. These organs filter by-products of metabolism from the bloodstream and concentrate the toxins into as little water as possible, producing urine. Urine is produced twenty-four hours a day and flows constantly from the kidneys through tiny tubes called ureters into the bladder. The bladder stores urine temporarily until it is eliminated outside of the body through the urethra which terminates at the external genitalia.
When urine obstruction occurs, the first problem is a matter of storage. As the bladder cannot empty, its normal capacity is exceeded. This is a very painful condition which causes the cat to frequent the litter pan to attempt to urinate without success. Straining to urinate can sometimes be confused with constipation. The cat may howl in discomfort, lick at the urethral opening, and repeatedly assume the position to urinate. In rare cases, the bladder can rupture; although most cats will succumb to other harmful consequences of urine obstruction before this occurs.
The next consequence is the effect of kidney failure that occurs when back pressure from the bladder causes urine production in the kidneys to cease. Uremia and azotemia describe the build up of urinary waste products in the bloodstream. These toxins can cause ulceration of the stomach lining or esophagus and lead to vomiting and appetite loss. The electrolyte potassium, which is normally excreted by the kidneys, can reach dangerous levels causing heart arrhythmias or cardiac arrest. On a blood-chemistry panel, the obstructed cat’s kidney function values may be extremely elevated. Only after restoring normal urine production and flow will it become clear whether permanent kidney damage has occurred and how significant the damage will be.
Finally, the bladder muscle that controls urine storage and elimination can be stretched to the point of long-term damage. Even after treatment, the cat may have problems being able to urinate normally.
Because it can be difficult to ascertain at home whether or not the cat can urinate normally (a urinary tract infection can mimic an obstruction because both involve straining to urinate, however, with infection the cat will pass small amounts of urine because the urethra is not obstructed), any cat suspected of urinary obstruction should be dealt with on an emergency basis. If the bladder is distended, the veterinarian will relieve the obstruction with urethral catheterization. This will immediately restore kidney urine flow and help to eliminate toxins from the bloodstream.
To remove the urethral obstruction, the cat will most likely require a general anesthetic to alleviate pain and facilitate treatment. The veterinarian will decide if the cat is stable enough to receive an anesthetic, as some cats may not be suitable candidates. In most cases, a small catheter can be used in a technique called hydropropulsion to force the urethral plug back up into the bladder using pressurized sterile saline. This will also help to break up the plug so that it can pass along with the urine. While under anesthesia, the veterinarian will take abdominal x-rays or perform an ultrasound to rule out bladder and kidney stones that may need to be removed surgically or dissolved with dietary modification after the cat has been stabilized. Finally, a small rubber catheter will be sutured in place in the urethra and left for 1 to 3 days to allow proper urine output.
During hospitalization, and until the cat is stable, intravenous fluids will be administered through an IV catheter to improve hydration, restore electrolyte balance, and dilute toxins in the bloodstream. This process is called diuresis. The cat’s kidney values, electrolytes, and other blood chemistries will be rechecked several times to verify systemic recovery and assess long-term damage.
Over the next several days and weeks, the underlying problems that lead to urine obstruction will be addressed. Antibiotics will be administered to treat and prevent bacterial infections, and drugs to improve muscle tone within the bladder may also be given. Special diets that change the pH of the urine may be prescribed to keep a urethral plug from reforming. There are drugs that can alter the pH of the urine as well.
Occasionally, a male cat may require a surgical procedure called a perineal urethrostomy to prevent recurring obstructions. This involves shortening and widening the urethra to allow urethral plugs and other potentially obstructing materials to be eliminated without travelling through the narrowed portion of the urethra in the penis. Cats receiving this procedure may still have recurring urinary tract disease but hopefully will not become obstructed in the future. The larger opening created in the urethra may make ascending bacterial infections more likely to occur after the procedure is done, but these are easier to deal with than a life-threatening emergency.
Preventing urinary obstructions from forming is a difficult endeavor. Commercial cat food manufacturers and veterinary specialists continually research the role that dietary constituents play in FLUTD. Your veterinarian is the best source for current feeding recommendations. In general, most experts agree that increasing water intake by offering canned food may be beneficial, but even cats fed strictly canned diets may develop a urinary obstruction.