Also known asischuria, a urinary obstruction (UO) is a medical emergency requiring immediate treatment. It occurs when the flow or urine is blocked anywhere along the urinary tract.
The most common cause of blockage is a urethral plug which contains mucus, protein, cellular debris, sloughed off epithelial cells and crystals (commonly struvite) in the core.
Other causes include:
Urinary crystals, most commonly struvite and calcium oxalate.
Uroliths (stones) as crystals grow in size, they can clump together forming uroliths.
Struvite forms more commonly in alkaline urine whereas calcium oxalate forms in acidic urine.
Congenital abnormality or the urethra.
Inflammation (urethritis) which may be due to crystals, urinary tract infection, trauma, prostate infection or cancer.
Scar tissue (from a previous blockage).
Tumours of the bladder neck or urethra.
Blood clots can form in the bladder and cause a blockage as they travel down the urethra which could be related to trauma. I recently read an article about a cat who was found hunched in somebody’s garden. He was picked up and found to have a urinary blockage. A catheter was inserted and bloody urine was drained from the bladder along with blood clots. It was later discovered the cat also had a broken pelvis, the trauma had obviously resulted in blood clots forming in the bladder.
Males are more prone to developing a urinary obstruction than females due to their longer urethra (the tube which drains urine from the bladder through and out of the penis) which narrows inside the penis. However, females can also be affected.
Left untreated, an obstruction can lead to a ruptured bladder and/or a uremic crisis as the kidneys are no longer functioning as they should, toxic levels of nitrogenous waste products (uremia) and potassium (hyperkalemia) build up in the blood and metabolic acidosis develops. It can take as little as 24 hours for this to occur. A distended bladder can also cause the bladder to lose its tone (bladder atony), resulting in urinary incontinence which may be permanent.
A urinary obstruction can occur in cats of all ages, although it is more commonly seen in adult cats.
What causes a urinary blockage in cats?
Urinary blockages can occur slowly, over a period of time, or very suddenly. The exact cause of mucus plug, crystal or urolith formation isn’t exactly understood, but contributing factors may include:
Diet – This has long been suspected due to the popularity of dry foods over the past 20 years. These diets often change the pH of your cat’s urine, making a more favourable environment for urinary crystals to develop. On top of that, dry food only contains a small amount of water compared to a wet diet (raw or canned) which is approximately 70% water. Many cats don’t make up for this imbalance by drinking more, so a cat on dry food will often have very concentrated urine due to inadequate intake. Urine which is concentrated is also more likely to result in the formation of urinary crystals.
Stress – There are two possible reasons why stress can lead to a blockage. Some stressful situations are the result of inter-cat aggression, which can spill over to litter tray usage. The stressed cat may delay going to the toilet for a number of reasons, leading to his urine becoming more concentrated which provides the ideal medium for crystal formation. Chronic stress can also trigger bladder inflammation which can produce large amounts of inflammation and debris.
Portosystemic shunt is a congenital disorder in which blood is shunted around the liver instead of through. As the liver is responsible for the detoxification of blood, toxins, including ammonia build up which can lead to the formation of ammonium biurate crystals in the urine.
Initially, there may be an incomplete blockage which means your cat is able to urinate but with difficulty.
Symptoms of difficult urination may include:
Weak flow of urine
Painful urination (stranguria)
Urinating in inappropriate locations
Frequent urination, with only a small amount of urine being passed (pollakuria)
Blood in urine (hematuria)
Licking of the genital region
The plug will continue to collect debris until it completely blocks the urethra. Once your cat has become completely blocked and is unable to void any urine at all, he, or she, is in danger unless they can be unblocked. A completely blocked cat is in a great deal of pain and discomfort. You may be able to feel the distended bladder towards the rear, unless it has ruptured. This is a medical emergency and veterinary attention is vital to unblock your cat.
Inability to urinate (many pet owners confuse this with constipation)
Additional symptoms may occur as the kidneys fail and toxins and potassium build up in the blood. These may include vomiting, loss of appetite, weakness, dehydration, lethargy, abnormal heart rhythm, drunken gait, neurological disturbances, bradycardia (slow heart beat) and ultimately collapse.
Your veterinarian should be able to make a tentative diagnosis based on presenting symptoms. He will perform a complete physical examination, at which time he will be able to feel a firm, full bladder, there will also be abdominal pain or discomfort.
He will need to run some diagnostic tests to determine the cause and to establish if any damage has occurred to the kidneys. Some tests may include:
Blood profiles to check blood potassium, creatinine and nitrogen levels and assess the kidneys for damage, look for signs of infection or systemic disease.
Urinalysis to look for infection and crystals in the urine and determine what type they are.
X-ray or ultrasound to evaluate for stones, congenital abnormalities, and tumours.
ECG (electrocardiogram) to monitor heart rhythm.
There are four necessary treatments in the blocked cat.
Removing the urine from the bladder
Unblocking the cat
Treating the biochemical and electrolyte imbalances
Supportive care such as pain medication and fluid therapy
Lower potassium levels. The first priority is to correct mineral imbalances in your cat. Treating hyperkalemia with sodium bicarbonate, insulin/dextrose or calcium gluconate.
Emptying the bladder. Your veterinarian may be able to manually express urine, or if this is not possible, by inserting a needle through the abdomen and into the bladder and withdrawing the urine (cystocentesis). This will offer instant relief as well as enable the kidneys to start filtering the blood again and prevent bladder rupture.
Once your cat’s potassium levels have dropped to a safe level, general anesthesia will be able to be performed.
Catheterisation may be used to allow the bladder to continue to void urine and may be in place for several days afterwards. Anesthesia will be required to catheterise the cat, which involves the insertion of a thin tube into the penis and up to the bladder. A sterile solution is flushed through the tube to push the obstruction back into the bladder, where it will dissolve or be surgically removed.
IV fluids to correct electrolyte imbalances and treat dehydration.
Once the obstruction has been removed, the kidneys are able to resume their job of urine production, removing toxins from the bloodstream. In the days after, urine production is increased as the kidneys clean the blood. This is known as post-obstructive diuresis. Intravenous fluids will be continued to prevent your cat from becoming dehydrated and developing hypokalemia (low blood potassium) as a result of increased urine output.
During this time, the catheter remains in place, urine output is carefully monitored by your veterinarian.
Painkillers and antispasmodic medications will be administered.
If an infection is present, antibiotics will be necessary.
Addressing the underlying cause will be necessary to prevent future occurrences. Increasing water consumption to dilute the urine is strongly recommended. Feeding a canned or raw diet may be recommended as this contains a higher amount of water than dry food.
Dissolving crystals: If your cat has urinary crystals, a prescription diet may be recommended to help dissolve them.
Surgery to remove stones: Uroliths may be too large to be dissolved or flushed out will need to be surgically removed. This is known as a cystomy.
Once the stones have been removed, they will be sent off to determine the type and a culture will be performed to determine what (if any) bacteria are also present so the most suitable antibiotic can be prescribed.
Perineal urethrostomy: For cats who have repeat blockages a perineal urethrostomy will be performed. This involves surgery to create a new urethral opening.
Follow your veterinarian’s instructions and administer medication as prescribed. Keep a close eye on your cat’s litter tray usage and take him straight to the veterinarian if he shows signs of blockage.
Increasing water consumption is important to keep the urine as dilute as possible which decreases the chances of crystal formation. Switching to a wet diet and encouraging your cat to drink by adding more water bowls or introducing a water fountain bowl, which many cats love.
Your cat should be kept as stress-free as possible to reduce chances of a recurrence. Litter trays should be kept scrupulously clean, and if there is any inter-cat aggression, this should be addressed and several litter trays provided. The general rule of thumb is one tray per cat, plus one extra.