In some case, spasms of the urinary tract can cause obstruction, too. This may be secondary to pain, infection, inflammation or cancer.
What you may notice at home is an increased need to go outside, frequent squatting and straining without production of any urine (or production of small amounts), restlessness, panting and a distended, tight belly. If untreated, dogs may develop vomiting and collapse. If you notice these signs, it is an emergency, and your dog should be evaluated immediately. Urinary obstruction can lead to bladder rupture if not addressed promptly. There is no specific safe treatment at home, thus you should seek veterinary care.
If, after a physical exam, your veterinarian suspects a bladder obstruction, he or she will start with X-rays of the urinary tract. This includes the kidneys, ureters, bladder and urethra. X-rays will determine if stones are the cause. Many bladder stones can be seen easily, although a certain subset of them are not. If no stones are seen, further investigation for a cause will need to be conducted.
Regardless of the underlying cause, relief of the obstruction is needed. This is accomplished by passing a urinary catheter into the bladder. In dogs, this isn’t possible without heavy sedation and/or anesthesia. Be prepared for this if your dog is not urinating.
Urinary obstruction causes imbalances in electrolytes. Instead of the kidneys excreting potassium into the urine, the body retains the potassium. As the bladder remains obstructed, potassium levels rise, leading to dangerous cardiac arrhythmias. Prior to sedation, your veterinarian will conduct blood work on your dog to ensure that electrolytes are normal. If they are not, fluids will be given to correct abnormalities.
Since fluid therapy will delay passing a urinary catheter, the veterinarian will do a cystocentesis. This is when a needle is passed through the body wall into the bladder. It is often done using an ultrasound to guide the needle. The bladder is then emptied of urine. This gives time for electrolytes and fluid imbalances to be corrected. As a result, sedation and anesthesia are much safer.
Depending on the cause of the obstruction, a urinary catheter may be left in place. If stones in the urethra were present, placing a urinary catheter will flush them back into the bladder. At that time, surgery (called a cystotomy) to remove the stones will be done. If spasms are the cause of the problem, medications may be given to decrease the inflammation, and the catheter left in place for one to three days. If a cause for the obstruction cannot be found, further testing such as ultrasound and CT scan of the urinary tract may be conducted.
Prognosis depends on the cause of the obstruction. The most important thing to know is that if your dog appears unable to urinate, an urgent veterinary trip is needed. Do not wait. The sooner this problem is addressed, the better the outcome.
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Catherine Ashe is a veterinarian, mother and freelance writer residing in Asheville, North Carolina. For nine years, she practiced emergency medicine and is now a relief GP. When not working, she spends time with her family of six, reading, writing and enjoying the Blue Ridge mountains.