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Client Library Article
URINARY OBSTRUCTION IN
DOGS
| Urinary Blockage- a
medical & possible surgical emergency |
| Urinary blockage is a medical emergency and
should be treated as soon as possible. Most dogs become blocked when a
bladder stone(s) passes into the urethra and becomes lodged thus preventing
the passage of urine. If the blockage is not relieved, severe
electrolyte imbalances involving potassium (K+) ensue leading to the
development of cardiac arrythmias (abnormal heart beat) and eventually
cardiac arrest & death. The urinary bladder can also rupture causing
urine leakage into the abdominal cavity and a chemical peritonitis to
develop.
Most dogs present for abdominal pain , crying / whining, and repeated
attempts with straining to urinate. Some dogs become partially
blocked when a stone acts as a ball valve in the urethra. These
dogs can pass only small amounts of urine- usually only drops at a time
which is not enough to empty the bladder nor prevent the electrolyte
imbalance. Partially blocked dogs must be differentiated from those
with urinary tract infections (UTI). Blockage occurs mostly in males
who have long thin urethras. Females have much shorter and wider
urethras and rarely become obstructed. Urinary tract infections (UTI)
can also lead to blocking by causing irritation and spasms of the
urethral smooth muscle. Dogs that have previously formed bladder
stones should be maintained on a specially formulated diet for life
and monitored closely for signs of repeat obstruction. |
| Bladder Stones (cystic
calculi) in dogs |
| The formation of bladder stones is fairly common,
especially in certain breeds of dogs. The three most common types of
stones are struvite (triple phosphate), calcium oxylate, and uric acid
stones. Dalmatians are predisposed to forming uric acid stones due to
a genetic defect in uric acid metabolism leading to a much higher
concentration of uric acid in the urine. Dogs with liver shunts are also at
a higher risk for uric acid stone formation. Struvite and calcium
oxylate stones seem to be more prevalent in small breed dogs, especially
Miniature Schnauzers, Lhasa Apso's, and Shih Tzu's. Stones & crystals form
in the kidneys or bladder when high concentrations of minerals precipitate
out of urine. Struvite stones & crystals form when the urine is very
alkaline (pH greater than 8) whereas calcium oxylate and uric acid stones
and crystals form in acidic urine (pH less than 7). Urine is evaluated to
look for the different types of crystals- identified based on their shape.
Additionally, many dogs with stones also suffer from chronic urinary tract
infections. Many dogs with crystals in their urine can be treated
medically by placing them on a special diet designed to dissolve existing
crystals and prevent future crystal & stone formation by limiting mineral
intake and manipulating urine pH Dogs with concurrent urinary tract
infections should also be treated with antibiotics. Large bladder (and
kidney) stones however will not dissolve completely and it is recommended
that they be surgically removed. If the stones are not removed, at some
point they are likely to pass into the urethra during urination and become
lodged causing a urethral obstruction. |
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Symptoms of urinary obstruction
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- Straining / crying when attempting to urinate (can be mistaken for
constipation)
- Painful abdomen / reluctance to move
- Only drops or no urine passed
- History of recent UTI or blood in urine
- Vomiting
- Anorexia / Lethargy
***Dogs with bladder stones often have no clinical signs other than
frequent urinary tract infections until they suddenly become obstructed. |
| Diagnosis |
- Urethral Obstruction- based on history,
clinical signs, and abdominal palpation where the bladder will be large,
hard, and painful.
- Inability to pass a urinary catheter into the bladder.
- Changes on blood work (electrolyte imbalance & high kidney values-BUN
& creatanine)
- Cardiac arrythmias (abnormal heart rhythm)
- Bladder stones- rarely can be palpated.
A radiograph (x-ray) is required to look for stones in the urinary tract
(kidneys, bladder, & urethra).
- Calcium oxylate and struvite crystals are radio-opaque and show up
easily on normal radiographs
- Uric acid stones are radiolucent and will not show up readily on
regular films. A special contrast x-ray study or ultrasound of the
bladder is needed to see uric acid stones.
- Urinalysis- look for infection & crystals- if present, check for
urinary tract stones
- If a stone is retrieved surgically, it should be identified via stone
analysis.
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| Treatment of Urethral
Obstruction |
- Treat for shock and electrolyte imbalances to stabilize the patient
- UNBLOCK the urethra- try with a urinary catheter, flush, and urethral
lavage & retropulsion- pushes stone back into the bladder
- Once unblocked, the catheter should be left in the bladder & urethra
until the dog has surgery
- If unable to unblock with a urinary catheter, the dog will require
emergency surgery
- After unblocking, medical care includes IV fluids to help flush
out the kidneys & bladder, antibiotics, antiinflamatories, and analgesics.
- Stones should be submitted for analysis
|
| Treatment of Bladder
Stones (cystic calculi) |
- Once unblocked and stable, a Cystotomy surgery is recommended for
patients who have remaining bladder stones seen on radiographs. If these
stones are not removed, the dogs is likely to reblock in the future.
- Post-operative care varies, from minimal to intensive, depending on
the patient.
- All dogs should be placed on a stone dissolving diet for at least
three months (if not life) after being blocked
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| Prognosis |
- Fair to good depending on early identification of bladder stones and
blockages, followed by aggressive medical and surgical
therapy.
- The dogs who do best are those maintained on special diets for life
and whose urinary tract infections are controlled.
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