Urethral obstruction in cats

Urethral obstruction is a problem that occurs almost exclusively in male cats. This is because the urethra of a male cat is much longer and much narrower than that of a female cat, and so is more susceptible to becoming blocked.

Urethral blockage is not a common condition, but when it occurs it is painful, the cat will be unable to urinate despite repeated efforts, and it is a life-threatening emergency as it can cause acute kidney failure and death within 2-3 days if not managed appropriately.

What are the signs of urethral obstruction?

A cat with urethral obstruction will usually show:

  • Repeated attempts to urinate that are unproductive
  • Crying or discomfort when straining to urinate
  • Increased agitation, and there may be some vomiting

Depending on the underlying cause, you may also have noticed some other changes in your cat's urinating behaviour over the preceding few days such as increased frequency of urination, straining, discomfort or even some blood in the urine.

Contact your vet immediately if you think your cat may have an obstructed urethra, as this is an emergency situation.

What causes urethral obstruction?

Several underlying conditions can cause obstruction of the narrow urethra of a male cat, including:

  • A 'plug' in the urethra - this is usually an accumulation of proteins, cells, crystals and debris in the bladder that accumulates and lodges in the urethra
  • A small stone (urolith) or an accumulation of very small stones - these form in the bladder but may become lodged in the urethra
  • Swelling and spasm of the urethra - during inflammation of the bladder and urethra, whatever the cause, the inflammation may cause swelling of the wall of the urethra which may contribute to blockage, and in a number of cases the inflammation and irritation causes the muscle around the urethra (the urethral sphincter muscle) to go into spasm - this too can cause obstruction if the cat is not able to relax the muscle.

How is urethral blockage managed?

If your cat's urethra is blocked, your vet will need to relieve the obstruction quickly. However, your vet will usually want to perform some tests first to see if there are any significant complications. In particular, cats with a blocked urethra may develop acute kidney failure and may develop very high blood potassium concentrations; these are life-threatening complications that should be checked when possible.

To relieve the obstruction, your vet will usually need to sedate or anaesthetise your cat. X-rays or ultrasound may be needed to help determine the underlying cause of the obstruction and to help determine the best treatment method.

Generally under heavy sedation or anaesthesia the urethra passing through the pelvis and penis of the cat will be carefully palpated (felt) to try to locate the region of the obstruction. Careful massage in some cases is sufficient to relieve the obstruction, but often a catheter needs to be passed into the urethra (via the penis) so that fluids can be infused to help flush out the obstruction (or sometimes to push it back into the bladder). These procedures have to be done very carefully to avoid damaging the delicate lining of the urethra.

If the obstruction is caused by spasm of the urethral muscle, simply sedating or anaesthetising the cat may be sufficient to allow easy passage of a catheter into the bladder.

What happens after the obstruction is relieved?

Once the obstruction has been relieved, your vet will want to infuse a sterile saline solution into the bladder via the catheter so that all the blood and debris (that will inevitably be present in the bladder) can be washed out. This is usually repeated several times to remove as much debris as possible to reduce the chance of re-obstruction.

Once this has been done, your vet will decide whether the urinary catheter can be removed, or whether it will need to remain in place for a few days. Where possible the catheter is removed because the presence of a catheter itself causes some inflammation and irritation to the urethra. However, if there has been a severe blockage, your vet may want to leave a catheter in for a few days (usually no more than 2-3 days) to ensure urine can be produced while treatment is commenced for the underlying disease and inflammation.

What other treatments are given?

Further treatment depends on the underlying cause of the obstruction, the severity of the obstruction, and what (if any) complications have arisen. Any damage to the kidneys may be completely reversible, but cats will often have to receive intravenous fluids for several days if the kidneys have been affected. In addition to intravenous fluids, other drugs commonly used to help manage cats include:

  • Local anaesthetics injected into the urethra through the catheter before it is removed to help relieve pain
  • Other pain-killing (analgesic) drugs
  • Drugs to help relieve spasm of the urethra (spasmolytics) - in most cases these will be helpful because of the inevitable urethral irritation that will have occurred. Usually a combination of two different muscle-relaxing drugs are used (a so-called 'smooth muscle relaxant' such as phenoxybenzamine or prazosin, with a 'skeletal muscle relaxant' such as diazepam or danteolene).
  • Anti-inflammatory drugs to relieve the swelling in the urethra - corticosteroids are often used for this purpose

Long-term management of the cat with urethral obstruction

Preventing any further episodes of obstruction is the main long-term goal. In the short-term, while the initial swelling in the urethra settles down, cats may need to be on anti-inflammatory drugs, spasmolytics, and perhaps analgesics for several days and even up to a week or two.

Longer term, management is aimed at the underlying cause of the urethral obstruction. Cases associated with uroliths (stones in the urethra and bladder) will need to be managed with special diets to reduce the risk of their recurrence (see: FLUTD - treatment). Most cats with urethral spasm or urethral plugs are thought to have underlying feline idiopathic cystitis. These cats should be managed as such (see: Feline Idiopathic Cystitis), but where there are urethral plugs, diets to minimise crystals in the urine may also be helpful (see: FLUTD - treatment).

If repeated episodes of obstruction occur despite appropriate management, in some cases a surgical operation can be performed (called perineal urethrostomy) to help open and widen the narrow end to the urethra. This should not be regarded as a first line therapy though as it does not deal with the underlying cause, and the surgery can sometimes be associated with complications such as the risk of stricture formation and an increased risk of bacterial urinary tract infections.