Between a rock and a hard place – Urinary tract obstructions in cats


Winter is coming and cats are spending more time indoors. Whether or not this is the reason, we have had a recent spate of a particular type of emergency that we see in cats -> lower urinary tract obstructions.  The blocked cat is your classic all or nothing emergency, like GDVs in dogs.  If it is not fixed urgently, the feline will not survive.  However, it is not necessarily an easy or straightforward complication to deal with. For nomenclature’s sake, we call the condition FLUTD (Feline Lower Urinary Tract Disease) obstructed.

Urinary tract obstruction secondary to FLUTD occurs almost exclusively in male cats.  It is not solely to do with development of crystals and stones in the bladder as sometimes crystals are not identified. Male cats have a longer and more narrow urethra than females, so they do tend to be more prone to blockages.

The exact cause for most cases is not clear -> why do some cats form crystals and others don’t?  Why do some obstruct without crystals being found? The majority of obstructed cats have struvite crystals forming a plug at the tip of the penis, the most narrow point of the anatomy.  Struvite are a particular type of crystal commonly formed in bladders, particularly when the urine pH is abnormal or there are build ups of certain minerals in the urine.  There are thoughts that factors including the cat’s metabolism, stress, genetics, body weight and diet play a role.  Stress does seem to be commonly associated with FLUTD, though is not always easy to identify in cats.  Cats can be very highly strung and very much creatures of habit.  Factors such as small changes in the household environment can play a role (i.e. a new rug or set of cushions even!).  Indoor cats are often overrepresented with urinary tract obstruction.  They may have periods where they do not drink enough to dilute their urine, or may not urinate as often to empty the bladder of the smaller crystals, leading to a build up of crystals resulting in obstruction.

blocked tom

The onset of urinary tract obstructions is not always obvious.  Some cats may show signs of straining to urinate, passing small volumes of bloody urine, occasionally urinating in inappropriate locations.  Others may just become more lethargic and particularly where entirely indoors, may not be noted to urinate for a day or two.  They develop very tense and painful bellies.  Diagnosis is often very quick with palpation of a large, often rock hard bladder in a painful abdomen.  Examining the prepuce may reveal evidence of crystals at the tip of the penis, or sometimes a discoloured (often purple) penis.

It is critical that these patients are attended to as early as possible.  Urine is full of toxic metabolites, on a course for elimination.  If they are unable to be eliminated, they build up in the blood stream leading to a range of complications, the most serious of which involve the heart function.  Untreated, an overload of potassium will eventually cause the heart to stop, and potassium can build to very high levels in urine.  Other signs noted include general malaise, vomiting, dehydration and depression as the problem evolves. Kidney function is also impaired by the pressure building in the bladder backing up to the kidneys, in combination with the dehydration that develops and the resultant cardiovascular compromise.

A quick assessment needs to be followed up by blood tests to evaluate the levels of potassium and kidney enzymes, as well as an ECG to categorize cardiac function.  If the heart function is abnormal and the potassium level very high, medical intervention may be necessary to improve these factors prior to anaesthetising for unblocking the urinary tract.  Once satisfied the patient is stable for an anaesthetic, the unblocking process can proceed, however, some patients won’t be stable until they are unblocked, so tough decisions may need to be made. Unfortunately, some patients will not survive the unblocking process if they are critical enough.

Unstable patients can also be unobstructed under epidural anaesthesia (a particular blockade called a “coccygeal block” can be performed at the tail base).  Relieving the obstruction can be challenging in some patients and potentially traumatising in itself.  In rare cases, an emergency perineal urethrostomy (surgery on the penis) needs to be performed as the only way to relieve the obstruction.

Once the passage is opened, we aim to flush the urethra and bladder with sterile saline to aid removal of as much crystal content as possible.  An indwelling urinary catheter is then placed and maintained for 24-48 hours, usually with a closed collection bag attached to monitor urine production.  Fluid therapy is very important in the post-obstructive phase and the challenge is to balance rehydration of the patient with a potentially greater urine output as the kidneys kick back into action and try to eliminate the accumulated toxins.

Medications, such as muscle relaxants and anti-anxiety drugs, may be utilised after the obstruction is relieved and the patient’s blood work begins to return to normal.  Sometimes very dramatic elevations of kidney enzymes are seen on the blood tests and fortunately, these often improve very quickly once the obstruction is relieved and appropriate fluid therapy is provided.  Antibiotics are rarely needed and should only be used if there is a proven urinary tract infection (UTI).  In general, they ideally should be withheld until the catheter is removed since this can encourage development of UTIs.

The next step is to remove the urinary catheter and monitor the cat until he begins to urinate on his own. This is extremely important, since some cats may obstruct again once the catheter is removed, especially if there are any residual crystals hanging around in the bladder. More often the type of complications I see after catheter removal involve irritation to the urethra caused by the crystals/obstruction, the catheterisation process or a combination of the two. The urethra is quite muscular and when irritated through this process, can spasm after the catheter is removed. This can sometimes lead to a functional obstruction rather than a physical obstruction. Regardless of the issue, if the cat cannot pee, it may need to be recatheterised.

Recurrence is common in these boys, unfortunately. We do send them home with special diets and instructions on environmental enrichment, however, it can occur again despite all best intentions and interventions. When this is the case, surgery can be very successful in reducing the recurrence rate (again may not be 100% successful if a stone lodges high up in the urethra). Amazingly many owners are proud to admit their cat has “had a sex change” – well, it is not really a sex change, but the anatomy of the penis is altered so the tip is more open, and I suppose the “boy bits” do resemble “girl bits” a little more closely. After the surgery, the boys may be more prone to urinary tract infections since one of the primary defence mechanisms has been removed, so cystitis can still occur and urination needs to be monitored.


Urinary tract obstruction is an issue that requires dedication from the feline owners since it can be an expensive outcome with potential for ongoing costs. It certainly highlights the need to closely observe your pets and quickly seek advice if anything seems amiss.



One thought on “Between a rock and a hard place – Urinary tract obstructions in cats

  1. […] Between a rock and a hard place – Urinary tract obstructions in cats […]

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