Blocked cat quiz

Diagnosing and treating the "blocked cat"

By David Liss, RVT, VTS (ECC, SAIM)

The “blocked cat” suffers from a urethral obstruction, and most often demonstrates signs of lower urinary tract disease, including stranguria, dysuria, hematuria, pollakiuria, and urolithiasis. Cats tend to get oxalate and struvite stones evenly, therefore technicians should be familiar with urinalysis and the appearance of these crystals. Patients are most often stable when presenting, but approximately 12% can have life-threatening electrolyte and acid-base abnormalities that may result in death if not treated immediately.


History and clinical signs

Often an owner will notice urine spotting, potentially with hematuria, frequent visits to the litter box, excessive perineal licking, yowling, vocalizing, lethargy, anorexia, constipation, or straining to urinate. These patients should have their bladder palpated immediately upon arrival, in addition to a TPR and primary survey. Clinical signs include a large firm bladder, abdominal pain, tachycardia, bradycardia, hypothermia, hyperthermia, tachypnea, lateral recumbency, obtundation, and vocalization.


Most cats obstruct due to a mucous plug or small urolith (grit) lodging in their urethra. As urinary output decreases, the bladder fills. Inability to urinate causes an increase in uremic toxins, such as BUN and creatinine, and decreased excretion of potassium and phosphorus ions. As water intake decreases, patients become dehydrated and hypovolemic. The severe metabolic derangements can contribute to a metabolic acidosis, caused by inability to excrete hydrogen ions and accumulation of lactate, and this worsens the process. Hyperkalemia can cause cardiovascular arrhythmias, which can result in death. As the bladder continues to fill, wall necrosis occurs, placing the animal at risk for bladder rupture and subsequent uroperitoneum. In addition to mucous plugs, neoplasms causing urethral obstruction are seen; these are typically associated with transitional and squamous cell carcinomas. In rare cases, urethral strictures can also cause obstruction.  

Initial interventions

The first goal is to identify and treat any underlying metabolic/acid-base abnormalities, followed by relieving the urethral obstruction.  In order to restore circulating volume, an IV catheter should be placed, and an ECG and minimum database performed. The minimum database often reveals low pH, low bicarbonate, low calcium, high potassium, high BUN, and high lactate. Initial IV fluid therapy is achieved with a balanced crystalloid solution. It was once recommended to use 0.9% NaCl fluids because they have no potassium, however, recent studies indicate the small amount of potassium in balanced solutions like Normosol-R, Lactated Ringer’s, or Plasma-lyte, rarely contribute to worsening hyperkalemia. In addition, these solutions have buffers to help restore normal blood pH; in contrast, 0.9% NaCL is acidic. Sometimes an initial fluid bolus will be enough to lower the serum potassium to normal, or lower than critical range. In addition, fluids may help restore perfusion and return lactate levels to normal. Common ECG findings with hyperkalemia include: depressed or absent P-waves (atrial standstill), wide QRS complexes, tall T-waves, ventricular tachycardia, or sinus tachycardia.

Metabolic and acid-base disturbances should be addressed before the patient is anesthetized/sedated for urethral de-obstruction procedures. Once IV fluids have been given, if the patient is still severely hyperkalemic other treatment should be instituted to address that.  Once the blocked cat has been stabilized and the serum potassium has been lowered, they are ready for de-obstruction.

Opioid/benzodiazepine combinations may provide enough sedation for urethral catheterization. Cats do not tend to do well with large doses of opioids. Oxymorphone, anecdotally, seems to be a decent choice for a pure mu opioid in the cat.

Butorphanol is an excellent sedative, but does not provide adequate analgesia. It can be combined with a benzodiazepine for excellent sedation. Ketamine/diazepam combinations are controversial; ketamine is excreted in the kidney in the cat, and urethral obstruction can cause accumulation of the drug. Yet if the goal is to quickly de-obstruct these patients some authors think it is not much of a concern. Since ketamine is contraindicated in heart disease, however, it is important to make sure the cat has first been auscultated.

Propofol can be used but it is a negative inotrope and vasodilator. Thus, it is recommended to use as little Propofol as possible.

Once anesthesia is achieved, these patients can be maintained on gas anesthesia and titrated as needed.

De-obstruction procedure

Once the patient is ready for catheterization, the penis can be extruded and should be examined for mucus or grit. Sometimes this can be teased out and the obstruction relieved. If urohydropropulsion is to be used, an open-end tomcat catheter, or sterilized olive tip catheter, can be used. The catheter is lubricated and gently advanced into the urethra until resistance or grit is felt. Saline is gently pulsed into the catheter to relieve the obstruction. The process can be long and tedious, but once the obstruction is popped back into the bladder, the bladder should be emptied. Then longer-term urinary catheterization is performed using a 3.5Fr or 5Fr Red rubber catheter. This catheter should be pre-measured, and an x-ray post placement should be taken to avoid excessive lengths of catheter in the bladder. This can be sutured in using a variety of methods including placing stay sutures, tape or Elastikon, staples, or suturing directly to the prepuce. An E-collar should be placed on the patient to avoid removal. The bladder should be flushed with copious amounts of saline. Anecdotally, it is recommended to flush until the urine is somewhat clear, especially if gross hematuria is present. Once this is done, the urinary catheter should be connected to a sterilized closed system. The majority of cases of urethral obstruction are caused by sterile cystitis, and some are caused by idiopathic cystitis unrelated to urolithiasis. Leaving a catheter open puts the patient at risk for an iatrogenic resistant UTI. Patients can be stabilized, discharged, and seen a few days later for a cystocentesis and urine culture submission.

Nursing care

Post-obstruction patients require intensive nursing care. Their analgesic needs can be met by administering intravenous, and later transmucosal buprenorphine. Patients may be started on anti-spasmodic medications such as phenoxybenzamine or prazosin. However, these drugs are vasodilators and hypotension can occur. It is recommended to monitor the cat’s cardiovascular status when starting these drugs. Since these patients have an invasive urinary catheter in place, proper care and maintenance is required to prevent iatrogenic UTI development. Catheters should be inspected for patency daily every 4-6 hours, and cleaned with a dilute chlorhexidine solution. Urinary output should be monitored daily every 4 hours by using a needle and syringe, and not disconnecting the IV bag from the soluset. The bag and line should be changed every 24 hours as needed. Urine output should be monitored closely in these patients. They often suffer from post-obstructive diuresis and the kidneys go into overdrive. In this case, the patient needs their IV fluids increased, not decreased. Lowering the fluids in evidence of excessive urinary output could be detrimental. Once patients are more stable, 12 hours after de-obstruction, their nursing care can be limited to pain assessment/scoring, urinary catheter care, and TLC (food and water should be offered). Most patients go home 2-3 days after obstruction relief.

Medical management

This is considered very important in feline patients to prevent recurrence of FLUTD. If the cause is not a urolith, it is often feline idiopathic sterile cystitis. Treatments include stress reduction, moist food, increased water intake, glycosaminoglycans (glucosamine and chondroitin), and potentially feline pheromones (Feliway®). If uroliths are the cause, feeding a canned urinary diet, with increased access to water (fountains, etc.) helps dilute urine. In addition, glycosaminoglycans can also be used. Urine should be submitted for culture and sensitivity, and antimicrobial medications used if indicated.

This article is based on a presentation given by Mr. Liss at the Atlantic Provinces Veterinary Conference in Halifax,NSCVT