Feline urethral obstruction (UO) is one of the most common and urgent conditions you will encounter in clinical practice, and it is a NAVLE® classic. Most often seen in young adult male cats, it is a blockage of the urethra that prevents normal urine flow and can rapidly lead to life-threatening hyperkalemia and acute kidney injury. Caused primarily by urethral plugs associated with feline lower urinary tract disease (FLUTD)/feline interstitial cystitis (FIC), though uroliths and other less common disorders are possible. Fast recognition and intervention directly determine morbidity and mortality by preventing severe metabolic and cardiovascular complications. A structured approach helps treat with confidence, as over 90% of cats survive to discharge. In this article, you’ll get an overview of how to recognize a pattern on the NAVLE® for diagnosis, stabilization, treatment, and long-term prevention.
Why Rapid Recognition is Necessary
Blocked cats often present with nonspecific clinical signs such as anorexia, vomiting, and depression. Sometimes owners report more specific urinary signs such as stranguria, dysuria, and hematuria. Hallmark physical exam findings include palpating a firm, painful, and distended urinary bladder, often along with dehydration +/- bradycardia.
UO causes rapid over-distension of the bladder, leading to bladder damage and even risk of rupture. This increased pressure is transmitted to the kidneys causing reduced blood flow and filtration, leading to rapidly rising potassium, metabolic acidosis, and azotemia. Without aggressive treatment, obstructed cats can develop fatal bradyarrhythmias within 24+ hours. While female cats can exhibit signs of FIC (e.g., dysuria), the long urethras of male cats that narrow sharply near the penile tip means that urethral plugs formed secondary to lower urinary track edema +/- crystalluria cause UO.
Focus on the Big Three Diagnostic Priorities
The NAVLE® asks about blocked cats, focusing on your ability to identify the most urgent diagnostics. Prioritize:
- Potassium: Hyperkalemia is the most immediate threat given the risk of cardiac arrest as arrhythmias worsen. IV calcium gluconate is temporarily cardioprotective. Used by itself, or in conjunction with short-acting insulin and dextrose CRI, terbutaline, or bicarbonate, all of which transiently reduce circulating potassium.
- Renal Values: Post-renal azotemia, acute kidney injury (AKI), dehydration, and shock all contribute to azotemia and hyperphosphatemia. Relieving the obstruction and using IV crystalloids to rehydrate and promote filtration resolves azotemia in most cases.
- ECG: As potassium rises to dangerous levels, ECG changes include tall, tented T waves, blunted or absent P waves (i.e., atrial standstill), and subsequent bradycardia. Occasionally cats present with normal heart rates due to sympathetic activation, but ECG changes persist.
Supplemental diagnostics, such as a CBC, full biochemistry, blood gas, focused ultrasound evaluation, and blood pressure are also important components of the initial evaluation.
Effectively Triage and Stabilize
Immediate Analgesia
Blocked cats are in severe pain. Use full µ-agonist opioids (e.g., methadone, hydromorphone), or buprenorphine if a pure µ-agonist is not available. Avoid NSAIDs since these patients already risk renal compromise.
Stabilization Prior to Unblocking
Place an IV catheter and begin fluids. Review initial diagnostics and treat hyperkalemia if present. Address indicators of shock, including low blood pressure or hypothermia. Always consider decompressive cystocentesis once sedated (or at presentation if moribund – the key is the cat must be still) to both provide rapid relief of bladder distension and reduce urethral pressure, thus facilitating catheter passage.
Sedation and Catheterization
Use anesthesia for catheterization, with drug choice dependent on patient severity. Benzodiazepines help reduce spasm. A coccygeal epidural can lower anesthetic requirements and improve catheterization success. Use soft, well-lubricated catheters and very gentle manipulation. Suture short-term indwelling catheters in place with closed urinary collection systems to continue drainage. Use physiologic saline to gently lavage the bladder after de-obstruction.
Next Diagnostic Steps
After stabilization and de-obstruction, undertake further diagnostics to complete the workup. Abdominal radiographs confirm proper catheter placement and check for radiopaque uroliths. Full urinalysis +/- culture (sample taken from the catheter prior to flushing) evaluates for infection and crystals.
Importance of Post-Obstruction Management
Continue IV crystalloids, analgesia (buprenorphine +/- gabapentin), and recheck blood work until normalized. Monitor electrolytes frequently (every two to four hours until normalized, then every eight to twelve). Repeat blood gas to monitor for resolution of acidemia if initially concerning. Check renal values every 24 hours.
Post-obstructive diuresis can be dramatic. Monitor urine output every one to two hours, and match losses with IV fluid administration to prevent dehydration and keep up with diuresis. Adjust rates as the cat stabilizes. Reduce in-hospital stressors as much as possible, with medications, environment, and handling considerations.
Four Signs It’s Time to Remove the Urinary Catheter
After at least 24 hours of catheterization, there are four important factors that help determine when to attempt urinary catheter removal:
- The urine must be clear (no longer bloody or cloudy)
- Urine output normalized
- IV fluid rate weaned
- Azotemia resolved
Ensure the patient can fully and comfortably void his bladder after urinary catheter removal. Consider urine culture post-catheter removal in case of iatrogenic infection. Discharge on short-term oral analgesics +/- antibiotics as indicated.
Preventing Reoccurrence is Multifactorial
Blocked cats have a 50% lifetime recurrence risk. Warn owners of the risks/signs of re-obstruction and discuss ways to increase the chances of prevention. Prevention strategies include increasing water intake (wet food, fountains, multiple bowls), reducing stress (especially environmental changes, such as number and cleanliness of litterboxes), and using prescription urinary diets when crystals are present.
Cats who experience repeated episodes of obstruction are candidates for perineal urethrostomy (PU), but due to the invasive nature and possible complications, this surgery is not a first-line treatment option. Cats with uroliths need a cystotomy for stone removal AFTER full stabilization and resolution of bloodwork abnormalities. Perform cystotomy prior to urinary catheter removal, given the immediate risk of re-obstruction. Stone analysis after removal dictates the type of life-long prescription diet necessary for these cats.
Instruct owners that stress is the primary driver of FIC and provide them many environmental, dietary, and pharmacological options to aid in prevention.
More on Feline Urethral Obstruction for Subscribers:
- Top 5 Feline ER Presentations: Urethral Obstruction Notes
- Top 5 Feline ER Presentations: Urethral Obstruction Lecture
Zuku Learning Resources:
- Master NAVLE® concepts
- Subscribe to the Question of the Day to receive a NAVLE® question delivered to your inbox daily
- Review the How to Triage your NAVLE® Study for Maximum Points blog
