What is urinary obstruction in intact male cats?

Urinary Obstruction in Intact Male Cats

Urinary obstruction in intact male cats is a life-threatening blockage of urine flow through the urethra, most commonly caused by urethral plugs (mucus and crystalline material), uroliths, or idiopathic functional obstruction, requiring immediate emergency intervention to prevent bladder rupture, post-renal azotemia, and death. 1, 2

Definition and Pathophysiology

Urinary obstruction occurs when urine flow is completely blocked, preventing bladder emptying 3. In male cats, the narrow urethra is particularly vulnerable to obstruction from:

• Physical obstructions: Mucous plugs (most common), urethral calculi (calcium oxalate or struvite), or blood clots 1, 2
• Functional obstructions: Idiopathic urethral spasm or inflammation without visible physical blockage 1
• Post-surgical complications: Bacterial cystitis following cystotomy can lead to secondary obstruction 4

The obstruction leads to progressive bladder distension, hydronephrosis, and life-threatening metabolic derangements 2.

Clinical Presentation

Diagnosis is typically straightforward based on history and physical examination 1:

• Behavioral signs: Straining to urinate (stranguria), vocalizing during attempts, frequent trips to litter box with no urine production 1, 2
• Physical examination: Firm, distended, painful bladder on abdominal palpation that cannot be manually expressed 3, 1
• Systemic illness: Lethargy, anorexia, vomiting, hypothermia in advanced cases 1, 2
• Severe cases: Visible distended/discolored penis (dark red to purple), indicating prolonged obstruction 3

Risk Factors

Multiple studies have identified consistent predisposing factors 2, 5:

• Age: Younger cats (mean age significantly lower than controls) 2
• Body weight: Higher body weight increases risk 1, 2
• Lifestyle: Indoor-only cats at significantly higher risk compared to indoor-outdoor cats 1, 2
• Diet: Exclusive dry food consumption increases risk 1, 2
• Seasonality: Regional variation exists—Northern US shows spring peak (April-May), particularly in Northeast but not Northwest coast 5
• Water intake: Decreased water consumption is a significant risk factor 1

Diagnostic Findings

Metabolic derangements develop rapidly and predict mortality 2:

• Electrolyte abnormalities: Hyperkalemia (life-threatening), hyperphosphatemia, hypocalcemia 4, 2
• Azotemia: Elevated BUN and creatinine from post-renal failure 4
• Hematology: Elevated WBC, RBC, and hematocrit from dehydration 4
• Urinalysis: Turbid appearance, hematuria (3+), proteinuria, low pH, crystalluria (calcium oxalate most common), bacteria if secondary infection present 4, 2
• Prognostic marker: Ionized calcium is significantly higher in survivors; hypocalcemia predicts mortality 2

Emergency Management Priority

Follow this algorithmic approach in order of priority 6:

1. Gentle distal urethral massage to dislodge plugs 6
2. Gentle bladder palpation to attempt voiding (avoid excessive pressure—rupture risk) 6
3. Cystocentesis: Controversial but appears safe and provides immediate decompression 1, 6
4. Retrograde urethral flushing with sterile saline 6
5. Combinations of above techniques 6
6. Diagnostic imaging (radiography/ultrasound) to determine if obstruction is intraluminal, mural, or extramural 6
7. Surgical intervention (perineal urethrostomy) only if absolutely necessary 6

Catheterization and Hospitalization

• Catheter size matters: Use 3.5 Fr catheters—smaller diameter associated with decreased reobstruction risk 1
• Fluid therapy: Any isotonic crystalloid is acceptable; rate determined by resuscitation needs and deficit replacement 1
• Antimicrobials: Do NOT use routinely during hospitalization; reserve for culture-proven infection at catheter removal 1, 4
• Antispasmodics: Commonly used but evidence is limited and conflicting 1

Prognosis and Recurrence

Overall survival is 90-95%, but recurrence is common 1:

• Recurrence rates: 22% at 6 months, 24% at 2 years 2
• Mortality rate: 8.5% overall 2
• Recurrence predictor: Lower urine pH at initial presentation significantly predicts recurrence 2
• Prevention strategies: Increase water intake and environmental modification decrease recurrence risk 1

Critical Pitfalls to Avoid

• Aggressive bladder palpation: Can cause bladder rupture in severely distended bladders 6
• Routine antibiotic use: Promotes resistance; use only when culture-indicated 1
• Ignoring hypocalcemia: Strong predictor of mortality—correct electrolytes before anesthesia 2
• Delayed intervention: Hyperkalemia can cause fatal cardiac arrhythmias within hours 4, 2