How can I diagnose a blocked Foley catheter in an adult patient with abdominal distension, especially if they have a spinal cord injury above T6?

Diagnosing a Blocked Foley Catheter

In patients with suspected catheter blockage, immediately assess for absent or reduced urine output, suprapubic distension, bladder palpability, and urine leakage around the catheter—these clinical findings confirm the diagnosis without requiring imaging. 1

Immediate Clinical Assessment

Primary Diagnostic Signs

• Absent or minimal urine output despite adequate hydration is the hallmark finding of catheter blockage 1
• Suprapubic fullness or distension on abdominal examination indicates bladder overdistension from obstructed drainage 1
• Palpable bladder on physical examination confirms urinary retention behind the blocked catheter 1
• Urine leakage around the catheter (bypassing) occurs when intravesical pressure exceeds the blockage, causing overflow incontinence 1

Critical Warning Signs in High Spinal Cord Injury (Above T6)

Patients with spinal cord injuries above T6 require immediate evaluation and treatment because bladder distension from a blocked catheter can trigger life-threatening autonomic dysreflexia. 2

• Sudden severe headache is the cardinal symptom of autonomic dysreflexia from bladder overdistension 2
• Profuse sweating above the level of injury, particularly facial and neck sweating 2
• Severe hypertension (systolic BP often >200 mmHg) develops rapidly 2
• Bradycardia or cardiac dysrhythmias may occur as a reflex response to hypertension 2
• Visual disturbances such as complaints of bright or glaring lights 2
• Altered consciousness or seizures indicate severe autonomic dysreflexia requiring emergency intervention 2

Diagnostic Approach

Step 1: Bedside Clinical Examination

• Palpate and percuss the suprapubic region for bladder distension—a palpable bladder extending above the pubic symphysis confirms retention 1
• Check the catheter drainage bag for absence of urine output over the preceding hours 1
• Inspect the catheter tubing for visible debris, sediment, or crystalline material suggesting encrustation 3, 4
• Assess vital signs immediately in patients with spinal cord injury above T6 to detect autonomic dysreflexia 2

Step 2: Attempt Manual Irrigation

• Gently attempt to flush the catheter with 30-50 mL of sterile saline using a catheter-tip syringe 1
• Complete resistance to flushing confirms catheter blockage 1
• Ability to instill but not aspirate fluid suggests one-way valve obstruction from debris 1
• Easy flushing with return of cloudy or sediment-laden urine indicates partial blockage that may respond to irrigation 1

Step 3: Bladder Scanning (If Available)

• Use portable bladder ultrasound to objectively measure bladder volume if clinical examination is equivocal 5
• Bladder volumes >400-500 mL with minimal catheter drainage confirm obstruction 5

Common Causes of Blockage

Crystalline Encrustation (Most Common)

• Proteus mirabilis infection is the primary cause of catheter encrustation and blockage, accounting for the majority of cases in long-term catheterized patients 1, 3, 4
• Urease production by P. mirabilis generates ammonia, alkalinizing urine and precipitating calcium and magnesium phosphate crystals 3, 4
• Crystalline biofilm formation progressively occludes the catheter lumen, typically causing blockage within 24-48 hours once established 3, 6
• All catheter types including silver-coated and silicone catheters are vulnerable to this mechanism 3

Other Obstructive Causes

• Blood clots from urethral trauma, recent instrumentation, or hematuria 1
• Mucus plugs particularly in patients with chronic inflammation 1
• Catheter kinking from external compression or malposition 1

Immediate Management

Once blockage is confirmed, immediately remove the obstructed catheter and replace it with a new catheter—do not waste time attempting prolonged irrigation of a completely blocked catheter. 2

In Patients with Spinal Cord Injury Above T6

• Treat as a medical emergency due to autonomic dysreflexia risk 2
• Remove the blocked catheter immediately without delay for additional testing 2
• Insert a new 14-French silicone Foley catheter promptly to decompress the bladder 2
• Administer sublingual nifedipine 5-10 mg if hypertension or autonomic dysreflexia symptoms are present, ideally before catheter manipulation 2
• Monitor for resolution of symptoms within 5 minutes of bladder decompression 2

Common Pitfalls to Avoid

• Do not delay catheter replacement in patients with complete obstruction—irrigation rarely succeeds once crystalline biofilm has formed 3, 4
• Do not underestimate the urgency in spinal cord injury patients above T6, even if they appear clinically stable on arrival—autonomic dysreflexia can develop suddenly and catastrophically 2
• Do not assume infection requires imaging—the diagnosis of catheter blockage is clinical, not radiographic 1
• Do not rely on patient symptoms alone in patients with impaired sensation—they may not perceive bladder distension until complications develop 2, 7

Prevention of Recurrent Blockage

• Increase fluid intake to maintain dilute urine and reduce crystal precipitation 4
• Consider citrated drinks (cranberry juice is ineffective for UTI prevention but citrate may reduce crystallization) 1, 4
• Eliminate Proteus mirabilis with targeted antibiotics as soon as it appears in urine cultures, before biofilm establishment 4
• Shorten catheter change intervals to every 5-7 days in patients with recurrent blockage from crystalline biofilm 3, 4