Small Bowel Fistula

A small bowel fistula is an abnormal communication between jejunum or ileum and another epithelial surface.

It may be:

• Enterocutaneous
• Enteroenteric
• Enterocolic
• Enterovesical
• Enterovaginal
• Enterobiliary

Postoperative anastomotic failure is a major cause. Crohn disease, malignancy, radiation injury and abdominal sepsis are other important causes.

External fistulas are classified by output:

• Low output: below 200 mL per day
• Moderate output: 200 to 500 mL per day
• High output: above 500 mL per day.

High proximal fistulas can rapidly cause sodium, water, magnesium and nutritional depletion.

External fistulas produce enteric drainage through a wound or drain site.

High output fistulas cause thirst, oliguria, hypotension, weight loss, hypokalaemia and hypomagnesaemia.

Internal fistulas present according to the target organ. Enterovesical disease produces pneumaturia, recurrent urinary infection or faecaluria. Enterocolic fistulas can cause diarrhoea and malabsorption.

Persistent fever or tachycardia should raise concern for an associated undrained abscess.

Measure fistula output accurately every 24 hours.

CT abdomen with oral and IV contrast where appropriate: define the tract and identify abscess, distal obstruction or active intestinal disease.

Anatomy is defined fully only after initial sepsis, fluid and electrolyte abnormalities have been stabilised.

Monitor renal function, sodium, potassium, magnesium, phosphate and nutritional status.

Priorities are sepsis control, replacement of losses, nutrition, skin protection and anatomical definition.

Drain associated abscesses percutaneously whenever feasible.

Replace measured fistula losses rather than prescribing static maintenance fluids.

Low output fistulas can often tolerate oral or enteral nutrition. High output fistulas frequently require parenteral nutrition, although distal enteral feeding or fistuloclysis should be used when suitable bowel is available.

For high output:

Loperamide 4 mg orally three to four times daily, ideally before meals and at bedtime, can be titrated according to output and tolerance.

For proximal hypersecretory output:

Omeprazole 40 mg orally once or twice daily can reduce gastric secretory volume.

Neither drug closes a fistula mechanically. Their role is output control.

Spontaneous closure is unlikely when there is distal obstruction, uncontrolled sepsis, active Crohn disease, malignancy, radiation injury, foreign body or a mature epithelialised tract.

Definitive surgery should be delayed until sepsis is eradicated, nutritional status has recovered and the hostile abdomen has matured. Complex postoperative fistulas commonly require several months before safe reconstruction, often 6 months or longer.

At definitive surgery, resect the fistula bearing bowel segment and restore healthy bowel continuity rather than simply oversewing the external opening.