High-output fistulas are usually from the proximal small bowel. The fluid contains digestive enzymes and produces significant skin breakdown. Malnutrition and electrolyte abnormalities lead to higher morbidity.

Medium-output fistulas are from the mid small bowel and have fewer problems than the high-output fistulas.

Low-output fistulas are from the distal ileum and have the highest chance of closing with conservative management.

Colon fistulas will rarely have electrolyte problems, but abscess and infection are the most frequent causes and antibiotics, drainage, and often diversion are necessary.

Rectal fistulas are usually the result of obstetrical injury or radiation injury.

When the fistula has an anatomic condition that will prevent spontaneous closure—such as a distal obstruction, foreign body, or tumor—surgical therapy will be needed after stabilization. All other patients should be given a chance at spontaneous closure with medical management.

The initial treatment is to assess and correct fluid and electrolyte balance, manage the malnutrition, and evaluate for signs of sepsis related to internal abscess or peritonitis.

Perform a CT scan with contrast to identify the level of bowel involved and determine complicating factors such as an abscess. If an abscess is identified, then IR drainage will be indicated.

Intestinal drainage from a small fistula opening may be managed with an ostomy bag.

Drainage through an open abdominal wound is more difficult to collect. The use of negative pressure wound therapy (NPWT) has been successful in increasing the rate of spontaneous fistula closure and allows for collection of the fluid to help in calculating fluid and electrolyte replacement. It also decreases bacterial infection.

Total parenteral nutrition (TPN) is administered to provide 40 to 45 kcal/kg per day.

Somatostatin analogs and proton pump inhibitors should be given for medium- and high-output fistulas.

In the absence of sepsis, distal obstruction, or cancer, one should allow 4 to 6 weeks of medical management before considering surgical treatment. Of all fistulas that are likely to close spontaneously, 85% to 90% close within 4 to 6 weeks after the initiation of conservative management. Patients with fistulas who show signs of improvement during this period may continue to be treated conservatively with the expectation of closure. Conversely, patients who show no signs of improvement should undergo surgical treatment. After 3 months of conservative treatment, fistulas that have not healed spontaneously will not heal.