Step 2 CK · Surgery

Surgical Nutrition, TPN & Enterocutaneous Fistula

Name: Surgical Nutrition, TPN & Enterocutaneous Fistula
Creator: Veli Bakalov, MD

Feed the gut when you can, the vein when you must, and the fistula patiently

Surgery·Perioperative Care·4 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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High-yield

Unintentional weight loss above 10% in about 6 months signals malnutrition; albumin below 3 g/dL predicts surgical complications.
Prealbumin half-life is about 2 days (short-term response to feeding) versus about 20 days for albumin (chronic status); both fall with inflammation.
Stressed surgical patients need about 25–30 kcal/kg/day and 1.2–2 g/kg/day of protein.
Enteral beats parenteral when the gut works: feed within 24–48 h of surgery and go post-pyloric for gastric intolerance.
TPN is for a gut that cannot be used; its complications are line sepsis, hyperglycemia, steatosis, cholestasis, and acalculous cholecystitis.
Refeeding syndrome brings hypophosphatemia, hypokalemia, and hypomagnesemia after feeding a starved patient: start at 10–20 kcal/kg/day and give thiamine first.
Enterocutaneous fistula: control sepsis, protect skin, NPO plus TPN, and octreotide; above 500 mL/day is high output.
FRIENDS prevents fistula closure: foreign body, radiation, inflammation or infection, epithelialization, neoplasm, distal obstruction, steroids.
Short bowel syndrome needs parenteral support during adaptation; teduglutide, a GLP-2 analog, reduces PN dependence.

Assessing nutritional status and needs

Recognizing malnutrition. Unintentional loss of more than 10% of body weight over about 6 months, poor intake for more than a week, BMI below 18.5, and visible muscle and fat wasting identify patients at risk of infection, poor wound healing, and anastomotic failure. Severely malnourished patients benefit from 7–14 days of nutrition support before major elective surgery.

Serum proteins. Albumin (half-life about 20 days) reflects chronic status, and a level below 3 g/dL predicts complications. Transferrin (about 8–10 days) is intermediate, and prealbumin (transthyretin, about 2 days) tracks recent intake and the response to feeding. All three are negative acute-phase proteins that also fall with inflammation, liver disease, or protein loss, so read them alongside CRP.

25–30 kcal/kgdaily energy for most stressed surgical patients

1.2–2 g/kgdaily protein, more after burns or major trauma (0.8 g/kg when unstressed)

Measuring balance. Indirect calorimetry is the most accurate measure of energy expenditure. Nitrogen balance equals protein intake in grams divided by 6.25, minus the 24-hour urine urea nitrogen plus 4 g; a positive balance means anabolism.

Enteral vs parenteral nutrition

If the gut works, use it. Enteral feeding preserves villi, gut IgA, and the mucosal barrier, limits bacterial translocation, and causes fewer infections at lower cost. Start within 24–48 hours of surgery, even after a bowel anastomosis; waiting for flatus is outdated. Obstruction, bowel ischemia, uncontrolled shock, and a high-output fistula are the contraindications.

Choosing the route. Nasogastric tubes suit short-term feeding. High gastric residuals, gastroparesis, recurrent vomiting, or aspiration call for post-pyloric (nasojejunal) feeding, and needs beyond about 4–6 weeks call for a percutaneous gastrostomy or surgical jejunostomy. Keep the head of the bed at 30–45°.

Enteral vs parenteral nutrition

Feature	Enteral	Parenteral (TPN)
Use when	The gut works and can be reached	Prolonged ileus, obstruction, high-output fistula, short bowel, severe malabsorption
Access	Nasogastric, nasojejunal, gastrostomy, jejunostomy	Central line (PICC or CVC) for hypertonic full-strength TPN
Gut mucosa	Barrier and immunity maintained	Villous atrophy, bacterial translocation
Timing	Within 24–48 h of surgery	After about 7 days if well nourished; early if malnourished

Peripheral parenteral nutrition is limited to dilute solutions (about 900 mOsm/L) and short courses.

TPN complications and refeeding syndrome

Line and metabolic problems. Catheter bloodstream infection (staphylococci, Candida), pneumothorax at insertion, and venous thrombosis. Hyperglycemia is the most common metabolic complication, followed by hypertriglyceridemia and electrolyte shifts.

Liver and gallbladder. Excess dextrose causes hepatic steatosis early, and prolonged TPN causes cholestasis. Without food in the duodenum, CCK is not released, the gallbladder does not empty, and sludge, stones, and acalculous cholecystitis follow.

Refeeding syndrome. In starved patients (alcohol use disorder, anorexia nervosa, little intake for more than 5–10 days, BMI below 16), a carbohydrate load triggers insulin release that drives phosphate, potassium, and magnesium into cells and consumes thiamine. Hypophosphatemia, the hallmark, depletes ATP and causes weakness, respiratory and heart failure, arrhythmias, rhabdomyolysis, hemolysis, and seizures; thiamine loss can precipitate Wernicke encephalopathy. Start at about 10–20 kcal/kg/day and advance over several days, replete electrolytes, give thiamine before the first calories, and check levels daily. If it develops, slow the feeding and replace electrolytes IV rather than adding dextrose or insulin.

Enterocutaneous fistula

Cause and output. Most fistulas follow an anastomotic leak or inadvertent enterotomy. Output below 200 mL/day is low, 200–500 moderate, and above 500 high. High-output fistulas, usually from the proximal small bowel, close less often and cause dehydration, hypokalemia, hypomagnesemia, and non-anion-gap acidosis.

Resuscitate, control sepsisCT-guided abscess drainage and antibiotics; early laparotomy in a hostile abdomen risks new enterotomies.
Protect skin, replace lossesPouching against caustic effluent; fluids and electrolytes.
Nutrition, reduce outputNPO with TPN for high-output or proximal fistulas; octreotide and PPIs cut output, though octreotide has not reliably raised closure rates.
Define the anatomyCT or fistulography.
Wait, then repairMost fistulas that will close do so within 4–6 weeks of sepsis control; definitive resection waits at least 3–6 months.

FRIENDS: factors that keep a fistula open

Factor	Example
Foreign body	Mesh or suture in the tract
Radiation	Irradiated bowel heals poorly
Inflammation or infection	Crohn disease, undrained abscess
Epithelialization	Mucosa lines the tract
Neoplasm	Tumor in the tract
Distal obstruction	Contents take the easier path out
Steroids	Impaired healing

A short tract (<2 cm), large defect (>1 cm), high output, and malnutrition also predict failure; a long tract favors closure.

Short bowel syndrome

Definition and consequences. Short bowel syndrome follows resection leaving less than about 200 cm of functional small bowel, typically for mesenteric ischemia, Crohn disease, volvulus, or necrotizing enterocolitis. Diarrhea, dehydration, and malabsorption result. Loss of the terminal ileum adds B12 deficiency and bile-acid diarrhea; with the colon in continuity, calcium oxalate stones and D-lactic acidosis appear.

Management. Parenteral fluids and nutrition come first while the remnant adapts over 1–2 years, followed by small frequent meals, loperamide, and PPIs for gastric hypersecretion. Teduglutide, a GLP-2 analog, promotes mucosal growth and reduces parenteral dependence; colonoscopy precedes it because it can accelerate polyp growth. Intestinal transplantation is reserved for intestinal failure.