Surgical nutrition

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Surgical Nutrition

1. Importance of Nutrition in Surgery

Nutrition and metabolism are inseparably linked in surgical patients. The surgical patient faces a unique metabolic challenge: tissue injury, inflammation, and physiologic stress all drive a catabolic state that, without nutritional intervention, depletes lean body mass and impairs healing. Both undernutrition and overnutrition worsen surgical outcomes - malnutrition increases morbidity and mortality, while overfeeding increases infectious complications and metabolic dysregulation.

Sabiston Textbook of Surgery, p. 616
Schwartz's Principles of Surgery, p. 94

2. Metabolic Response to Surgery

Surgery triggers a predictable stress response:

Neuroendocrine response:

Release of catabolic hormones: cortisol, glucagon, catecholamines
Suppression of insulin and anabolic hormones
Results in hyperglycemia, increased proteolysis, lipolysis

Cytokine/Immune response:

Surgical stress releases IL-6, TNF-alpha, and other pro-inflammatory cytokines
These contribute to insulin resistance and metabolic alterations
Neutrophils and macrophages are mobilized to the surgical site
Prolonged or severe stress temporarily suppresses adaptive immunity, increasing infection risk

Consequences:

Increased nitrogen loss (urinary), proportional to injury severity (see Fig. 2-23, Schwartz)
Preferential oxidation of fat and protein as energy substrates
Skeletal muscle wasting; visceral protein depletion if prolonged

3. Nutritional Assessment

History and Physical Examination

Assess for:

Weight loss (recent, rate, extent)
Chronic illness (cancer, IBD, malabsorption, renal/hepatic disease)
Dietary habits, socioeconomic factors, substance abuse
Prior GI surgery or congenital malabsorption

Physical findings: loss of muscle and adipose tissue, skin/hair changes, edema, signs of vitamin deficiency.

Anthropometric data: weight, BMI, skinfold thickness, mid-arm circumference.

Serum Markers - Important Caveat

Traditional markers (albumin, prealbumin, transferrin, retinol binding protein) are unreliable indicators of nutritional status in surgical patients. Their levels fall due to the inflammatory response (acute-phase reactants outcompete synthesis), not purely due to malnutrition. Albumin remains normal until severe malnutrition (BMI <12) in otherwise healthy individuals. These markers better reflect inflammation severity than nutritional status.

Sabiston, p. 616

Validated Scoring Tools

Nutritional Risk Screening (NRS-2002): Recommended for all hospitalized patients
NUTRIC Score: Validated for the critically ill ICU patient
These should be used alongside GI function assessment and aspiration risk

4. Energy Requirements

Gold standard: Indirect calorimetry - measures O2 consumption and CO2 production. Recommended for critically ill patients. Caveat: may overestimate requirements, leading to overfeeding.

Predictive equations (when calorimetry unavailable):

Resting energy expenditure (REE) adjusted for stress factor
Simple weight-based formula: 25-30 kcal/kg/day for most patients

Caloric targets by BMI:

BMI	Classification	Daily Caloric Target
<18.5	Underweight	30-40 kcal/kg actual body weight
18.5-24.9	Normal	25-30 kcal/kg actual body weight
25.0-39.9	Overweight/Obese	11-14 kcal/kg actual body weight
>50	Extreme obesity	22-25 kcal/kg ideal body weight

Protein requirements:

Standard surgical patients: 1.2-1.5 g/kg/day
Critically ill: >1.2 g/kg/day (minimum)
Obese patients: 2.0-2.5 g/kg ideal body weight/day (to preserve lean mass)
Sabiston, Table 34.7

5. Routes of Nutritional Support

A. Enteral Nutrition (EN) - Preferred Route

Indications: Any patient with a functional GI tract who cannot meet nutritional needs orally.

Advantages over TPN:

Maintains gut mucosal integrity and barrier function
Prevents bacterial translocation
Preserves gut-associated lymphoid tissue (GALT)
Stimulates IgA secretion; maintains gut immune defenses
Lower cost, fewer complications (especially infectious)
Maintains portal hepatotrophic factors

When to use: Start within 24-48 hours of ICU admission or major surgery if hemodynamically stable. Early EN reduces infection rate, ICU length of stay, and mortality.

Formulas:

Standard polymeric: for patients with intact digestion (contains whole proteins, complex carbohydrates, long-chain fats)
Elemental/semi-elemental: for impaired digestion/absorption (pre-digested nutrients); used in short bowel syndrome, severe pancreatitis, high-output fistulas
Disease-specific formulas: renal (low K+/PO4), hepatic (branched-chain AA enriched), pulmonary (high-fat, low-carbohydrate)
Immune-enhancing formulas: supplemented with arginine, omega-3 fatty acids, glutamine - evidence mainly for major elective surgery

Access:

Nasogastric tube (most common)
Nasojejunal tube (if gastroparesis or high aspiration risk)
Percutaneous endoscopic gastrostomy (PEG) - for long-term EN
Surgical jejunostomy - placed at time of major abdominal surgery

B. Parenteral Nutrition (PN)

Indications: When EN is contraindicated or insufficient:

Intestinal obstruction or ileus
GI fistula with high output preventing enteral access distal to fistula
Severe short bowel syndrome
Mesenteric ischemia
Failure of EN to meet >60% of requirements after 3-5 days

Total Parenteral Nutrition (TPN) / Central PN:

Delivered via large-caliber central vein (subclavian, jugular, PICC)
Dextrose concentration: 15-25%
Amino acid concentration: 3-5%
Also provides lipid emulsions, vitamins, trace minerals, electrolytes

Peripheral Parenteral Nutrition (PPN):

Lower osmolality solution (dextrose 5-10%, protein 3%)
Used when central access unavailable or as supplemental support
Not for severe malnutrition - cannot concentrate enough nutrients
Short-term use only (<2 weeks); switch to TPN if longer needed

TPN Components:

Dextrose: primary non-protein energy source (1 g = 3.4 kcal)
Amino acids: for protein synthesis and gluconeogenesis
Lipid emulsions: essential fatty acids + energy (1 g fat = 9 kcal); prevent EFA deficiency
Electrolytes: Na, K, Cl, PO4, Mg, Ca - adjusted daily
Vitamins: standard IV multivitamin prep + weekly vitamin K (not in most commercial solutions)
Trace elements: Zn, Cu, Mn, Se, Cr - essential in prolonged TPN

TPN Complications:

Category	Complication
Metabolic	Hyperglycemia, hypophosphatemia (refeeding syndrome), electrolyte disturbances, hypertriglyceridemia
Hepatic	TPN-associated liver disease (steatosis, cholestasis) with prolonged use
Infectious	Central line-associated bloodstream infection (CLABSI) - most serious
Mechanical	Pneumothorax, hemothorax on insertion; line occlusion, thrombosis
Deficiency	Zinc (eczematoid rash at intertriginous areas), copper (microcytic anemia), chromium (glucose intolerance), essential fatty acids (dry scaly skin, hair loss)

6. Critical Illness Nutrition

Hypocaloric (Permissive Underfeeding) Strategy

Current guidelines recommend hypocaloric, high-protein nutrition in the first week of critical illness:

Calories: <20 kcal/kg/day (or <80% of estimated needs)
Protein: >1.2 g/kg/day
This minimizes hyperglycemia and insulin resistance, reducing infectious complications

Glucose control: Target blood glucose 140-180 mg/dL in ICU patients. Tight control (<110 mg/dL) was not found to be superior and increases hypoglycemia risk.

EN vs TPN in the ICU

EN is preferred as the primary route when GI tract is functional
TPN is reserved for patients in whom the gut cannot be used or EN is insufficient
Combination EN + supplemental PN (SPN) may be used after day 3-7 if EN goals not reached

7. ERAS (Enhanced Recovery After Surgery) Protocols

ERAS integrates perioperative nutritional management to accelerate recovery:

Preoperative:

Carbohydrate loading with clear liquids up to 2 hours before surgery (reduces insulin resistance, improves well-being)
Continue solid food up to 6-8 hours before surgery (revised from midnight fasting)
Screen and treat preoperative malnutrition (consider 7-10 days prehabilitation nutrition if severely malnourished)

Intraoperative:

Minimize opioids (slow gut motility); use multimodal analgesia
Avoid excessive IV fluids (dilutional hypoalbuminemia, gut edema)

Postoperative:

Initiate oral/enteral nutrition as soon as patient is awake and can swallow - do not wait for bowel sounds or passage of flatus
Aim for normal diet within 24-48 hours of most elective procedures
Early feeding reduces hospital length of stay and infection rate

8. Refeeding Syndrome

A potentially fatal complication of reintroducing nutrition after prolonged starvation (>5-7 days):

Driven by: sudden carbohydrate load → insulin surge → massive intracellular uptake of PO4, K+, Mg2+
Hypophosphatemia is the hallmark (severe: <0.5 mmol/L)
Manifestations: cardiac arrhythmias, respiratory failure, rhabdomyolysis, seizures, hemolytic anemia
Prevention: start nutrition slowly (10-20 kcal/kg/day, increase over 4-7 days), supplement PO4/K+/Mg2+ prophylactically, give thiamine before starting feeds

High-risk patients: chronic alcoholism, anorexia nervosa, cancer, prolonged starvation, malabsorption syndromes.

9. Special Surgical Situations

Condition	Nutritional Considerations
Short Bowel Syndrome	EN preferred; high-output managed with elemental formula + anti-motility agents; TPN for severe cases; consider intestinal rehabilitation with GLP-2 analogs (teduglutide)
Enterocutaneous Fistula	TPN historically preferred; EN increasingly used if fistula output controlled; high protein requirements (2-2.5 g/kg/day)
Pancreatitis (acute)	Early EN (within 24-48 h) via nasojejunal tube preferred over TPN in severe AP; reduces infection, organ failure, mortality
Bariatric Surgery	Lifelong micronutrient supplementation (B12, iron, folate, vitamin D, calcium, thiamine)
Malignancy	Malnutrition common; preoperative nutritional optimization 7-14 days if severely malnourished; immunonutrition (arginine, omega-3, nucleotides) beneficial perioperatively
Inflammatory Bowel Disease	EN with elemental formula for Crohn's (induces remission); TPN for severe disease/high-output fistula
Transplant	Aggressive preoperative nutrition; post-transplant: early EN, steroid-related hyperglycemia management
Burns	Highest metabolic demand of any surgical condition; 2-2.5× REE; protein 2.5-3 g/kg/day; very early EN within 6 hours

10. EN vs TPN - Summary

Feature	Enteral Nutrition	Parenteral Nutrition
Route	GI tract	Central/peripheral vein
Gut integrity	Preserved	Not maintained
Infection risk	Lower	Higher (CLABSI)
Cost	Lower	Much higher
Feasibility	Requires functional gut	Independent of gut function
Metabolic complications	Less frequent	More frequent
Preferred	Yes (when feasible)	When EN contraindicated/insufficient

Sources:

Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice - Chapter 34: Surgical Nutrition
Schwartz's Principles of Surgery, 11th Edition - Chapter 7: Nutrition in the Surgical Patient

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