Ch05: Surgical Nutrition Support（外科营养支持）

Preparatory Mindset

Surgical patients are frequently malnourished — illness, surgery, and sepsis increase catabolism. The exam focuses on: nutritional assessment, enteral vs parenteral nutrition (when to choose which), complications of each, and the metabolic response to surgery (catabolism → anabolism). The lecture (new version, 19.8KB) is thorough.

Exam mindset: "If the gut works, use it" — enteral is preferred. Know the indications for PN, the PN composition (glucose, amino acids, fat, electrolytes, vitamins, trace elements), and the complications (catheter sepsis, hyperglycemia, refeeding syndrome, liver dysfunction).

Core Concepts

1. Metabolic response to surgery/trauma (MUST KNOW)

• Phase 1 — Catabolic (ebb, 1-3 days): neuroendocrine stress response → ↑ catecholamines, cortisol, glucagon → hyperglycemia, protein breakdown, lipolysis; insulin resistance; negative nitrogen balance
• Phase 2 — Anabolic (flow, recovery): tissue repair, restoration of stores, positive nitrogen balance
• Consequences of starvation/catabolism: loss of lean body mass, immune dysfunction, delayed wound healing, increased complications
• Key mediators: cortisol, catecholamines, glucagon, growth hormone, inflammatory cytokines (IL-1, IL-6, TNF)

2. Nutritional assessment (MUST KNOW)

• History & physical: recent weight loss (>10% in 6 months = significant), BMI < 18.5, poor intake, chronic illness, dysphagia
• Laboratory: albumin (< 30 g/L = malnutrition) — note: albumin is a negative acute-phase reactant, affected by inflammation; prealbumin (shorter half-life, reflects recent intake); transferrin, total lymphocyte count (immune status)
• Screening tools: MUST, NRS-2002, SGA (subjective global assessment)
• When to support: inability to eat > 5-7 days post-op, weight loss >10%, severe catabolism (sepsis, burns, major surgery), pre-existing malnutrition

3. Routes of nutrition support (MUST KNOW)

- Routes: nasogastric, nasojejunal, gastrostomy (PEG), jejunostomy (PEJ) - Uses the gut (preserves mucosal integrity, barrier function, immune function), cheaper, fewer metabolic complications - Contraindications: bowel obstruction/ileus, severe shock, intestinal ischemia, uncontrolled vomiting, high-output fistula (some), peritonitis

- Indications: bowel obstruction, short bowel syndrome, severe ileus, high-output enterocutaneous fistula, severe acute pancreatitis (delayed), inflammatory bowel disease, prolonged inability to use the gut - Routes: peripheral (PPN — short term, low osmolarity) vs central (CPN via CVC — long term, hyperosmolar) - Composition (all-in-one): carbohydrate (glucose), amino acids, fat (lipid emulsion), electrolytes, vitamins, trace elements, water + insulin as needed - Components & calorie targets: total 25-30 kcal/kg/day; protein 1.2-2.0 g/kg/day; non-protein calories ~60% carbohydrate : 40% fat

• Oral diet — always preferred when possible
• Enteral nutrition (EN) (肠内营养) — first choice when oral inadequate:
• Parenteral nutrition (PN) (肠外营养):

4. Enteral vs parenteral — the comparison (MUST KNOW)

5. Complications

Enteral:

• Diarrhea (most common), nausea/vomiting, abdominal distension
• Aspiration pneumonia (esp. NG in supine patients — head up 30-45°)
• Refeeding syndrome (with rapid feeding in severe malnutrition)
• Tube displacement/blockage

Parenteral:

• Catheter-related bloodstream infection (CRBSI) — most serious; aseptic CVC care
• Hyperglycemia (common; control with insulin, target <10 mmol/L)
• Hypertriglyceridemia
• Liver dysfunction (steatosis, cholestasis — from excess glucose/lipids; "PN-associated liver disease")
• Refeeding syndrome: hypophosphatemia, hypokalemia, hypomagnesemia, fluid overload, arrhythmias — in severely malnourished patients; start slowly, replace electrolytes, monitor phosphate
• Mechanical: pneumothorax (CVC insertion), thrombosis, catheter occlusion
• Metabolic: metabolic acidosis (excess chloride), hyperammonemia (rare)

6. Special situations

• Burns: high calorie/protein requirements (25-40 kcal/kg, up to 2-3 g/kg protein)
• Sepsis: early EN preferred (if tolerated); treat the infection, moderate protein, avoid overfeeding
• Acute pancreatitis: historically PN; modern approach: early EN via nasojejunal is preferred (when tolerated); PN if EN fails (protects gut barrier)
• Perioperative: avoid routine pre-op fasting (clear fluids up to 2 h, light meal 6 h); ERAS (enhanced recovery): early oral feeding, early mobilization, minimal drains/catheters, opioid-sparing analgesia

High-Yield Points

• "If the gut works, use it" — EN first; PN when the gut fails
• PN indications: obstruction, short bowel, severe ileus, high-output fistula, severe pancreatitis (delayed), IBD
• PN composition: glucose + amino acids + fat + electrolytes + vitamins + trace elements
• Albumin < 30 g/L = malnutrition marker
• EN complications: diarrhea (most common), aspiration; PN complications: catheter sepsis (CRBSI), hyperglycemia, liver dysfunction
• Refeeding syndrome: hypophosphatemia — start slowly in the malnourished
• Metabolic response: catabolic ebb phase (cortisol/catecholamine/glucagon → hyperglycemia, protein loss) → anabolic flow phase
• Calories: 25-30 kcal/kg/day; protein 1.2-2.0 g/kg/day
• ERAS: early feeding, early mobilization, minimal tubes

Topic Summary

Surgery induces a catabolic stress response (ebb: catecholamines/cortisol/glucagon → hyperglycemia, protein catabolism, negative nitrogen balance) then anabolic recovery. Assess nutrition (weight loss, albumin <30, prealbumin, screening tools) and support when intake fails. Enteral nutrition is first choice ("if the gut works, use it") — preserves the mucosal barrier; parenteral nutrition (central, all-in-one: glucose, amino acids, fat, electrolytes, vitamins, trace elements) is for when the gut fails. EN complications: diarrhea, aspiration; PN complications: catheter sepsis, hyperglycemia, liver dysfunction, refeeding syndrome (hypophosphatemia). Target 25-30 kcal/kg/day. ERAS promotes early feeding/mobilization.