In adult surgical or critically ill patients and neonates, after how many days of nil by mouth should total parenteral nutrition (including SMOFlipid) be initiated, what should its composition be, should trace elements and minerals be added, and at what infusion rate should it be administered?

When to Initiate TPN After Nil By Mouth (NBM)

Timing of TPN Initiation

In critically ill or surgical patients who cannot be fed enterally, start TPN after 7 days of NBM if the patient is at low nutritional risk, but initiate immediately in severely malnourished or high-risk patients. 1

For Low Nutritional Risk Patients:

• Withhold exclusive TPN for the first 7 days if oral intake or enteral nutrition is contraindicated 1
• Provide intravenous glucose (2–3 g/kg/day) when patients must abstain from food for more than 12 hours 1
• Start full TPN when the fasting period exceeds 72 hours 1
• Consider supplemental TPN after 7–10 days if unable to meet >60% of energy and protein requirements by enteral route 1

For High Nutritional Risk or Severely Malnourished Patients:

• Start TPN as soon as possible in moderately or severely malnourished patients who cannot be fed sufficiently orally or enterally 1
• Initiate early and progressive PN in severely malnourished patients 1
• Begin PN immediately in the postoperative phase once hemodynamic stability is achieved 1, 2

For Neonates:

• Most neonates with short bowel or surgical conditions require parenteral nutrition for the first 7–10 days after resection 1
• Do not start PN until the neonate is hemodynamically stable and fluid/electrolyte balance has been reached 1

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TPN Composition

Energy Requirements:

• Target 25–30 kcal/kg ideal body weight per day for most adult patients 1, 3
• Use 25 kcal/kg as baseline; increase to 30 kcal/kg in severe stress or critical illness 3
• Provide energy to cover 1.3 × resting energy expenditure (REE) in liver disease and alcoholic steatohepatitis 1

Macronutrient Distribution:

Protein:

• 1.2–2.0 g/kg/day in critically ill patients (ASPEN/SCCM recommends 1.2–2 g/kg/day) 1
• 1.5 g/kg ideal body weight per day (approximately 20% of total energy) 3
• 1.2–1.5 g/kg/day in liver cirrhosis and alcoholic steatohepatitis 1
• 0.8–1.2 g/kg/day in acute liver failure 1

Carbohydrates:

• 50–60% of non-protein energy (or 50–70% of total energy) 1, 3
• Glucose infusion rate: 2–3 g/kg/day initially, can increase to 4–5 g/kg/day if tolerated 1, 4
• Reduce glucose to 2–3 g/kg/day in case of hyperglycemia 1

Lipids:

• 30–40% of non-protein energy (or 20–30% of total energy) 3, 4
• Do not exceed 1 g/kg/day to prevent chronic cholestasis 2
• Optimal infusion rate: 80 mg/kg/hour 3

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SMOFlipid vs Traditional Lipid Emulsions

Use SMOFlipid (mixed-oil emulsion) rather than pure soybean oil emulsions to reduce the risk of parenteral nutrition-associated cholestasis (PNAC), especially in neonates. 5, 6

Evidence for SMOFlipid:

• Reduces PNAC incidence from 16.4% to 2.5% in neonates receiving PN ≥14 days 5
• Provides lower peak direct bilirubin levels (3.2 vs 7.1 mg/dL) compared to soybean-based lipids 6
• Contains lower n-6 unsaturated fatty acids than traditional pure soybean oil emulsions 1
• Recommended in ESPEN guidelines for hepatology patients 1

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Trace Elements and Minerals

Yes, trace elements and minerals must be added daily from day 1 of TPN therapy. 1, 3

Essential Micronutrients:

• Daily multivitamins and trace elements should be started from the first day of PN 1, 3
• Water-soluble vitamins and trace elements must be given daily 1
• Some micronutrients require increased amounts due to digestive losses (e.g., zinc, magnesium) 1, 2

Special Considerations:

• Administer vitamin B1 prior to starting glucose infusion to reduce the risk of Wernicke's encephalopathy, especially in alcoholic liver disease 1
• Monitor phosphate, potassium, and magnesium levels when refeeding malnourished patients to prevent refeeding syndrome 1, 3
• Maintain magnesium balance carefully, as deficiency may develop despite normal serum levels 1

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Rate of Administration

Administer TPN continuously over 24 hours when all components (protein, fat, glucose) are delivered simultaneously. 3

Infusion Protocol:

• Continuous 24-hour infusion provides optimal nitrogen sparing and metabolic stability 3
• Maintains stable metabolic parameters and prevents fluctuations in blood glucose and electrolytes 3
• Central venous access is required for standard TPN formulations due to high osmolarity (>850 mOsm/L) 3

Gradual Initiation:

• Start with a low-calorie regimen and build up gradually over 2–3 days to prevent refeeding syndrome 3
• Initial energy targets should be 20–25 kcal/kg/day during the first 72–96 hours 3
• Progress to full targets by day 3–5 1, 3

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Metabolic Monitoring

Glucose Control:

• Maintain blood glucose ≤10 mmol/L (≈180 mg/dL) during TPN 3
• Monitor blood glucose at least daily while on PN 1
• Insulin infusion rates should not exceed 4–6 units per hour 3

Lipid Monitoring:

• Maintain triglyceride levels <400 mg/dL (<12 mmol/L) to prevent lipid-related complications 3

Electrolyte Monitoring:

• Monitor phosphate, potassium, magnesium, and calcium daily, particularly in the first 72 hours, to prevent refeeding syndrome 3
• Employ repeat blood sugar determinations to detect hypoglycemia and avoid PN-related hyperglycemia 1

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Critical Pitfalls to Avoid

• Never initiate TPN in patients who can tolerate enteral nutrition, as it increases morbidity without benefit 3
• Do not exceed 30 kcal/kg/day, as this is detrimental and increases complications 3
• Never suddenly stop TPN, as this can cause rebound hypoglycemia 3
• Always prioritize enteral nutrition when feasible, as it is associated with improved outcomes compared to TPN 3, 7
• Do not delay nutritional support in patients who cannot meet their nutritional needs orally 2