What is the appropriate dose and rate of Total Parenteral Nutrition (TPN) for a critically ill adult patient?

TPN Dose and Rate for Critically Ill Adults

For critically ill adult patients, initiate TPN at 25 kcal/kg/day (based on ideal body weight) with protein at 1.3-1.5 g/kg/day, infused continuously over 24 hours via central venous access, increasing to target over 2-3 days while avoiding hyperglycemia. 1, 2

Energy Requirements

Target 25 kcal/kg/day initially, increasing to measured energy expenditure or maximum 30 kcal/kg/day over 2-3 days. 1, 2

• In the absence of indirect calorimetry (which is often unavailable), provide 25 kcal/kg/day as the starting point 1
• Energy should be provided as close as possible to measured energy expenditure to decrease negative energy balance 1
• Maximum caloric load should not exceed 30 kcal/kg/day, and should be reduced to 15-20 kcal/kg/day in patients with SIRS, MODS, or refeeding syndrome risk 1
• Avoid overfeeding at the acute stage of critical illness, as hyperalimentation increases complications 1, 3

Macronutrient Composition

Protein/Amino Acids

Provide 1.3-1.5 g/kg ideal body weight per day of balanced amino acid solution. 1, 2

• This dose optimizes whole body protein sparing effects in trauma and sepsis 1
• For unstressed patients with normal organ function, 0.8-1.0 g/kg/day is sufficient 1
• Higher requirements (up to 2.0 g/kg/day) may be needed in severely catabolic patients 1
• For obese patients (BMI 30-40 kg/m²), use 75% of calculated dose; for BMI >50 kg/m², use 65% 1

Carbohydrates

Glucose should provide 50-60% of non-protein energy, with maximum infusion rate of 5-7 mg/kg/min. 1, 2, 4

• Minimum carbohydrate requirement is approximately 2 g/kg/day 1
• Dextrose provides 3.4 kcal/mL as monohydrate 2
• Maintain blood glucose between 4.5-10 mmol/L (approximately 140-180 mg/dL) to prevent infectious complications and mortality 1, 2
• Monitor blood glucose at least daily, optimally every 6 hours 2

Lipids

Lipids should provide 20-30% of total calories (or 40% of non-protein energy), infused at 0.7-1.5 g/kg/day over 12-24 hours. 1, 2, 4, 3

• For long-term TPN (>6 months), do not exceed 1 g/kg/day of soya-based lipid 1
• Essential fatty acid requirement is 7-10 g daily, corresponding to 14-20 g LCT fat from soya oil 1
• Keep serum triglycerides <400 mg/dL (optimally), absolutely <700-800 mg/dL 2
• Mixed LCT/MCT emulsions and olive oil-based emulsions are well tolerated 1
• Fish oil-enriched emulsions may decrease length of stay 1

Non-Protein Energy Ratio

Maintain non-protein energy provision at 100-150 kcal per gram of nitrogen (approximately 70-85% glucose, 15-30% lipid). 1

Glutamine Supplementation

Add 0.2-0.4 g/kg/day of L-glutamine (0.3-0.6 g/kg/day alanyl-glutamine dipeptide) to the amino acid solution for critically ill patients. 1

• Glutamine supplementation reduces mortality risk (RR 0.67, CI 0.48-0.92, p=0.01) in critically ill patients 1
• Doses of 10-30 g glutamine/24h are safely tolerated and restore plasma levels 1
• This should be considered standard of care for ICU patients on PN 1

Micronutrients

All PN prescriptions must include daily multivitamins and trace elements from day one. 1, 2

• Vitamin requirements: A (10,000-50,000 units daily), C (200-500 mg), D (1600 units daily), E (30 IU daily), K (10 mg weekly) 2
• Trace elements: Zinc (220-440 mg daily), Selenium (60-100 µg daily), Iron (as needed) 2
• Administer thiamine (Vitamin B1) prior to starting glucose infusion to prevent Wernicke's encephalopathy in malnourished patients 5, 4
• Micronutrients are frequently omitted (in up to 50% of patients) despite being essential—this is a critical error 1

Insulin Management

Add regular insulin to TPN bag at initial dose of 0.1 U/g dextrose. 2

• Provide subcutaneous correctional insulin every 6 hours using regular insulin or every 4 hours with rapid-acting insulin 2
• If >20 units correctional insulin needed in 24 hours, increase TPN insulin dose 2
• If supplemental insulin exceeds 0.2 U/g dextrose, increase lipid percentage and decrease dextrose 2
• Critical safety point: If TPN is interrupted, immediately start 10% dextrose infusion to prevent hypoglycemia 2

Infusion Rate and Route

Infuse continuously over 24 hours via central venous catheter with tip in superior or inferior vena cava. 1, 2

• Central route is preferred to deliver high osmolarity solutions (>850 mOsmol/L) 1
• Peripheral access may be considered only for low osmolarity solutions (<850 mOsmol/L) covering partial needs 1
• Use single-lumen catheter to minimize infection and thrombosis risk 2
• Administer as complete all-in-one bag to reduce line manipulations and infection risk 1

Cycling for Stable Patients

• Once metabolically stable, compress infusion to overnight (typically 10-hour period with 30-60 minute taper) 2
• Cycle gradually by decreasing time periods in 2-4 hour increments 2

Timing of Initiation

Start PN within 24-48 hours if enteral nutrition is contraindicated or inadequate, after achieving hemodynamic stabilization. 1

• All patients not expected to resume normal nutrition within 3 days should receive PN if EN is contraindicated 1
• For malnourished critically ill patients, start PN immediately alongside any partial enteral nutrition 3
• Patients receiving <targeted enteral feeding after 2 days should receive supplementary PN 1

Critical Monitoring Requirements

Monitor blood glucose at least daily (optimally every 6 hours), electrolytes daily initially, and triglycerides regularly. 2, 5

• Baseline labs before initiation: electrolytes (sodium, potassium, calcium, phosphorus, magnesium), glucose, triglycerides, liver function tests, renal function 5
• Daily monitoring: glucose, electrolytes (especially in first few days) 5
• Regular monitoring: triglycerides, vitamin and mineral levels, weight, nutritional status 2, 5

Common Pitfalls and How to Avoid Them

Refeeding syndrome is the most dangerous complication—provide additional phosphate, potassium, magnesium, and water-soluble vitamins in malnourished patients. 2, 5, 4

• Assess refeeding risk based on clinical history and baseline electrolytes 5
• In high-risk patients, start at lower caloric provision (15-20 kcal/kg/day) 1
• Monitor phosphate, potassium, and magnesium closely in first 3-5 days 4

Avoid exceeding maximum dextrose infusion rate of 5-7 mg/kg/min to prevent hyperglycemia and hepatic complications. 2

Never abruptly discontinue TPN without backup dextrose infusion ready to prevent hypoglycemia. 2

Do not forget micronutrients—they are essential from day one and frequently omitted. 1

Monitor triglycerides when using lipid emulsions, as hypertriglyceridemia increases complications. 2