TPN Order Composition and Dosing
For a normally nourished adult patient, TPN should provide 25-30 kcal/kg/day based on ideal body weight, with protein at 1.0-1.5 g/kg/day and lipids comprising 20-30% of total calories. 1
Macronutrient Composition
Dextrose (Carbohydrate)
- Provides 3.4 kcal/mL as a monohydrate 1
- Maximum infusion rate: 5-7 mg/kg/min 1
- Should comprise 50-70% of total calories 2
- Target blood glucose: 140-180 mg/dL during therapy 3
- Monitor blood glucose at least daily, optimally every 6 hours 1, 3
Protein (Amino Acids)
- Dose: 1.0-1.5 g/kg/day based on ideal body weight for adults 1
- More catabolic patients (burns, severe trauma) require 2.0 g/kg/day 4
- Optimal calorie-to-nitrogen ratio: 150-200 2
Lipids
- Provide 20-30% of total infused calories 1
- 20% lipid emulsion is more calorically dense than dextrose 1
- Maximum infusion rate: 80 mg/kg/hr 2
- Keep serum triglycerides <400 mg/dL (optimally), absolutely <700-800 mg/dL 1
- Increase lipid percentage if supplemental insulin exceeds 0.2 U/g dextrose 1
Insulin Management
Add regular insulin to TPN bag at initial dose of 0.1 U/g dextrose 1, though newer guidelines suggest 1 unit per 10g carbohydrate 3. The American Gastroenterological Association's lower starting dose of 0.1 U/g dextrose is more conservative and appropriate for initial orders 1.
- Adjust insulin if requirements exceed 0.2 U/g dextrose 1
- Provide subcutaneous correctional insulin every 6 hours using regular insulin or every 4 hours with rapid-acting insulin 3
- If >20 units correctional insulin needed in 24 hours, increase TPN insulin dose 3
- Critical safety point: If TPN interrupted, immediately start 10% dextrose infusion to prevent hypoglycemia 3
Micronutrient Supplementation
Daily Vitamin Requirements 1
- Vitamin A: 10,000-50,000 units daily
- Vitamin C: 200-500 mg
- Vitamin D: 1600 units DHT daily (may require 25-OH or 1,25(OH)-D3)
- Vitamin E: 30 IU daily
- Vitamin K: 10 mg weekly
- Vitamin B12: 300 µg subcutaneously monthly (for terminal ileal resections/disease)
Trace Elements 1
- Zinc: 220-440 mg daily (sulfate form)
- Selenium: 60-100 µg daily
- Iron: As needed (not routinely required without hemorrhage)
- Magnesium, Calcium, Bicarbonate: Individualized based on monitoring
Important caveat: Use vitamin supplementation cautiously in patients with cholestatic liver disease 1. All supplementation must be monitored routinely and tailored based on serum levels 1.
Infusion Strategy
Initial Phase
- Infuse continuously while addressing postoperative complications and stabilizing metabolic issues 1
- Begin TPN within 7-10 days post-surgery for patients requiring nutritional support 1
Transition to Home TPN
- Compress infusion to overnight (typically 10-hour period with 30-60 minute taper) 1
- Cycle gradually by decreasing time periods in 2-4 hour increments 1
- Some patients with fluid management issues cannot tolerate compressed infusion 1
Venous Access
Infuse via single-lumen catheter with tip positioned in superior vena cava (SVC) or inferior vena cava (IVC) to minimize infection and thrombosis risk 1. For home use, employ tunneled catheters, implantable ports, or PICCs 1.
Monitoring Requirements
- Blood glucose: At least daily, optimally every 6 hours 1, 3
- Serum triglycerides: Regular monitoring, especially when using lipid emulsions 1
- Electrolytes: Daily initially, then as clinically indicated 1
- Vitamin and mineral levels: Routine monitoring to guide supplementation 1
- Weight and nutritional status: Ongoing assessment 1
Common Pitfalls to Avoid
- Refeeding syndrome risk: Malnourished patients require additional phosphate, potassium, magnesium, and water-soluble vitamins 1
- Overfeeding: Do not exceed maximum dextrose infusion rate of 5-7 mg/kg/min 1
- Inadequate monitoring: Failure to check blood glucose frequently enough leads to poor glycemic control 1
- Lipid overload: Monitor triglycerides; hypertriglyceridemia increases complications 1
- Abrupt TPN discontinuation: Always have backup dextrose infusion ready 3