How should total parenteral nutrition be initiated and administered?

How to Administer Total Parenteral Nutrition (TPN)

TPN should be administered continuously over 24 hours via central venous access, starting at 20–25 kcal/kg/day and advancing to 25–30 kcal/kg/day by day 3–5, with thiamine given before any glucose-containing fluids to prevent Wernicke's encephalopathy. 1

Route of Administration

Central venous access is the preferred route for TPN delivery. 2 The central route should be used when TPN is needed because standard TPN formulations have high osmolarity (>850 mOsm/L) that causes thrombophlebitis in peripheral veins. 1

• Subclavian vein cannulation is the traditional route of choice, providing access to the superior vena cava with appropriate confirmation of catheter tip location. 2
• Peripherally inserted central catheters (PICC lines) are an acceptable alternative when central access is needed, particularly for non-ICU patients requiring TPN for less than 14 days. 3
• Peripheral parenteral nutrition may be considered only if the anticipated duration is less than 14 days, but this approach is prone to thrombophlebitis and is less suitable for standard TPN formulations. 2

Infusion Protocol

Administer TPN continuously over 24 hours when all components (protein, fat, glucose) are delivered simultaneously. 1 Continuous 24-hour infusion provides optimal nitrogen sparing and metabolic stability in adult patients. 1

• Cycling TPN (infusion over 10–14 hours) may prevent cholestasis in children and can be considered once patients are stable, but requires gradual tapering at the start and end of infusion to prevent hyperglycemia and hypoglycemia. 2
• Use an infusion pump that allows gradual rate changes during the first 1–2 hours and tapering during the last 1–2 hours when cycling. 2

Energy and Macronutrient Targets

Energy Requirements

Target 25–30 kcal/kg ideal body weight per day for most adult patients. 1, 2 Start with a lower caloric regimen and build up gradually over 2–3 days to prevent refeeding syndrome. 1

• Initial phase (days 1–3): Start with 20–25 kcal/kg/day during the first 72–96 hours. 1
• Advancement phase (days 3–5): Increase to full target of 25–30 kcal/kg/day as tolerated. 1
• Severe stress or critical illness: May require up to 30 kcal/kg/day, but exceeding this is detrimental and increases complications. 1, 2
• SIRS, MODS, or refeeding syndrome risk: Reduce to 15–20 kcal/kg/day. 2

Protein Requirements

Provide 1.2–1.5 g/kg ideal body weight per day of amino acids (equivalent to 0.2–0.24 g nitrogen/kg/day). 2, 1 Parenteral amino acid infusion does not affect pancreatic secretion or function. 2

• Critically ill patients may require 1.2–2.0 g/kg/day to preserve lean body mass. 1
• Consider parenteral glutamine supplementation (>0.30 g/kg Ala–Gln dipeptide) when PN is indicated. 2

Carbohydrate Provision

Glucose should be the preferred carbohydrate energy source, comprising 50–60% of non-protein calories. 2, 1

• Start glucose infusion at 2–3 g/kg/day; may increase to 4–5 g/kg/day if tolerated. 1
• Reduce to 2–3 g/kg/day when hyperglycemia occurs. 1
• Maintain blood glucose ≤10 mmol/L (≈180 mg/dL) during TPN. 1

Lipid Provision

Lipids should provide 30–40% of non-protein calories at an infusion rate of 0.8–1.5 g/kg/day. 2, 1

• Maintain triglyceride levels <12 mmol/L (<400 mg/dL). 2, 1
• Temporarily discontinue lipid infusion if persistent hypertriglyceridemia (>12 mmol/L) occurs for more than 72 hours. 2
• SMOFlipid (mixed-oil emulsion) is preferred over pure soybean-oil emulsions for hepatic protection. 1

Micronutrient Supplementation

Daily multivitamins and trace elements must be started from day 1 of TPN therapy. 1, 2

• Standard TPN should contain trace elements (zinc, copper, manganese, chromium, selenium) and water-soluble vitamins (B-complex and vitamin C) from the first day. 1
• Administer thiamine 100–300 mg IV before commencing glucose-containing TPN to prevent Wernicke's encephalopathy, particularly in malnourished patients, those with alcohol use disorder, or those at risk of refeeding syndrome. 1, 4
• Monitor and supplement phosphate, potassium, and magnesium closely, especially in the first 72 hours, to prevent refeeding syndrome. 1

Timing of TPN Initiation

TPN is indicated only when enteral nutrition is impossible or cannot provide >60% of energy needs. 1, 2

When to Start TPN

• Severely malnourished or high nutritional risk patients: Start TPN as soon as hemodynamic stability is achieved (usually 24–48 hours from admission). 2, 1
• Low nutritional risk patients: Delay exclusive TPN for the first 7 days when oral/enteral intake is not feasible; provide IV glucose at 2–3 g/kg/day if fasting exceeds 12 hours. 1
• Fasting >72 hours: Start full TPN when the fasting period exceeds 72 hours. 1
• Post-operative patients: May begin PN immediately once hemodynamic stability and fluid/electrolyte balance are secured. 1

Specific Indications

• Complete gastrointestinal obstruction or discontinuity 1
• High-output enterocutaneous fistula (>500 mL/day) 1
• Prolonged ileus, complex pancreatic fistulae, or abdominal compartment syndrome 2, 1
• Anticipated inability to meet oral/enteral intake for >7–10 days 1

Monitoring Requirements

Monitor blood glucose at least once daily while on PN; perform repeat checks to detect hypoglycemia and avoid hyperglycemia. 1

• Daily monitoring of phosphate, potassium, and magnesium for the first 3–5 days in at-risk patients. 1
• Monitor triglyceride levels to maintain <12 mmol/L. 2
• Insulin infusion rates should not exceed 4–6 units per hour. 1

Transitioning and Weaning from TPN

Attempt early oral intake within 24 hours after surgery when feasible; TPN may be stopped abruptly once oral/enteral intake reaches ≥50–60% of estimated energy needs—no tapering protocol is required. 1

• As enteral tolerance improves, reduce the proportion of PN proportionally. 1
• Supplemental (partial) TPN can be used temporarily when enteral intake provides 40–60% of nutritional needs. 1
• Give some enteral feed whenever possible, even if only a minimal amount is tolerated, to maintain gut mucosal structure and encourage adaptation. 2

Critical Pitfalls to Avoid

Never initiate TPN in patients who can tolerate enteral nutrition, as it increases morbidity without benefit. 1

• Avoid overfeeding: Exceeding 30 kcal/kg/day is detrimental and increases complications. 2, 1
• Never suddenly stop TPN: Abrupt cessation may cause rebound hypoglycemia; however, gradual weaning is not required once adequate enteral nutrition is established. 2, 1
• Do not delay thiamine administration: Always give thiamine before glucose-containing fluids in at-risk patients (malnourished, alcohol use disorder, refeeding syndrome risk). 1, 4
• Strict aseptic technique must be used in catheter insertion and TPN administration to prevent infection. 5

Special Populations

Severe Acute Pancreatitis

• TPN should be used only when enteral feeding is impossible (e.g., prolonged ileus, complex fistulae, abdominal compartment syndrome). 2, 1
• The majority of patients with severe pancreatitis can be managed with enteral nutrition. 2

Liver Disease

• Energy provision should equal 1.3 × resting energy expenditure. 2, 1
• Protein should be limited to 1.2–1.5 g/kg/day in cirrhosis to reduce hepatic encephalopathy risk. 1
• Administer vitamin B1 before glucose infusion in alcoholic liver disease. 1

Pediatric Patients

• Preterm and term infants up to 12 months require 0.35–0.50 mg/kg/day thiamine. 4
• Older children require 1.2 mg/day thiamine. 4
• Minimal enteral feeding should be given whenever possible to maintain gut mucosal structure and reduce PN-associated liver disease risk. 2