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Total parenteral nutrition: indications, monitoring, complications
Last reviewed: 04.07.2025
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Parenteral nutrition is by definition given intravenously. Partial parenteral nutrition provides only part of the daily nutritional requirements, supplementing oral nutrition. Many hospitalized patients receive dextrose or amino acid solutions by this method. Total parenteral nutrition (TPN) provides all daily nutritional requirements. TPN can be given in the hospital or at home. Because TPN solutions are concentrated and can cause peripheral venous thrombosis, a central venous catheter is usually used.
[ Indications for total parenteral nutrition
Total parenteral nutrition (TPN) is indicated for patients with a nonfunctional gastrointestinal tract. A common but poorly studied indication is to prevent malnutrition (less than 50% of metabolic requirements met) lasting longer than 7 days. TPN is indicated before and after treatment of severely malnourished patients who are unable to take large amounts of food orally and who are being prepared for surgery, radiation therapy, or chemotherapy. TPN may reduce morbidity and mortality after major surgery, severe burns, head trauma, and especially in patients with sepsis. Patients with disorders requiring significant bowel function impairment (some stages of Crohn's disease, ulcerative colitis, severe pancreatitis) or children with disorders (congenital malformations; prolonged diarrhea regardless of cause) often also respond well to TPN.
Nutrient Content
Total parenteral nutrition requires water (30-40 ml/kg/day), energy (30-60 kcal/kg/day depending on energy expenditure), amino acids (1-2.0 g/kg/day depending on the degree of catabolism), essential fatty acids, vitamins and minerals. In children who require total parenteral nutrition, fluid requirements may vary, but energy (120 kcal/kg/day) and amino acid (2.5-3.5 g/kg/day) requirements are significantly higher.
Stock solutions for total parenteral nutrition are prepared under sterile conditions in liter containers according to standard formulas. Typically 2 liters of stock solution are needed daily. Solutions may be modified based on laboratory findings, the presence of underlying disorders, hypermetabolism, or other factors. Commercially available lipid emulsions are often added to provide essential fatty acids and triglycerides; 20-30% of total energy is supplied by lipids. However, avoiding lipids and their energy may help obese patients mobilize endogenous fat stores, thereby increasing their sensitivity to insulin.
Solutions for total parenteral nutrition
Various solutions are commonly used. Electrolytes may be added to meet the patient's needs.
Patients who have renal failure and are not on dialysis, or who have liver failure, require solutions with reduced protein content and a high percentage of essential amino acids. In patients with cardiac or renal failure, the volume (fluid) administered should be limited. In patients with respiratory failure, a lipid emulsion should provide most of the nonprotein calories to minimize CO 2 production during carbohydrate metabolism. Neonates require lower dextrose concentrations (17-18%).
Initiation of total parenteral nutrition procedure
Because the central venous catheter must remain in place for a long time, strict sterile precautions are necessary during insertion and maintenance. The TPN system should not be used for any other purpose. The outer tube should be changed every 24 hours from the time the first bag is inserted. The use of in-line filters is controversial and probably not helpful. Linens should be kept sterile and usually changed every 48 hours under complete sterility. If TPN is given outside the hospital, patients should be taught to recognize the symptoms of infection and good home care should be provided.
The infusion is started slowly, at a rate of 50% of the calculated requirement, using 5% dextrose to compensate for the fluid balance. Energy and nitrogen should be given simultaneously. The amount of standard units of insulin added directly to the TPN solution depends on the blood glucose level; if the level is normal and the final solution contains the usual 25% dextrose concentration, the usual starting dose is 5-10 standard units of insulin/L TPN fluid.
Monitoring total parenteral nutrition
The flow chart should accompany the procedure. The nutritional support team, if available, should monitor the patient continuously. Body weight, complete blood count, and electrolytes should be checked repeatedly (daily for inpatients). Blood glucose should be checked every 6 hours until stabilized. Fluid intake and output should also be monitored continuously. Once the patient is stabilized, blood tests may be done less frequently.
Liver function tests should be done. Plasma proteins (eg, serum albumin, possibly transthyretin or retinol-binding protein); prothrombin time; plasma and urine osmolality; Ca, Mg, and phosphate (not during glucose infusion) should be measured twice weekly. A full nutritional assessment (including BMI calculation and anthropometric measurements) should be repeated at 2-week intervals.
Complications of total parenteral nutrition
With careful monitoring by the nutrition team, the complication rate can be less than 5%. Complications may be related to the central venous catheter or to the nutritional supply.
Deviations from normal glucose levels are quite common. Hyperglycemia can be avoided by continuous monitoring of blood glucose levels, adjusting the dose of insulin in the total parenteral nutrition solution, and administering insulin subcutaneously when necessary. Hypoglycemia can be corrected by immediate administration of concentrated dextrose. Treatment, depending on the degree of hypoglycemia, consists of intravenous administration of 50% dextrose or infusion of 5% or 10% dextrose for 24 hours before resuming total parenteral nutrition via a central venous catheter.
Deviations from normal levels of electrolytes and minerals in the blood should be corrected by modifying subsequent infusions or, if correction is urgently required, by initiating appropriate infusions into peripheral veins. Vitamin and mineral deficiencies are rare if solutions are administered correctly. Dehydration can be corrected by giving water and 5% dextrose into a peripheral vein.
Hypervolemia (suggested by weight gain greater than 1 kg/day) may occur when large daily energy requirements require large volumes of fluid.
Metabolic bone disease, or bone demineralization (osteoporosis or osteomalacia), develops in some patients receiving total parenteral nutrition for more than 3 months. The mechanism is unknown. Progression of the disease may cause severe periarticular pain, pain in the lower extremities, and pain in the lower back. Temporary or permanent cessation of total parenteral nutrition is the only known treatment.
Adverse reactions to lipid emulsions (including dyspnea, allergic skin reactions, nausea, headache, back pain, sweating, dizziness) are rare but can occur rapidly, especially if lipids are given at rates greater than 1.0 kcal/kg/h. Transient hyperlipidemia may occur, especially in patients with renal or hepatic impairment; treatment is usually not required. Late adverse reactions to lipid emulsions include hepatomegaly, moderate elevations in liver function tests, splenomegaly, thrombocytopenia, leukopenia, and, especially in premature infants with respiratory distress syndrome, pulmonary dysfunction. Temporary or permanent slowing or stopping of lipid emulsion infusion may prevent or minimize these adverse reactions.
Liver complications include liver dysfunction, painful hepatomegaly, and hyperammonemia. They may develop at any age but are most common in infants, especially premature infants, whose livers are functionally immature. Transient liver dysfunction may occur early in TPN, with increases in transaminase, bilirubin, and alkaline phosphatase. Late or persistent increases may be due to excess amino acids. Pathogenesis is unknown. Cholestasis and inflammation probably contribute. Progressive fibrosis sometimes develops. Reducing protein intake may be helpful in these situations. Painful hepatomegaly indicates fat accumulation; carbohydrate intake should be reduced. Hyperammonemia may develop in infants. Symptoms include drowsiness, twitching, and general paralysis. Treatment is with arginine supplementation at a rate of 0.5–1.0 mmol/kg/day. In infants with liver complications, amino acids should be limited to 1.0 g/kg/day.
Gallbladder complications include cholelithiasis, bile stasis, and cholecystitis. These complications may be caused or aggravated by prolonged stagnation of bile in the gallbladder. Stimulating its contraction by providing 20-30% of energy from fats and stopping glucose infusion for several hours per day helps. Oral and enteral nutrition also helps. Some patients with cholelithiasis benefit from the use of metronidazole, ursodeoxycholic acid, phenobarbital, and cholecystokinin.