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Parenteral nutrition is by definition given IV. Partial parenteral nutrition supplies only part of daily nutritional requirements, supplementing oral intake. Many hospitalized patients receive dextrose or amino acid solutions by this method. Total parenteral nutrition (TPN) supplies all daily nutritional requirements. TPN can be used in the hospital or at home. Because TPN solutions are concentrated and can cause thrombosis of peripheral veins, a central venous catheter is usually required.

Indications: TPN is indicated for patients whose GI tract is not functional. A general but untested indication is anticipation of undernutrition (< 50% of metabolic needs met) for > 7 days. TPN is given before and after treatment to severely undernourished patients who cannot ingest large volumes of oral feedings and are being prepared for surgery, radiation therapy, or chemotherapy. TPN may reduce morbidity and mortality after major surgery, severe burns, and head trauma, especially in patients with sepsis. Patients with disorders requiring complete bowel rest (eg, some stages of Crohn's disease, ulcerative colitis, severe pancreatitis) or with pediatric GI disorders (eg, congenital anomalies; prolonged diarrhea, regardless of its cause) often respond well to TPN.

Nutritional content: TPN requires water (30 to 40 mL/kg/day), energy (30 to 60 kcal/kg/day, depending on energy expenditure), amino acids (1 to 2.0 g/kg/day, depending on the degree of catabolism), essential fatty acids, vitamins, and minerals (see Table 2: Nutritional Support: Basic Adult Daily Requirements for Total Parenteral Nutrition). Children who need TPN may have different fluid requirements and need more energy (120 kcal/kg/day) and amino acids (2.5 to 3.5 g/kg/day).

Table 2
Basic Adult Daily Requirements for Total Parenteral Nutrition Nutrient Amount Water (/kg body wt/day) 30–40 mL Energy*     Medical patient 30 kcal Postoperative patient 30–45 kcal Hypercatabolic patient 45–60 kcal Amino acids (/kg body wt/day)     Medical patient 1.0 g Postoperative patient 2.0 g Hypercatabolic patient 3.0 g Minerals     Acetate/gluconate 90 mEq Calcium 15 mEq Chloride 130 mEq Chromium 15 μg Copper 1.5 mg Iodine 120 μg Magnesium 20 mEq Manganese 2 mg Phosphorus 300 mg Potassium 100 mEq Selenium Some Trade Names SELSUN Click for Drug Monograph 100 μg Sodium 100 mEq Zinc 5 mg Vitamins     Ascorbic acid 100 mg Biotin 60 μg Cobalamin 5 μg Folic acid 400 μg Niacin Some Trade Names NIACOR NIASPAN SLO-NIACIN Click for Drug Monograph 40 mg Pantothenic acid 15 mg Pyridoxine 4 mg Riboflavin 3.6 mg Thiamin 3 mg Vitamin A 4000 IU Vitamin D 400 IU Vitamin E 15 mg Vitamin K 200 μg *Requirements for energy increase by 12% per 1 C of fever.

Basic TPN solutions are prepared using sterile techniques, usually in liter batches according to standard formulas. Normally, 2 L/day of the standard solution is needed. Solutions may be modified based on laboratory results, underlying disorders, hypermetabolism, or other factors. Commercially available lipid emulsions are often added to supply essential fatty acids and triglycerides; 20 to 30% of total calories is usually supplied as lipids. However, withholding lipids and their calories may help obese patients mobilize endogenous fat stores, increasing their insulin Some Trade Names
HUMULIN
NOVOLIN
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sensitivity.

Solutions: Many solutions are commonly used. Electrolytes can be added to meet the patient's needs.

Patients who have renal insufficiency and are not receiving dialysis or who have liver failure require solutions with reduced protein content and a high percentage of essential amino acids. For patients with heart or kidney failure, volume (liquid) intake must be limited. For patients with respiratory failure, a lipid emulsion must provide most of nonprotein calories to minimize CO₂ production by carbohydrate metabolism. Neonates require lower dextrose concentrations (17 to 18%).

Beginning TPN administration: Because the central venous catheter needs to remain in place for a long time, strict sterile techniques must be used during insertion and maintenance. The TPN line should not be used for any other purpose. External tubing should be changed q 24 h with the first bag of the day. In-line filters are controversial and may not help. Dressings should be kept sterile and are usually changed q 48 h using strict sterile techniques. For TPN given outside the hospital, patients must be taught to recognize symptoms of infection, and qualified home nursing must be arranged.

The solution is started slowly at 50% of the calculated requirements, using 5% dextrose to make up the balance of fluid. Energy and nitrogen should be given simultaneously. The amount of regular insulin Some Trade Names
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given (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 to 10 units of regular insulin Some Trade Names
HUMULIN
NOVOLIN
Click for Drug Monograph
/L of TPN fluid.

Monitoring: Progress should be followed on a flowchart. An interdisciplinary nutrition team, if available, should monitor the patient. Weight, CBC, electrolytes, and BUN should be monitored often (eg, daily for inpatients). Blood glucose should be monitored q 6 h until stable. Fluid intake and output should be monitored continuously. When the patient becomes stable, blood tests can be done much less often.

Liver function tests should be done. Plasma proteins (eg, serum albumin, possibly transthyretin or retinol-binding protein); prothrombin time; plasma and urine osmolality; and Ca, Mg, and phosphate (not during glucose infusion) should be measured twice/wk. Full nutritional assessment (including BMI calculation and anthropometric measurements—see Undernutrition: Physical examination; see Obesity and the Metabolic Syndrome: Body composition analysis) should be repeated at 2-wk intervals.

Complications: With close monitoring by a nutrition team, the complication rate may be < 5%. Complications may be related to the central venous catheter (see Table 5: Approach to the Critically Ill Patient: Complications Associated With Central Venous Lines) or to the provision of nutrition.

Glucose abnormalities are common. Hyperglycemia can be avoided by monitoring blood glucose often, adjusting the insulin Some Trade Names
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dose in the TPN solution, and giving subcutaneous insulin Some Trade Names
HUMULIN
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as needed. Hypoglycemia can be precipitated by suddenly discontinuing constant concentrated dextrose infusions. Treatment, depending on the degree of hypoglycemia, may consist of 50% dextrose IV or infusion of 5 or 10% dextrose for 24 h before resuming TPN via the central venous catheter.

Abnormalities of serum electrolytes and minerals should be corrected by modifying subsequent infusions or, if correction is urgently required, by beginning appropriate peripheral vein infusions. Vitamin and mineral deficiencies are rare if solutions are given correctly. Elevated BUN may reflect dehydration, which can be corrected by giving free water as 5% dextrose via a peripheral vein.

Volume overload (suggested by > 1 kg/day weight gain) may occur when high daily energy requirements require large fluid volumes.

Metabolic bone disease, or bone demineralization (osteoporosis or osteomalacia), develops in some patients receiving TPN for > 3 mo. The mechanism is unknown. Advanced disease can cause severe periarticular, lower extremity, and back pain. Temporarily or permanently discontinuing TPN is the only known treatment.

Adverse reactions to lipid emulsions (eg, dyspnea, cutaneous allergic reactions, nausea, headache, back pain, sweating, dizziness) are uncommon but may occur early, particularly if lipids are given at > 1.0 kcal/ kg/h. Temporary hyperlipidemia may occur, particularly in patients with kidney or liver failure; treatment is usually not required. Delayed adverse reactions to lipid emulsions include hepatomegaly, mild elevation of liver enzymes, splenomegaly, thrombocytopenia, leukopenia, and, especially in premature infants with respiratory distress syndrome, pulmonary function abnormalities. Temporarily or permanently slowing or stopping lipid emulsion infusion may prevent or minimize these adverse reactions.

Hepatic complications include liver dysfunction, painful hepatomegaly, and hyperammonemia. They can develop at any age but are most common among infants, particularly premature ones (whose livers are immature). Transient liver dysfunction, evidenced by increased transaminases, bilirubin, and alkaline phosphatase, is common with the initiation of TPN. Delayed or persistent elevations may result from excess quantities of amino acids. Pathogenesis is unknown. Contributing factors probably include cholestasis and inflammation. Progressive fibrosis occasionally develops. Reducing protein delivery may help. Painful hepatomegaly suggests fat accumulation; carbohydrate delivery should be reduced. Hyperammonemia can develop in infants. Signs include lethargy, twitching, and generalized seizures. Correction consists of arginine Some Trade Names
R-GENE
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supplementation at 0.5 to 1.0 mmol/kg/day. For infants who develop any hepatic complication, limiting amino acids to 1.0 g/kg/day may be necessary.

Gallbladder complications include cholelithiasis, gallbladder sludge, and cholecystitis. These complications can be caused or worsened by prolonged gallbladder stasis. Stimulating contraction by providing about 20 to 30% of calories as fat and stopping glucose infusion several hours a day is helpful. Oral or enteral intake also helps. Treatment with metronidazole Some Trade Names
FLAGYL
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, ursodeoxycholic acid, phenobarbital Some Trade Names
LUMINAL
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, or cholecystokinin helps some patients with cholestasis.

Last full review/revision November 2005

Content last modified November 2005