Dyslipidemia

Baseline triglyceride levels should be obtained prior to the initiation of TPN. Hyperlipidemia can result from excessive carbohydrate administration as well as a diminished clearance of fats. Patients experiencing a stress response to infection or injury may see a reduction in lipid clearance resulting in hyperlipidemia. The use of medications that alter fat metabolism, such as corticosteroids and immune suppressing medications, can contribute to increased lipid levels. Patients with diabetes, liver disease, renal failure, pancreatitis, and organ failure are at high risk for dyslipidemia with TPN.

For patients at high risk of hypertriglyceridemia fat emulsions can be limited and provided in small amounts once or twice weekly. In such cases, an infusion of 0.5-1 gram/kg/day or 250 mL of 20% fat emulsion twice weekly can provide the necessary essential fatty acids. Higher concentrations of lipid emulsions, such as 30%, are associated with lower levels of triglycerides and cholesterol.

Withholding or reducing fat emulsions to 4-6% of total energy may be appropriate if levels become very high, above 500 mg/dL or if the serum is lipemic. Pediatric patients may benefit from withholding lipid infusion when serum triglyceride levels top 275 mg/dL. If oral or enteral consumption of fats is not an option, safflower or soybean oil can be used topically to help in preserving essential fatty acid availability.

Gastrointestinal-Related Complications

When parenteral nutrition is the sole source of nutrient intake the risk for gastrointestinal (GI) complications is higher. The lack of  intestinal stimulation causes the villi to atrophy and decreases both the absorptive surface and impairs the protective barrier against infection. This process, known as bacterial translocation, can lead to septicemia. The resulting acute phase reaction can cause altered metabolism and increases the risk for metabolic complications, such as insulin resistance, fluid and electrolyte disturbances, and others. The risk for bacterial translocation can be reduced by introducing oral and/or enteral feeding in addition to the intravenous feeding. How much is required to prevent this gastrointestinal complication remains unclear, but even small amounts are likely to benefit the maintenance of gastrointestinal function.

During the initial introduction of parenteral nutrition, it is common to observe transient mild increases in liver function tests and alkaline phosphatase values. These increases often return to normal over a period of time as the body adjusts to the therapy. With the discontinuation of therapy, the elevated values are almost always reversed.

Hepatobiliary complications can also occur, particularly if there is no gastrointestinal stimulation through feeding. Steatosis can result when sepsis is present or with the administration of carbohydrates at a rate higher than the suggested 5 mg per kilogram per minute. In addition, deficiencies of carnitine, essential fatty acids, and choline contribute to fatty infiltration of organ tissues. Treating infections, lowering the rate of carbohydrate infusion and substituting these calories with fat emulsions, cycling patients off TPN for 8-10 hours each day, and initiating oral/enteral nutrition to encourage normal bile flow can help to manage hepatobiliary complications. A balanced infusion of dextrose, amino acids, and fat can help to reduce fatty infiltration of tissues. In some cases, ursodiol may be recommended along with the initiation of oral/enteral support.

Jaundice and elevated levels of bilirubin are fairly rare in adults. However, elevations in conjugated bilirubin and alkaline phosphatase in pediatric patients can be a signal for risk of cholestasis. Cholestasis can be a life-threatening complication of long-term parenteral nutrition in pediatric patients. This complication is associated with excessive levels of carbohydrate administration, recurrent sepsis and bacterial overgrowth. Cholestasis  has been estimated to occur in 30-60% of pediatric patients on long-term TPN. The incidence of this complication may be reduced through early initiation of oral/enteral nutrition, prevention of and prompt treatment for sepsis, cyclic feeding  for longer-term TPN therapy, and the prevention of overfeeding with carbohydrates and fats. Infants may benefit from specialized pediatric amino acid formulations to prevent cholestasis.