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Metabolic Complications

Metabolic complications of parenteral nutrition include alterations in fluid and electrolyte balance, acid-base balance, glucose control, dyslipidemia, refeeding syndrome, vitamin and mineral status, hepatobiliary and renal function, and bone diseases. The following text will explore each type of complication, their clinical features and strategies for prevention and treatment. Appendix A summarizes metabolic complications of TPN, including prevention strategies, signs and symptoms of complications, and treatment strategies.

 

Fluid and Sodium Imbalance

Fluid imbalance can occur early in TPN. Prevention strategies against dehydration and fluid overload should consider the patient’s risk profile for fluid intolerance and formula volume. Fluid intake and output should be monitored on a daily basis along with daily weights  to identify fluid imbalances. Most complete nutrition prescriptions will include between 1.5 to 3 liters of volume. A typical calorie infusion will provide approximately 1 calorie/mL of fluid. In some cases, volume intolerance may require alterations in this ratio. Fluid restrictions, in patients with pulmonary, renal, or hepatic failure, may require a more concentrated formulation. For instance, fluid overload can occur in patients with cardiac disease and a predisposition to congestive heart failure) and those with renal disease. In these cases, the rate of infusion can be decreased and the concentration of the formula may be increased according to tolerance. Fat emulsions can be used to provide adequate calories in high-risk patients who may require volume restrictions.

 

Fluid imbalances can affect the balance of electrolytes, which can also occur early in the course of TPN. Lab values should be monitored often in the early stages of TPN until stabilized, at which time routine monitoring can be implemented. Fluid overload in excessive hypotonic formulations can lead to hyponatremia, and fluid restriction may result in hypernatremia. Adrenal insufficiency, nephritis, syndrome of inappropriate antidiuretic hormone, cirrhosis with ascites, and congestive heart failure can cause fluid imbalance and hyponatremia. Clinical symptoms include confusion, hypotension, lethargy, and in some cases seizures. Balanced fluids and, in some cases, use of diuretics will help to overcome these alterations. If sodium intake is inadequate, sodium could be increased in the parenteral nutrition formulation.

 

Though rare, hypernatremia can occur when there are excessive water losses or excessive sodium intake. Clinical symptoms are typically increases in thirst, loss of skin turgor and “tenting”, and irritability. Oral fluid intake may be important to reduce the effect of dehydration and hypernatremia. Sodium content of the formulation can also be reduced.

         

Refeeding Syndrome and Carbohydrate-Dependent Nutrients

This multifactoral complication involves imbalances of fluids, electrolytes, and other micronutrients can occur at the beginning of a course of TPN. High-risk populations include patients with a history of alcoholism and anorexia nervosa or other causes of marasmus.

 

Aggressive refeeding, especially with high-dextrose concentrations, can trigger refeeding syndrome in the malnourished patient as anabolic processes quickly shift nutrients into and out of body compartments. Markers of refeeding syndrome include low levels of the three carbohydrate dependent minerals: magnesium, phosphorus, and potassium. Other associated findings may include hemolytic anemia, cardiac arrhythmias, respiratory distress, and tetany. The mortality rate can be high and prompt recognition and treatment is essential to survival and recovery. Refeeding syndrome may require the discontinuation of TPN. Once carbohydrate is increased, care should be taken to proportionately increase the carbohydrate-dependent minerals (potassium, magnesium, and phosphorus). Limiting sodium to 20 mEq or less per day may also lower the risk for refeeding syndrome.