Prevention of refeeding syndrome in high-risk patients may require the stabilization of potassium, magnesium, phosphorus, and vitamins prior to initiation of TPN. Slow initiation of TPN with an initial formulation that limits carbohydrate to 150 g/day and volume to 800 mL/day may be prudent in very high-risk patients. Careful monitoring and administration of potassium, magnesium, phosphorus, and vitamins according to the amount of carbohydrate supplied can help to maintain a balance and prevent the consequences of refeeding syndrome.

 

Solutions that are high in glucose concentration can also trigger alkalosis and an increase in insulin levels causing a rapid shift of potassium into the cells. The risk for hypokalemia is greater in patients with diarrhea or renal losses of potassium. Medications can increase potassium losses and caution should be taken with patients taking loop and thiazide diuretics, cathartics, antibiotics, and antifungal medications. Nutrients can interact and lead to electrolyte imbalances. For example, a low level of magnesium can lead to lower levels of potassium, which should be corrected to support normal potassium levels. Increased levels of potassium intake can usually be accomplished through oral/enteral or parenteral potassium supplementation.

 

Hyperkalemia can result in patients with renal dysfunction, metabolic acidosis, or using potassium-sparing diuretics. Clinical signs/symptoms include diarrhea, tachycardia, oliguria, and heart attack. Levels of potassium can be adjusted in the solution to restore potassium balance. In severe cases it may be necessary to use potassium binders, insulin, and/or dialysis.

 

Hypomagesemia is caused by refeeding syndrome and the use of diuretics, chronic nasogastric suction, increased stool volume, diabetic ketoacidosis, and the use of magnesium-losing medications. Low levels are associated with symptoms of arrhythmia, muscle weakness, and tetany. Because oral supplementation of magnesium is limited by poor absorption, parenteral administration is typically used to treat this problem.

 

Hypermagnesemia can occur in renal dysfunction and lead to hypotension, lethargy, liver dysfunction, respiratory paralysis, and heart attack. While most problems can be alleviated with balanced or reduced magnesium intake, more severe levels may require dialysis.

 

Lower levels of phosphate can be seen in refeeding syndrome, inadequate intake, and prolonged alcoholism and can result in arrhythmias, congestive heart failure, anemias and leukocyte dysfunction, respiratory failure, tubular necrosis, and paralysis. Interactions of hypophosphatemia can lead to losses of bicarbonate and glucose. Intravenous phosphate administration is used to treat this condition.

 

High levels of phosphate are seen in cases of excessive intake and renal dysfunction. Hypertension, confusion, and arrhythmias can occur in the short-term and tissue calcification may result from longer-term hyperphosphatemia. Phosphate binders and a decrease in phosphate intake are indicated for treatment.

          

Glucose Tolerance

Hyperglycemia is defined as blood glucose levels above 180 mg/dL or plasma glucose above 220 mg/dL in adults. Hyperglycemia can lead to immune suppression and can increase the risk of infection. Elevated glucose levels are a common complication in TPN, especially during the first few weeks. Maintenance of blood glucose levels at closer to normal levels is associated with better patient outcomes with a significant reduction in mortality and septicemia.

 

For patients with baselines above 300 mg/dL, glycemic control should be achieved prior to the initiation of TPN. Patients with metabolic stress, diabetes, obesity, and excessive carbohydrate infusion are more likely to experience hyperglycemia. Close monitoring to adjust the dose of carbohydrate during the first few days of TPN may include monitoring blood glucose up to three times or more daily in patients at high risk compared to a daily monitoring regimen in lower-risk patients. For high-risk patients, a slower rate and volume of carbohydrate, such as dextrose solutions that provide 100-150 grams/day or up to 2-3 mg/kg/minute, can be started and increased to meet around 40% of energy needs while maintaining good blood sugar control. The rate and amount should not be increased until reasonable blood glucose control can be maintained. A maximum rate of 5-7 mg/kg/minute can help to maintain blood sugar control in lower risk patients.

 

For patients previously treated with insulin or oral antidiabetic medications or if blood glucose is consistently elevated it may be necessary to include a base level of insulin in the TPN formula. Supplemental insulin can be initiated at 0.1 units per gram of dextrose. If glycemic control cannot be achieved with additional insulin of more than 0.3 units per gram of dextrose, a separate insulin drip should be considered. Patients who are discontinuing the use of corticosteroids should also be closely monitored for changes in glucose tolerance and possible reduction in insulin needs.

 

Neonates, particularly preterm babies, may have immature body mechanisms to maintain equilibrium. This population typically has a high carbohydrate requirement, and low body glycogen stores. These conditions can put the baby at risk for developing both hyperglycemia and hypoglycemia. Pediatric hyperglycemia is defined as >150 mg/dL plasma glucose or >125 mg/dL in whole blood and may be inversely related to weight and developmental age. As with adults, risk factors for hyperglycemia in pediatric patients include sepsis, injury or surgery, respiratory distress, prematurity, and overload of TPN carbohydrates. Hypoglycemia is fairly rare, but can develop with an abrupt cessation of TPN, especially in neonates and infants. Careful monitoring of glucose concentrations includes checking blood sugar levels within 15-60 minutes of TPN initiation and cessation. Transitional periods should include a slow tapering of TPN over a one to two hour period to avoid hypoglycemic episodes.