Parenteral nutrition can be associated with various metabolic complications. Hyperglycemia is common; because this complication can be associated with poorer outcomes, it is important to avoid extremes of high blood sugars, and blood sugar is typically monitored several times daily at initiation of PN. Frequency of blood sugar monitoring can be decreased when stability is demonstrated. Regular insulin is frequently added to PN solutions, and subcutaneous sliding scale insulin is also frequently administered. Use of long-acting insulin, such as insulin glargine, may be useful in selected patients on PN, although this use is problematic if the PN is unexpectedly discontinued or held. Separate insulin drips are frequently utilized in ICU patients receiving PN. Hypoglycemia can occur when PN is abruptly discontinued. Although this is not commonly a problem, some institutions cut the rate of PN in half for an hour or so before discontinuing. Home PN patients often run their solution at lower rates for the first and last hours of their daily infusion cycle.
Abnormalities of electrolytes are frequently seen in PN patients. Hypophosphatemia, hypokalemia, and hypomagnesemia may require increases in the amounts of these electrolytes added to the PN, additional bolus dosages, or both. These electrolyte abnormalities, especially hypophosphatemia, can be associated with the so-called refeeding syndrome in chronically malnourished patients. These electrolytes should be monitored at least twice a week upon initiation of PN; frequency of monitoring can be cut back when levels have demonstrated stability. Hyperphosphatemia, hyperkalemia, and hypermagnesemia occur primarily during renal insufficiency and require decreasing these electrolytes in the PN solution. Mild hyponatremia is common in PN patients. Addition of more sodium to the PN is not always appropriate; the patient could already be fluid-overloaded and thus the decreased serum sodium is due to dilution. Acid–base imbalances are not typically secondary to PN therapy itself. Acetate in PN solutions is converted to bicarbonate in the liver. Decreasing the acetate to chloride ratio in the PN may help correct metabolic alkalosis, whereas increasing this ratio may be helpful in metabolic acidosis.
Hypertriglyceridemia, defined as a serum triglyceride concentration above 400 to 500 mg/dL, may occur in patients receiving IV lipid. Hypertriglyceridemia of this magnitude can be associated with increased risk of pancreatitis. With hypertriglyceridemia in this range, generally the amount of lipid emulsion infused is decreased. Triglycerides should be measured prior to initiation of lipid emulsion, after a day of administration, and approximately weekly thereafter in hospitalized patients. Caution is warranted if lipid emulsion is completely withheld in patients receiving PN for more than a couple of weeks; essential fatty acid deficiency could develop if there is no intake of fat.
Liver function abnormalities have been associated with PN therapy. Two general patterns have been described. The first pattern, characterized by elevation of aspartate and alanine aminotransferase, typically occurs within a few days of initiation of PN and is associated with hepatic steatosis, or fat accumulation in the liver. This pattern is seen in patients being overfed especially with dextrose. The second pattern is cholestasis characterized by an increase in alkaline phosphatase and total bilirubin. This pattern tends to develop after two or more weeks of PN in adult patients. Liver function tests should be monitored weekly in hospitalized patients receiving PN.
Mechanical complications of PN include problems with insertion of the central venous catheter such as pneumothorax (punctured lung). Catheter occlusion or thrombosis may also occur. Occlusion may be treated by infusion of a thrombolytic agent or hydrochloric acid, depending on the nature of the occlusion.
Catheter-related infections are common in patients receiving PN. Such infections present with symptoms such as fever, chills, and rigors. Because placement of a permanent central venous catheter is expensive and invasive, attempts to salvage infected catheters are frequently made in long-term home PN patients where IV access sites may also be limited. Administration of IV antibiotics and/or placement of a small amount of antibiotic as an antibiotic lock of the catheter may be utilized. Most catheter-related infections are secondary to gram-positive bacteria, although gram-negative bacteria or fungi may also be culprits. Typically, fungal infection requires catheter removal and replacement.