Complications Associated With Parenteral Nutrition
Hyperglycemia both at admission and during hospitalization has been associated with an increased risk of complications including infections and renal failure, longer hospital stays, and reduced survival in humans and horses with critical illness or injury.60,61 In a landmark prospective, randomized, controlled clinical trial of humans admitted to the ICU, tight glycemic control using intensive insulin therapy during hospitalization was associated with a significant improvement in morbidity and mortality compared with the more traditional, less stringent glycemic control.62 Tight glycemic control (maintained between 80 and 110 mg/dL compared with 180 to 200 mg/dL) decreased the incidence of infections, acute renal failure, and days of mechanical ventilation and improved neurologic outcome in brain injury patients.63 Additional studies using less stringent glucose control have found similar results.64,65 As previously mentioned, hepatic gluconeogenesis is upregulated during the acute phase of critical illness.
Insulin resistance and loss of exercise-associated uptake of glucose, as well as the increased production of glucose, are thought to result in hyperglycemia. Normal cells downregulate glucose transporters during periods of hyperglycemia to protect against glucose toxicity.66 During inflammation this protective response is lost, allowing glucose to enter the cell along a steep concentration gradient.67,68 Elevated intracellular glucose concentrations have been associated with increased oxidative stress, mitochondrial dysfunction, and altered energy metabolism.69 The use of insulin therapy to maintain blood glucose levels within the normal range has been shown to have the added benefit of correcting dyslipid- emias.70 Additional reported beneficial effects of maintaining euglycemia include improved immune function due to improved phagocytosis, decreased glycosylated nonfunctional immunoglobulin, and blunting of the catabolic process.71-74While extrapolation to a different species with different underlying diseases should always be performed cautiously, it would seem prudent to try to maintain blood glucose concentrations within or close to normal range. It is unclear at this time if strict glycemic control is better than a less stringent control.
In cases where hyperglycemia persists, the use of intensive insulin infusions is recommended to attempt to normalize the blood glucose concentration.Lipid infusions have been associated with allergic reactions, hyperlipemia, alterations in liver function, and fat embolism. The risk of fat embolization is higher in larger droplet emulsions or in emulsions that have been stored too long and have begun to destabilize. Although solutions containing lipids are useful in providing additional calories, their use needs to be determined on a case-by-case basis. Lipids should be avoided in patients with a predisposition to or preexisting hyperlipemia or underlying liver dysfunction. Thrombocytopenia, coagulopathy, fat embolization, and alterations in cellular immunity are reported with lipid infusions. Triglyceride levels and platelet counts should be monitored regularly when lipids are added to PN solutions.
Additional complications reported with PN include hyperammonemia and elevations in serum urea nitrogen due to excess protein catabolism, hypercapnia due to excess carbohydrate metabolism, thrombophlebitis due to hypertonicity, pulmonary embolism (thought due to destabilized lipid emulsions), and sepsis.46,51,75-77