Postoperative total parenteral nutrition

Surgical trauma induces complex physiologic changes that lead to catabolism and loss of body cell mass. This reaction is usually mild but can be exacerbated by previous malnutrition and postoperative complications. To avoid severe metabolic distress, nutritional therapy may be prescribed, using the enteral route whenever possible. Postoperative total parenteral nutrition (TPN) is indicated for patients already receiving TPN preoperatively, those severely malnourished prior to major surgery, those unable to eat satisfactorily for 7 days, or patients presenting with severe complications. Postoperative TPN should last for at least 7 days. The total energy requirements are between 30 and 35 kcal/kg/day. About 50% to 70% should be provided in the form of carbohydrates, and 20% to 30% in the form of lipids. The optimal input rates for glucose and lipids are 4 to 5 g/kg/day and 80 mg/kg/hr, respectively. The ideal nitrogen administration is 250 to 300 mg/kg/day, and the optimal calorie/nitrogen ratio is 150 to 200. Some specific amino acids can be added as intravenous dipeptides. An adequate follow-up must include clinical and biochemical parameters. Several trials evaluated the impact of TPN in postoperative patients, but further well designed, controlled clinical trials are still necessary to address a great number of unanswered questions.