Total parenteral nutrition in surgical illness: how much? How good?

Using primed constant infusions of isotopes and indirect calorimetry, we assessed protein, glucose, and fat kinetics in severely ill surgical patients suffering from sepsis, major trauma, gastrointestinal cancer, or nutritional depletion from benign disease. We also assessed the effect of 5 days of total parenteral nutrition (TPN) on abnormal metabolism in these states. In the basal state, patients with sepsis, trauma, or cancer had an elevated rate of net protein catabolism due to an increased rate of whole-body protein catabolism, whereas whole-body protein synthesis was not impaired. TPN had no impact on the elevated rate of whole-body protein catabolism in these conditions but decreased the rate of net protein catabolism, suggesting that increased substrate availability optimizes whole-body protein synthesis. Consequently, few surgical patients became anabolic while receiving TPN. In contrast, patients with nutritional depletion from benign disease had a decreased rate of net protein loss compared with volunteers and could be made anabolic with the administration of TPN. All patients studied had an elevated rate of plasma glucose production, impaired glucose oxidation, and an increased rate of Cori cycling in the basal state. After 5 days of TPN, most surgical patients showed improved ability to oxidize glucose, but the high rates of glucose recycling to lactate persisted. Patients suffering from sepsis, trauma, or cancer had an enhanced rate of lipolysis in the basal state associated with an increased rate of whole body-fat oxidation compared with healthy volunteers. After administration of TPN, whole-body fat oxidation was significantly decreased in patients with trauma but increased in patients with sepsis or cancer.(ABSTRACT TRUNCATED AT 250 WORDS)