Metabolic Utilization of Intravenous Fat Emulsion During Total Parenteral Nutrition

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Abstract
The effect of nutritional therapy on the use of an i.v. fat emulsion was studied in patients with injury, infection and nutritional depletion using 1-14C-trioleate labeled Intralipid. The plasma fractional removal rate and 14C-Intralipid oxidation rate was 55 and 25% higher, respectively, in patients following trauma and during periods of infection receiving 5% dextrose than in healthy control subjects. Total parenteral nutrition (TPN) was administered as either nonprotein calories given as glucose (Glucose System) or equal proportions of glucose and i.v. fat emulsion (Lipid System). In comparison to TPN with the Lipid System, administration using the Glucose System resulted in higher plasma clearance rates and lower oxidation rates in both acutely ill and depleted patients. There was no correlation between the rates of plasma removal and oxidation of the intravenous fat emulsion (r = -0.04; NS [not significant]) indicating that the removal of exogenous fat from plasma cannot be used as an indicator of oxidation. A negative linear relationship was seen between the oxidation rate of intravenous fat and carbohydrate intake (r = -0.92; P < 0.001). Glucose intakes exceeding energy expenditure did not totally inhibit oxidation of the fat emulsion. The oxidation rate of 14C-Intralipid was linearly related to net whole body fat oxidation calculated using indirect calorimetry (r = -0.90; P < 0.001) suggesting that the fat emulsion was oxidized in a similar manner to endogenous lipids. Fat emulsions administered i.v. are apparently utilized as an energy substrate in patients with major injury, infection or nutritional depletion. This observation, along with a relative unresponsiveness to glucose in surgical patients suggests that fat emulsions may be useful as a calorie source in patients receiving parenteral nutrition.