Abstract
This study is based on the premises that (1) fat emulsions may be a valuable energy source for trauma and septic patients, and (2) whereas long-chain triglycerides (LCTs) may not be completely oxidized and some long-chain fatty acids may be reesterified to triglycerides in the liver, medium-chain triglycerides (MCTs) are more rapidly cleared from the circulation than LCT emulsions and are metabolized faster. When MCTs are cleared, the authors cite published studies1,2 suggesting MCTs may enter cell mitochondria relatively independently of the carnitine acyltransferase transportation system and that MCTs are used in muscle at a twofold to threefold greater rate than LCTs.3 This suggests that MCTs may be a more efficient energy source for muscle.
In addition, the authors cite other published studies suggesting MCTs are ketogenic and ketones may have protein sparing effects when used as an energy source.4 One commercial emulsion containing a 50:50 mixture of MCTs and LCTs is Lipofundin MCT 10% (B. Braun Inc, Melsungen, Germany). The purpose of this study was to compare this MCT emulsion with a pure LCT emulsion (10% Endolipid, B. Braun Inc, France) in perioperative patients receiving TPN and in normal healthy volunteers. The two fat emulsions were compared with regard to (1) forearm muscle utilization, (2) total body nitrogen balance, (3) serum insulin and β-hydroxybutyrate concentrations, and (4) general hematologic parameters and indices of organ function.
In this study, 12 adult patients requiring major abdominal surgery for gastric ulcer, gastric cancer, or colon cancer were enrolled. Eligible patients were required to demonstrate (1) normal nutritional status as determined by body weight, physical exam, and various laboratory parameters; (2) no evidence of metastatic disease; and (3) no evidence of diabetes, other chronic disease, or glucocorticoid use.
Patients who were operated on were randomized into two groups. The control group received parenteral nutrition with LCT emulsion (10% Endolipid). The study group received 10% Lipofundin (MCTs). Total parenteral nutrition (TPN) was started 2 days before surgery and continued through the seventh postoperative day. Patients were given 30 nonprotein kcal/kg body weight per day, with 50% of the calories provided as carbohydrates. Amino acids (MoriProne 18 F, Ajinomoto, Tian-jin, China) were administered to provide 0.2 g of nitrogen per kilogram of body weight per day. On the day TPN was initiated and was stopped, various laboratory parameters were determined including serum glutamic-pyruvic transaminase, blood urea nitrogen, glucose, bicarbonate, cholesterol, and triglyceride levels. Nitrogen balance was determined daily. On the day before surgery and the third postoperative day, a fat emulsion clearance test was performed during which the arteriovenous (A-V) difference across the forearm was determined.
In another study, six healthy volunteers were studied for 3 days on two occasions separated by 2 weeks. In each 3-day period, TPN without fat was administered for 16 hours per day (8:00 AM to midnight). On the second and third days, the fat emulsion clearance test was performed with either MCTs or LCTs. Two weeks later, the protocol was repeated with the other fat emulsion.
In the group that was operated on, all measured parameters of organ and hematologic functions between the MCT and LCT groups were similar, except there was a greater weight loss in the LCT than in the MCT group (2.4 ± 0.2 vs 1.5 ± 0.2 kg, respectively). In both groups, postoperative clearance of triglycerides was enhanced compared with clearance presurgery. When the triglyceride A-V concentration difference across the forearm during the fat clearance test was integrated with respect to time in the postoperative period, the A-V difference associated with the MCT infusion was significantly greater than that with the LCT infusion. During this fat clearance test, serum concentrations of β-hydroxybutyrate were significantly increased in the MCT group compared with the LCT group (5.58 ± 0.34 versus 3.43 ± 0.15 mg/dL, respectively). Cumulative nitrogen balance tended to be less negative in patients receiving MCTs compared with LCTs (+142 ± 46 versus -91 ± 120 mg/kg per 7 days, respectively; .05 < p < .1). After 6 days of TPN, serum glucose levels were similar in both groups but serum insulin levels were significantly increased in the MCT group compared with the LCT group (92 ± 14 versus 52 ± 12 μU/mL, respectively).
In the normal volunteers, the fat clearance test resulted in similar arterial triglyceride levels. However, when the triglyceride A-V concentration difference across the forearm during the fat clearance test was integrated with respect to time, the result again suggested that fat clearance with MCTs was significantly increased compared with LCTs.
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