Use of Lipid Calories During Pneumococcal Sepsis in the Rhesus Monkey

Abstract

A number of studies in patients and monkeys have suggested that intravenous infusion of lipids can be utilized as a major source of calories during sepsis and/or trauma. Others, however, have observed that lipid calories were not as effective as glucose calories in sparing body protein in severely septic and/or burned patients. In trying to resolve this controversy, a parenteral nutrition model was utilized during pneumococcal sepsis in the rhesus monkey. Earlier studies indicated that when monkeys were infused with 0.55 grams amino acid nitrogen and 13 kilocalories per kilogram per day, they lost approximately 13% of their body protein as a result of the clinical illness associated with pneumococcal sepsis. Addition of 85 kilocalories per kilogram per day of either dextrose or lipid emulsion (Intralipid) effectively prevented this infection-related loss of body protein. The present study was designed to determine whether the elevated plasma insulin concentrations associated with glucose infusions are necessary for protein sparing or would interfere with utilization of lipid calories. In this study, septic and control monkeys were infused with a hypocaloric amino acid-dextrose solution to which was added lipid emulsion. If septic monkeys were totally maintained on a hypocaloric infusion of amino acids and 32 kilocalories per kilogram per day from dextrose, they lost 6.8 ± 1.0% of their body protein over the 6-day experimental period. Addition of lipid calories (55 kilocalories per kilogram per day) to this mixture resulted in a gain of 1.1 ± 0.7% of body protein. In both experimental groups plasma insulin was approximately 100 to 200 microunits per milliliter, which resulted in a marked inhibition of ketogenesis and lipolysis. Despite elevated plasma insulin, the septic monkey appeared able to utilize the fatty acids from the infused lipid effectively as a calorie source to spare body protein. Since lipid emulsion contains approximately 13% glycerol calories, septic monkeys were infused with a hypocaloric amino acid-dextrose solution and an amount of glycerol calories equivalent to that found in Intralipid. Under these conditions, the loss of body protein was very similar to that seen when the hypocaloric amino acid-dextrose solution alone was infused in the septic monkey. Thus, the protein-sparing effects of the lipid emulsion are not related to its glycerol content.