Ketamine anesthesia causes greater muscle catabolism in rabbits than does propofol

Whereas ketamine and propofol are popular anesthetics in the intensive care unit and trauma/burn surgery, their metabolic effects are not known. Because traumatized patients are under catabolic state and may need multiple operations over the acute period of treatment, the knowledge of metabolic effects of anesthetics should have clinical relevance. We have compared muscle protein kinetics in rabbits under ketamine or propofol anesthesia. Because propofol is given in a fat emulsion (Intralipid), we have also tested the effect of Intralipid in an additional group of animals under ketamine anesthesia by giving the same dose of Intralipid as in the propofol group. In all animals, xylazine was used as a supplemental anesthetic and a balanced amino acid infusion (10% Travasol) was infused at 2 mg · kg^-1 · min^-1. L-[ring-¹³C₆]phenylalanine was infused as a tracer and the arteriovenous balance method was applied to the hindlimb for determination of muscle protein kinetics. Results: the rate of muscle protein breakdown was significantly greater in the ketamine group than in the propofol group and intermediate in the lipid group. These results were consistent with whole body protein breakdown rates reflected by total phenylalanine flux. Rates of muscle protein synthesis were not significantly different among the groups. Consequently, the ketamine group had significantly greater net loss of muscle protein. We conclude that in relation to propofol, ketamine has a greater catabolic effect on muscle protein, which can be attenuated by lipid infusion. Therefore, ketamine is not an optimal anesthetic for catabolic patients.