The critically ill, stressed patient has been characterized as having altered cellular metabolism. Altered protein metabolism is manifested as negative nitrogen balance, reduced whole-body protein synthesis, and increased proteolysis. An increased oxidation of the branched-chain amino acids (BCAA) leucine, isoleucine, and valine has also been observed. Exogenous administration of BCAA as part of a total parenteral nutrition (TPN) regimen has been proposed to compensate for the altered protein metabolism in the stressed patient by sparing endogenous sources of BCAA, thereby reducing skeletal muscle catabolism and increasing protein synthesis. Numerous clinical studies have been performed investigating this theory. The results are controversial. Differences in study outcomes appear to be related to study design, especially patient selection. Our review of those studies which were randomized, prospective, and controlled indicates that an improvement in nitrogen retention and visceral protein status can be achieved in stress-stratified patients who receive a TPN regimen containing a BCAA-enriched formula. The significance of these outcomes on morbidity, length of hospital stay, and mortality has not been evaluated.
Altered protein synthesis is a trigger for long-term memory formation
