Background: The metabolic response to surgery includes alterations in protein metabolism, resulting in a net loss of proteins. Protein hypercatabolism is considered an unavoidable consequence of injury, and an important source of morbidity and mortality. Our purpose was to determine the effect of nutrition on protein metabolism following gastrointestinal surgery, and to elucidate whether postoperative protein loss can be prevented with adequate nutritional support.
Methods: Patients who had undergone gastrointestinal surgery were given four different parenteral nutritions with increasing glucose, lipid and amino acid content during the 7 days following surgery. Nitrogen balance, protein synthesis and protein breakdown were determined using in vivo stable isotope labelling. Other metabolites (3-methylhistidine, creatinine, urea, cortisol, glucose, insulin, amino acids and C-reactive protein) were measured.
Results: A nutrition-dependent alteration of protein metabolism was found in response to surgical injury. Nutrition modified nitrogen balance, whole-body protein breakdown and, to a lesser extent, whole-body protein synthesis and muscle protein breakdown. The low-energy parenteral nutrition without amino acids produced a negative nitrogen balance (postoperative day 7=-0.381 g protein kg(-1)day(-1)) and important alterations in postoperative protein metabolism that did not normalize during the study period (day 7 protein synthesis=239% and protein breakdown 217% vs preoperative). Patients receiving the two low energy parenteral nutritions containing amino acids had a less negative nitrogen balance (day 7=-0.011 and -0.133 g protein kg(-1)day(-1)) and a transient increase in protein metabolism. The complete parenteral nutrition maintained, during all studied days, protein metabolism parameters within the preoperative reference range (synthesis day 2=92%, day 4=110% day 7=79%; breakdown day 2=85%, day 4=80%, day 7=76% vs preoperative) and a positive nitrogen balance (day 2=+0.0387, day 4=+0.578 and day 7=+0.227 g protein kg(-1)day(-1)).
Conclusion: Complete nutritional support can prevent protein loss after gastrointestinal surgery and maintain protein metabolism without alterations.