 In this protocol, we will investigate fibrinogen metabolism in burn and trauma patients, using an 8h infusion of stable isotopes labeled amino acids 1-13C-phenylalanine, 2H5-phenylalanine, and 2H3-ketoisocaporate. The increase of the labeled amino acids incorporating into fibrinogen during the infusion and the decay of labeled fibrinogen after stopping the isotopes infusion as measured by GC-MS will be used to calculate fibrinogen synthesis and degradation. Stable isotopes are non-radioactive. 