Dynamics of the protein metabolic response to burn injury

The protein metabolic response to burn injury was assessed in 17 children aged 7.1 ± 1.1 years (mean ± SEM) and a mean burn size of 65 ± 7% total body surface area (TBSA) during the acute, flow, convalescent, and recovery phases. Stable isotopes of leucine, valine, lysine, and urea were infused in postabsorptive patients in order to measure protein kinetics. The absolute rate of protein breakdown was assessed from the plasma flux of the essential amino acids (EAA), and the rate of urea production (Ra urea) was used as an index of net protein catabolism. Compared to values obtained in recovered patients, the plasma fluxes of all three EAAs were significantly increased (P < .05), indicating an increased protein breakdown, during the acute, flow, and convalescent phases of injury. Ra urea, however, was only significantly increased during the flow phase (P < .01), suggesting that protein breakdown was adequately counteracted in the acute and convalescent phases by elevations in protein synthesis but not in the flow phase. The protein kinetic response did not correlate with changes in the metabolic rate since resting energy expenditure (REE) was significantly increased above predicted levels during the acute and flow phases (by 40% and 50%, respectively), and returned to normal in convalescence. We conclude that (1) protein breakdown is elevated in the acute, flow, and convalescent phases of response to burn injury; (2) there is a significant increase in net loss of N only in the flow phase; and (3) the switch from net protein catabolism in the flow phase to net protein anabolism in convalescence occurs in spite of an elevated protein breakdown rate.