Background: Burn injury results in increased skeletal muscle protein turnover, where the magnitude of protein breakdown outweighs synthesis, resulting in muscle wasting. The effect of increased amino acid (AA) provision on skeletal muscle fractional synthesis rate (FSR) in severely burned patients during their convalescence after discharge from hospital is not known. Subsequently, the purpose of this study was to determine skeletal muscle FSR in response to AA infusion in severely burned pediatric patients at discharge from hospital and at 6 and 12 months after injury.
Methods: Stable isotope infusion studies were performed in the fasted state and during intravenous AA infusion. Skeletal muscle biopsies were obtained and isotope enrichment was determined to calculate skeletal muscle FSR. Patients were studied at discharge from hospital (n = 11) and at 6 (n = 15) and 12 months (n = 14) after injury.
Results: The cohorts of patients studied at each time point after injury were not different with regard to age, body mass, or burn size. AA infusion failed to stimulate FSR above basal values at discharge from hospital (mean [SEM]: 0.27% [0.04%] vs. 0.26% [0.06%] per hour), 6 months after injury (0.20% [0.04%] vs. 0.22% [0.03%] per hour), and 12 months after injury (0.16% [0.03%] vs. 0.15% [0.03%] per hour). Daily FSR was numerically lower at 6 months after burn (5.13% [0.78%] per day) and significantly (p < 0.05) lower at 12 months after burn (3.67% [0.65%] per day) relative to discharge group (6.32% [1.02%] per day).
Discussion: The findings of the current study suggest that the deleterious effect of burn injury on skeletal muscle AA metabolism persists for up to 1 year post burn. In light of these findings, nutritional and pharmacological strategies aimed at attenuating muscle protein breakdown post burn may be a more efficacious approach to maintaining muscle mass in severely burned patients.
Level of evidence: Prognostic study, level II.