Whole body protein kinetics measured with a non-invasive method in severely burned children

Persistent and extensive skeletal muscle catabolism is characteristic of severe burns. Whole body protein metabolism, an important component of this process, has not been measured in burned children during the long-term convalescent period. The aim of this study was to measure whole body protein turnover in burned children at discharge (95% healed) and in healthy controls by a non-invasive stable isotope method. Nine burned children (7 boys, 2 girls; 54 ± 14 (S.D.)% total body area burned; 13 ± 4 years; 45 ± 20 kg; 154 ± 14 cm) and 12 healthy children (8 boys, 4 girls; 12 ± 3 years; 54 ± 16 kg; 150 ± 22 cm) were studied. A single oral dose of ¹⁵N-alanine (16 mg/kg) was given, and thereafter urine was collected for 34 h. Whole body protein flux was calculated from labeling of urinary urea nitrogen. Then, protein synthesis was calculated as protein flux minus excretion, and protein breakdown as flux minus intake. At discharge, total protein turnover was 4.53 ± 0.65 (S.E.) g kg body weight^-1 day^-1 in the burned children compared to 3.20 ± 0.22 g kg ^-1 day^-1 in controls (P = 0.02). Expressed relative to lean body mass (LBM), the rates were 6.12 ± 0.94 vs. 4.60 ± 0.36 g kg LBM^-1 day^-1 in burn vs. healthy (P = 0.06). Total protein synthesis was also elevated in burned vs. healthy children, and a tendency for elevated protein breakdown was observed. Conclusion: Total protein turnover is elevated in burned children at discharge compared to age-matched controls, possibly reflecting the continued stress response to severe burn. The oral ¹⁵N-alanine bolus method is a convenient, non-invasive, and no-risk method for measurement of total body protein turnover.