Adult patients are more catabolic than children during acute phase after burn injury: a retrospective analysis on muscle protein kinetics.

Purpose: This study was performed to determine if there is an age-related specificity in the response of muscle protein metabolism to severe burn injury during acute hospitalization. This is a retrospective analysis of previously published data.
Methods: Nineteen adult and 58 pediatric burn-injured patients (age 43.3 ± 14.3 vs. 7.2 ± 5.3 years, adult vs. children) participated in stable isotope [ring-(2)H(5)]phenylalanine (Phe) infusion studies. Femoral arterial and venous blood samples and muscle biopsy samples were collected throughout the study. Data are presented as means ± standard deviation (SD). A p value less than 0.05 was considered statistically significant.
Results: Muscle net protein balance (NB) was higher in children (adult vs. children, -43 ± 61 vs. 8 ± 68 nmol Phe/min/100 ml leg volume, p < 0.05). Muscle protein fractional synthesis rate (FSR) was higher in children (adult vs. children, 0.11 ± 0.05 vs. 0.16 ± 0.10 %/h, p < 0.05). Leg muscle protein breakdown was not different between the groups (adult vs. children, 179 ± 115 vs. 184 ± 124 nmol Phe/min/100 ml leg volume, p > 0.05); synthesis rate was 134 ± 96 and 192 ± 128 nmol Phe/min/100 ml leg volume in adults and children, respectively (p = 0.07). Age significantly correlated with muscle protein NB (p = 0.01) and FSR (p = 0.02); but not with breakdown (p = 0.67) and synthesis (p = 0.07) rates measured by using a three-pool model.
Conclusion: In burn injury, the muscle protein breakdown may be affected to the same extent in adults and children, whereas synthesis may have age-related specificities, resulting in a better but still low NB in children.