Predictors of muscle protein synthesis after severe pediatric burns

Abstract

Background: Following a major burn, skeletal muscle protein synthesis rate increases but is often insufficient to compensate for massively elevated muscle protein breakdown rates. Given the long-term nature of the pathophysiologic response to burn injury, we hypothesized that muscle protein synthesis rate would be chronically elevated in severely burned children. The objectives of this study were to characterize muscle protein synthesis rate of burned children over a period of 24 months after injury and to identify predictors that influence this response.

Methods: A total of 87 children with 40% or greater total body surface area (TBSA) burned were included. Patients participated in stable isotope infusion studies at 1, 2, and approximately 4 weeks after burn and at 6, 12, and 24 months after injury to determine skeletal muscle protein fractional synthesis rate. Generalized estimating equations with log link normal distribution were applied to account for clustering of patients and control for patient characteristics.

Results: Patients (8 ± 6 years) had large (62, 51-72% TBSA) and deep (47% ± 21% TBSA third degree) burns. Muscle protein fractional synthesis rate was elevated throughout the first 12 months after burn compared with established values from healthy young adults. Muscle protein fractional synthesis rate was lower in boys, in children older than 3 years, and when burns were greater than 80% TBSA.

Conclusion: Muscle protein synthesis is elevated for at least 1 year after injury, suggesting that greater muscle protein turnover is a component of the long-term pathophysiologic response to burn trauma. Muscle protein synthesis is highly affected by sex, age, and burn size in severely burned children. These findings may explain the divergence in net protein balance and lean body mass in different populations of burn patients.

Level of evidence: Prognostic study, level III.

Trial registration: ClinicalTrials.gov NCT00675714.

Figure 1

Skeletal muscle FSR (mean±SEM) from 1 week (wk) to 24 months (mo) post-burn. n = 33 (1 wk), 37 (2 wk, 4wk, 6 mo), 40 (12 mo), and 7 (24 mo). The gray line represents postprandial FSR values for seven healthy young adults(20). FSR= fractional synthesis rate.

Figure 2

Adjusted (showing the effect of time on FSR post-burn) and unadjusted FSR values up to 24 months post-burn. The dotted line represents muscle FSR values after adjusting for age, sex, % TBSA burned, % TBSA third degree burned, smoke inhalation injury, and delayed care. FSR= fractional synthesis rate; TBSA= total body surface area.

Figure 3

Effect of sex on FSR values after major burn-injuries in children. FSR values are adjusted for age, TBSA burned, % TBSA third degree burned, smoke inhalation injury, and delayed care. FSR= fractional synthesis rate; TBSA= total body surface area.

Figure 4

The impact of age on skeletal muscle FSR after burn. FSR values are adjusted for sex, % TBSA burned, % TBSA third degree burned, smoke inhalation injury, and delayed care. FSR= fractional synthesis rate; TBSA= total body surface area.