Assessment of whole body protein metabolism in critically ill children: can we use the [15N]glycine single oral dose method?

Background & aims: Most stable-isotope methods to evaluate whole body protein metabolism in patients are invasive and difficult to use in children. In this study protein metabolism was evaluated with the non-invasive [15N]glycine single oral dose method in critically ill children and the value of the method is discussed. Methods: [15N]glycine (100 mg) was given orally to children (mean age 5.5 years; range 0.6–15.5 years) with meningococcal septic shock (MSS, n=8), pneumonia (n=5), and to healthy, fed and post-absorptive children (n=10). Urine was collected during 9 h, total amount of NH3, labelled NH3 and nitrogen were measured, and protein turnover, synthesis and breakdown were calculated using urinary NH3 as end-product. Results: Mean protein turnover in children with MSS, pneumonia and fed and post-absorptive healthy children was 0.63±0.13, 0.38±0.10, 0.28±0.03 and 0.28±0.02 g N/kg/9 h, respectively. Mean protein synthesis was 0.55±0.12, 0.29±0.09, 0.18±0.02, 0.20±0.02 g N/kg/9 h, respectively. Mean protein breakdown was 0.56±0.14, 0.28±0.12, 0.08±0.03, 0.28±0.02 g N/kg/9 h, respectively. Protein turnover, synthesis and breakdown were significantly increased in MSS patients compared to fed healthy children (P<0.01) and post-absorptive children (P<0.05). Protein turnover, protein synthesis, protein breakdown were significantly correlated with disease severity and body temperature (P<0.05). Conclusion: Results of whole body protein metabolism measured with the [15N]glycine single oral dose method in children with MSS and in healthy children were in line with expectations based on results obtained in earlier reports and with different methods.