Effect of short-term, high protein intake on whole-body protein synthesis and breakdown and stress response in infants after cardiac surgery

In critical illness, hypermetabolic stress response markedly increases whole
body protein breakdown with concomitant lesser increase of protein synthesis,
resulting in negative nitrogen balance and loss of lean body mass. Clinically
this contributes to a higher morbidity and mortality, more ventilator days and
increased length of stay on an Intensive Care Unit. Stimulation of synthesis of
whole body protein improves protein balance. In adults, maximum protein
synthesis capacity is 1.5-1.7 g/kg/d. In chronically catabolic, stunted
children protein balance is increased by a dietary protein intake of 5 g/kg/d.
Data on optimal protein intake in critically ill children is lacking.
Furthermore it has been suggested that several nutrients like glutamine,
arginine, nucleotides and polyunsaturated fatty acids have beneficial effects
on the stress response.

Primary: To measure the effect of a high protein diet on whole body protein
synthesis and -breakdown, as well as on net whole body protein balance and
production of urea in children after cardiac surgery
Secondary: To measure the effect of a high protein diet on the post-operative
hypermetabolic stress response and also defining an evidence based
recommendation for optimal daily protein intake in children in the direct
post-operative phase after cardiac surgery.

24 children will be randomly allocated in two groups of 12 before their
surgery. Both groups receive an isocaloric diet during 3 days by bottle feeding
and/or nasogastric tube starting direct postoperatively with a protein load of
2 g/kg/day or 5 g/kg/day. On day 3 whole body protein synthesis and -breakdown
rates are measured by infusion of stable isotopes and collection of blood- and
breathsamples. Also determinants of post-operative stress response will be
measured in the bloodsamples.

Diet with high protein load (5 g/kg/day)

At 4 set times during the study period (T=0 and 3x around T=46 hours) blood
samples will be taken from already exsisting lines. Breath samples will be
taken at 5 moments (T=0, 27,5 and 3x around T=46 hours) via the nasopharyngeal
tube. The burden and risks associated with all the interventions will be
negligible for the patients