Short term amino acid infusion improves protein balance in critically ill patients

INTRODUCTION: Evidence behind the recommendations for protein feeding during critical illness is weak. Mechanistic studies are needed to elucidate the effects of amino acid/protein supplementation on protein metabolism before larger clinical trials with higher protein feeding are initiated. METHODS: Here we study the effects of parenteral amino acid supplementation (equivalent to 1 g/kg/day) over 3 h on whole body protein turnover in critically ill patients in the ICU during the first week after admission. Patients were studied at baseline during ongoing nutrition and during extra amino acid supplementation. If the patient was still in the ICU 2-4 days later, these measurements were repeated. Protein kinetics were measured using continuous stable isotope labeled phenylalanine and tyrosine infusions. RESULTS: Thirteen patients were studied on the first study occasion only and 7 were studied twice. Parenteral amino acid supplementation significantly improved protein balance on both occasions; from median -4 to +7 mumol phenylalanine/kg/h (P = 0.001) on the first study day and from median 0 to +12 mumol phenylalanine/kg/h (P = 0.018) on the second study day. The more positive protein balance was attributed to an increased protein synthesis rate which reached statistical significance during the first measurement (from 58 to 65 mumol phenylalanine/kg/h; n = 13; P = 0.007) but not during the second measurement (from 58 to 69 mumol phenylalanine/kg/h; n = 7; P = 0.09). Amino acid oxidation rates, estimated by phenylalanine hydroxylation, did not increase during the 3 h amino acid infusion. A positive correlation (r = 0.80; P < 0.0001)) between total amino acids/protein given to the patient and whole body protein balance was observed. CONCLUSION: Extra parenteral amino acids infused over a 3 hour period improved whole body protein balance and did not increase amino acid oxidation rates in critically ill patients during the early phase (first week) of critical illness.