[Strategies for the use of amino acids. Catabolism and retention]

Extensive Catabolism is a hallmark of patients with acute renal failure (ARF) complicating critical illnesses. Catabolism is due to dysregulation of protein metabolism as well as a consequence of diminished renal excretion and renal replacement therapy (RRT). Inadequate nutritional support predisposes patients to malnutrition and increased mortality risk. Since the catabolic rate varies widely in ARF patients and can not be predicted by clinical parameters, direct quantification of the protein catabolic rate should be performed regularly. The urea nitrogen appearance rate (UNA) is a valid and reproducible estimate of nitrogen balance in critically ill patients undergoing continuous RRT. Amino acid losses up to 50 g/day and protein losses up to 15 g/day occur during continuous RRT and need to be compensated for. In order to achieve neutral or positive nitrogen balance a nutritional regimen providing 1.5-2.0 g protein/kg/day and 25-35 kcal/kg/day may be required. Since glutamine losses during continuous RRT may exceed 4 g/day, glutamine supplementation (0.3-0.5 g/kg/day) appears to be recommendable.