Nutrition support in critical illness: amino acids.

The general approach to the nutritional care of the catabolic, malnourished or critically ill patient involves delivery of a balanced diet including energy (in the form of carbohydrates and lipids), an adequate amount of nitrogen, all essential nutrients (amino acids, fatty acids, vitamins, electrolytes) and fluid [1]. Traditionally, the qualitative and quantitative composition of dietetic measures in patients was derived from recommended daily allowances for healthy adults with addition of a so-called ‘safety margin’. In the past 2 decades, this view has been fundamentally modified. Firstly, overwhelming evidence has been brought forward that critical illness is associated with profound alterations in carbohydrate, lipid, and protein metabolism [2, 3]. Consequently, nutrient demands of patients can considerably differ in comparison with healthy adults. Presently, great efforts are being undertaken to define ‘diseaserelated’ recommendations and, in line with this novel concept, to provide ‘tailor-made’ formulas for specific patient groups like children, renal and liver diseases, and critical illness. Secondly, evidence was found that various nutrients including amino acids and fatty acids possess more than the wellknown ‘nutritive’ effects on body function and metabolism [4]. In vitro and in vivo studies showed that nutrients can modify the immune response as well as the integrity of organs and tissues in health and disease in a dose-dependent manner. Moreover, the extent and target of this ‘pharmacological’ effect can be controlled by the timing and the way (oral/enteral, intravenous) of substrate administration. Indeed, this approach opens the possibility to modulate the metabolic response to stress.