Semi-elemental diets: for which intensive care unit patients?

Abstract

The main features of semi-elemental enteral diets consist in their specific nitrogen fraction, made of a protein hydrolysate containing di- and tripeptides, which represent the main forms of nitrogen absorption by gastrointestinal tract. Indications focus on acute situations of malnutrition accompanied by reduced capacities of digestion and absorption. Many experimental studies support the interest of semielemental diets. However, clinical studies have been conducted mostly on small groups of patients (single centre studies in the intensive care unit) and have compared semi-elemental diets with polymeric diets, which differ most often not only by the molecular form of nitrogen supply, but also by the amino acid profile, nitrogen concentration, and other nutrients profiles (e.g. lipids, vitamins). Studies with formulas containing almost di-and tripeptides reported no metabolic benefits, because of fast kinetics regarding amino acids absorption, leading to a dramatic increase in liver oxidation, without beneficial effect on protein synthesis. This issue resulted in the development of semi-elemental enteral formula with different peptide profiles, allowing oral use (better palatability) and a drop in manufacturing costs. These formulae improve some parameters of the protein balance. However, clinical use of semi-elemental formula remains limited, in relation to the absence of documented benefits on clinical outcome including morbidity, mortality, and length of hospital stay, also because recent clinical studies are scarce. Currently accepted indications for semi-elemental diets in intensive care patients include post-operative nutritional support after digestive surgery (mainly after small bowel resection), acute pancreatitis, and adaptive phase of intestinal transplantation. Semi-elemental formula may also be used in other patients as second-line diets in case of documented intolerance to polymeric formula.