Immunonutrition

Abstract

Immunonutrition describes the enteral or parenteral administration of certain substrates (arginine, omega-3 fatty acids, nucleotides, glutamine and antioxidants) with a putative immunomodulating function. Thus far, with the exception of glutamine and antioxidants, these immunomodulating substrates have not been examined separately but only in various combinations to establish their clinical efficacy. In critically ill patients who predominantly require parenteral nutrition, there is evidence from large meta-analyses that parenteral glutamine supplementation may significantly lower septic morbidity and mortality. Therefore, parenteral glutamine supplementation is currently part of all concepts and recommendations addressing nutritional issues in critical care. With respect to selective parenteral or enteral application of arginine or omega-3 fatty acids, there are still insufficient data on clinical effects or side effects to allow a definitive conclusion for nutritional care in the critically ill. Only one metaanalysis addressed the clinical importance of a selective antioxidant therapy. It was concluded that such a therapy lowered mortality rates by about one third. However, this effect was unrelated to an improvement of infectious morbidity. Still, parenteral antioxidant supplementation (especially of selenium) is currently considered beneficial in critically ill patients. At the moment, two different substrate mixtures of various immunomodulating compounds are commercially available. One type contains arginine, omega-3 fatty acids, and antioxidants ± glutamine (classic mixture), the other omega-3 fatty acids, dihomogamma linoleic acid and antioxidants (modified mixture). Due to the mixture concept, only summary effects can be examined clinically, and interactions between different substrates cannot be excluded. According to large metaanalyses, there are neither beneficial nor detrimental effects of the classic mixture when used in unselected cohorts of critically ill patients. In patients with severe sepsis, negative side effects of the classical mixture may possibly exist (enhancement of immunosuppression in the specific immune system). Therefore, use of the classical mixture is not recommended in the latter patients. On the other hand, there is increasing evidence for beneficial clinical effects of the modified mixtures in critically ill and also in septic patients. The modified mixture improved pulmonary function and outcome in ventilated patients significantly, and is currently incorporated into nutritional recommendations of various societies.