Combination of arginine and omega-3 fatty acids enteral nutrition in critically ill and surgical patients: a meta-analysis

Figure 1. Number of trials evaluated at each stage of the meta-analysis.
(Figure omitted. See article PDF.)

Trauma, surgery or other medical conditions may be life-threatening and frequently require intensive care. Aggressive surgical and medical interventions can promote a state of hypermetabolism and catabolism [1]. These metabolic alterations in combination with bed rest and a lack of nutritional intake can lead to a rapid loss of lean body mass. Nutritional supplementation in intensive care patients helps slow the rate of net protein catabolism [1]. Patients suffering from trauma, sepsis or major surgery are also at a high risk of developing nosocomial infection owing to a depressed immune function [2]. Nosocomial infections in the critically ill are associated with increased mortality, increased length of stay (LOS) in hospital and increased costs [2,3]. Immune-enhancing enteral preparations enriched with arginine, glutamine, omega-3 fatty acids, nucleotides and other immunonutrients are designed to help improve immune function.

Arginine is a nonessential amino acid. It contains a highly basic side chain, a guanidino group that is protonated at physiological pH. Arginine modulates immune and inflammatory processes by several mechanisms and is involved in the processes of innate resistance and cell-mediated immunity [4]. Cytokine-inducible nitric oxide synthase (iNOS) oxidizes the terminal guanidino nitrogen in arginine to an inorganic nitric oxide (NO) that affects multiple functions and processes. NO regulates gene expression and cellular differentiation and may be the main mechanism of arginine's effect [5,6]. Evidence suggests that when cells are depleted of arginine, iNOS produces superoxide (O ₂ ^- ) instead of NO. O₂ ^- reacts to produce cell destruction and death. Insufficient tissue perfusion during ischemia and wound healing may contribute to low tissue arginine concentrations and subsequent O₂ ^- formation [7].

There are short-chain and long-chain fatty acids. Omega 3 and omega 6 are long-chain fatty acids that humans are unable to synthesize [8,9]. Arachidonic acid, an omega 6 fatty acid, leads to the production of several inflammatory eicosanoids, such as leukotrienes, prostraglandins and thromboxane, and increases the production and metabolism of interleukins [8]. Omega-3 fatty acids have an inhibitory effect on the production of arachidonic acid [9].

A number of studies have evaluated the effect of immunonutrition on clinical outcomes in the critically ill. Most of...