Nutrients with immune-modulating effects: what role should they play in the intensive care unit?

Abstract

This review will summarize recent clinical and experimental data on the use of immune-modulating nutrients in critical illness. It will present the concept of these nutrients as pharmacologic agents or 'nutraceuticals' administered in addition to protein, calorie, vitamin, and trace element sources. Studies have defined the physiologic roles of arginine in critical illness, such as its role as a precursor for the production of nitric oxide. Investigations have determined that, in critical illness, glutamine levels decrease and severe glutamine deficiency is associated with increased mortality. Experimental studies have revealed that glutamine attenuates proinflammatory cytokine responses, improves gut barrier and immune cell functions, increases the ability to mount a stress response, and decreases mortality. Clinical trials and meta-analyses of studies testing immune-modulating nutritional formulations have reported numerous benefits but also some conflicting results. Dose and route of administration are key factors that influence the benefit, or lack thereof, of these nutraceuticals. Cumulative studies of enteral immune-modulating nutritional formulations report benefits in surgical critically ill patients such as burn, trauma, or gastrointestinal surgery populations. Conflicting data in patients with sepsis warrant concern and further evaluation; in particular, controversy seems to stem around the use of arginine. Glutamine is beneficial when given in high doses or via the parenteral route (>0.20-0.30 g/kg per day or >or=30 g/day). Providing both omega-3 and omega-6 polyunsaturated fatty acids is important in immune modulation. The best doses and combinations of immune-modulating components remain unclear.