Immunonutrition in Critical Illness: What Is the Role?

Abstract

Acute illness-associated malnutrition leads to muscle wasting, delayed wound healing, failure to wean from ventilator support, and possibly higher rates of infection and longer hospital stays unless appropriate metabolic support is provided in the form of nutrition therapy. Agreement is still lacking about the value of individual immune-modulating substrates for specific patient populations. However, it has long been agreed that there are 3 primary targets for these substrates: 1) mucosal barrier function, 2) cellular defense function, and 3) local and systemic inflammation. These targets guide the multitude of interventions necessary to stabilize and treat the hypercatabolic intensive care unit patient, including specialized nutrition therapy. The paradigm shift that occurred 30 years ago created a unique role for nutrition as an agent to support host defense mechanisms and prevent infectious complications in the critically ill patient. This overview of immunonutrition will discuss the evidence for its role in critical illness today.

Plasma Glutamine Levels in Relation to Intensive Care Unit Patient Outcome

“…For this reason, routine supplementation of glutamine to all critically ill patients is not recommended by various Societies like ESPEN (European Society for Clinical Nutrition and Metabolism) [32]; ASPEN (American Society for Parenteral and Enteral Nutrition) [33]; and the German Nutrition Guidelines [34]. Although glutamine is thought to have an important role in critically ill patients, the recognized contra-indications to glutamine supplementation must be adhered to, such as the presence of multiple organ failure (especially renal and liver failure) [1,7,10,14,32,34] and patients with septic shock requiring vasopressor support [1,7,10,34]. When supplementing with glutamine, the dose should not exceed 0.5 g/kg body weight per day [7,10,14]; it should not be supplemented during the early acute phase of critical illness [10,34]; it should be administered together with full nutrition support [14] and the glutamine dose should not exceed 30% of the prescribed nitrogen supply [7].…”

“…Immunonutrition refers to the administration of nutrients to modulate the immune system to improve the clinical outcome. These nutrients include glutamine, arginine, omega-3 fatty acids, and a host of antioxidants [1]. Of these, glutamine is the most studied supplement.…”

Nutrition in Sepsis: A Bench-to-Bedside Review

“…Pharmaco-nutrition refers to the addition of nutrients with specific beneficial actions (e.g., antioxidant effects) to standard feeding, and specifically aims to invigorate gut mucosal and systemic immune defense mechanisms, and to shackle an excessive pro-inflammatory response during the catabolic phase of illness [42,43]. The most relevant "pharmaco-nutrients" in septic patients are the amino-acids glutamine and arginine, omega-3 fatty acids, selenium, and vitamin C.…”

Nutrition in the Neurocritical Care Unit: a New Frontier

“…The mechanisms involved are multifactorial and beyond the scope of this review, though are the basis for the theory that nutrients can modulate the immune and inflammatory response [50], often referred to as "immunonutrition." Potential mechanisms for immune-modulating effects include delivery of specific amino acids as preferred fuel sources for enterocytes, omega-3 (n-3)rich polyunsaturated fatty acids (PUFAs) to manipulate eicosanoid production and downstream anti-inflammatory cytokine response [50,51], as well as reducing oxidative stress through delivery of specific vitamins, minerals, and phytochemicals involved in human antioxidant systems [50] (Table 1).…”