"improving intensive care in Scotland"

Nutrition in ICU

9. Other Nutrients

Clinical micronutrient deficiency states are rare in the UK, but sub-clinical deficits may have an effect on outcome on the critically ill patient. Critical illness results in increased micronutrient requirements as a result of metabolic stress and increased losses from dialysis, fistulae etc. Whilst it is important to include these minerals in feeding regimes, there is no evidence as yet that supra-physiological supplementation is of any benefit.

Micronutrient

Effects of deficiency

Zinc

Impairs T-cell function and hypersensitivity Increased susceptibility to infection. Reduced antioxidant defence.

Copper

Reduced antioxidant defence, reduced tissue repair, increased susceptibility to infection

Selenium

Reduced antioxidant defence, reduced tissue repair, increased susceptibility to infection

Thiamine

Impaired carbohydrate metabolism Neurological deficits

Riboflavin and folic acid

Impaired immune function

Glutamine

Glutamine is an amino acid essential for cell synthesis and repair and for immune cell function. During critical illness there is an increased cellular demand for glutamine which results in a relative deficiency. Intravenous supplementation of glutamine in patients on PN has been shown in a number of small studies to improve survival and infection rates, particularly in burns and trauma patients. The power of these studies was inadequate to provide conclusive evidence and routine glutamine supplementation in enteral and parenteral feed is expensive; few units in Scotland do this at present. The SIGNET trial, taking place in Scottish ICUs until November 2008, aims to clarify the role of Glutamine and Selenium in a heterogeneous ICU population.

Immunonutrition

Nutritional products supplemented with antioxidants (selenium, beta-carotene, vitamins A, C and E in supra-physiologic concentrations), L-arginine, fish oils containing omega-3 fatty acids (eicosapentanoic and linoleic acid), and RNA are collectively known as Immunonutrition.

Theoretically these substances should have many beneficial effects on the immune system, as well as reducing oxidative stress and improving wound healing. Many studies have been carried out using various formulations containing immunonutrients and some have shown improvements in morbidity and mortality. The problem with these studies is that most are small and firm conclusions cannot be drawn. Until large-scale studies of individual immunonutrients in homogeneous groups of critically ill patients are carried out, it will be impossible to know if there is a significant benefit from their use, and any benefits may vary depending on the patient group.

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