Chapter 11

• Nutrients and gastrointestinal structure and function are linked to the pathophysiology of infection, organ dysfunction, and survival in critically ill patients.
• Nutrition support may both positively and negatively influence the morbidity and mortality of critically ill patients.
• When considering nutrition support in critically ill patients, enteral nutrition (EN) should be used in preference to parenteral nutrition (PN).
• Strategies to optimize delivery of EN (e.g., starting EN early, use of a feeding protocol with a high threshold of gastric residual volume, use of prokinetic agents, and use of small bowel feeding) and minimize the risks of EN (e.g., elevation of the head of the bed) should be considered.
• When initiating EN, PN should not be used in combination with it.
• For most patient populations in critical care in whom EN is not possible or feasible, standard therapy (IV fluid resuscitation without artificial nutrition support) is preferable to PN for the first 7 to 10 days.
• When PN is indicated, strategies that maximize the benefit (e.g., supplementing with glutamine) and minimize the risks of PN (e.g., hypocaloric dose, withholding lipids, continued use of EN, and the use of intensive insulin therapy to achieve tight glycemic control) should be considered.

Nutrition support is considered an integral component of standard supportive care in the critically ill patient. In humans, during stress associated with trauma, sepsis, or other critical illness, there is high consumption of various nutrients by the gastrointestinal tract, immune cells, kidneys, and other organs. Requirements for and losses of these nutrients may outstrip synthetic capacity, leading to an erosion of body stores and depletion of proteins and other key nutrients. Historically, in an attempt to mitigate such deficiencies and preserve lean body mass, traditional nutrition (protein, calories, vitamins, etc) has been provided to critically ill patients. The relative merits of nutrition were evaluated in the context of protein-calorie economy (weight gain, nitrogen balance, muscle mass and function, etc). In this chapter we take a broader view of the benefits and risks of nutrition support. The benefits of nutrition support in general include improved wound healing, a decreased catabolic response to injury, enhanced immune system function, improved GI structure and function, and improved clinical outcomes, including a reduction in complication rates and length of stay with accompanying cost savings.1 Independent of their effects on nutritional status of the patients, key nutrients such as glutamine, arginine, and omega-3 fatty acids may also have favorable direct effects on organ function and clinical outcomes of critically ill patients. Thus nutrition support may be considered a specific therapeutic intervention by which the critically ill patient's disease course may be altered, leading to a more favorable outcome.

There is considerable evidence linking nutrition (and lack thereof) and GI function to the pathogenesis of infection and organ failure in critical illness.2 Failure to obtain enteral access and to provide nutrients via the enteral route results in a proinflammatory state mediated by macrophages and monocytes. Oxidative stress is increased, ...

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