CHAPTER 20

#### KEY POINTS

• Nutrients and gastrointestinal structure and function are linked to the pathophysiology of infection, organ dysfunction, and survival in critically ill patients.

• Nutrition therapy may both positively and negatively influence the morbidity and mortality of critically ill patients.

• When considering artificial nutrition in critically ill patients, enteral nutrition (EN) should be used in preference to parenteral nutrition (PN).

• Strategies to optimize delivery of EN (eg, starting EN early, use of a feeding protocol with a high gastric residual volume threshold, use of prokinetic agents, and use of small bowel feeding) and minimize the risks of EN (eg, elevation of the head of the bed) should be considered.

• For most patient populations in critical care in whom EN is not possible or feasible, the role of PN is controversial. Similarly, when to initiate supplemental PN when hypocaloric EN is not meeting the patient’s calorie or protein requirements is also controversial. Use of PN in these circumstances should be evaluated on a case-by-case basis taking into consideration the underlying nutrition risk of the patient.

• Nutrition risk in the ICU can be identified by considering preexisting weight loss, decreased oral intake, prior stay in hospital before admission to ICU, preexisting comorbidities, and severity of current illness.

• When PN is indicated, strategies that maximize the benefit (eg, supplementing with glutamine) and minimize the risks of PN (eg, hypocaloric dose, withholding soy-bean emulsion lipids, continued use of EN, and adequate glycemic control) should be considered.

Nutrition is considered an integral component of standard 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 and we consider it as therapy that has the ability to modulate the underlying disease process, favorably alter immune responses, and impact outcomes of critically ill patients. The benefits of nutrition therapy 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 There are several studies that document that inadequate provision of nutrition to critically ill patients is associated with increased complications, prolonged length of stay in ICU and hospital, increased mortality, and increased health care costs.2-7 On the other hand, there are good data from ...

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