Page 228 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

132 PART 2: General Management of the Patient

CHAPTER Nutrition Therapy in the on nutritional status of the patients, key nutrients such as glutamine,
arginine, and omega-3 fatty acids may also have direct effects on organ
20 Critically Ill function and clinical outcomes of critically ill patients. Thus, nutrition
therapy may be considered a specific therapeutic intervention by which
Daren K. Heyland the critically ill patient’s disease course may be altered, leading to a more
Rupinder Dhaliwal favorable outcome.
Stephen A. McClave There is considerable evidence linking nutrition (and lack thereof)
and GI function to the pathogenesis of infection and organ failure in
critical illness. Failure to obtain enteral access and to provide nutrients
13
KEY POINTS via the enteral route results in a proinflammatory state mediated by
macrophages and monocytes. Oxidative stress is increased, severity of
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• Nutrients and gastrointestinal structure and function are linked to illness is exacerbated, and the likelihood of infectious morbidity, multi-
the pathophysiology of infection, organ dysfunction, and survival organ failure, and prolonged length of stay is increased. 14-16 In contrast,
in critically ill patients. the provision of enteral nutrition results in higher levels of secretory IgA
• Nutrition therapy may both positively and negatively influence the at mucosal surfaces throughout the body (lungs, lacrimal glands, tonsils,
morbidity and mortality of critically ill patients. nares, and genitourinary system), greater preservation of gut-associated
• When considering artificial nutrition in critically ill patients, lymphoid tissue, and less intestinal permeability, all of which translates
enteral nutrition (EN) should be used in preference to parenteral into improved clinical outcomes for critically ill patients. 1
nutrition (PN). However, providing micro- and macronutrients is not without adverse
• Strategies to optimize delivery of EN (eg, starting EN early, use of a effects or risks. Acquired infection, particularly ventilator- associated
pneumonia (VAP), is a major problem for critically ill patients, resulting
feeding protocol with a high gastric residual volume threshold, use of in increased morbidity, mortality, and health care costs. 17,18 Pneumonia
prokinetic agents, and use of small bowel feeding) and minimize the is likely due to aspiration of contaminated oropharyngeal/tracheal
risks of EN (eg, elevation of the head of the bed) should be considered. secretions and this is more likely to occur in a patient on EN, where
• For most patient populations in critical care in whom EN is not pos- EN promotes gastric colonization, gastroesophageal reflux, and pul-
sible or feasible, the role of PN is controversial. Similarly, when to monary microaspiration. Parenteral nutrition has been associated
initiate supplemental PN when hypocaloric EN is not meeting the with gut mucosal atrophy, overfeeding, hyperglycemia, adverse effects
patient’s calorie or protein requirements is also controversial. Use of on immune function, an increased risk of infectious complications,
PN in these circumstances should be evaluated on a case-by-case basis and increased mortality in critically ill patients. While providing
19
taking into consideration the underlying nutrition risk of the patient. supplemental glutamine to seriously stressed critically ill patients may
20
• Nutrition risk in the ICU can be identified by considering preexisting increase their chances of survival, depending on the circumstances,
21
weight loss, decreased oral intake, prior stay in hospital before admis- providing arginine to the same patients may increase their mortality.
sion to ICU, preexisting comorbidities, and severity of current illness. Therefore, nutrition therapy must be viewed as a double-edged sword,
• When PN is indicated, strategies that maximize the benefit (eg, and strategies that maximize the benefits of nutrition support while
minimizing the associated risks need to be considered in formulating
supplementing with glutamine) and minimize the risks of PN (eg,
hypocaloric dose, withholding soy-bean emulsion lipids, continued clinical recommendations.
In developing such recommendations, the patient populations to
use of EN, and adequate glycemic control) should be considered.
which these recommendations will be applied must also be considered.
Studies of nutrition in noncritically ill patient populations may not be
generalizable to critically ill patients. For example, the treatment effect
Nutrition is considered an integral component of standard care in the of PN in elective surgery patients is significantly different than the treat-
critically ill patient. In humans, during stress associated with trauma, ment effect of PN in critically ill patients. 19
sepsis, or other critical illness, there is high consumption of various Even within subpopulations of critically ill patients, differences in
nutrients by the gastrointestinal tract, immune cells, kidneys, and other outcome between the two routes of providing nutrition support are
organs. Requirements for and losses of these nutrients may outstrip more likely to be seen with greater severity of illness. For example, the
synthetic capacity, leading to an erosion of body stores and depletion correlation between the importance of maintaining gut integrity and
of proteins and other key nutrients. Historically, in an attempt to miti- greater disease severity was demonstrated by a study evaluating septic
gate such deficiencies and preserve lean body mass, traditional nutri- complications in trauma patients, randomized at the time of surgery, to
tion (protein, calories, vitamins, etc) has been provided to critically ill PN or to enteral tube feeding. In patients with high Abdominal Trauma
22
patients. The relative merits of nutrition were evaluated in the context Index (ATI) scores (>24), the incidence of septic complications was
of protein-calorie economy (weight gain, nitrogen balance, muscle greater in the PN group than the group on enteral tube feeding (47.6% vs
mass and function, etc). In this chapter, we take a broader view of the 11.1%, p <0.05). For those patients with moderate illness and lower ATI
benefits and risks of nutrition and we consider it as therapy that has scores (<24), there was no significant difference in the incidence of sep-
the ability to modulate the underlying disease process, favorably alter tic complications between the parenteral and enteral groups (29.2% vs
immune responses, and impact outcomes of critically ill patients. The 20.8%, p = NS). Furthermore, in studies of EN versus PN in acute pan-
22
benefits of nutrition therapy in general include improved wound heal- creatitis, faster resolution of the inflammatory response and significant
ing, a decreased catabolic response to injury, enhanced immune system differences in clinical outcomes (reduced septic morbidity and overall
function, improved GI structure and function, and improved clinical complications in the EN group) were seen in studies in which there were
outcomes, including a reduction in complication rates and length of more patients with severe pancreatitis compared to studies with a higher
stay with accompanying cost savings. There are several studies that proportion of patients with mild to moderate pancreatitis. 23-25
1
document that inadequate provision of nutrition to critically ill patients In this chapter, we will discuss the relationships among nutrition,
is associated with increased complications, prolonged length of stay in GI structure and function, immune function, and outcomes in critical
ICU and hospital, increased mortality, and increased health care costs. illness. Upon this theoretical foundation, we will propose recommen-
2-7
On the other hand, there are good data from large-scale observational dations favoring the use of enteral nutrition over parenteral nutrition.
studies and randomized trials 10-12 that suggest better fed patients have Regardless of the route of artificial nutrition, we will suggest strategies
8,9
better clinical and economic outcomes. Independent of their effects that maximize the benefits and minimize the risks of both PN and EN.

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