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Updated guidelines for the nutrition support in the adult critically ill patient: SCCM and ASPEN

Introduction
It is well documented and well understood in the hospital setting, particularly the critical care arena, the importance and necessity of nutrition support. Critical illness is typically associated with a catabolic state. This catabolic state is further complicated with demonstration of the systemic inflammatory response, increased infectious morbidity, multi-organ dysfunction, prolonged hospitalization, and disproportionate mortality.¹ Traditionally, nutrition support was considered adjunctive care; however, the new goals of nutrition support are therapeutic and more focused such as: specifically attempting to attenuate the metabolic pathways associated with stress response, preventing oxidative cellular injury, and improving the immune response. Delivering early nutrition, particularly enteral nutrition, is seen as a therapeutic strategy to attain these new goals as well as to reduce disease severity and complications, decrease length of stay in the intensive care unit (ICU), and favorably impact patient outcome. In May 2009, the Society of Critical Care Medicine (SCCM) and American Society of Parenteral and Enteral Nutrition (A.S.P.E.N.) collaborated and released guidelines for the provision and assessment of nutrition support therapy in the adult critically ill patient. This document will be a review of these guidelines with a focus on when and how to initiate enteral nutrition (EN) and parenteral nutrition (PN). The grading system for recommendations in the guidelines is summarized in table 1.

Guideline Summary
Assessment and Initiation of Enteral Feeding
Assessment of nutritional status previously has been through markers of protein such as albumin, prealbumin, and transferrin.¹ These markers have been shown to be a reflection of the acute phase response and do not accurately represent nutritional status in the ICU. Rather, evaluation of weight loss, previous nutrition intake prior to admission, level of disease severity, comorbid conditions, and function of the gastrointestinal (GI) tract are recommended (Grade: E).

Enteral nutrition supports the functional and structural integrity of the gut and is the preferred route of nutrition support (Grade: B).¹ It has clearly been shown in numerous prospective randomized control trials that enteral nutrition has beneficial effects when compared to PN in critical illness including trauma, burns, head injury, major surgery, and acute pancreatitis. The most consistent effect from EN as shown in the literature, is reduction of infectious morbidity. Other significant benefits include: reduction in length of stay, reduced cost of nutrition therapy, and return of cognitive function (in head trauma patients). The use of enteral feeding protocols has been shown to increase the overall percentages of goal calories provided and should be implemented (Grade: C).

It is recommended that EN be started within 24 to 48 hours following admission to the ICU once fluid resuscitation and hemodynamic stability have been reached (Grade: C).¹ Hemodynamic stability is essential to avoid further gut ischemia caused by underlying pathophysiology such as sepsis, GI dysmotility, and hypotension. Thus signs of intolerance (abdominal distention, increased residuals, decreased stool/flatus passing, hypoactive bowel sounds, and increasing metabolic acidosis) must be differentiated and evaluated as early signs of ischemia. Advancement of feedings toward goal should be accomplished over the following 48 to 72 hours (Grade: E). If early EN is not feasible or available the first 7 days following admission to the ICU in previously adequately nourished patients, no nutrition support should be provided.

Patients should not have enteral feeding withheld due to absence of bowel sounds and/or stool or flatus (Grade: B).¹ Due to the high rate of GI dysfunction in this patient population (up to 70% of patients) bowel sounds are only indicative of contractility and do not necessarily relate to mucosal integrity, barrier function, or absorptive capacity. There has been great debate over the placement of the enteral feeding tube in critically ill patients. Recommendation is to use gastric feeding in critically ill patients unless they are at high risk for aspiration. The patients at high risk (Grade: C) include:

In those patients at high risk measures should be taken to decrease this risk for aspiration including:

If intolerance continues, small bowel placement of feeding tube may be necessary.¹ Intolerance of enteral nutrition can be determined by patient complaints of pain and/or distention, physical exam, passage of flatus and stool, and abdominal radiographs. Gastric residuals themselves are not indicative of intolerance and former practice of 50 to 250 mL of gastric residual being indicative of intolerance, have been disproven. Having repeated gastric residuals >500 mL warrants consideration of small bowel placement of the feeding tube (Grade: B).

The target goal of EN (defined by energy requirements) should be determined and clearly identified at the time of initiation of nutrition support (Grade: C).¹ While it is often difficult to provide 100% of caloric needs to patients, patients who receive protocol driven nutrition support receive greater volumes of enteral nutrition, have fewer infectious complications, and have a shorter hospital length of stay. Studies suggest that providing >50% to 65% of goal calories is required to have the beneficial outcomes seen in burn, bone-marrow transplant, head trauma, and general critically ill patients. If energy requirements (100%) are not meet in the first 7 to 10 days, consideration of supplemental PN should occur.

Enteral Formulations
In selection of appropriate enteral formulations for the critically ill patient, the clinician must determine first if a patient is a candidate for immune modulating enteral nutrition (IMEN).¹ Immune modulating enteral nutrition are those supplemented with arginine, glutamine, nucleic acid, omega-3 fatty acids, or antioxidants. Those patients that have been shown to have significant benefit from IMEN include:

No data support use of IMEN in other subgroups.¹ Patients with acute respiratory distress syndrome (ARDS) and severe acute lung injury (ALI) should be placed on enteral formulations with an anti-inflammatory lipid profile (omega-3 fish oils, etc.) and antioxidants (Grade: A). Benefit has also been shown with addition of glutamine to enteral formulas in which glutamine was not an ingredient. Therefore, all critically ill patients should be considered to have glutamine, antioxidant vitamins, and trace elements added to their enteral formula if not already fortified (Grade: B).

Assessment and Initiation of Parenteral Nutrition
As stated previously in this review, enteral feeding is the route of choice if feasible in critically ill patients.¹ If early EN is not feasible or available the first 7 days of admission in previously well nourished patients admitted to the ICU, no nutrition support should be provided. Parenteral nutrition could then be considered for initiation after 7 days of admission in these patients. A meta-analysis of seven studies in critically ill patients where no EN was available and with an absence of malnutrition upon admission showed that PN increased risk of infectious morbidity and trended toward an increase in overall complications versus no nutrition. Another meta-analysis looked at this same patient population (critically ill, no EN available, no malnutrition) and showed an increase in mortality with PN. As patients have increased duration of severe illness, the benefit of PN becomes apparent and then becomes warranted and thus is recommended after 7 days of admission if EN is not feasible (Grade: C).

If there is evidence upon admission of protein-calorie malnutrition as defined as >10% to 15% recent weight loss or actual body weight <90% of ideal weight and EN is not feasible, PN is recommended as soon as hemodynamic stability is established (Grade: C).¹ In the surgical arena, PN often is used due to complex GI surgical interventions. If a malnourished patient is to undergo major upper GI surgery and EN is not feasible, PN should be started 5 to 7 days prior to procedure and must be initiated only if patient is expected to be NPO for >7 days postoperatively. Initiation of PN should never occur postoperatively, due to increase risk of complications, but rather should be held until the postoperative day 5 to 7 if required (Grade: B).

The guidelines contain information for special patient populations including patients with pulmonary conditions, renal failure, hepatic failure, acute pancreatitis, obesity, and those at the end of life.¹ The reader is encouraged to consult the publication for these recommendations.

Conclusions
These new guidelines from SCCM and A.S.P.E.N. provide practitioners with evidence-based recommendations for providing nutrition to critically ill patients. The emphasis is now on providing nutrition therapy vs. nutrition support, and enteral nutrition is the preferred route of feeding. No nutrition is preferred over PN in patients who are well nourished and cannot eat for 7 days or less. When PN is used, it should be done carefully to maximize efficacy and minimize complications.

Reference

By Scott Benken