Early enteral nutritional intervention in critically ill patients reduces infectious-complication rates, decreases lengths of stay, and improves outcomes.

Bread.jpg (11815 bytes)Although there is heightened awareness regarding the role of nutritional support in critically ill patients, routine implementation of early enteral nutritional support for mechanically ventilated patients is not yet commonplace in everyday practice. The window of opportunity for the initiation of enteral nutrition, as it relates to patient outcomes, has not been well defined.1

Early Enteral Nutrition
The overall benefits of enteral feeding far outweigh potentially deleterious effects. Primary benefits include physiologic and metabolic maintenance of gut integrity, improved nutrient utilization, and safety in administration, as well as significantly reduced cost.2 The physiologic benefit of enteral nutrition encompasses synergistic processing of enteral nutrients in the gut and liver prior to their release into systemic circulation. This process is known as first-pass metabolism.3 Nutrients are also used more efficiently and effectively through the enteral, versus the parenteral, route due to first-pass metabolism. Nitrogenous waste products such as ammonia are eliminated after first-pass metabolism before nutrients are released into systemic circulation. First-pass metabolism is important, since the liver produces secretory proteins and immunoglobulins. Enteral nutrients stimulate the manufacture of secretory immunoglobulin A, which prevents attachment of bacteria to the intestinal wall.4,5 Provision of enteral nutrition attenuates endotoxin and/or bacterial translocation;6 however, its effect on outcomes remains unresolved.7

The metabolic benefits of enteral feeding include preservation of gastrointestinal integrity. Enteral nutrients promote a trophic effect on gastrointestinal mucosal cells. Bowel rest with total parenteral nutrition (TPN) alone impairs human response to infection by endotoxin-producing bacteria.8 A lack of gastrointestinal stimulation by enteral nutrients is associated with a loss of upper respiratory tract immunity.9 Preliminary animal studies suggest that meeting a minimum of 20% to 30% of estimated caloric needs is required to prevent immune dysfunction related to both bowel rest and the use of parenteral nutrition.10,11 The composition of enteral-nutrition formulas is nutritionally more complete than that of parenteral-nutrition solutions.12 Some gut-specific substrates include nutrients such as glutamine and dietary fiber, which are not commercially available in TPN products. The administration-safety benefits of enteral nutrition pertain to the avoidance of complications associated with central catheters, such as pneumothorax and catheter sepsis.13 The cost benefits are multiple and including savings in the cost of formula, equipment, and specialists required for the preparation and administration of parenteral nutrition.13-17

The specific window of opportunity for the initiation of enteral nutrition, in relation to patient outcomes, has not yet been completely defined. A comprehensive review of early versus delayed enteral feeding studies by Zaloga1 compared feeding within 24 hours with feeding within 3 to 5 days of the initiation of critical care. The author reported that approximately 84% of the 19 prospective, controlled studies supported improved outcomes with early enteral nutritional intervention for critically ill patients; therefore, early enteral nutritional support was assessed as a level-IV recommendation for critical care patients.

Nutritional Support Guidelines
In 1997, the American College of Chest Physicians (ACCP) developed a consensus statement regarding nutrition implementation for adult intensive care unit (ICU) patients.12 The purpose of the consensus panel was to develop recommendations based upon a thorough review of applied clinical nutrition studies. The panel’s aims included defining:
• guidelines for patient selection intended to improve outcomes for medical nutritional therapy,
• nutritional support goals, and
• the nutrient needs of critically ill patients.
The ACCP panel created an elegant, comprehensive summary based on clinical research. Table 1 is an abbreviated outline of the ACCP consensus statement.

Malnutrition in critically ill patients
    • Malnutrition is defined as body composition disorder characterized by deficiencies in macronutrients (protein, carbohydrate, fat) or micronutrients (vitamins, minerals, trace elements) from inadequate nutritional intake
    • End results of malnutrition
    • Decreased organ function
    • Decreased body mass
    • Abnormal blood chemistry
    • Suboptimal outcomes
    • Altered substrate metabolism partially attributed to disease processes
        and hypermetabolism
    • Alternate energy source results from gluconeogenesis and protein breakdown

Body weight loss
    • Body weight measurements may not parallel body-cell mass, since
            edema is prevalent in critical care
    • Ideal body weight loss >10% is considered a dependable indication
        of malnutrition

Nutritional assessment
    • Use of various parameters recommended to evaluate nutritional status
    • Limitations for each parameter should be recognized

Goals for nutritional support
    • Provide tailored nutritional support based upon
    • Medical condition
    • Route of administration
    • Individualized nutritional status
            • Appropriate nutrient quantities for metabolism
    • Prevent or provide medical nutrition therapy for
    • Macronutrient (protein, carbohydrate, fat) deficiencies
    • Micronutrient (vitamin, mineral, trace element) deficiencies
    • Complications pertaining to nutrition support administration
    • Improve clinical outcomes

Principles of nutritional support
Energy and nutrient needs

  • Energy estimates: 25 kcal/kg usual body weight per day
    • Carbohydrate
        • 30%-70% total kcal
        •  2-5 g glucose/kg/day
        • Maintain serum glucose <225 mg/dL
    • Fat
        • 15%-30% total kcal
        • Ž 7% total kcal w-6 polyunsaturated fatty acids
    • Protein
        • 15-20% total kcal
        • Initiate ~1.2-1.5 g/kg/day
    • Micronutrients
        • Exact goals for trace elements, minerals, and vitamins have not
            been determined

Administration route
   • Enteral nutrition administration route is preferred
        • If gastric residual >150 mL, may need to consider adjusting infusion
            rate, small bowel feeding, or supplemental parenteral nutrition
        • Positive bowel sounds, flatus, or stool excretion is not required for
            initiating tube feedings
        • Feeding into small bowel is typically effective unless intolerance to
            enteral support develops for patients with the following conditions:
            • <500 mL/day enterocutaneous fistula output
            • Mild pancreatitis
            • Resolving pancreatitis
            • If diarrheal output is > 15 L/day, evaluation is necessary
    • Parenteral nutrition administration is recommended for
            • Inaccessible enteral route
            • Unusable gastrointestinal tract
            • Inadequate provision of enteral feeding with parenteral supplement                  required
    • Complications associated with parenteral nutrition
            • Increased rate of infections
            • Significantly increased costs
            • Potential nutrient deficiency, since parenteral solutions are nutritionally                  incomplete compared with enteral nutrition

    • Avoid overfeeding
            • Respiratory quotient >1 usually reflects overfeeding
            • Reduce total kcal (fat and glucose) to decrease CO2 production in
            respiratory dysfunction patients receiving parenteral nutrition
    • Maintain nitrogen retention while avoiding excessive protein loads
            • Protein is typically well tolerated if blood urea nitrogen is <100                  mg/dL
            • Specialized acute renal failure formulas do not improve patient out-                 comes
            • Consider dialysis or hemofiltration in order to meet nutritional needs
            • Assess nitrogen balance weekly to modify protein dosing
    • Check serum triglyceride levels
            • Serum triglyceride  500 mg/dL with concurrent 24-hour fat infusion
            is acceptable for some critical care clinicians

• Monitor visceral protein stores weekly (prealbumin or transferrin levels)
        • Potential limitations of visceral protein levels in critical care situations
            • May not necessarily reflect feeding response
            • Not well correlated with clinical outcomes
    • Monitor electrolyte and fluid status carefully
            • Watch potassium, phosphate, calcium, magnesium, and zinc status

TABLE 1. Summary of the American College of Chest Physicians’ consensus statement on nutritional support for adult ICU patients. Adapted from Chest.12

Enteral Formulas
The provision of calories from any macronutrient (carbohydrate, fat, or protein) source is associated with increased oxygen use and carbon dioxide production.18 The main therapy goals for patients who have respiratory compromise focus on limiting or controlling metabolic demand. Options include reducing the feeding (or modifying the quantities) of fat and carbohydrate; however, it is vital to avoid overfeeding for the purpose of preventing excessive carbon dioxide production.18

Although early work suggested that feeding increased fat calories with reduced carbohydrate calories would generate a lower respiratory quotient, as well as better gas exchange, there are insufficient studies having sample sizes large enough to substantiate improved patient outcomes and universal benefits for ventilator-dependent patients.18-20 A more recent preliminary study21 examined the benefits of specialty enteral formulas containing eicosapentaenoic acid (a fish oil), g-linolenic acid (borage oil), and supplemental antioxidants. Primary results suggested improvements in gas exchange and pulmonary neutrophil recruitment, and decreases in duration of mechanical ventilation, length of ICU stay, and incidence of new organ failure in patients who have adult respiratory distress syndrome.

Most patients who are critically ill may be fed enterally using standard polymeric (intact-macronutrient) formulas.22,23 Nitrogen balance has been reported to be similar for patients with normal digestive and absorptive capacity who were fed intact protein, partially hydrolyzed protein, and amino acids with approximately the same amino acid profiles.24 Specialty formulas designed for specific organ dysfunction are considerably more expensive. General indications for using specialty products include the specific worsening of a condition due to demonstrated intolerance of a standard enteral formula or unique nutrient needs.23 Pulmonary disease, in and of itself, is not necessarily an indication for the use of specialized enteral formulas.25 Their high fat content may result in diarrhea due to fat malabsorption for some patients.22 If formulas with modified fat and carbohydrate content are used, then clinical conditions, carbon dioxide production, and ventilation should be closely monitored.2 Most studies26,27 have not demonstrated significant advantages for the use of high-fat formulas, as long as there is not overfeeding of total calories.

Some medical centers have reported success in cost-effectiveness and best practices with protocols implemented.28,29

In an editorial review on early feeding, Alexander30 noted that the lack of correlation between early enteral nutritional support and either total days of mechanical ventilation and/or ICU length of stay might be eclipsed by radical variations of individual patients’ conditions.31 Moore et al32 observed lower infectious-complication rates in trauma patients who were fed enterally than in those who received parenteral nutrition. Hedberg et al33 reported reduced infection rates, lengths of stay, and costs with early enteral nutrition for postoperative bowel-resection patients. Early enteral feeding appeared to improve early wound-healing phases.34 Implementation of early enteral nutritional intervention in critically ill patients is associated with improved outcomes such as reduced infectious-complication rates, decreased lengths of stay, and improvement in other patient outcomes.35-38 Future developments related to outcomes may entail closer examination of specific nutrients and therapeutic dosages of nutrient combinations, as well as pinpointing timing for attaining a minimum percentage of calorie and/or nutrient needs.

Katherine Ideno, MS, RD, CNSD, is a member of the pulmonary care team; Shawn Forney, RD, CNSD, is a clinical dietition specialist; Connie Sixta, MSN, MBA, is vice president of operations; Cathy Meents, RRT, is director of respiratory care services; Donna Doxakis, BSN, CCRN, is nurse manager of the Surgical ICU; and Kim Bloom, MD, is medical director for the pulmonary team all at Methodist Hospital, Texas Medical Center, Houston.

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34. Kiyama T, Witte MB, Thornton FJ, et al. The route of nutrition support affects the early phase of wound healing. JPEN J Parenter Enteral Nutr. 1998;22:276-279.
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