Enteral Versus Parenteral Nutrition
Differentiating Two Types of Clinical Nutrition Support
The choice of nutrition support and route of administration depends on the patient’s clinical state. The rule of thumb is, “if the gut works, use it.” However, supplemental or total parenteral nutrition is indicated when nutritional requirements cannot be met via oral or enteral feeding or if oral or enteral feeding are contraindicated.
Enteral and Parenteral Nutrition Defined
Enteral nutrition (EN) includes oral nutritional supplements (ONS) and enteral tube feeding via nasogastric, nasoenteral or percutaneous tubes.1 EN provides nutrients and energy to the mucosal cells, stimulating epithelial cell metabolism, bile flow and pancreatic secretions as well as the release of enterotrophic gastrointestinal (GI) hormones, and increasing mucosal blood flow.2 Whereas parenteral nutrition (PN) provides nutrients, via an intravenous infusion, directly into the systemic circulation, bypassing the gastrointestinal (GI) tract.
The following chart illustrates how the choice of nutrition support can be determined:
Indications for EN
In patients with a functioning gastrointestinal (GI) tract, EN is ideally started within 24 to 48 hours of intensive care unit (ICU) admission, and is generally preferred over exclusive PN.3,4,5,6,7,8
When PN Is Recommended
EN alone is often insufficient in providing the required amount of energy and protein.9 This may result in nutritional deficits known to worsen clinical outcomes.10 In these cases, PN can help to fill the caloric gap.9 If EN is contraindicated or a limited tolerance for EN over a prolonged period does not allow sufficient intake to cover the patient’s entire nutritional needs, PN is indispensable for supplementing or replacing enteral tube feeding in order to avoid disease-related malnutrition.11,12
What Nutrients Are Provided Through PN?
Clinical nutritional therapy provided through PN includes water and essential nutrients such as amino acids, carbohydrates, fats and micronutrients.
These nutrients are infused in their essential form:
- Carbohydrates: Infused as glucose with the goal to provide rapidly available energy.
- Proteins: Present as amino acids that will be used by the body as primary constituents of muscles, as well as playing a role in biochemical reactions and immune response.
- Fats: Represented by lipid emulsions containing triglycerides. They serve as a compact way to store energy because of their high energy and low water content. They also supply essential fatty acids and constitute an important part of the structure of the cells.
All three macronutrients in the right amounts make for balanced and adequate nutrition support that can positively affect clinical outcomes such as infection rates, length of hospital stay or mortality.
Nutritional support is not restricted to the exclusive administration of EN or PN, but PN and EN may complement each other, e.g. with the use of PN plus minimal “trophic” enteral feeding or EN plus supplemental PN.
- 1. Kreymann KG, Berger MM, Deutz NE et al. ESPEN Guidelines on Enteral Nutrition: Intensive care. Clinical Nutrition 2006;25(2):210–223.
- 2. Druml W. Clinical strategies for prevention of bacterial translocation. In: Herbert MK, editor. Problems of the gastrointestinal tract in anesthesia. Springer Verlag 1999:118-126.
- 3. Heyland DK. Parenteral nutrition in the critically-ill patient: More harm than good? Proc Nutr Soc 2000;59:457-466.
- 4. Heyland DK, Dhaliwal R, Drover JW et al. Canadian clinical practice guidelines for nutrition support in mechanically ventilated, critically ill adult patients. JPEN 2003;27:355-373.
- 5. Gramlich L, Kichian K, Pinilla J et al. Does enteral nutrition compared to parenteral nutrition result in better outcomes in critically ill adult patients? A systematic review of the literature. Nutrition 2004;20:843-848.
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- 7. McClave SA, Martindale RG, Vanek VW et al. Guidelines for the Provision and Assessment of Nutrition Support Therapy in the Adult Critically Ill Patient: Society of Critical Care Medicine (SCCM) and American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.). JPEN 2009;33:277-316.
- 8. Singer P, Berger MM, Van den Berghe G et al. ESPEN Guidelines on Parenteral Nutrition: intensive care. Clin Nutr 2009;28(4):387-400.
- 9. a. b. Heidegger CP, Berger MM, Graf S et al. Optimisation of energy provision with supplemental parenteral nutrition in critically ill patients: a randomised controlled clinical trial. Lancet 2013;381(9864):385-393.
- 10. Thibault R, Heidegger CP, Berger MM et al. Parenteral nutrition in the intensive care unit: cautious use improves outcome. Swiss Med Wkly 2014;144:w13997.
- 11. National Collaborating Centre for Acute Care (UK). Nutrition Support for Adults Oral Nutrition Support, Enteral Tube Feeding and Parenteral Nutrition. NICE Clinical Guidelines, No. 32 London 2006.
- 12. Kreymann KG. Early nutrition support in critical care: A European perspective. Curr Opin Clin Nutr Metab Care 2008;11:156-159.