Enteral and Parenteral Nutrition Therapy: Introduction

The ability to provide specialized nutritional support (SNS) represents a major advance in medical therapy. Nutritional support, via either enteral or parenteral routes, is used in two main settings: (1) to provide adequate nutritional intake during the recuperative phase of illness or injury, when the patient's ability to ingest or absorb nutrients is impaired, and (2) to support the patient during the systemic response to inflammation, injury, or infection during an extended critical illness. SNS is also used in patients with permanent loss of intestinal length or function. In addition, an increasing number of elderly patients living in nursing homes and chronic care facilities receive enteral feeding, usually as a consequence of inadequate nutritional intake.

Enteral refers to feeding via a tube placed into the gut to deliver liquid formulas containing all essential nutrients. Parenteral refers to the infusion of complete nutrient solutions into the bloodstream via a peripheral vein or, more commonly, by central venous access to meet nutritional needs. Enteral feeding is generally the preferred route because of benefits derived from maintaining the digestive, absorptive, and immunologic barrier functions of the gastrointestinal tract. Small-bore pliable tubes have largely replaced large-bore rubber tubes, making placement easier and more acceptable to patients. Infusion pumps have also improved the delivery of nutrient solutions.

For short-term use, enteral tubes can be placed via the nose into the stomach, duodenum, or jejunum. For long-term use, these sites can be accessed through the abdominal wall using endoscopic, radiologic, or surgical procedures. Intestinal tolerance of tube feeding may be limited during acute illness by gastric retention or diarrhea. Parenteral feeding has greater risk of infection, reflecting the need for venous access, and a greater propensity for inducing hyperglycemia. However, these risks can generally be managed successfully by SNS teams. For the postoperative patient with preexisting malnutrition, or in trauma patients who were previously well nourished, SNS is strikingly cost-effective. In the most critically ill patient in the intensive care unit, SNS can dramatically enhance survival. Although enteral nutrition (EN) can be provided by most health care teams caring for hospitalized patients, safe and effective parenteral nutrition (PN) usually requires specialized teams.

Harrison's Internal Medicine > Part 4. Nutrition > Chapter 73. Enteral and Parenteral Nutrition Therapy >