When correctly implemented, specialized nutritional support (SNS) plays a major and often life-saving role in medicine. SNS is used for two main purposes: (1) to provide an appropriate nutritional substrate in order to maintain or replenish the nutritional status of patients unable to voluntarily ingest or absorb sufficient amounts of food, and (2) to maintain the nutritional and metabolic status of adequately nourished patients who are experiencing systemic hypercatabolic effects of severe inflammation, injury, or infection in the course of persistent critical illness. Patients with permanent major loss of intestinal length or function often require lifelong SNS. Many patients who require treatment in chronic-care facilities receive enteral SNS, most often because their voluntary food intake is deemed insufficient or because impaired chewing and swallowing create a high risk of aspiration pneumonia.
Enteral SNS is the provision of liquid formula meals through a tube placed into the gut. Parenteral SNS is the direct infusion of complete mixtures of crystalline amino acids, dextrose, triglyceride emulsions, and micronutrients into the bloodstream through a central venous catheter or (rarely in adults) via a peripheral vein. The enteral route is almost always preferred because of its relative simplicity and safety, its low cost, and the benefits of maintaining digestive, absorptive, and immunologic barrier functions of the gastrointestinal tract. Pliable, small-bore feeding tubes make placement relatively easy and acceptable to patients. Constant-rate infusion pumps increase the reliability of nutrient delivery. The chief disadvantage of enteral SNS is that many days may be required to meet the patient’s nutrient requirements.
For short-term use, the feeding tube can be placed via the nose into the stomach, duodenum, or jejunum. For long-term use, these sites may be accessed through the abdominal wall by endoscopic or surgical procedures. The chief disadvantage of tube feeding in acute illness is intolerance due to gastric retention, risk of vomiting, or diarrhea. The presence of severe coagulopathy is a relative contraindication to the insertion of a feeding tube. In adults, parenteral nutrition (PN) almost always requires aseptic insertion of a central venous catheter with a dedicated port. Many circumstances can delay or slow the progression of enteral SNS, whereas parenteral SNS can provide a complete substrate mix easily and promptly. This practical advantage is mitigated by the need to infuse relatively large fluid volumes and the real risk of inadvertent toxic overfeeding.
APPROACH TO THE PATIENT: Requirements for Specialized Nutritional Support INDICATIONS FOR SPECIALIZED NUTRITIONAL SUPPORT
Approximately one-fifth to one-quarter of patients in acute-care hospitals suffer from at least moderate protein-energy malnutrition (PEM), the defining features of which are malnutrition-induced weight loss and skeletal muscle atrophy. Usually, but not always, other features further compromise clinical responses; these features include a subnormal adipose tissue mass, with the accompanying adverse consequences of weakness, skin thinning, and breakdown; reduced ventilatory drive; ineffective cough; immunodeficiency; and impaired thermoregulation. Commonly, PEM is already ...