Protein–energy malnutrition (PEM), which includes significant loss of lean body mass and fat stores, and depletion of micronutrients (including essential vitamins and trace elements), is common among hospitalized surgical patients [1–7]. Various studies among total hospital admissions and in intensive care unit (ICU hereafter) settings have reported that varying degrees of malnutrition can occur in 20% to as high as 60% of surgical and medical patients [1–3]. While most patients gradually progress to an oral diet shortly following surgery and require little or no nutritional intervention, major surgery or postoperative complications can delay the progression of an oral diet. The extent of PEM worsens over time in such patients due to the stress of surgery, increased nutritional needs to support wound healing, and increased metabolic rate associated with postoperative recovery, insufficient ad libitum dietary intake and repeated catabolic insults [8,9].
Protein–energy malnutrition prior to, and inadequate nutritional intake during, hospitalization are each associated with increased morbidity and mortality, as well as longer hospital stay and cost [9–15]. In 1936, Studley was the first to recognize a direct correlation between preoperative weight loss and operative mortality rate, independent of age, impaired cardio/respiratory function, and types of surgery . Giner et al. subsequently confirmed that malnutrition is a major determinant for the development of postoperative complications . In highly catabolic surgical ICU patients, nutritional depletion has been associated with higher incidence of infectious complications, poor wound healing, impaired skeletal muscle strength, and the need for postsurgical mechanical ventilation [4,5,10–15]. Multiple pathophysiologic challenges may compromise nutritional status in patients undergo elective or major surgery (Table 2.1) . Ensuring adequate nutritional intake has been a major focus among surgeons. Nutritional interventions can be safely performed either with enteral nutrition (EN; enteral nutrient supplements and tube feedings) or with complete parenteral nutrition (PN) . Both EN and PN provide fluid, calories (as carbohydrate, protein/amino acids, and fats) and known essential amino acids, fats, electrolytes, vitamins, and trace elements. The delivery of these interventions is the focus of this chapter.