ABSTRACT
Parenteral nutrition was introduced as an important adjunct in the care of critically ill patients who were unable to take an oral diet adequate to meet nutritional and metabolic needs. Initial clinical studies by investigators at that time focused on the effect of parenteral feeding on several parameters of systemic immunity including total lymphocyte count, in vitro blastogenesis of circulating peripheral lymphocytes, and delayed cutaneous hypersensitivity responses to antigens. The rst experiments that generated subsequent work investigating nutrition and gut immunity started in a laboratory of Dr. George Sheldon in the late 1970s. These studies examined the effect of malnutrition on susceptibility to intraperitoneal sepsis using hemoglobin and Escherichia coli in a rat model. Peterson et al. [1] demonstrated that well-nourished animals survived the septic challenge approximately 70% of the time. Animals administered a nutrient-poor agar orally for 2 weeks lost approximately 20% of their weight, resulting in a 10% survival to the septic challenge. Refeeding malnourished animals with chow prior to the septic challenge resulted in a survival rate comparable to the well-nourished mice, but surprisingly, two groups of animals fed adequate amounts of parenteral nutrients-either with or without fat-sustained a near-100% mortality after the septic insult (Figure 24.1). While it was speculated that the parenteral formula might be lacking some nutrients essential for the rat, there were a confounding variables; the enterally fed animals received a solid chow diet, while the parenterally fed animals received a liquid diet of glucose and amino acids. A subsequent experiment randomized previously malnourished animals to chow or to pair feeding with parenteral nutrition administered orally or intravenously [2]. The result demonstrated no de- ciencies with the parenteral formula itself; animals that received nutrition via the gastrointestinal tract survived like well-nourished animals, whereas the animals that received the same formula intravenously survived like malnourished animals. This experiment was repeated in well-nourished animals with identical results [3].
