After total parenteral nutrition (TPN) was established as a feasible approach for feeding patients lacking a functional gut, physicians extended the practice of TPN to many circumstances where “logic” and “clinical experience” suggested that it would be better than EN. For example, one such indication was in the patient with acute pancreatitis, where, in the 1970s, many clinicians thought that a period of TPN would put the gut and pancreas at “rest,” allowing for resolution of pain and weight loss. Unfortunately, “logic” and “clinical experience” were incorrect. Now, the worldwide consensus expressed in clinical practice guidelines is that patients with acute pancreatitis (and indeed all others with functioning guts) will have worse outcomes if TPN is provided, rather than EN.
Today, the indications for TPN are narrow and include patients who cannot absorb enteral solutions (small bowel obstruction, short gut syndrome, etc.); partial PN may be indicated to supplement EN, in cases in which EN cannot fully provide for nutritional needs. In the latter circumstance, recent evidence suggests that the decision to add supplemental PN should be made only after a week’s time in previously well-nourished patients. Earlier initiation of supplementary PN in previously well-nourished patients, as had been supported by 2009 European guidelines, resulted in worse outcomes in a large randomized clinical trial; however, these results are not firmly established, as smaller randomized clinical trials have suggested findings to the contrary. The divergent results from these recent trials may be associated with the type of parenteral formulations being used, types of patients being studied, timing of parenteral nutritional administration, and treatment in the control groups. Thus, further studies are needed to better define patients that may benefit from PN, as well as the optimal timing of nutritional support and formulations for feeding. In short, EN should be the primary mode of nutritional support, and PN should be used when EN is not indicated, not tolerated, or insufficient.