Parenteral Nutrition (TPN) Basics

Parenteral nutrition (PN) delivers dextrose, amino acids, lipid injectable emulsion, electrolytes, vitamins, and trace elements directly into the venous circulation. It bypasses the gastrointestinal tract rather than merely reducing its workload. That makes PN useful when the gut is unavailable, inaccessible, or unable to absorb enough nutrition, such as with bowel obstruction, prolonged ileus, short bowel syndrome, a high-output enterocutaneous fistula, mesenteric ischaemia, or severe malabsorption. Enteral nutrition is preferred whenever the gastrointestinal tract can safely receive and absorb nutrients because it preserves gut structure and function. That preference does not mean PN is automatically delayed in every critically ill patient. ASPEN found no significant outcome or harm difference between exclusive PN and exclusive enteral nutrition during the first week of critical illness when enteral nutrition could not be delivered adequately. ASPEN also recommends against adding supplemental PN to inadequate enteral nutrition before day 7 of ICU admission because early supplementation has not shown a clinically important benefit. Nutrition risk changes the timing. A patient at low nutrition risk who cannot tolerate enteral nutrition can generally wait about 7 days...