Total Parenteral Nutrition

TPN bypasses the entire GI tract and delivers nutrition directly into the bloodstream — but the wrong dextrose concentration in the wrong line can be fatal. Do you know which access is required and why?

Total parenteral nutrition (TPN) is an IV solution containing dextrose (15–70%), amino acids, lipids, electrolytes, vitamins, and trace elements, used when the GI tract is nonfunctional or must be rested (bowel obstruction, severe pancreatitis, short bowel syndrome, prolonged ileus). Because the high dextrose concentration is hypertonic (typically >900 mOsm/L), TPN must be infused through a central venous access device — PICC line, subclavian, or internal jugular catheter — never a peripheral IV, which cannot tolerate the osmolarity and will cause phlebitis or tissue necrosis. Peripheral parenteral nutrition (PPN) exists but uses lower dextrose concentrations (≤10%) for short-term, partial supplementation. TPN requires an infusion pump and a dedicated lumen; no other medications or blood products piggyback on the TPN line. The rate is never abruptly increased or stopped — gradual titration up over 24 hours prevents hyperglycemia, and tapering down prevents rebound hypoglycemia. Blood glucose monitoring every 4–6 hours is standard, especially during initiation. Insulin may be added to the TPN bag or administered separately per protocol. Weekly labs include a comprehensive metabolic panel, prealbumin, triglycerides, and liver function tests to detect complications like refeeding syndrome (watch for hypophosphatemia), hyperglycemia, or hepatic steatosis.

Key Distinctions

Don't confuse TPN (central line, high dextrose, long-term) with PPN (peripheral IV, low dextrose, short-term). Students often think any IV can handle TPN — peripheral veins cannot tolerate the osmolarity. Abruptly stopping TPN causes rebound hypoglycemia, not hyperglycemia — the pancreas is still secreting insulin for the high glucose load that suddenly disappears. If TPN is unavailable, hang D10W at the same rate to prevent hypoglycemia until the new bag arrives.

Clinical Pearl

TPN bag late? Hang D10W at the same rate. The patient's pancreas is already pumping insulin for all that dextrose — sudden removal crashes their glucose.