4.4 Enteral & Parenteral Nutrition Support
Key Takeaways
- Enteral nutrition (EN) is preferred over parenteral nutrition (PN) whenever the gut is functional — 'if the gut works, use it' — because it preserves gut integrity and lowers infection risk and cost.
- Short-term enteral access (under 4-6 weeks) uses nasogastric or nasojejunal tubes; long-term access uses gastrostomy (PEG) or jejunostomy tubes placed endoscopically or surgically.
- Parenteral nutrition is for a nonfunctional or inaccessible gut; central PN tolerates high osmolarity (dextrose over 10%), while peripheral PN is limited to about 900 mOsm/L for short-term support.
- Refeeding syndrome is an insulin-driven shift of phosphorus, potassium, and magnesium into cells; hypophosphatemia is the hallmark, and thiamin must be given before feeding.
- Refeeding prevention starts feeding low (about 10-20 kcal/kg/day), advances slowly, and corrects electrolytes before and during initiation.
The Decision Algorithm: 'If the Gut Works, Use It'
Nutrition support begins with a single branching question: can the client meet needs orally? If not, ask whether the gastrointestinal (GI) tract is functional and accessible. If it is, choose enteral nutrition (EN) — feeding into the gut via tube. If the GI tract is nonfunctional or inaccessible, choose parenteral nutrition (PN) — feeding into a vein.
EN is favored whenever feasible because it maintains gut mucosal integrity and the gut-associated immune barrier, prevents bacterial translocation, costs far less, and carries a substantially lower infection risk than PN. Selecting PN when EN is feasible is the most common nutrition-support distractor on the exam. The hierarchy to advance toward is always oral > enteral > parenteral, and the goal is to step a client back down that ladder as tolerance improves.
Enteral Access Routes and Formulas
Access by Duration
- Short-term (< 4-6 weeks): nasogastric (NG) or nasojejunal (NJ) tubes — placed at the bedside, no surgery
- Long-term (> 4-6 weeks): percutaneous endoscopic gastrostomy (PEG) or jejunostomy (J-tube)
The 4-6 week mark is the deciding threshold and is frequently tested. Post-pyloric placement (NJ or J-tube) is chosen when aspiration risk is high or the stomach must be bypassed — gastroparesis, severe reflux, gastric outlet obstruction, or recurrent aspiration. Post-pyloric feeds must run continuously by pump because the small bowel cannot accommodate a bolus.
Formula Selection
| Formula Type | Best For |
|---|---|
| Standard polymeric | Intact GI function; intact whole proteins (1.0 kcal/mL) |
| Elemental / semi-elemental | Impaired digestion or absorption; hydrolyzed peptides/amino acids |
| Concentrated (1.5-2.0 kcal/mL) | Fluid restriction (renal, cardiac, volume overload) |
| Disease-specific | Renal, hepatic, pulmonary, or glucose-control needs |
Delivery into the stomach can be continuous, intermittent, or bolus (the stomach acts as a reservoir); jejunal feeding requires continuous pump-controlled delivery. A worked item: a client with severe gastroparesis and recurrent aspiration needs an NJ or J-tube with continuous pump feeding, not an NG bolus.
Parenteral Nutrition (PN): Indications and Access
Parenteral nutrition (PN) delivers nutrients intravenously, bypassing the GI tract entirely. Indications all share a gut that cannot be used: mechanical bowel obstruction, short bowel syndrome with inadequate absorptive surface, severe malabsorption, paralytic ileus, intractable vomiting or diarrhea, high-output enterocutaneous fistula, or a situation where EN simply cannot meet needs.
Central vs. Peripheral
- Central PN (often called total parenteral nutrition, TPN): delivered through a large central vein (subclavian, internal jugular, or a PICC) where high blood flow rapidly dilutes the solution; it tolerates high osmolarity (dextrose concentrations > 10%) and supports full, long-term nutrition
- Peripheral PN (PPN): delivered through a small peripheral vein; limited to lower osmolarity (about < 900 mOsm/L) to avoid phlebitis, so it is used only for short-term, partial support
The osmolarity/access pairing is high-yield: if a client needs concentrated, complete nutrition, the answer is central access, not peripheral. PN solutions contain dextrose, amino acids, intravenous lipid emulsion (IVLE), electrolytes, vitamins, and trace elements. Standard energy distribution avoids overfeeding dextrose (a maximum glucose oxidation rate around 4-5 mg/kg/min) to limit hyperglycemia and hepatic steatosis. Monitor for catheter-related bloodstream infection, hyperglycemia, hypertriglyceridemia, and PN-associated liver disease.
A frequent trap: choosing PPN for a client who needs full long-term nutrition — the high osmolarity required mandates central access.
Refeeding Syndrome
Refeeding syndrome is a potentially fatal fluid and electrolyte shift when nutrition — especially carbohydrate — is reintroduced to a severely malnourished client. Reintroducing glucose triggers an insulin surge that drives phosphorus, potassium, and magnesium intracellularly and promotes sodium and water retention, with sudden demand for thiamin as a cofactor in carbohydrate metabolism.
Hallmarks and Prevention
- Hypophosphatemia is the classic, defining feature; hypokalemia and hypomagnesemia accompany it, and severe cases cause arrhythmia, respiratory failure, and cardiac collapse
- High-risk groups: prolonged starvation, anorexia nervosa, chronic alcohol use, malabsorption, low BMI, or little/no intake for 5-10+ days
- Give thiamin (vitamin B1) before and during initiation to prevent Wernicke encephalopathy
- Start low: about 10-20 kcal/kg/day (lower for the highest-risk), advancing gradually over 4-7 days
- Correct electrolytes before and during feeding and monitor phosphorus, potassium, and magnesium closely
The exam reliably pairs a malnourished client (often anorexia nervosa or a long ICU starvation) with new aggressive feeding and asks which electrolyte to watch — the answer is phosphorus, and the management is to slow the calories and replete electrolytes, not push more nutrition.
Monitoring Nutrition Support
Monitor support closely to catch metabolic and mechanical complications early:
- Electrolytes (phosphorus, potassium, magnesium, sodium) — frequent at initiation, daily early on
- Blood glucose — hyperglycemia is common with dextrose-heavy PN; cover with insulin per protocol
- Fluid balance, daily weight, and intake/output
- Triglycerides when running IV lipid emulsion (hold if markedly elevated)
- GI tolerance for EN: distension, nausea, diarrhea, and aspiration signs (gastric residual volumes are now used cautiously, not as a routine stop)
- Liver function for long-term PN (PN-associated cholestasis)
- Catheter site for redness, drainage, or fever suggesting infection
Always reassess whether the client can advance to a less invasive route — PN to EN to oral — because that transition reduces infection risk and cost and is the standing goal of nutrition support.
A severely malnourished client with anorexia nervosa is admitted and aggressive enteral feeding is started. On day 2, the client develops muscle weakness and cardiac arrhythmia. Which laboratory finding is the hallmark of the likely complication?
A client has a functioning GI tract but cannot safely swallow after a stroke and is expected to need tube feeding for at least three months. Which access route is MOST appropriate?
A client requires complete, long-term intravenous nutrition with a high-dextrose solution. Which access is required and why?