Nutrition Support (Enteral and Parenteral)
Core concepts
Understand indications, contraindications, access routes, and complications of enteral nutrition (EN) and parenteral nutrition (PN). EN is preferred when the gut works ("if the gut works, use it"), and short-term access is nasogastric or nasoenteric; long-term is gastrostomy or jejunostomy. PN is indicated when the GI tract cannot be used or is insufficient; peripheral PN is limited by osmolarity, so central access is needed for high-osmolar formulas. Know formula selection (polymeric vs elemental vs disease-specific), initiation and advancement, and monitoring (electrolytes, glucose, triglycerides, liver enzymes, fluid balance). Recognize complications: aspiration, diarrhea, tube dislodgement, refeeding syndrome for EN; catheter-related bloodstream infection, hyperglycemia, and hepatobiliary dysfunction for PN.
Traps
Questions test whether you know that gastric residual volumes are no longer routinely used to guide feeding, that EN is preferred over PN even in pancreatitis when tolerated, and that "permissive underfeeding" differs from starvation. Watch for confusion between osmolality and osmolarity and between central and peripheral PN limits.
Worked example
A patient requiring 25 kcal/kg and 1.2 g/kg protein: for a 60 kg patient, 1500 kcal and 72 g protein. If using a 1 kcal/mL formula, that is 1500 mL/day (~63 mL/h over 24 h). Rule of thumb: calculate energy and protein first, then choose the formula volume and rate.
Rule of thumb
Use the gut when possible; start EN early in critical illness, advance slowly, and monitor electrolytes and glucose.