Parenteral nutrition

Definition and indications. Intravenous delivery of nutrients when the gastrointestinal tract cannot be used. Indications are a non-functioning, inaccessible or obstructed gut — short bowel syndrome, high-output enterocutaneous fistula, prolonged ileus, complete intestinal obstruction, severe malabsorption, severe mucositis, and severe pancreatitis not tolerating enteral feeding. The governing principle is "if the gut works, use it" — enteral nutrition is always preferred.

Routes. Central parenteral nutrition through a subclavian, internal jugular or PICC line with the tip in the superior vena cava is required for hyperosmolar complete formulations. Peripheral parenteral nutrition is limited to short-term use (under 10–14 days) with osmolarity below about 850 mOsm/L. Total PN supplies all requirements; supplemental PN tops up inadequate enteral intake.

Composition. Energy 20–30 kcal/kg/day (use the lower end in the elderly and critically ill), protein as amino acids 1.0–1.5 g/kg/day, glucose not exceeding 4–5 mg/kg/min, and lipid emulsions providing 25–30% of non-protein calories. Add electrolytes, trace elements (zinc, selenium, copper, chromium) and both water- and fat-soluble vitamins, including thiamine. Modern practice uses all-in-one three-chamber bags.

Timing and geriatric considerations. Start only when inadequate oral or enteral intake is expected for more than 7 days (earlier if the patient is already malnourished), begin at about 50% of the target and build up over 2–3 days. Older patients have less physiological reserve, higher infection risk and reduced cardiac and renal tolerance — restrict volume, monitor for fluid overload, and always define the goal of therapy before starting.

Catheter-related complications. Catheter-related bloodstream infection is the commonest serious complication; also pneumothorax, arterial puncture, air embolism, catheter tip malposition, central venous thrombosis and catheter occlusion. Prevention requires strict aseptic insertion and handling with a dedicated lumen used only for nutrition, and ultrasound-guided insertion.

Metabolic complications and monitoring. Hyperglycaemia (and rebound hypoglycaemia on abrupt withdrawal), refeeding syndrome, electrolyte disturbance, hypertriglyceridaemia, fluid overload, parenteral nutrition-associated liver disease (steatosis and cholestasis), metabolic bone disease and gut mucosal atrophy with bacterial translocation. Monitor glucose, electrolytes, phosphate and magnesium daily at first, then weekly liver function, triglycerides, trace elements and nitrogen balance, with regular weight and fluid balance.

ESPEN practical guideline on clinical nutrition and hydration in geriatrics — recommends that every older patient be screened with a validated tool such as the MNA-SF, that nutritional goals be individualised through shared decision-making, and, critically, that artificial nutrition (enteral or parenteral) should not be started in advanced dementia or in the terminal phase of illness, where careful hand-feeding and comfort feeding give better outcomes and quality of life. Parenteral nutrition is justified only when it can achieve an outcome the patient actually values — a point examiners increasingly expect to be linked to advance care planning.