16.1 PN Indications & Composition

Indications for Parenteral Nutrition

Parenteral nutrition (PN) is the intravenous delivery of nutrients — amino acids, dextrose, lipids, electrolytes, vitamins, and trace elements — that bypasses the gastrointestinal (GI) tract entirely. The CSP exam treats PN as the necessary inverse of the enteral principle: PN is indicated only when the GI tract is nonfunctional, unsafe to feed, or cannot absorb enough to sustain growth. Prolonged PN carries infection and liver-disease risk, so the indication must be real, and enteral nutrition should always be introduced as early as possible, even as minimal trophic feeds.

Core pediatric indications:

• Congenital GI anomalies — gastroschisis, omphalocele, intestinal atresia, and malrotation with volvulus, where bowel function is absent for days to weeks after repair.
• Necrotizing enterocolitis (NEC) — medical NEC (Bell stage II) typically warrants 7–14 days of bowel rest on PN; surgical NEC (Bell stage III) requires PN plus resection, often leaving short bowel.
• Short bowel syndrome (SBS) and intestinal failure — insufficient functional bowel to absorb fluids and nutrients; the leading cause of long-term pediatric PN dependence.
• Extreme prematurity — the extremely low birth weight (ELBW, <1,000 g) infant cannot tolerate full enteral feeds in the first days of life, and even brief nutritional deficits compromise postnatal growth and neurodevelopment, so PN begins on day 1.
• Severe malabsorption or intractable diarrhea — microvillus inclusion disease, tufting enteropathy, and severe enteritis unresponsive to enteral trials.
• Miscellaneous — prolonged ileus, severe acute pancreatitis failing jejunal feeding, chylothorax, and profound mucositis after hematopoietic stem cell transplant.

Relative contraindications matter as exam traps: PN is generally not appropriate when a functioning gut is simply underused, when aggressive support no longer fits goals of care, or in the first hours of hemodynamic instability before the child is resuscitated.

Macronutrient Composition by Age

Amino acids. Protein is the nutrient the CSP exam expects you to start first and advance aggressively in neonates. ELBW and preterm infants should receive amino acids on day 1 at 2–3 g/kg/day, advanced toward 3.5–4 g/kg/day, because fetal accretion rates are high and every day of delay deepens a nitrogen deficit that catch-up feeding cannot fully repair. Term neonates typically receive 2.5–3 g/kg/day; older infants 2–3 g/kg/day; children 1–2 g/kg/day; and adolescents 0.8–1.5 g/kg/day, all increased in critical illness and wound healing.

Dextrose provides the bulk of non-protein calories at 3.4 kcal per gram of hydrated glucose. In neonates, carbohydrate is prescribed as the glucose infusion rate (GIR) in mg/kg/min: start at 4–6 mg/kg/min in preterm infants (6–8 in term infants) and advance by 1–2 mg/kg/min per day toward a ceiling of roughly 10–12 mg/kg/min. Persistent hyperglycemia, not the schedule, sets the true limit. Older children are usually dosed in g/kg/day with GIRs closer to 4–7 mg/kg/min, falling toward adult rates of 2–5 mg/kg/min by adolescence.

Intravenous fat emulsion (IVFE) supplies concentrated energy and prevents essential fatty acid deficiency (EFAD), which can appear within one to three weeks of fat-free PN in young infants. Start at 1 g/kg/day and advance by 0.5–1 g/kg/day to a usual maximum of 2.5–3 g/kg/day in infants and 1–2 g/kg/day in older children. Emulsion choice is heavily tested:

• Soybean oil emulsion (Intralipid) — the historical standard; 100% soybean oil, rich in omega-6 linoleic acid and phytosterols, implicated in intestinal failure–associated liver disease when used at full dose long-term.
• Composite/mixed-oil emulsion (SMOFlipid) — roughly 30% soybean, 30% medium-chain triglycerides, 25% olive, and 15% fish oil; preferred by ESPGHAN as first-line in children expected to need prolonged PN because it lowers omega-6 and phytosterol exposure.
• Fish oil monotherapy (Omegaven) — reserved as rescue therapy for established PN-associated cholestasis, typically at 1 g/kg/day.

Twenty percent emulsions are preferred over 10% because their lower phospholipid-to-triglyceride ratio produces less hypertriglyceridemia. Energy density is about 2 kcal/mL for a 20% emulsion.

Pediatric Formulations Differ from Adult Ones

Pediatric crystalline amino acid solutions — TrophAmine, Premasol, and Aminosyn-PF — are patterned after the amino acid profile of breast milk rather than high-quality adult protein. Compared with adult formulations they contain taurine (conditionally essential in infancy for bile acid conjugation and retinal and neurologic development), are supplemented with cysteine (the cystathionase enzyme that converts methionine to cysteine is immature in preterm infants), provide more tyrosine and histidine, and contain less phenylalanine and methionine, which immature neonatal livers clear poorly. Their lower pH also improves calcium and phosphorus solubility, critical because neonatal bone mineralization demands far more Ca and P per kilogram than adult maintenance. Pediatric multivitamin and trace element products are likewise dosed by weight bands, and aluminum contamination of PN additives is a recognized pediatric toxicity concern, particularly with renal impairment.

Central Versus Peripheral Access

Access selection is a function of osmolarity and expected duration. Peripheral parenteral nutrition (PPN) is limited to solutions of approximately 900 mOsm/L or less — in practice dextrose no more than about 10–12.5%, amino acids around 3–3.5%, and generous lipids to supply calories without osmotic load. More concentrated solutions cause thrombophlebitis and infiltration injuries, so PPN suits only short courses, generally under two weeks. Central access — peripherally inserted central catheters (PICC), tunneled cuffed catheters (Broviac-type), and implanted ports — delivers into high-flow central veins and has no osmolarity ceiling; it is required for concentrated dextrose, long-term therapy, and fluid-restricted patients. Long-term pediatric PN should run through a dedicated lumen that is never used for medications or blood draws, a key bloodstream-infection prevention measure.