Gastrointestinal & Hepatic · Topic 25 of 26

Parenteral Nutrition

Nutrition · parenteral feeding

Parenteral Nutrition

Parenteral nutrition is for a gut that cannot be used: wait a week in low-risk patients, start now in high-risk ones, and guard the line and the glucose.

Key numbers

Low risk: hold PN 7 daysday 7

Over 900 mOsm/L needs central line> 900 mOsm/L

Keep glucose under 180 mg/dL< 180 mg/dL

Cap dextrose at 5 mg/kg/min≤ 5 mg/kg/min

01 · The rulePN only if gut unusable

Use PN when the GI tract cannot be used or needs rest (bowel obstruction, short bowel syndrome), not routinely with an intact gut — PN brings more complications, poorer gut preservation and higher cost.

02 · DoLow risk: hold PN 7 days

Without feasible EN, withhold exclusive PN for the first 7 ICU days in low-risk patients (NRS-2002 ≤ 3); start it as soon as possible when risk is high (NRS-2002 ≥ 5) or malnutrition severe.

03 · DoOver 900 mOsm/L needs central line

PN with osmolarity over 900 mOsm/L (central PN) requires a central venous catheter; peripheral PN must stay at or below 900 mOsm/L to avoid thrombophlebitis and supplies most calories as fat.

Causes & risk factors

Why it happens

Start dextrose low in refeeding riskPN usually starts with 100–150 g dextrose on day 1; with refeeding risk (alcohol use, weight loss, low BMI, prolonged NPO) advance about a third of goal every 1–2 days while replacing phosphate, potassium, magnesium.

Diagnosis & monitoring

Work-up

Keep glucose under 180 mg/dL must knowKeep glucose under 180 mg/dL on PN (ICU target 140–180): check it every 6 hours until stable; add regular insulin — the only insulin compatible with PN, often 1 unit per 10 g dextrose.

Daily electrolytes, phosphate, magnesium and weightOn inpatient PN, check weight, electrolytes, magnesium, phosphate, BUN and creatinine daily, liver tests at least weekly and triglycerides at least twice weekly with lipids; gaining over 1 kg/day suggests volume overload.

Management

Orders

Supplemental PN only after day 7When enteral feeding meets under 60% of energy and protein needs, consider supplemental PN only after 7–10 days; starting it earlier does not help and may harm.

Hypocaloric PN with full protein in week 1In high-risk or malnourished ICU patients needing PN, consider hypocaloric dosing for the first week — 20 kcal/kg/day or less (or 80% of needs) with at least 1.2 g/kg/day of protein.

Limit soybean-oil lipid in critical illnessKeep 100% soybean-oil lipid emulsion under 1 g/kg/day in critically ill patients (pro-inflammatory omega-6 load); mixed-oil emulsions (olive oil, MCT, fish oil) allow more fat and less dextrose.

Red flags & don'ts

Avoid harm

Dedicated lumen and sterile line care complicationCentral-line complications occur in about 5–10% of PN patients: use strict sterile insertion and site care and reserve the PN lumen for PN only; avoiding overfeeding and hyperglycemia also lowers infection.

Abrupt PN stop can cause hypoglycemia complicationSuddenly stopping a concentrated dextrose infusion can cause hypoglycemia; treat short-term with 50% dextrose, or run 5–10% dextrose for 24 hours before resuming PN.

Cap dextrose at 5 mg/kg/min complicationDextrose is usually capped at about 5 mg/kg/minute; overfeeding (mostly excess carbohydrate) causes hyperglycemia, excess CO₂ production and fatty liver.

PN liver disease and gallbladder sludge complicationPN can raise transaminases, bilirubin and alkaline phosphatase (often transient at start; persistent with excess amino acids) and causes gallbladder sludge, stones and cholecystitis from stasis — any enteral intake helps.

The rules

Know these

No early PN in septic shockDo not use exclusive or supplemental PN early in the acute phase of severe sepsis or septic shock, whatever the nutrition risk.

Enteral or parenteral?

Commonly confused

Needs	A functioning GI tract
Access	Feeding tube
Complications	Fewer
Gut structure and cost	Preserves gut; lower cost

More detail

Reference

Show 6 reference facts

Typical adult PN needs: water 25–40 mL/kg/day, energy 25–35 kcal/kg/day (medical patient), amino acids 1.2–2.0 g/kg/day when critically ill and 1.5–2.5 g/kg/day on CRRT; energy needs rise about 12% per °C of fever.

Infuse PN through a 1.2-micron in-line filter, change the tubing every 24 hours with the first bag of the day, and change dressings with sterile technique, usually every 48 hours.

Metabolic bone disease (osteoporosis or osteomalacia) develops in some patients on PN for more than 3 months.

Standardized premixed PN and compounded PN have similar outcomes; adding electrolytes or drugs to a standardized bag risks precipitation, so a pharmacist must review any change.

ASPEN 2022 found no outcome difference between isocaloric PN and EN in critical illness and lowered the early energy target to 12–25 kcal/kg/day; EN stays preferred when the gut works.

Early adverse reactions to lipid emulsion (dyspnea, rash, nausea, back pain) are more likely at rates above 1 kcal/kg/hour; temporary hyperlipidemia occurs mainly with kidney or liver failure.

Pearl

The bag is easy, the line is dangerous: a dedicated sterile lumen, glucose under 180 and a steady taper keep PN safe.

Sources · Merck Manual Professional — Parenteral Nutrition (PN) · McClave SA, Taylor BE et al. Guidelines for the Provision and Assessment of Nutrition Support Therapy in the Adult Critically Ill Patient: SCCM and ASPEN. Crit Care Med 2016;44:390–438 / JPEN 2016;40:159–211 · de Man AME, Gunst J, Reintam Blaser A. Nutrition in the intensive care unit: from the acute phase to beyond. Intensive Care Med 2024 (Table 2: ASPEN 2022 vs ESPEN) · Compher C et al. Guidelines for the provision of nutrition support therapy in the adult critically ill patient: ASPEN. JPEN 2022;46:12–41 · ASPEN 2020 refeeding syndrome consensus recommendations table (da Silva JSV et al., Nutr Clin Pract 2020;35:178–195), reproduced on WikEM — Refeeding syndrome · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).