Nutrition and metabolic support

Parenteral nutrition

Reviewed Nov 2026·5 references
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When to start PN (severe malnutrition early, others after day 3-7), how to prescribe and monitor, and complications.

Definition
PN is indicated when EN is contraindicated or insufficient. ESPEN: in patients who cannot eat or be fed enterally, start PN within 3-7 days; in severe malnutrition start early, progressively. Supplemental PN can be considered when EN is < 60% of target after the first week.

At the bedside

  1. 1

    Decide timing

    Well-nourished low-risk patients: delay PN (EPaNIC showed harm with early supplemental PN). Malnourished/high-risk with contraindication to EN: start PN early and advance slowly (refeeding precautions).

  2. 2

    Access

    Dedicated lumen of a central venous catheter (or PICC) for standard PN; peripheral PN only for low-osmolarity short-term solutions (< 850-900 mOsm/L).

  3. 3

    Prescription

    Use commercial 3-in-1 bags (glucose, amino acids, lipid) plus electrolytes, trace elements and vitamins; glucose ≤ 5 mg/kg/min; lipid ≤ 1.5 g/kg/day.

  4. 4

    Monitor

    Glucose 4-6 hourly initially (insulin if > 180 mg/dL), electrolytes including phosphate and Mg daily at first, triglycerides (reduce lipid if > 400 mg/dL), LFT weekly.

  5. 5

    Complications

    CLABSI (strict asepsis, dedicated lumen), hyperglycaemia, refeeding syndrome, PN-associated liver disease, overfeeding.

  6. 6

    Transition

    Reduce PN as EN delivery reaches ~60-75% of target.

Red flag · call your senior now
Fever with PN running through a central line: suspect CLABSI - cultures from line and periphery; consider line removal.
Pitfall
Starting full-dose PN on day 1 in a well-nourished patient.
Pitfall
Adding lipid without accounting for propofol.
Pearl
CALORIES: early PN was not more harmful than early EN when calories were matched - route matters less than avoiding overfeeding.

References

  1. 1

    Singer P, Blaser AR, Berger MM, et al. ESPEN guideline on clinical nutrition in the intensive care unit. Clin Nutr 2019;38:48-79.

  2. 2

    Singer P, Blaser AR, Berger MM, et al. ESPEN practical and partially revised guideline: clinical nutrition in the intensive care unit. Clin Nutr 2023;42:1671-89.

  3. 3

    Compher C, Bingham AL, McCall M, et al. Guidelines for the provision of nutrition support therapy in the adult critically ill patient: the American Society for Parenteral and Enteral Nutrition. JPEN J Parenter Enteral Nutr 2022;46:12-41.

  4. 4

    Casaer MP, Mesotten D, Hermans G, et al. Early versus late parenteral nutrition in critically ill adults (EPaNIC). N Engl J Med 2011;365:506-17.

  5. 5

    Harvey SE, Parrott F, Harrison DA, et al. Trial of the route of early nutritional support in critically ill adults (CALORIES). N Engl J Med 2014;371:1673-84.

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