The Basics

Ensuring that adequate nutrition is provided to ICU patients is something that should be reviewed daily. Each ICU will have their own policy and protocol regarding enteral and parental nutrition, but here are some key points:

  • Daily Nutritional Requirements:
    • Water 30 mls/kg
    • Calories 25 kcal/kg
    • Sodium 1-2mmol/kg
    • Potassium 0.8-1 mmol/kg
  • Enteral (i.e. NG feed) is preferred to parenteral, which bypasses the GI tract (i.e. TPN) if normal diet is not tolerated.
  • Ideally, enteral feeding should be started within 48 hours of ICU admission. The timeframe for starting TPN is more contentious.
  • 10% Dextrose can be used as a temporising measure until feeding can be commenced.
  • The position of NG tubes must be confirmed radiologically prior to use.
  • TPN must be administered centrally (via PICC or CVC).
  • Feeds should be commenced slowly and increased to a target rate (which will usually be advised by the dieticians).
  • NG feeds must be ceased and NG tube aspirated prior to extubation or surgical procedure / transport for scan.
  • Common feeds used include:
    • NG – e.g. Nutrison Protein Plus Multifibre. The number refers to the calorie content (e.g. 1.28 kcal/ml).
    • TPN – e.g. Baxter Olimel or SMOFKabiven. TPN mixtures must be kept refrigerated until required, and be shielded from light. Pharmacy teams can compound these mixtures to “personalise” electrolyte and trace element content so may need to be prescribed some time prior to being needed.

Common Issues with Enteral and Parental Feeding

  • High Aspirates:
    • During initiation of feeding then the NG tube should be aspirated every 4 hours.
    • High aspirates (>500ml/4 hours) suggest feed intolerance.
    • Strategies for management of high aspirates include reducing rate of feeds, ensuring patient at 30-45 degrees head up, or the addition of prokinetics (metoclopramide 10mg IV QID and erythromycin 200mg IV BD if no contraindications such as prolonged QTc).
  • Hyperglycaemia:
    • This may require an increase in usual insulin requirements or an initiation of an insulin infusion (or basal bolus regime).
    • Insulin infusion: 50 units Actrapid in 50mls 0.9% NaCl.
  • Hypernatraemia:
    • The use of lower sodium feeds (e.g. Neopro) can be considered or addition of free water flushes (depending on fluid state).

Refeeding Syndrome

This is a constellation of findings that occur when feeding is re-commenced in malnourished individuals.

A simple explanation is that during starvation, decreased blood glucose leads to decreased insulin levels. When feeding is recommenced (particularly carbohydrates), the rapid rise in insulin causes large shifts in electrolytes (mainly phosphate, potassium, and magnesium) into cells resulting in low serum levels.

The management of refeeding syndrome includes:

  • Recognition of those at risk.
  • Starting feeds at low rates.
  • Ensure replacement of thiamine and trace vitamins/elements.
    • 100-300mg daily of thiamine and multivitamin (e.g. Cernevit) should be prescribed.
  • Aggressive electrolyte replacement is needed and thus frequent (daily at least) checking of electrolytes including calcium, magnesium and phosphate levels is required.

References and Further Reading

British Journal Anaesthesia Education: Nutrition in Critical Care

Author: George Walker