Parenteral Nutrition in Critically Ill Patients

Introduction to Parenteral Nutrition

Parenteral nutrition (PN) should be initiated within 24-48 hours in critically ill ICU patients when enteral nutrition (EN) is contraindicated or insufficient, using a complete formulation tailored to the patient's metabolic needs 1
The American Society for Parenteral and Enteral Nutrition recommends starting PN within 24-48 hours if the patient is not expected to resume normal nutrition within 3 days and enteral nutrition is contraindicated or the patient cannot tolerate enteral feeding 1

Contraindications to enteral feeding requiring early PN include uncontrolled shock, uncontrolled hypoxemia and acidosis, uncontrolled upper GI bleeding, gastric aspirate >500 ml/6 hours, bowel ischemia, bowel obstruction, abdominal compartment syndrome, and high-output fistula without distal feeding access 2

Aim for 25 kcal/kg/day, increasing to target over 2-3 days in the initial phase of acute illness 1
Avoid exceeding 20-25 kcal/kg/day in the acute phase as this may worsen outcomes, according to the European Society for Clinical Nutrition and Metabolism 3
Ideally, measure energy expenditure using indirect calorimetry, as recommended by the Society of Critical Care Medicine 4
Minimum carbohydrate requirement is 2 g/kg glucose per day 1
Maintain blood glucose <10 mmol/L to prevent infectious complications, as suggested by the American Diabetes Association 1
Administer 0.7-1.5 g/kg of lipids over 12-24 hours 1
Provide 1.3-1.5 g/kg ideal body weight/day of amino acids 1
Include 0.2-0.4 g/kg/day of L-glutamine (0.3-0.6 g/kg/day alanyl-glutamine dipeptide) 1

All PN prescriptions should include daily doses of multivitamins and trace elements 1
Consider evaluation of micronutrient levels after 5-7 days in patients at risk of deficiencies, such as those on continuous renal replacement therapy (CRRT), as recommended by the National Institute of Diabetes and Digestive and Kidney Diseases 4
Central venous access is typically required for high osmolarity PN formulations designed to fully meet nutritional needs 1
Peripheral venous access may be used for lower osmolarity mixtures (<850 mOsmol/L) intended to supplement nutrition 1
Begin with low-dose PN in the early phase of critical illness (first 1-2 days) and gradually increase to target over 2-3 days while monitoring metabolic tolerance, as suggested by the Society of Critical Care Medicine 4
Avoid overfeeding, which can be as detrimental as underfeeding, according to the American Society for Parenteral and Enteral Nutrition 1

Implement strict glycemic control protocols and maintain blood glucose <10 mmol/L 1
Be aware of increased risk of hypoglycemia with tight glucose control (4.5-6.1 mmol/L) 1
Delaying nutritional support, overfeeding, poor glycemic control, and inadequate monitoring can lead to increased morbidity and mortality 1, 3, 4
Focusing exclusively on EN may lead to nutritional deficits if EN is insufficient, and supplemental PN should be considered, as recommended by the European Society for Clinical Nutrition and Metabolism 1