What are the considerations for using Total Parenteral Nutrition (TPN) in critically ill, post-operative, hemodynamically unstable adult patients in the Intensive Care Unit (ICU)?

Use of TPN in ICU, Post-operative, Hemodynamically Unstable Patients

In hemodynamically unstable post-operative ICU patients, delay TPN initiation until shock is controlled and hemodynamic goals are achieved, then start low-dose enteral nutrition first; only initiate TPN after 3-7 days if enteral feeding remains insufficient, providing hypocaloric nutrition (20-25 kcal/kg/day, approximately 50% of full needs) rather than full feeding. 1, 2, 3

Hemodynamic Stability Requirements Before Any Nutrition

Delay all nutrition support if shock is uncontrolled and tissue perfusion goals are not reached. 1 Specific contraindications include:

• Vasopressor requirements exceeding 1 μg/kg/min norepinephrine with persistent hyperlactatemia or other signs of end-organ hypoperfusion 1
• Uncontrolled life-threatening hypoxemia, hypercapnia, or acidosis 1
• Overt bowel ischemia 1

Start low-dose enteral nutrition (10-20 mL/hour) as soon as shock is controlled, even if vasopressors are still required at lower doses. 1, 2

Enteral Nutrition Must Be Attempted First

Enteral nutrition reduces infectious complications by 50% (RR 0.50,95% CI 0.37-0.67) compared to early parenteral nutrition and should be initiated within 24-48 hours once hemodynamically stable. 2, 3

In post-operative patients specifically:

• Early enteral nutrition is preferred over delayed enteral nutrition after abdominal or esophageal surgery 1
• Enteral nutrition should be preferred over parenteral nutrition unless GI tract discontinuity, obstruction, or abdominal compartment syndrome is present 1
• Trauma patients should preferentially receive early enteral nutrition instead of early parenteral nutrition 1

When to Initiate TPN: Timing Algorithm

The decision to start TPN depends on nutritional risk and duration of enteral feeding failure:

High Nutritional Risk Patients (Malnourished or SOFA >4):

• Initiate TPN after 3 days if enteral nutrition remains insufficient or not feasible 1, 2, 3
• This applies to patients with expected ICU stay >3 days and organ failure 2, 3

Low Nutritional Risk Patients:

• Withhold TPN for the first 7 days if enteral nutrition is insufficient 1
• Initiate or continue TPN after day 7 if oral/enteral intake remains inadequate, now targeting full energy requirements 1, 2

The ESPEN 2019 guidelines support starting PN in malnourished patients by day 4 at the latest, based on large multicenter studies comparing early versus late PN supplementation. 1

TPN Dosing Strategy: Avoid Overfeeding

During the acute phase (days 1-7), provide hypocaloric nutrition at 20-25 kcal/kg/day (approximately 50% of predicted needs) to avoid the harmful effects of early full feeding demonstrated in multiple studies. 1, 2, 3

Specific Dosing Recommendations:

Energy targets:

• Acute phase (days 1-2): Target 70% of measured energy expenditure 2
• Days 3-7: Provide 20-25 kcal/kg/day 2, 3
• Recovery phase (after day 7): Increase to match measured energy expenditure using indirect calorimetry when available 2

Protein targets:

• Start low (<0.8 g/kg/day) early 2
• Progress to 1.3-1.5 g/kg/day as patients stabilize 2, 3
• Target ≥1.2 g/kg/day during recovery phase 2

The ESPEN 2017 surgery guidelines note that 25 kcal/kg with 1.5 g/kg protein showed no increased risk of hyperglycemia or infectious complications while significantly improving nitrogen balance. 1

Administration Route Requirements

Central venous access is required for high osmolarity TPN mixtures (>850 mOsmol/L) designed to cover full nutritional needs. 1, 2, 3

• Peripheral access may be used only for low osmolarity solutions (<850 mOsmol/L) providing partial nutrition 1, 2
• If peripheral PN does not allow full provision of patient needs, switch to central administration 1
• For expected PN duration 4-7 days, hypocaloric nutrition (2 g carbohydrate and 1 g amino acids/kg) can be administered peripherally 1
• For expected duration >7-10 days, central venous catheter insertion is recommended 1

All-in-One Bag System

Use all-in-one bags (three-chamber or pharmacy-prepared) instead of multibottle systems (Grade B recommendation). 1

This approach:

• Significantly reduces bloodstream infections 1
• Decreases costs compared to separate container systems 1
• Minimizes IV line manipulations and administration errors 1

Special Considerations for Sepsis/Septic Shock

In patients with sepsis or septic shock, provide 20-50% of nutrition support early, then increase gradually according to GI tolerance once hemodynamic alterations resolve (typically a few days after admission). 1, 2

For septic patients where enteral nutrition is not feasible for prolonged periods (bowel discontinuity, etc.), prescribe PN after successful resuscitation up to approximately half of predicted or measured energy needs. 1

Critical Monitoring and Pitfalls

Hyperglycemia is a major risk factor that increases mortality and infectious complications. 2, 3

• Maintain blood glucose between 4.5-10 mmol/L (81-180 mg/dL) 3
• Reduce glucose-based calories if blood sugar exceeds 180 mg/dL 1
• Intensive insulin therapy carries incalculable hypoglycemia risk in post-surgical patients on general wards with less staffing 1

Energy deficits correlate strongly with infectious complications, duration of mechanical ventilation, and ICU length of stay. 3 However, overfeeding during the acute phase causes harm, as demonstrated in the EPaNIC study showing reduced infection rates with late versus early full PN (29.9% vs 40.2%, p=0.01). 1

Specific Post-Operative Scenarios

For unrepaired anastomotic leak, internal/external fistula:

• Aim for feeding access distal to the defect to administer enteral nutrition 1
• If distal feeding access not achieved, withhold enteral nutrition and commence PN 1

For high-output stoma or fistula:

• Evaluate appropriateness of chyme reinfusion or enteroclysis 1

For open abdomen:

• Early enteral nutrition is suggested 1