Parenteral Nutrition in Critically Ill Patients on Double Pressor Support
Parenteral nutrition should NOT be initiated in critically ill patients on double pressor therapy; instead, delay nutritional support beyond IV glucose until vasopressor requirements decrease to norepinephrine equivalent <0.3 mcg/kg/min, at which point enteral nutrition should be attempted first. 1
Hemodynamic Stability is the Primary Determinant
The presence of double pressor therapy indicates hemodynamic instability that represents an absolute contraindication to both enteral and parenteral nutrition:
Patients requiring norepinephrine equivalent ≥0.3 mcg/kg/min should have full nutritional support delayed until reasonable vasopressor weaning occurs. 1 This threshold applies regardless of whether one or multiple pressors are being used.
Uncontrolled shock with unresuscitated hemodynamic instability is an absolute contraindication to enteral nutrition, and by extension, makes parenteral nutrition inappropriate as well. 1
The rationale is that high vasopressor requirements indicate inadequate splanchnic perfusion, creating risk for bowel ischemia and inability to utilize delivered nutrients effectively. 1
What to Provide During the High Vasopressor Phase
While on double pressor support:
Provide only IV glucose/dextrose for minimal caloric provision rather than attempting parenteral or enteral nutrition. 2, 1
This approach is supported by the Surviving Sepsis Campaign's strong recommendation against early parenteral nutrition in septic shock patients. 2
The EPaNIC trial demonstrated that late initiation of PN (started on day 8) led to better outcomes including increased proportion of patients discharged alive from ICU (HR 1.06; 95% CI 1.00-1.13; p=0.04) compared to PN commenced within 48 hours. 2
Algorithm for Nutrition Initiation After Vasopressor Weaning
Step 1: Assess Hemodynamic Improvement
Once norepinephrine equivalent decreases to <0.3 mcg/kg/min AND lactate has normalized, initiate enteral nutrition without delay. 1
Do not assume stability based solely on blood pressure; confirm with lactate clearance, urine output, and clinical perfusion markers. 1
Step 2: Prioritize Enteral Over Parenteral Route
Enteral nutrition should be attempted first even at low trophic rates (10-20 mL/hour) when the GI tract is functional, as it reduces infectious complications by 50% compared to parenteral nutrition (RR 0.50,95% CI 0.37-0.67). 3, 4
The Surviving Sepsis Campaign provides a strong recommendation against parenteral nutrition in favor of enteral nutrition in septic shock patients who can be fed enterally. 2, 1
Step 3: Consider Parenteral Nutrition Only After Day 3-7
Parenteral nutrition should only be considered if enteral nutrition remains insufficient or not feasible after 3 days in patients with expected ICU stay >3 days and organ failure (SOFA score >4). 3
The European Society for Clinical Nutrition and Metabolism recommends against parenteral nutrition alone or combined with enteral feeds over the first 7 days, favoring IV glucose and advancing enteral feeds as tolerated. 2
Step 4: Use Hypocaloric Dosing When PN is Initiated
If parenteral nutrition becomes necessary, provide only 20-25 kcal/kg/day (approximately 50% of full needs) during the acute phase (days 3-7) to avoid overfeeding. 3
Protein should start low (<0.8 g/kg/day) early, then progress to 1.3-1.5 g/kg/day as patients stabilize. 3
The Nutrirea-3 trial showed increased ICU length of stay by one day in intubated patients on vasopressors receiving full nutrition versus low-dose nutrition. 1
Critical Monitoring Parameters
When vasopressors are being weaned and nutrition is being considered:
Monitor closely for abdominal distension, pain, or increasing intra-abdominal pressure as signs of feeding intolerance or mesenteric ischemia. 1
Monitor gastric residuals if feeding intolerance is suspected. 1
Blood glucose should be maintained between 140-180 mg/dL (7.8-10 mmol/L). 4
Common Pitfalls to Avoid
Do not initiate parenteral nutrition in the first 7 days if any enteral feeding is feasible, as this increases infectious complications (22.8% vs 26.2%, p=0.008) without mortality benefit. 2, 1
Do not attempt full caloric feeding early in ICU stay on high-dose vasopressors, as the EPaNIC trial showed harm with early aggressive nutrition. 2, 1
Do not use the presence of open abdomen, neuromuscular blockade, therapeutic hypothermia, ECMO, or prone positioning as reasons to delay enteral nutrition once vasopressors are <0.3 mcg/kg/min. 1
Special Consideration for Malnourished Patients
Even in malnourished patients, parenteral nutrition should be delayed until hemodynamic stability is achieved (vasopressor weaning to <0.3 mcg/kg/min). 1
While malnourished patients may theoretically benefit from earlier nutrition, they were either excluded or rarely represented in major trials, and hemodynamic stability remains the priority. 2