When is epinephrine (Epi) used versus norepinephrine in critical care situations?

Epinephrine vs. Norepinephrine Use in Critical Care

Norepinephrine should be used as the first-choice vasopressor in most critical care situations, while epinephrine should be reserved as a second-line agent or for specific scenarios like cardiac arrest and pediatric cold septic shock. 1

First-Line Vasopressor Selection

Septic Shock

• First choice: Norepinephrine (Grade 1B recommendation) 1

  • Initial dose: 0.05-0.1 μg/kg/min
  • Titration: 0.05-0.1 μg/kg/min every 5-15 minutes
  • Target: Mean arterial pressure (MAP) ≥65 mmHg 2

• Second choice: Epinephrine (Grade 2B recommendation) - added to or substituted for norepinephrine when an additional agent is needed to maintain adequate blood pressure 1

  • Dosing: 0.05 μg/kg/min to 2 μg/kg/min IV infusion 3
  • Important caveat: Epinephrine causes transient lactic acidosis, higher heart rate, more arrhythmias, and inadequate gastric mucosal perfusion compared to norepinephrine 4

Cardiac Arrest

• Standard dose epinephrine (1 mg) is recommended for cardiac arrest (weak recommendation, very low-quality evidence) 1
• Vasopressin should not be used instead of epinephrine in cardiac arrest (weak recommendation, low-quality evidence) 1

Pediatric Considerations

• In pediatric septic shock:
  • Dopamine was historically used as first-line but is now less favored
  • Epinephrine may be more effective than dopamine for resolution of shock in the first hour (OR 4.8; 95% CI 1.3-17.2) 1
  • Norepinephrine plus dobutamine may lead to earlier shock resolution compared to epinephrine alone in pediatric cold septic shock 5

Specific Clinical Scenarios

Cardiogenic Shock

• Norepinephrine plus dobutamine is preferred over epinephrine alone
  • This combination provides:
    • Lower heart rates
    • Fewer arrhythmias
    • Better lactate metabolism
    • Improved splanchnic perfusion
    • Better diuresis 4

Ventricular Septal Rupture

• Norepinephrine is recommended as first-choice vasopressor 2
• Consider dobutamine (2.5-20 μg/kg/min) if there is evidence of myocardial dysfunction or persistent hypoperfusion despite adequate blood pressure 2

Physiological Effects and Considerations

Norepinephrine

• Mechanism: Predominantly alpha-adrenergic effects with some beta-1 activity
• Effects:
  • Increases MAP via vasoconstriction
  • Minimal change in heart rate
  • Less increase in stroke volume compared to dopamine 1
  • Less risk of tachyarrhythmias 1

Epinephrine

• Mechanism: Alpha and beta (β1 and β2) adrenergic effects
• Effects:
  • Increases cardiac output and MAP
  • Causes tachycardia
  • Increases myocardial oxygen demand
  • Causes transient lactic acidosis
  • May impair splanchnic perfusion 4, 6
  • FDA approved for hypotension associated with septic shock 3

Common Pitfalls and Caveats

1. Delayed fluid resuscitation: Vasopressors should ideally be started after adequate fluid resuscitation, but may be needed early in severe shock when diastolic blood pressure is too low 1

2. Failure to monitor for adverse effects:

   • With epinephrine: Monitor for tachycardia, arrhythmias, and lactic acidosis
   • With norepinephrine: Watch for excessive vasoconstriction affecting peripheral perfusion

3. Inadequate dose titration: Both agents require careful titration to achieve target MAP while minimizing side effects

4. Ignoring combination therapy potential: Adding dobutamine to norepinephrine may improve cardiac output and tissue perfusion when needed 4, 6

5. Route of administration: Always administer into a large vein to avoid extravasation and tissue necrosis 3

6. Failure to wean: Once hemodynamic stability is achieved, vasopressors should be weaned gradually 3

In summary, norepinephrine is the first-choice vasopressor for most critical care situations, particularly septic shock, while epinephrine is valuable as a second-line agent or in specific scenarios like cardiac arrest and certain pediatric conditions.