Study Notes: Vasopressors in Critical Care

General Principles

• Vasopressors are used in shock states to restore perfusion pressure.

• Many options exist, but few are first-line.

• Norepinephrine is the preferred first-line agent for most causes of shock.

1. Dopamine

• Old “classic” vasopressor; rarely used now.

• Problems: ↑ risk of atrial/ventricular tachyarrhythmias.

• Indication: Hypotension + bradycardia (rare).

• Not recommended for routine use.

2. Phenylephrine

• “Pure alpha in a bottle.”

• Causes direct vasoconstriction → ↑ afterload.

• Problem: If LV function is poor, ↑ afterload worsens cardiac output.

• Indications:

  • Brief hypotension during RSI (offsets induction drug vasodilation).

  • AFib cardioversion in awake patients: bolus raises BP → allows sedation/analgesia before cardioversion.

• Not a first-line vasopressor for shock.

3. Norepinephrine (Levophed)

• First-line agent; “king/queen of vasopressors.”

• Receptor profile:

  • Alpha → ↑ afterload.

  • Beta → ↑ contractility (balances the ↑ afterload).

  • Venoconstriction → ↑ venous return/preload.

• Uses:

  • Septic shock (first-line).

  • Cardiogenic shock.

  • Most shock states.

• Cautions: May provoke arrhythmias (beta stimulation).

4. Epinephrine

• Alpha + Beta, but more beta effect than norepinephrine.

• Problems:

  • Higher arrhythmia risk.

  • ↑ lactate (not always due to worsening shock).

• Dose effect:

  • Low dose (0.01–0.05 mcg/kg/min) → inotrope (beta > alpha).

  • Higher doses → vasopressor (alpha effect increases).

• Used when additional support is needed, but usually after norepinephrine.

5. Vasopressin

• Mechanism: V1 receptor agonist → ↑ afterload (different receptor than norepi/epi → synergistic).

• Advantages:

  • Does not ↑ pulmonary vascular resistance → helpful in RV failure or pulmonary hypertension.

  • Other effects: ↑ cortisol, ↑ insulin, ↑ renal GFR.

• Use: Second-line, added to norepinephrine.

• When to add: Typically at moderate norepinephrine doses (~0.1–0.2 mcg/kg/min, ~15 mcg/min).

6. Angiotensin II

• Newer agent, works on vasculature and kidney.

• Studied in septic/distributive shock.

• Problems: Very expensive, limited availability.

• Role still evolving; not first-line.

Quick Summary

• Dopamine: Rare, only for hypotension + bradycardia.

• Phenylephrine: Short-term use (RSI, AFib cardioversion with sedation).

• Norepinephrine: First-line for nearly all shock states.

• Epinephrine: Similar to norepinephrine but more arrhythmogenic, ↑ lactate.

• Vasopressin: Best second-line add-on; synergistic with norepinephrine.

• Angiotensin II: Experimental/expensive; future option.