Epinephrine 1 mg IV is recommended every 3–5 minutes in cardiac arrest. What is the proposed mechanism by which epinephrine improves coronary and cerebral perfusion during CPR?

• A Beta-1 stimulation increases cardiac output during compressions
• B Beta-2 bronchodilation improves alveolar ventilation
• C Alpha-1 peripheral vasoconstriction increases aortic diastolic pressure, improving coronary and cerebral perfusion pressure ✓
• D Direct inotropy restores organised cardiac rhythm

Explanation

During CPR, the beneficial haemodynamic effect of epinephrine is mediated primarily through alpha-1 adrenoceptor-induced peripheral vasoconstriction. This increases aortic diastolic pressure without a corresponding rise in right atrial pressure, thereby increasing coronary and cerebral perfusion pressures. The beta-adrenergic effects (increased heart rate and contractility) may actually be harmful by increasing myocardial oxygen demand during fibrillation. The PARAMEDIC2 trial showed epinephrine improved survival to hospital discharge but not long-term neurological outcomes compared with placebo.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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