At high-dose epinephrine infusion (>0.15 mcg/kg/min), what are the predominant receptor effects and the hemodynamic consequence?

At high-dose epinephrine infusion (>0.15 mcg/kg/min), what are the predominant receptor effects and the hemodynamic consequence?

• A. Alpha and Beta activation; SVR increases; HR and contractility increase; stroke volume may decrease due to high afterload
• B. Beta activation only; HR decreases; SVR decreases
• C. Alpha activation only; HR unchanged; SVR increases
• D. Beta-2 dominant; HR increases; SVR unchanged

Answer: (A)

Epinephrine’s effects depend on dose because it hits multiple receptors with different vascular and cardiac actions. At higher infusion rates, alpha-1 effects become dominant, causing vasoconstriction and a rise in systemic vascular resistance (SVR), i.e., higher afterload. The heart still receives beta-1 stimulation, which increases heart rate (chronotropy) and contractility (inotropy). That boost in contractility tends to raise cardiac output, but the markedly increased afterload can blunt the amount of blood the ventricle can eject, so stroke volume may actually decrease. Beta-2–mediated vasodilation that can occur at lower doses is overridden by alpha-1 vasoconstriction at high doses, reinforcing the rise in SVR. So the best description is simultaneous alpha and beta activation with increased SVR, higher heart rate and contractility, and a possible decrease in stroke volume due to the high afterload.

Epinephrine’s effects depend on dose because it hits multiple receptors with different vascular and cardiac actions. At higher infusion rates, alpha-1 effects become dominant, causing vasoconstriction and a rise in systemic vascular resistance (SVR), i.e., higher afterload. The heart still receives beta-1 stimulation, which increases heart rate (chronotropy) and contractility (inotropy). That boost in contractility tends to raise cardiac output, but the markedly increased afterload can blunt the amount of blood the ventricle can eject, so stroke volume may actually decrease. Beta-2–mediated vasodilation that can occur at lower doses is overridden by alpha-1 vasoconstriction at high doses, reinforcing the rise in SVR. So the best description is simultaneous alpha and beta activation with increased SVR, higher heart rate and contractility, and a possible decrease in stroke volume due to the high afterload.