What potential effect might occur with high-dose norepinephrine beyond increasing MAP?

• A. Decreased venous return
• B. Increased urine output
• C. Decreased systemic vascular resistance
• D. Improved left ventricular function

Answer: (A)

High-dose norepinephrine raises mean arterial pressure mainly through alpha-1–mediated vasoconstriction, which increases systemic vascular resistance (and may be helped by some beta-1 inotropy). But this same intense vasoconstriction can extend to the venous system, reducing venous capacitance and altering the pressure gradient that drives blood back to the heart. In preload-dependent patients, venous constriction can raise right atrial pressure and diminish venous return, so preload falls and venous return can decrease despite the higher MAP. This is a potential adverse effect to watch for with high-dose norepinephrine.

Urine output tends to decrease rather than increase because renal perfusion can be reduced by vasoconstriction. Decreased systemic vascular resistance and improved LV function aren’t expected with high-dose norepinephrine; SVR tends to increase, and afterload can impair LV function rather than improve it.