The effect of phenylephrine on myocardial oxygen consumption is best described as which of the following when hypertension is avoided?

The effect of phenylephrine on myocardial oxygen consumption is best described as which of the following when hypertension is avoided?

• A. Increases
• B. Decreases
• C. No change
• D. Slightly increases

Answer: (C)

Phenylephrine works mainly by increasing afterload through alpha-1 vasoconstriction, raising systemic vascular resistance and arterial pressure, but it does not directly increase heart rate or myocardial contractility. If you titrate to avoid true hypertension, the rise in afterload is modest and heart rate remains unchanged, so the heart’s work doesn’t meaningfully increase. Additionally, higher diastolic pressure can improve coronary perfusion, helping oxygen supply. Taken together, the net myocardial oxygen consumption stays essentially the same. If afterload became substantial enough to cause hypertension, then oxygen demand would rise due to increased wall stress and work.

Phenylephrine works mainly by increasing afterload through alpha-1 vasoconstriction, raising systemic vascular resistance and arterial pressure, but it does not directly increase heart rate or myocardial contractility. If you titrate to avoid true hypertension, the rise in afterload is modest and heart rate remains unchanged, so the heart’s work doesn’t meaningfully increase. Additionally, higher diastolic pressure can improve coronary perfusion, helping oxygen supply. Taken together, the net myocardial oxygen consumption stays essentially the same. If afterload became substantial enough to cause hypertension, then oxygen demand would rise due to increased wall stress and work.