QBDOTW: A 29-year-old Female with Pheochromocytoma
Welcome to MedSmarter’s USMLE Style Question Break Down of the Week. For those preparing for the USMLE Step 1, this week we break down a high-yield Endocrinology question. As always you want to begin with reading the last sentence of the vignette first to get an understanding of what the question is asking for.
Question Break Down of the Week:
A 29-year-old woman with pheochromocytoma is being treated with phenoxybenzamine prior to surgical excision of the tumor. After successful surgical removal of the pheochromocytoma, the patient has an episode of hypotension requiring 30 seconds of cardiopulmonary resuscitation and subsequent treatment in the intensive care unit. The attending physician asks his medical students what physiologic responses he would expect to see if the patient had been given epinephrine during resuscitation. What would have been observed following the administration of epinephrine?
A) Decrease in blood pressure
B) Decrease in heart rate
C) Increase in blood pressure
D) Increase in respiratory rate
E) No changes in vital signs
The correct answer choice is A: Phenoxybenzamine is a nonselective α-antagonist that will block both α1- and α2-receptors. In this patient, the administration of high-dose epinephrine (which is both an α- and a β-agonist) would result in unopposed β1- (increased heart rate, increased contractility) and β2- (vasodilation, bronchodilation) agonist effects because the α-effects of epinephrine are blocked by prior phenoxybenzamine administration. The net effect will be β-agonist effects, including an increase in heart rate and a decrease in blood pressure.
Did you think the answer was different?
Did you think that the correct answer choice was other than A? You can view this video for a deeper discussion of why B, C, D, and E were not the correct answer choices.
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