If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 2 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.  

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A 19-year-old woman comes to the emergency department after a syncopal event one hour ago. While working in the garden, she accidentally disturbed a wasps' nest and was stung on her right hand. She has never been stung before. The woman tried to rest at home but felt extremely ill and called for an ambulance. She says she is dizzy and is concerned about some swelling in both of her hands and feet. Her temperature is 37.8ordmC (100.0ordmF), blood pressure is 83/40 mm Hg, pulse is 130 per minute, and respirations are 22 per minute. Oxygen saturation is 97% on room air. Pulmonary examination shows a diffuse mild wheeze in all lung fields.

Which of the following is the most appropriate next step in management?

A. Administer epinephrine.

B. Bolus patient with 500 mL of half-normal saline.

C. Perform endotracheal intubation.

D. Prescribe diphenhydramine and cimetidine.

E. Start IV corticosteroids.

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The correct answer is A.

All of the listed choices are appropriate interventions. In this patient, however, the first treatment should be to administer epinephrine, as the patient shows signs of anaphylactic shock. Epinephrine can reverse both the hypotension and the bronchospasm in this patient. Among patients who have anaphylaxis, fatality rates are highest among patients whose treatment with epinephrine is delayed. Median times to death are five minutes in iatrogenic anaphylaxis, 15 minutes in stinging insect, venom-induced anaphylaxis, and 30 minutes in food-induced anaphylaxis.

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Study tips for USMLE® or COMLEX-USA®

Epinephrine administration in anaphylaxis:

  • Administered as a 0.3-mg IM injection in the thigh or deltoid.
  • Concentration for IM injection is 1:1,000 (0.3 mL/0.3 mg).
  • Concentration for IV injection is 1:10,000, used during cardiac arrest.
  • If the patient does not respond to initial IM dose, then another dose should be administered five minutes later.
  • If the patient continues to worsen, then IV epinephrine should be considered as an IV drip at approximately two to 10 mcg per minute.

Choice B: Fluid boluses are likely to be needed. First administer epinephrine, however, as the major pathophysiologic problem is poor vascular tone. Additionally, the patient should not be bolused with hypotonic fluids, such as half-normal saline, but should receive normal saline or lactated Ringer's solution.

Choice C: Endotracheal intubation is the first priority if there is significant angioedema or stridor. This patient does not need to be intubated at this time, however, although close monitoring is warranted. First administer epinephrine, which will reverse her bronchospasm and treat her wheezing. Administration of epinephrine may prevent intubation and will be effective within minutes. If this patient did not respond to epinephrine, then intubation would be very reasonable.

Choice D: Diphenhydramine and cimetidine will block histamine, a key mediator in anaphylaxis. Both have a delayed effect, however. The first priority is making sure this patient receives epinephrine.

Choice E: Intravenous corticosteroids will prevent the late phase reaction from IgE-mediated histamine release. This is a delayed effect, however. Although the steroids should be provided in an expedient manner, the first treatment should be epinephrine.

  • Anaphylaxis treatment: epinephrine IM 1:1000 is the immediate first step.
  • IV fluids, steroids, and antihistamines are adjuvant treatments.

For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series

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