Clinical Pharmacology, USMLE Step 1 - Full Vignette with Extended Explanations

Описание: A 106-year-old woman with prior schistosomiasis and chronic hepatitis C develops hoarseness, throat tightness, periorbital edema, and wheezing shortly after a scalp lesion is excised under local anesthesia at a community clinic. Given her history of anesthetic-related swelling and new symptoms, what clinical reasoning and key physical findings should guide your next steps in acute management for this patient?

VIDEO INFO
Category: Clinical Pharmacology, USMLE Step 1
Difficulty: Expert - Expert level - For those seeking deep understanding
Question Type: Differential Physical History
Case Type: Rare Presentation

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QUESTION
A 106-year-old woman with remote schistosomiasis and chronic hepatitis C, sober from alcohol for 2 years, undergoes dermatologic excision of a bleeding scalp lesion under local infiltration anesthesia in a community clinic. Fifteen minutes after infiltration she becomes hoarse and complains of throat tightness and lightheadedness. Vitals on arrival to the ED: pulse 91 bpm, blood pressure 104/73 mm Hg, respiratory rate 22 breaths/min, oxygen saturation 91% on room air, temperature 36.7 degreesC....

OPTIONS
A. IgE-mediated anaphylaxis from local anesthetic exposure; give intramuscular epinephrine 0.3-0.5 mg of 1 mg/mL in the lateral thigh now and repeat every 5-15 minutes as needed, with supine positioning.
B. Bradykinin-mediated angioedema; administer icatibant 30 mg subcutaneously once and avoid epinephrine as it is not indicated; arrange observation for delayed airway compromise in a monitored care area for at least six hours.
C. Scombroid (histamine) fish poisoning encountered at lunch; treat with oral antihistamine and ondansetron with observation only, and report the suspected contaminated source to public health authorities for traceback.
D. Panic attack with hyperventilation; provide reassurance and oral lorazepam 0.5-1 mg without parenteral therapies, and schedule cognitive behavioral therapy referral for recurrence prevention.

CORRECT ANSWER
A. IgE-mediated anaphylaxis from local anesthetic exposure; give intramuscular epinephrine 0.3-0.5 mg of 1 mg/mL in the lateral thigh now and repeat every 5-15 minutes as needed, with supine positioning.

EXPLANATION
The correct answer is "IgE-mediated anaphylaxis from local anesthetic exposure; give intramuscular epinephrine 0.3-0.5 mg of 1 mg/mL in the lateral thigh now and repeat every 5-15 minutes as needed, with supine positioning." The patient developed hoarseness, throat tightness, mucosal edema, wheeze, pruritus, and hypotoxemia within minutes of local anesthetic infiltration-hallmarks of anaphylaxis with respiratory involvement. Immediate, site-appropriate IM epinephrine is the first-line therapy; delays increase morbidity. The 2023/2024 anaphylaxis practice parameter emphasizes prompt IM epinephrine in the lateral thigh at 0.3-0.5 mg of 1 mg/mL, repeated every 5-15 minutes as needed, plus positioning and airway preparation....


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