Toxicology USMLE Step 1 Practice Question
A 35-year-old woman and her two children develop headache, dizziness, and nausea while sleeping in a house with a faulty furnace during winter. The mother presents with BP 128/82, HR 102, RR 18, and confusion. Pulse oximetry is normal at 98% on room air. Carboxyhemoglobin level is elevated at 22%. She denies dyspnea. Which of the following best explains the mechanism of her poisoning?
Answer choices
- AOxidation of hemoglobin iron from Fe2+ to Fe3+
- BCompetitive inhibition of cytochrome oxidase by cyanide
- CIncreased affinity of hemoglobin for oxygen with impaired release to tissuesCorrect answer
- DDirect GABA-A receptor blockade
- EIrreversible inhibition of acetylcholinesterase
- FInhibition of mitochondrial electron transport chain at Complex IV
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