A 33-year-old woman is brought to the emergency department 30 minutes after being rescued from a fire in her apartment. She reports nausea, headache, and dizziness. Physical examination shows black discoloration of her oral mucosa. Pulse oximetry shows an oxygen saturation of 99% on room air. The substance most likely causing symptoms in this patient primarily produces toxicity by which of the following mechanisms?

Question

Quizplus · Accepted Answer

Eductional Objective: This patient's presentation is consistent with carbon monoxide poisoning. Nausea, headache, worsening dizziness, and history of exposure to a domestic fire strongly suggest CO exposure. CO is a colorless, odorless, and tasteless gas with much greater affinity for hemoglobin than oxygen. The resulting carboxyhemoglobin that forms has a decreased oxygen-carrying capacity, which shifts the oxygen dissociation curve to the left, decreasing the release of oxygen to tissues. Common findings in CO poisoning include a "cherry-red" skin tone and metabolic acidosis. Pulse oximetry oxygen saturation, as seen in this patient, is characteristically normal. Patients should receive 100% or possibly hyperbaric O₂ to offset CO bound to heme.

A 33-Year-Old Woman Is Brought to the Emergency Department 30