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Carbon monoxide poisoning in pregnancy — ABIM Board MCQ

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HardOxygen TherapyCarbon monoxide poisoning in pregnancyABIM Board

A 28-year-old woman at 18 weeks’ gestation is brought to the emergency department after a gasoline-powered generator was operated in her basement during a power outage. She was found confused and had a witnessed 2-minute loss of consciousness. Emergency medical personnel removed her from the house and administered 100% oxygen by nonrebreather mask. Ninety minutes later, she is alert and reports resolution of headache and nausea. Temperature is 98.6°F (37.0°C), blood pressure is 118/72 mm Hg, pulse is 88/min, and conventional pulse oximetry shows 100% saturation. Neurologic examination is normal. Venous carboxyhemoglobin concentration is 11%, arterial pH is 7.40, and serum troponin concentration is normal. Fetal heart rate and ultrasonography are reassuring. Which of the following is the most appropriate next management strategy?

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Correct answer: B — Continue 100% normobaric oxygen while arranging urgent hyperbaric oxygen therapy

This patient should continue receiving 100% normobaric oxygen while urgent hyperbaric oxygen therapy is arranged. Three features are decisive: she is pregnant, she had transient loss of consciousness, and her measured carboxyhemoglobin concentration was obtained after removal from exposure and 90 minutes of oxygen. Pregnancy warrants an aggressive approach because fetal carbon monoxide clearance is slower and fetal hemoglobin binds carbon monoxide avidly. CDC guidance identifies hyperbaric oxygen as the treatment of choice for pregnant patients even when poisoning appears less severe. Loss of consciousness is also an independent high-risk feature supporting hyperbaric treatment. The carboxyhemoglobin value of 11% does not exclude clinically important exposure; concentrations decline after oxygen administration and correlate poorly with poisoning severity. Conventional pulse oximetry is similarly unreliable because it cannot distinguish oxyhemoglobin from carboxyhemoglobin. Option E is appropriate normobaric management for selected nonpregnant patients with mild poisoning and no high-risk features. Option A incorrectly makes a post-treatment concentration greater than 25% a prerequisite; clinical history and pregnancy override that threshold. Option C is unnecessary because she is protecting her airway and ventilating normally; intubation does not substitute for indicated hyperbaric therapy. Option D undertreats both maternal and fetal exposure and relies inappropriately on symptom resolution, reassuring fetal testing, and conventional pulse oximetry.

Reference: Clinical Guidance for Carbon Monoxide Poisoning Following Disasters and Severe Weather (Reviewed August 21, 2026; updated July 8, 2024) — https://www.cdc.gov/carbon-monoxide/hcp/clinical-guidance/index.html