Correct!
4. Pregnancy

The authors of UpToDate recommend hyperbaric oxygen in the following situations (3):

• COHb level >25 percent
• COHb level >15 percent in a pregnant patient
• Loss of consciousness
• Severe metabolic acidosis (pH <7.25)
• Evidence of end-organ ischemia (e.g., ECG changes, elevated cardiac biomarkers, respiratory failure, focal neurologic deficit, or altered mental status)

The threshold to use hyperbaric oxygenin pregnant patients is lower because of the greater affinity and longer half-life of CO bound to fetal hemoglobin, the inability to substantially increase placental perfusion, and the direct effects of hypoxemia and acidosis on the fetus (3). Experience is limited but severe maternal poisoning resulted in adverse outcomes in three of five pregnant patients treated with normobaric oxygen alone. Hyperbaric oxygen was used in two other cases, and those children did not demonstrate evidence of prenatal injury (3).

References

1. Nañagas KA, Penfound SJ, Kao LW. Carbon Monoxide Toxicity. Emerg Med Clin North Am. 2022 May;40(2):283-312. [CrossRef] [PubMed]
2. Ernst A, Zibrak JD. Carbon monoxide poisoning. N Engl J Med. 1998 Nov 26;339(22):1603-8. [CrossRef] [PubMed]
3. Manaker S, Perry H. Carbon monoxide poisoning. UpToDate. September 21, 2022. Available at: https://www.uptodate.com/contents/carbon-monoxide-poisoning (accessed 9/27/22).

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