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Carbon Monoxide Poisoning

Carbon Monoxide Poisoning is a topic covered in the 5-Minute Clinical Consult.

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  • Carbon monoxide (CO) is an odorless, tasteless, colorless gas that has the potential to cause sudden illness and death if inhaled.
  • CO is produced by combustion of carbon-containing compounds (wood, charcoal, oil, gas):
    • CO inhalation leads to displacement of oxygen from binding sites on hemoglobin.
    • Detrimental effects are related to tissue hypoxia from decreased oxygen content and a (left) shift of the oxyhemoglobin dissociation curve that impairs oxygen unloading from hemoglobin.
  • CO binds to mitochondrial cytochrome oxidase, impairing adenosine triphosphate (ATP) production. It also binds to myoglobin, affecting muscle function.
  • System(s) affected: cardiovascular, pulmonary, musculoskeletal, nervous

Pregnancy Considerations
Tissue hypoxia due to CO poisoning may cause significant fetal abnormalities. CO has a greater affinity for (and longer half-life bound to) fetal hemoglobin. A pregnant mother may be unaffected, whereas the fetus is adversely impacted.



Third leading cause of unintentional poisoning deaths in the United States with an average 438 deaths annually

  • ~50,000 emergency department visits annually
  • Unintentional poisoning is most common during winter months in cold climates.
  • Intentional CO poisoning ~10 times higher than unintentional poisonings
  • Likely underdiagnosed because some patients may not seek medical attention due to vague symptoms

Etiology and Pathophysiology

  • CO is rapidly absorbed in lungs.
  • CO has ~240 times the affinity for hemoglobin compared to oxygen.
  • CO binds to hemoglobin to form carboxyhemoglobin (COHb), resulting in impaired oxygen-carrying capacity, utilization, and delivery:
    • CO interferes with peripheral oxygen utilization by inactivating cytochrome oxidase.
  • Delayed neurologic sequelae, related to lipid peroxidation by toxic oxygen species generated by xanthine oxidase
  • The half-life of CO on room air is ~320 minutes, whereas breathing 100% oxygen via a tight-fitting, nonrebreathing face mask decreases to ~74 minutes. With 100% hyperbaric oxygen, T1\2 is ~30 minutes (1).
  • CO can promote nitric oxide release causing profound hypotension.
  • CO affects L-type myocardial calcium channels causing myocardial depression.
  • Inhaled or ingested methylene chloride (from paint remover [dichloromethane]) is metabolized to CO by the liver, potentially resulting in acute CO toxicity.

Risk Factors

  • Alcohol use; smoking
  • Elderly and infants at higher risk if exposed
  • Closed or improperly ventilated space with faulty furnace, stove, engine, or other fuel-burning device
  • Cigarette smoking
  • Use of generators during power outages and storms
  • Underlying cardiovascular disease, anemia, chronic respiratory conditions
  • Exposure to exhaust (e.g., riding in the back of enclosed pickup trucks or swimming near a motor boat) in precatalytic converter era automobiles
  • Employment in a coal mine, as an auto mechanic, paint stripper, or in the solvent industry
  • Increased endogenous production in patients with hemolytic anemia

General Prevention

  • Appropriate ventilation, especially around fuel-burning devices
  • Use of CO monitors
  • Determining the mechanism of exposure is critical in cases of accidental poisoning helps limit future risk.
  • Victims must not return to contaminated environment.
  • Regular building maintenance to ensure safe environment and adequate ventilation
  • Public policy to ensure building code safety

Commonly Associated Conditions

  • CO and cyanide poisoning can occur simultaneously following smoke inhalation (synergistic effect).
  • Consider CO poisoning in a burn victim who has been in an enclosed space.

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Stephens, Mark B., et al., editors. "Carbon Monoxide Poisoning." 5-Minute Clinical Consult, 27th ed., Wolters Kluwer, 2019. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/816786/all/Carbon_Monoxide_Poisoning.
Carbon Monoxide Poisoning. In: Stephens MB, Golding J, Baldor RA, et al, eds. 5-Minute Clinical Consult. 27th ed. Wolters Kluwer; 2019. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/816786/all/Carbon_Monoxide_Poisoning. Accessed April 18, 2019.
Carbon Monoxide Poisoning. (2019). In Stephens, M. B., Golding, J., Baldor, R. A., & Domino, F. J. (Eds.), 5-Minute Clinical Consult. Available from https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/816786/all/Carbon_Monoxide_Poisoning
Carbon Monoxide Poisoning [Internet]. In: Stephens MB, Golding J, Baldor RA, Domino FJ, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2019. [cited 2019 April 18]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/816786/all/Carbon_Monoxide_Poisoning.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Carbon Monoxide Poisoning ID - 816786 ED - Stephens,Mark B, ED - Golding,Jeremy, ED - Baldor,Robert A, ED - Domino,Frank J, BT - 5-Minute Clinical Consult, Updating UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/816786/all/Carbon_Monoxide_Poisoning PB - Wolters Kluwer ET - 27 DB - Medicine Central DP - Unbound Medicine ER -