top of page

Carbon Monoxide





  • Carbon monoxide (CO) is odorless, tasteless, & colorless

    • formed from hydrocarbon combustion

    • volatile anesthetics can produce CO when used w/ CO2 absorbents

  • CO binds to Hb w/ much greater affinity than O2 → forms carboxyhemoglobin (COHb)

    • impairs O2 transport/delivery w/ leftward shift of OxyHb dissociation curve & utilization

    • can precipitate inflammatory cascade w/ delayed neuro effects

  • Symptoms: headache, malaise, nausea, CP, SOB, dizziness, confusion, seizures, LOC; may see "cherry red" lips/skin

  • Dx

    • standard SpO2 doesn't identify CO poisoning

    • COHb levels measured by co-oximetry on ABG

      • Levels >5% in non-smokers or >10-15% in smokers consistent w/ CO poisoning

      • Levels don't correlate w/ degree of poisoning

  • Elimination via competitive binding of Hb to O2; dependent on degree of oxygenation & MV

    • ½ life of CO on room air: 4 hrs

    • ½ life of CO w/ high-flow O2 via nonrebreather: 60-90 mins

    • ½ life of CO w/ 100% hyperbaric O2: 20-30 mins

  • Mortality 1-3%


  • Life threatening emergency situation 

  • Coexisting diseases:

    • Burns, smoke inhalation, cyanide toxicity

  • Multisystem failure: 

    • Cardiovascular: myocardial ischemia, ventricular arrhythmias, pulmonary edema

    • CNS: seizures, ↓ LOC; may develop a delayed neuropsychiatric syndrome

    • Metabolic: profound lactic acidosis



  • Remove from source of CO

  • High-flow O2 via NRB mask until CO <5%

    • intubate & ventilate w/ 100% O2 if sig ↓ LOC

  • Consult toxicology & hyperbaric oxygen (HBO) specialist esp if severe

  • HBO treatment - ideally start w/in 6 hrs

    • CO >25-40%

    • CO >15-20% if pregnant

    • LOC

    • Severe metabolic acidosis (pH <7.2)

    • End-organ ischemia (CP, ECG changes, altered mental status, etc)

  • Source identification to limit risk to others (ex by fire department)



  • Chenoweth JA, Albertson TE, Greer MR. Carbon Monoxide Poisoning. Crit Care Clin. 2021 Jul;37(3):657-672. doi: 10.1016/j.ccc.2021.03.010.


bottom of page