Carbon Monoxide
Background
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Carbon monoxide (CO) is odorless, tasteless, & colorless
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formed from hydrocarbon combustion
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volatile anesthetics can produce CO when used w/ CO2 absorbents
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CO binds to Hb w/ much greater affinity than O2 → forms carboxyhemoglobin (COHb)
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impairs O2 transport/delivery w/ leftward shift of OxyHb dissociation curve & utilization
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can precipitate inflammatory cascade w/ delayed neuro effects
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Symptoms: headache, malaise, nausea, CP, SOB, dizziness, confusion, seizures, LOC; may see "cherry red" lips/skin
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Dx
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standard SpO2 doesn't identify CO poisoning
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COHb levels measured by co-oximetry on ABG
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Levels >5% in non-smokers or >10-15% in smokers consistent w/ CO poisoning
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Levels don't correlate w/ degree of poisoning
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Elimination via competitive binding of Hb to O2; dependent on degree of oxygenation & MV
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½ life of CO on room air: 4 hrs
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½ life of CO w/ high-flow O2 via nonrebreather: 60-90 mins
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½ life of CO w/ 100% hyperbaric O2: 20-30 mins
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Mortality 1-3%
Considerations
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Life threatening emergency situation
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Coexisting diseases:
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Burns, smoke inhalation, cyanide toxicity
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Multisystem failure:
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Cardiovascular: myocardial ischemia, ventricular arrhythmias, pulmonary edema
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CNS: seizures, ↓ LOC; may develop a delayed neuropsychiatric syndrome
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Metabolic: profound lactic acidosis
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Treatment
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Remove from source of CO
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High-flow O2 via NRB mask until CO <5%
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intubate & ventilate w/ 100% O2 if sig ↓ LOC
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Consult toxicology & hyperbaric oxygen (HBO) specialist esp if severe
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HBO treatment - ideally start w/in 6 hrs
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CO >25-40%
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CO >15-20% if pregnant
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LOC
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Severe metabolic acidosis (pH <7.2)
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End-organ ischemia (CP, ECG changes, altered mental status, etc)
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Source identification to limit risk to others (ex by fire department)
References
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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.