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Updated: Dec 24 2021

Carbon Monoxide Poisoning

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  • Snapshot
    • A 35-year-old painter presents to the emergency room for nausea, vomiting, and a headache. He reports that a large vat of paint thinner had spilled, and he had spent the afternoon cleaning it up. While at the time he felt fine, an hour after he finished, he started experiencing these symptoms. On physical exam, he is oriented to self and place but not the year. He is tachycardic with a pulse of 112/min. Pulse oximetry reveals an oxygen saturation of 96% on room air. A CO-oximetry shows carboxyhemoglobin levels of 23%. He is started on 100% oxygen. A lactic acid level is drawn to assess for concomitant cyanide poisoning.
  • Introduction
    • Clinical definition
      • carbon monoxide (CO) poisoning results from exposure to CO resulting in hypoxia
    • Pathogenesis
      • mechanism
        • displaces oxygen from hemoglobin
          • causes left-shift of oxygen-hemoglobin curve, leading to decreased delivery of oxygen to tissues
        • binds to cytochrome oxidase
          • disrupts electron transport chain
        • increases lipid peroxidation in the central nervous system
    • Associated conditions
      • cyanide poisoning
  • Epidemiology
    • Incidence
      • leading cause of death from unintentional poisoning
      • common in industrialized patients
    • Risk factors
      • use of charcoal, gas, or petroleum
      • wood-burning heaters
      • cooking in poorly ventilated areas
      • building fires
      • smoke inhalation
      • motor vehicle exhaust
      • exposure to methylene chloride (paint thinners)
        • metabolized into CO
        • delayed CO poisoning
  • Presentation
    • Symptoms
      • headache
      • lightheadedness
      • nausea and vomiting
      • improvement when removed from the exposure
    • Physical exam
      • normal pulse oximetry
      • tachycardia
      • dyspnea
      • altered mental status
        • confusion
      • cherry-red skin
        • late finding of CO poisoning
  • Studies
    • Diagnostic testing
      • studies
        • pulse oximetry
          • normal oxygen saturation level
        • ↑ carboxyhemoglobin (COHb) levels
          • must be assessed before supplemental oxygen is administered
            • arterial blood gas
            • venous blood gas
            • portable CO-oximetry devices (not regular pulse oximetry)
          • > 3% for nonsmokers
          • > 9% for smokers
        • lactic acid
          • decreased delivery of oxygen to tissues
        • ↑ troponin
          • CO poisoning may cause myocardial injury due to relative hypoxemia
  • Differential
    • Cyanide poisoning
      • distinguishing factor
        • ↑ lactic acid
        • does not respond to oxygen therapy
    • Making the diagnosis
      • based on clinical presentation and laboratory studies
        • carboxyhemoglobin levels > 20%
  • Treatment
    • Management approach
      • remove all sources of CO from the patient
      • 100% or hyperbaric oxygen
    • First-line
      • 100% oxygen
        • to displace CO from hemoglobin
        • decreases half-life of CO in most patients from 4-5 hours to 1 hour
        • decreases half-life of CO from methylene chloride from 13 hours to 6 hours
    • Second-line
      • hyperbaric oxygen
        • indication
          • neurological deficits
          • pregnant women
          • children
          • elderly
          • significantly elevated COHb levels
          • methylene chloride as cause of CO poisoning
  • Complications
    • Myocarditis
    • Acute respiratory distress syndrome
  • Prognosis
    • Worse with very young or very old age
    • Worse with prolonged or intentional exposures
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