Carbon Monoxide Poisoning

Snapshot

• A 25-year-old woman is brought to the emergency room by her boyfriend after being found unconscious in her car in the garage while it was turned on. He reports that he is unsure but less than an hour had passed since he saw her in their kitchen. He denies any knowledge of suicidal ideation on her part. Her pulse oximetry is normal. Upon evaluation by the emergency medicine physician, she regains consciousness and reports a slight headache. She appears confused initially. After administration of 100% oxygen, she is alert and oriented to person, place, and time, and reports feeling better.

Introduction

• Clinical definition
  • carbon monoxide (CO) poisoning results from exposure to CO resulting in hypoxia
• 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
• Pathogenesis
  • mechanism
    • displaces oxygen from hemoglobin through competitive inhibition  
      • causes a left shift of the 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
• Prognosis
  • worse with very young or very old age
• worse with prolonged or intentional exposures

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
• a late finding of CO poisoning

Studies

• Pulse oximetry
  • normal oxygen saturation level
• Labs
  • ↑ carboxyhemoglobin 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
• Making the diagnosis
  • based on clinical presentation and laboratory studies
• carboxyhemoglobin levels > 20%

Differential

• Cyanide poisoning 
  • distinguishing factor
    • ↑ lactic acid
• does not respond to oxygen therapy

Treatment

• Management approach
  • remove all sources of CO from the patient
  • 100% or hyperbaric oxygen
• Medical
  • 100% oxygen
    • indication
      • first line
      • to displace CO from hemoglobin
      • decreases the half-life of CO in most patients from 4-5 hours to 1 hour
      • decreases the half-life of CO from methylene chloride from 13 hours to 6 hours
  • hyperbaric oxygen
    • indication
      • second-line
      • persistent altered mental status despite 100% oxygen administration
      • pregnant women
      • children
• methylene chloride as cause of CO poisoning

Complications

• Myocarditis
• Acute respiratory distress syndrome