Carbon Monoxide Poisoning

Aka: Carbon Monoxide Poisoning, Carbon Monoxide, Carbon Monoxide Toxicity

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II. Epidemiology

  1. Emergency Department visits per year: 50,000 in U.S.
  2. Leading cause of toxin related death in United States
    1. Accidental or Intentional (Suicide) deaths per year: 5000

III. Sources: Carbon Monoxide

  1. Gas powered engine
    1. Car with faulty exhaust system
    2. Passengers riding in back of a pickup truck
    3. Swimmers at back of a houseboat
    4. Propane fueled forklifts
    5. Ice skating rink Zamboni
    6. Indoor tractor pulls
  2. Home
    1. Indoor Heaters (most common cause)
      1. Furnace
      2. Home water heaters
      3. Gas heaters
      4. Pool heaters
      5. Kerosene heaters
    2. Indoor Flames
      1. Wood stoves
      2. Indoor charcoal fires
      3. Sterno fuel
    3. Tobacco smoke
      1. Tobacco Smokers
        1. Carboxyhemoglobin levels may reach 6-10%
      2. Hookah Smokers
        1. Carboxyhemoglobin levels may reach 15-20%
      3. Nonsmokers exposed to passive smoke
        1. Cigarette tip 2.5 fold greater CO than inhaled
  3. Industrial or Occupational
    1. Fire fighters
    2. Steel foundry
    3. Pulp paper mill
    4. Formaldehyde and coke producing plants
    5. Methylene Chloride
      1. Found in paint strippers and industrial solvents
      2. Transdermal exposure or inhalational (esp. in poorly ventilated areas)
      3. Cytochrome P450 2E1 (CYP2E1) oxidizes methylene chloride to formyl chloride, which is metabolized to CO
      4. Carbomyl bromide (another industrial chemical) may also cause similar effects
  4. Fire
    1. Building or structure fire
    2. Wilderness fire
  5. Suicide Attempt
    1. Closed garage with car Running
    2. Ingestion of formic acid and sulfuric acid (sulphuric acid)
      1. Combination yields Carbon Monoxide
      2. Strong acid fumes may also result in Burn Injury and lung injury
      3. Swadron and Nordt (2022) EM:Rap 22(6): 5-7

IV. Pathophysiology

  1. Carbon Monoxide Properties (no warning features that gas is present until symptoms develop)
    1. Colorless
    2. Odorless
    3. Non-irritating gas
    4. Small molecule that crosses through some barriers into closed spaces (e.g. drywall)
  2. Exposures leading to Toxicity
    1. Carbon Monoxide Toxicity occurs at Ambient levels >200-500 parts per million
    2. More severe illness occurs with longer exposure times
  3. Carbon Monoxide inhalation
    1. Carbon Monoxide has a high affinity for Hemoglobin (>200-250 times higher affinity than oxygen)
      1. In the tissues, Carbon Monoxide binds myoglobin
    2. Displaces Oxygen and produces Carboxyhemoglobin (COHb)
      1. Impairs oxygen off-loading from Hemoglobin And oxygen tissue delivery
      2. Shifts oxygen dissociation curve left with poor delivery of any residual oxygen to tissues
      3. Functional Anemia is however not responsible for Carbon Monoxide's lethal effects
  4. Direct neurotoxic effects of Carbon Monoxide
    1. Mechanisms of Carbon Monoxide neurotoxicity
      1. Mitochondrial dysfunction
        1. Binds cytochrome oxidase (Complex 4)
      2. Displaces nitric oxide
        1. Nitric oxide levels increase and result in CNS micovascular effects
    2. Inflammatory cascade (responsible for neurologic toxicity)
      1. White Blood Cell response
      2. Glutamic Acid (inflammatory)
      3. Free radicals
    3. Neurotoxicity effects
      1. Basal Ganglia (Parkinsonism)
      2. Occiput (occipital blindness)
      3. Frontal cortex (personality change)
  5. Other toxicity
    1. Indirect Sodium channel activation

V. History

  1. Multiple persons (e.g. family, coworkers, pets) in the same environment with similar symptoms

VI. Symptoms

  1. Dull, frontal, constant Headache (88%)
  2. Dizziness (83%)
  3. Nausea (75%)
  4. Drowsiness (75%)
  5. Dry Mouth (44%)
  6. Syncope
  7. Hypotension
  8. Chest Pain
  9. Shortness of Breath
  10. Blurred Vision
  11. Myalgias
    1. Carbon Monoxide also binds myoglobin

VII. Signs

  1. Precautions
    1. Do NOT rely on Oxygen Saturations (not accurate see below)
    2. Do NOT use Co-Oximetry devices (inaccurate; used to measure total Hemoglobin, not Carboxyhemoglobin)
  2. Cherry-red skin and mucosa
    1. Late or post-mortem finding
  3. Bounding Pulse
  4. Hypertension
  5. Neurologic
    1. Muscular Fasciculations
    2. Stertorous breathing
    3. Dilated pupils
    4. Convulsions
    5. Altered Mental State to coma

VIII. Findings: Carboxyhemoglobin level

  1. Carboxyhemoglobin: 10%
    1. Frontal Headache
  2. Carboxyhemoglobin: 20%
    1. Throbbing Headache
    2. Dyspnea on exertion
      1. Severe Hypoxemia requiring intubation may occur at this level
  3. Carboxyhemoglobin: 30%
    1. Impaired judgment
    2. Nausea or Vomiting
    3. Dizziness
    4. Visual disturbance
    5. Fatigue
  4. Carboxyhemoglobin: 40%
    1. Confusion
    2. Syncope
  5. Carboxyhemoglobin: 50%
    1. Coma
    2. Seizures
  6. Carboxyhemoglobin: 60%
    1. Hypotension
    2. Respiratory Failure
  7. Carboxyhemoglobin: 70%
    1. Death

IX. Pharmacokinetics

  1. Elimination Half-Life (via ventilation): 4 hours
  2. Half-Life decreases to 1-2 hours with 100% Supplemental Oxygen

X. Labs

  1. Blood grossly appears abnormal red color
  2. Venous Blood Gas
  3. Carboxyhemoglobin
    1. Normal background Carboxyhemoglobin is 2-3%
    2. Carboxyhemoglobin elevated >25% is significant and associated with toxicity
      1. See above for findings related to Carboxyhemoglobin levels
  4. Complete Blood Count
    1. Leukocytosis
  5. Lactic Acid
  6. Serum Troponin
  7. Creatine Phosphokinase (CPK)
  8. bHCG (Pregnancy Test in women of child-bearing age)

XI. Precautions

  1. Oxygen Saturation (Pulse Oximeter) data is inaccurate
    1. Does not distinguish Carboxyhemoglobin from oxygenated Hemoglobin
  2. Drywall does not deter Carbon Monoxide
    1. Carbon Monoxide diffuses across drywall and may permeate separated rooms in multi-tenant housing
  3. Consider concurrent Cyanide toxicity in structure fires
    1. Smoke Inhalation and Lactic Acid >8 suggests cyanide Poisoning
    2. Especially with Altered Level of Consciousness
  4. Start oxygen while awaiting lab testing results if higher level of suspicion
    1. Start 100% oxygen via non-rebreather
  5. Hyperglycemia is a Neurotoxin and worsens outcomes
    1. Consider Insulin for Glucose >300 mg/dl

XII. Management: Mild Poisoning

  1. Criteria
    1. Carboxyhemoglobin <30%
    2. No Neurologic or Cardiovascular Impairment
  2. Management
    1. Oxygen 100% Non-Rebreathing Mask
      1. Continue until Carboxyhemoglobin <5%
      2. Carbon Monoxide decreases 50% in 6 hours on room air
      3. Carbon Monoxide decreases 50% in 60 minutes on Non-Rebreather Mask
      4. Carbon Monoxide decreases 50% in 30 minutes on 100% oxygen while intubated
    2. Continuous Positive Airway Pressure (CPAP) with oxygen lowers Carbon Monoxide faster than oxygen alone
      1. Bal (2020) Eur J Emerg Med 27(3):217-22 +PMID:31815874 [PubMed]
    3. Hyperbaric Oxygen Indications
      1. See Hyperbaric Oxygen below
      2. Carboxyhemoglobin >25% and associated factors (cardiac or neurologic findings, age >36 years old)
      3. Consider in Pregnancy
    4. Other measures
      1. Consider Dexamethasone 10 mg daily for 3 days
        1. Kim (2023) Clin Toxicol 61(2):98-103 +PMID: 36744989 [PubMed]
    5. Admission criteria
      1. All patients with Carboxyhemoglobin >25%
      2. Abnormal cardiac exam or lab markers
      3. Underlying heart disease
      4. Persistent neurologic symptoms

XIII. Management: Moderate Poisoning

  1. Criteria
    1. Carboxyhemoglobin: 30-40%
    2. No Neurologic Impairment
  2. Management
    1. Oxygen 100% Non-Rebreathing Mask
      1. Continue until Carboxyhemoglobin <5% (see above)
    2. Admission to telemetry (cardiovascular monitor)
    3. Other measures
      1. Consider Dexamethasone 10 mg daily for 3 days
        1. Kim (2023) Clin Toxicol 61(2):98-103 +PMID: 36744989 [PubMed]
    4. Consider hyperbaric oxygen (see below)
      1. Cerebellar signs
      2. Focal neurologic deficit
      3. Persistent severe Headache
      4. Loss of consciousness, Seizure or coma
      5. Glasgow Coma Scale (GCS) <15
      6. Age >36 years old
      7. Prolonged Carbon Monoxide exposure
    5. Venous Blood Gas
      1. Determine acid-base status

XIV. Management: Severe Poisoning

  1. Criteria
    1. Carboxyhemoglobin: >40%
    2. Neurologic Impairment
  2. Management
    1. Oxygen 100% Non-Rebreathing Mask
      1. Continue until Carboxyhemoglobin <5% (see above)
    2. Admission to telemetry (cardiovascular monitor)
    3. Endotracheal Intubation may be required due to severe Hypoxemia
    4. Venous Blood Gas
      1. Follow acid-base status
    5. Other measures
      1. Consider Dexamethasone 10 mg daily for 3 days
        1. Kim (2023) Clin Toxicol 61(2):98-103 +PMID: 36744989 [PubMed]
    6. Extracorporeal Membrane Oxygenation (VA-ECMO)
      1. Indicated in refractory cardiovascular collapse
    7. Hyperbaric oxygen (see below)
      1. Ideally performed within 6 hours of presentation
      2. Chamber immediately available OR
      3. No improvement in 4 hours
        1. Cardiovascular status
        2. Neurologic status

XV. Management: Hyperbaric oxygen chamber

  1. Mechanism
    1. Carbon Monoxide decreases 50% in 20-30 minutes on hyperbaric oxygen at 2.8 atm
    2. Allows oxygen to dissolve in blood at a much greater extent (beyond Hemoglobin binding)
    3. Decreases inflammatory cascade
    4. Decreases reperfusion injury
  2. Efficacy
    1. Decreases risk of delayed neuropsychiatric effects
      1. Reduces risk of personality change, Parkinsonism, cognitive effects
    2. Better short-term and long-term cognitive outcome
    3. Weaver (2002) N Engl J Med 347:1057-67 [PubMed]
    4. Rose (2018) Crit Care Med 46(7): e649-55 [PubMed]
  3. Indications
    1. Carboxyhemoglobin: >40%
    2. Carboxyhemoglobin: >25-30% and associated factors
      1. Neurologic Impairment or Altered Mental Status
      2. Transient or prolonged loss of consciousness
      3. Severe acidosis
      4. Cardiac involvement
      5. Abnormal neuropsychiatric findings
      6. Age >36 years old
    3. Carboxyhemoglobin: <15%
      1. Consider hyperbaric oxygen for pregnant patients

XVI. Complications

  1. Hypoxic Encephalopathy
    1. Delayed Neurological Sequelae or Delayed Neuropsychiatric Syndrome (DNS or D/PNS)
    2. Risk Factors
      1. Age >36 years
      2. Exposure for >24 hours
      3. Syncope
      4. Increased Lactic Acid level
      5. CT Brain white matter hypodense Subcortical Regions (including at Globus Pallidus)
        1. Appearance within 1 day of exposure is associated with poor prognosis
    3. Findings
      1. Cognitive effects may persist for weeks to months or even permanently (up to 15-40% of cases)
        1. Reduced risk with hyperbaric oxygen therapy (see above)
      2. Parkinsonism
      3. Occipital blindness
      4. Personality change
  2. Coronary ischemia or myocadial infarction
  3. Increased risk of Coronary Artery Disease
    1. Henry (2006) JAMA 295(4): 398-402 [PubMed]

XVII. Prevention

  1. Adequate Ventilation
  2. Carbon Monoxide detectors
    1. Alarm sounds when Ambient Carbon Monoxide levels are >50 parts per million
    2. Carbon Monoxide Toxicity occurs at Ambient levels >200-500 parts per million

XVIII. Resources

  1. Consumer Products Safety Commission
    1. http://www.cpsc.gov/en/safety-education/safety-education-centers/carbon-monoxide-information-center/

XIX. References

  1. Carroll (2025) Crit Dec Emerg Med 39(11): 36
  2. Kinker and Glauser (2021) Crit Dec Emerg Med 35(9): 19-27
  3. Moayedi and Swaminathan in Herbert (2016) EM:Rap 16(7): 13-14
  4. Nordt and Shoenberger in Herbert (2019) EM:Rap 19(1): 4-6
  5. Reisdorf (1996) in Tintinelli (1996)
  6. (1995) MMWR Morb Mortal Wkly Rep 44:765-7 [PubMed]

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