Rosen & Barkin's 5-Minute Emergency Medicine Consult (124 page)

• Endogenous:
  
  • Result of normal metabolism
    
• Incomplete combustion of carbonaceous fossil fuel:
  
  • Internal combustion engines
    
  • Natural gas
    
  • Heaters
    
  • Indoor grills
    
  • Fireplaces
    
  • Furnaces
    
  • Accidental fires
    
  • Tobacco smoke
    
• Methylene chloride:
  
  • Found in some solvents for paint removal and furniture stripping
    
  • Converted in vivo to CO after exposure
    
  • Peak carboxyhemoglobin levels delayed after exposure
    
  • Half-life is ∼2 times that of inhaled CO
    

DIAGNOSIS

• CNS:
  
  • Headache
    
  • Dizziness
    
  • Ataxia
    
  • Confusion
    
  • Syncope
    
  • Seizures
    
• GI:
  
  • Nausea
    
  • Vomiting
    
• Cardiovascular:
  
  • Chest pain
    
  • Palpitations
    
• Respiratory:
  
  • Dyspnea
    
• Ophthalmologic:
  
  • Decreased visual acuity
    

• CNS:
  
  • Acute encephalopathy
    
  • Seizures
    
  • Coma
    
• Cardiovascular:
  
  • Tachycardia
    
  • Premature ventricular contractions
    
  • Dysrhythmias
    
  • Myocardial ischemia/infarction
    
• Respiratory:
  
  • Tachypnea
    
  • Noncardiogenic pulmonary edema
    
• Ophthalmologic:
  
  • Retinal hemorrhage
    
• Other:
  
  • Respiratory alkalosis
    
  • Rhabdomyolysis
    
  • Lactic acidosis
    

• History:
  
  • Maintain a high index of suspicion
    
  • Symptoms may be mild, nonspecific
    
  • Inquire about the following:
    
    • Similar symptoms in other household members
      
    • Malfunctioning furnaces
      
    • Use of space heaters, open ovens for supplemental heat
      
    • Ill pets
      
• Arterial blood gas:
  
  • Normal PaO
    ₂
    
  • Normal calculated O
    ₂
    saturation
    
  • Low measured O
    ₂
    saturation
    
  • Metabolic acidosis in severe cases
    
• Carboxyhemoglobin level:
  
  • Measure as soon as possible
    
  • Level may not reflect clinical severity:
    
    • Patient may be critically ill despite unimpressive carboxyhemoglobin level.
      
    • May be misleadingly low if significant time has passed since exposure
      
    • Normal range is 0–3% (up to 10% in smokers).
      

• Pulse oximetry:
  
  • Falsely elevated SaO
    ₂
    reading
    
  • Pulse oximeter cannot distinguish oxyhemoglobin from carboxyhemoglobin.
    
• Electrolytes:
  
  • Metabolic acidosis and elevated anion gap associated with increased clinical severity
    
• Cardiac enzymes:
  
  • When myocardial ischemia/infarction suspected
    
• Pregnancy test
  
• ECG:
  
  • CO may precipitate myocardial ischemia/infarction.
    
  • Dysrhythmias
    
  • Nonspecific ST-segment and T-wave abnormalities
    

• Chest radiography:
  
  • Pulmonary edema
    
• CT scan of the head:
  
  • To evaluate for intracranial causes of altered mental status when indicated
    
  • Bilateral globus pallidus low-density lesions may be clue to CO poisoning in unclear cases.
    

• Viral illness/viral syndrome
  
• Meningitis/encephalitis
  
• Intracranial hemorrhage
  
• Gastroenteritis
  
• Migraine headache
  
• Tension headache
  
• Ethanol intoxication
  
• Sedative–hypnotic overdose
  
• Cyanide poisoning
  
• Salicylate overdose
  
• Toxic alcohol exposure
  

TREATMENT

Administer 100% O
₂

• ABCs
  
• Establish IV access
  
• 100% oxygen
  
• Cardiac monitor
  

• Oxygen:
  
  • Administer 100% normobaric O
    ₂
    :
    
    • Via face mask or endotracheal tube
      
  • Continue O
    ₂
    therapy until carboxyhemoglobin level <10%.
    
  • Half-life of carboxyhemoglobin:
    
    • ∼300 min in ambient air
      
    • ∼90 min in 100% normobaric O
      ₂
      
    • ∼20 min at 3 atm (hyperbaric O
      ₂
      )
      
• Hyperbaric O
  ₂
  :
  
  • Dose:
    
    • 100% O
      ₂
      at 3 atm
      
    • May be repeated
      
  • Benefits:
    
    • May reduce delayed neurologic sequelae
      
    • Decreases half-life of carboxyhemoglobin
      
  • Potential adverse effects:
    
    • Tympanic membrane rupture
      
    • Pneumothorax
      
    • Seizure
      
    • Decompression sickness
      
    • Pulmonary edema
      
  • Use of hyperbaric O
    ₂
    remains controversial
    
  • Indications for consulting hyperbaracist:
    
    • Altered mental status/coma
      
    • Focal neurologic deficits
      
    • Seizures
      
    • Cardiovascular compromise (infarction, persistent dysrhythmia)
      
    • Persistent metabolic acidosis
      
    • Carboxyhemoglobin level >25%
      
    • Pregnancy with carboxyhemoglobin level >10%
      

• Fetal hemoglobin has higher affinity for CO than adult hemoglobin.
  
• Fetal carboxyhemoglobin levels 10–15% higher than maternal levels
  
• Delayed clearance of fetal carboxyhemoglobin compared with maternal
  

FOLLOW-UP

• Persistent symptoms after 4 hr of treatment with 100% oxygen
  
• Evidence of myocardial ischemia or cardiac instability
  
• Seizures
  
• Persistent metabolic acidosis
  
• Syncope
  

• Asymptomatic after 4 hr of observation
  
• Absence of aforementioned admission criteria
  
• Psychiatric clearance if suicidal exposure
  

Need for hyperbaric oxygen therapy

Contact local fire department in cases of CO home exposures.

• Suspect CO poisoning in patients who present with headaches when home heaters are initiated.
  
• Suspect CO poisoning when family members living in the same enclosed space have similar symptoms.
  
• Administer 100% O
  ₂
  and transfer to hyperbaric facility if the above-described criteria is met.
  

• Buckley NA, Juurlink DN, Isbister G, et al. Hyperbaric oxygen for carbon monoxide poisoning.
  Cochrane Database Syst Rev
  . 2011;13(4):CD002041.
  
• Guzman JA. Carbon monoxide poisoning.
  Crit Care Clin
  . 2012;28(4):537–548.
  
• Kao LW, Nanagas KA. Carbon monoxide poisoning.
  Emerg Med Clin North Am
  . 2004;22(4):985–1018.
  
• Weaver LK. Carbon monoxide poisoning.
  N Engl J Med
  . 2009;360:1217–1225.
  

See Also (Topic, Algorithm, Electronic Media Element)

Hyperbaric Oxygen

CODES