Basics
Description
- Carbon monoxide (CO) is a colorless, odorless, nonirritating gas.
- Binds to hemoglobin to form carboxyhemoglobin:
- Decreases O2-carrying capacity
- Direct cellular toxin
- Impairs cellular O2 utilization
Etiology
- 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
Signs and Symptoms
History
- CNS:
- Headache
- Dizziness
- Ataxia
- Confusion
- Syncope
- Seizures
- GI:
- Cardiovascular:
- Respiratory:
- Ophthalmologic:
Physical Exam
- CNS:
- Acute encephalopathy
- Seizures
- Coma
- Cardiovascular:
- Tachycardia
- Premature ventricular contractions
- Dysrhythmias
- Myocardial ischemia/infarction
- Respiratory:
- Tachypnea
- Noncardiogenic pulmonary edema
- Ophthalmologic:
- Other:
- Respiratory alkalosis
- Rhabdomyolysis
- Lactic acidosis
Essential Workup
- 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 PaO2
- Normal calculated O2 saturation
- Low measured O2 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).
Diagnosis Tests & Interpretation
Lab
- Pulse oximetry:
- Falsely elevated SaO2 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
Imaging
- Chest radiography:
- 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.
Differential Diagnosis
- 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
Pre-Hospital
Administer 100% O2
Initial Stabilization/Therapy
- ABCs
- Establish IV access
- 100% oxygen
- Cardiac monitor
Ed Treatment/Procedures
- Oxygen:
- Administer 100% normobaric O2:
- Via face mask or endotracheal tube
- Continue O2 therapy until carboxyhemoglobin level <10%.
- Half-life of carboxyhemoglobin:
- ~300 min in ambient air
- ~90 min in 100% normobaric O2
- ~20 min at 3 atm (hyperbaric O2)
- Hyperbaric O2:
- Dose:
- 100% O2 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 O2 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
Disposition
Admission Criteria
- Persistent symptoms after 4 hr of treatment with 100% oxygen
- Evidence of myocardial ischemia or cardiac instability
- Seizures
- Persistent metabolic acidosis
- Syncope
Discharge Criteria
- Asymptomatic after 4 hr of observation
- Absence of aforementioned admission criteria
- Psychiatric clearance if suicidal exposure
Issues for Referral
Need for hyperbaric oxygen therapy
Followup Recommendations
Contact local fire department in cases of CO home exposures.
Pearls and Pitfalls
- 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% O2 and transfer to hyperbaric facility if the above-described criteria is met.
Additional Reading
- 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
ICD9
986 Toxic effect of carbon monoxide
ICD10
- T58.11XA Toxic effect of carb monx from utility gas, acc, init
- T58.91XA Toxic effect of carb monx from unsp source, acc, init
- T58.92XA Toxic effect of carb monx from unsp source, self-harm, init
- T58.94XA Toxic effect of carb monx from unsp source, undet, init
- T58.8X1A Toxic effect of carb monx from oth source, accidental, init
SNOMED
- 17383000 Toxic effect of carbon monoxide (disorder)
- 95873000 carbon monoxide poisoning from faulty furnace AND/OR heater (disorder)
- 420057003 Accidental poisoning by carbon monoxide
- 242840004 Self poisoning by carbon monoxide (disorder)
- 95872005 Carbon monoxide poisoning from motor vehicle exhaust