Carbon Monoxide

Given the Planet Hoth like winter weather out there, we are likely to see a few cases of….

Carbon Monoxide Poisoning

Carbon Monoxide is a colorless, odorless and nonirritating gas produced by the incomplete combustion of carbonaceous materials. Thus, we often see an increase in presentations during the winter, secondary to the use of indoor heating sources. It is one of the most common causes of unintentional poisoning deaths in the United States.

Carbon Monoxide impairs oxygen delivery to the tissues because of the high binding of CO to hemoglobin. 240x the affinity of oxygen! And thus causes a left shift in the oxyhemoglobin dissociation curve.

High Risk Exposures: smoke inhalation, stoves, portable heaters, gasoline powder generators, automobile exhaust, charcoal grills, inhaling spray paint

In acute poisonings, you can see:

• Central Nervous System: headache (most common symptom), malaise, confusion, depression, impulsiveness, hallucinations, agitation, drowsiness, visual disturbances, syncope, seizure, coma
• Gastrointestinal symptoms: abdominal pain, nausea, vomiting, diarrhea
• Respiratory symptoms: shortness of breath
• Cardiac: chest pain, palpitations, myocardial injury
• Delayed Neuropsychiatric syndrome: can arise 3 –240 days after recovery
• Note: often diagnosed as a viral syndrome

Examination and Tests:

• Suspect it! If you do not consider it, you cannot diagnosis it
• Base work-up on the patient’s symptoms and clinical exam
• HbCO … elevated levels are significant, but, a normal level does not rule out exposure
• Level does not correlate well with the clinical signs and symptoms
• Normal: 0.4-3%
• Smokers: 0-5% (some can have up to 10-15%)
• Mild poisoning: greater than 10% without clinical symptoms
• Moderate poisoning: greater than 10% with minor clinical signs/symptoms (headache, fatigue)
• Severe poisoning: greater than 20% with loss of consciousness, confusions or signs for cardiac ischemia
• SpO2 is not helpful as standard pulse oximetry cannot screen for CO, as it does not differentiate carboxyhemoglobin from oxyhemoglobin
• ABG
• Lactic acid
• BMET (look for hyperglycemia, hypokalemia, renal failure)
• CPK (look for signs of rhabdomyolysis)
• CXR (if there are pulmonary symptoms)
• Head CT (in patients who do not improve rapidly)
• ECG
• Cardiac Enzymes (if abnormal ECG or history of cardiac disease)
• Cyanide level (if smoke exposure)

Management:

• Remove the patient from the source (duh!)
• ABCs
• Oxygen. Oxygen Administration enhances the elimination of carbon monoxide from the body.  If the patient is symptomatic in the Emergency Department, use a NRB.
• Carbon Monoxide half-life on room air is 4-5 hours
• Carbon Monoxide half-life on 100% NRB is about 60-90 minutes
• Carbon Monoxide half-life with HBO treatment is about 30 minutes
• Treat until asymptomatic
• If pregnant, consult OB as they may need treatment for 24 hours
• Consider transferring for hyperbaric treatment if COHb is greater than 25%, if there is evidence for ongoing end-organ ischemia, if there is severe metabolic acidosis (pH less than 7.1), if there was a loss of consciousness, or in pregnant women with a level greater than 20% or signs of fetal distress.
• Note: These are controversial
• Don't forget other potiental exposures!  Make sure everyone else has been removed from the environment