Author: Dr. Nupur Shah, PGY3

BackgroundCarbon monoxide poisoning is the most common cause of injury and death due to poisoning worldwide. It has been estimated that more than 40,000 people per year seek medical attention for carbon monoxide poisoning in the United States. The CDC estimates that approximately 400 people die yearly from unintentional carbon monoxide exposure in the United States. 

Most common sources of carbon monoxideCarbon monoxide is produced secondarily from combustion of organic matter when there is limited oxygen supply which prevents complete oxidation to carbon dioxide CO2. Common sources that most people are familiar with include house fires, faulty furnaces, heaters, wood-burning stoves, internal combustion vehicle exhaust, electrical generators, and propane-fueled equipment such as portable stoves. Additionally, you should also consider gasoline-powered tools such as leaf blowers, lawn mowers, high-pressure washers. 

Pathophysiology Carbon monoxide is an odorless, tasteless, colorless gas, and thus many people that suffer from toxicity cannot sense its presence. When carbon monoxide enters the body, it binds to hemoglobin with greater affinity (nearly 240x more) than oxygen forming carboxyhemoglobin (CoHb) which results in impaired oxygen transport and utilization. 

Signs and Symptoms of Carbon Monoxide PoisoningTwo of the major factors that influence signs and symptoms include exposure duration and carbon monoxide level. Minor symptoms include fatigue, headache, malaise, nausea. More severe signs and symptoms include neurological complaints such as dizziness, confusion, ataxia. Most severe is when the degree of poisoning causes significant hypoxia causing major organ infarction: myocardial infarction and/or brain infarction. 

Diagnostic evaluation For all patients where you suspect carbon monoxide poisoning, immediately place patient on 100% non re-breather oxygen face mask until patient is asymptomatic. If patient is pregnant, the patient should be on 100% non re-breather oxygen face mask for 5x the length of time needed for carbon monoxide level to be less than 5%. The goal is to continue therapy until COHb level is less than 10, or less than 5 for pregnant patients. For more moderate or severe symptoms or CoHb > 25, consider end organ damage, and thus can obtain EKG/troponin, ABG with lactate, chemistry panel, CT head noncontrast for patients with neurological disturbances looking for cerebral edema or basal ganglia defects (literature has noted these may be present in severe CO poisoning). If the patient had underlying cardiac risk factors, they may have higher risk for cardiac ischemia. For COHb levels greater than 25 and patients with moderate symptoms, consider consulting a hyperbaricist for further management recommendations. Patients presenting comatose or with severely impaired mental status secondarily to carbon monoxide poisoning should be intubated without delay and mechanically ventilated using 100 percent oxygen. Additionally, if smoke inhalation caused carbon monoxide toxicity, you must also consider cyanide toxicity, and if there is suspicion, consider giving hydroxocobalamin, sodium thiosulfate. 

Treatment ConsiderationsStatistically, the mortality from carbon monoxide poisoned patients presenting to a hospital is around 3%. The main therapy is 100% oxygen until HbCO 3%. For HbCO levels greater than 20, hyperbaric therapy can be considered in consultation with a hyperbaricist. Hyperbaric therapy is utilized for prevention of long term neurologic dysfunction and has no proven mortality reduction.


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