What is Carbon Monoxide Poisoning?
Carbon monoxide poisoning is caused by exposure to a colourless, odourless gas known as carbon monoxide (CO). CO is found in combustion fumes. CO poisoning is usually caused by car or truck exhaust, wood stoves, and other fuel burning appliances, smoke from a fire or blocked fireplaces, nonelectric heaters, malfunctioning gas appliances, and faulty heating exhaust systems in the home or garage.
Known as a silent killer, CO displaces the oxygen in the bloodstream when the CO is mixed in the normal air you breathe. If a heater's combustion system malfunctions and CO seeps out of it, for example, the gas can kill people while they are asleep. CO poisoning typically occurs at home, in a garage or car, or in another enclosed space like a camper, trailer, or tent.
Who is at Risk?
Everyone is at risk for CO poisoning from combustion fumes, especially during the winter when windows are closed. Some people are more susceptible than others. These include babies, pregnant women, and people with heart problems, breathing problems, or anemia.
CO binds to hemoglobin with 200 times the affinity of oxygen. CO also shifts the oxygen dissociation curve to the left (the Haldane effect), which decreases oxygen release to tissues. CO can also bind cytochrome oxidase aa3/C and myoglobin. Reperfusion injury can occur when free radicals and lipid peroxidation are produced.
Treatment with HBOT
The treatment of CO poisoning with hyperbaric oxygen therapy (HBOT) is based upon the theory that oxygen competitively displaces CO from hemoglobin. While breathing room air, this process takes about 300 minutes. While on a 100% oxygen nonrebreather mask, this time is reduced to about 90 minutes. With HBOT, the time is shortened to 32 minutes. HBOT (but not normobaric oxygen) restores cytochrome oxidase aa3/C and helps to prevent lipid peroxidation. HBOT is also used to help prevent the delayed neurologic sequelae (DNS). Treatment instituted sooner is more effective.
Patients with CO poisoning can present with myriad symptoms that they may not initially attribute to CO poisoning, as CO is considered the “great imitator” of other illnesses. Presentation can include flulike symptoms such as headache, visual changes, dizziness, and nausea. More serious manifestations include loss of consciousness, seizures, chest pain, ECG changes, tachycardia, and mild to severe acidosis.
Candidates for HBOT are those who present with morbidity and mortality risks that include pregnancy and cardiovascular dysfunction and those who manifest signs of serious intoxication, such as unconsciousness (no matter how long a period), neurologic signs, or severe acidosis. CO-hemoglobin (Hgb) level usually does not correlate well with symptoms or outcome; many patients with CO-Hgb levels of 25-30% are treated.
Pregnant females often have a CO level that is 10-15% lower than the fetus. Fetal Hgb not only has a higher affinity for CO but also has a left-shifted oxygen dissociation curve compared with adult hemoglobin. Exposure to CO causes an even farther leftward shift, in both adult and fetal hemoglobin, and decreased oxygen release from maternal blood to fetal blood and from fetal blood to fetal tissues. Pregnant patients with CO-Hgb levels greater than 10% should be treated with HBOT.
The following documents are sourced from respected medical journals regarding Carbon Monoxide (CO) Poisoning and Hyperbaric Oxygen Therapy (HBOT).
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Journal of Medicine (Baltimore)
Volume 97, Issue 39, Pages 1–8
Published: August 2018
The New England Journal of Medicine
Volume 347, Issue 14, Pages 1057–1067
Published: October 2002
American Journal of Respiratory and Critical Care Medicine
Volume 176, Issue 5, Pages 491–497
Published: May 2007