carbon monoxide poisoning

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Carbon Monoxide Poisoning



Carbon monoxide (CO) poisoning occurs when carbon monoxide gas is inhaled. CO is a colorless, odorless, highly poisonous gas that is produced by incomplete combustion. It is found in automobile exhaust fumes, faulty stoves and heating systems, fires, and cigarette smoke. Other sources include woodburning stoves, kerosene heaters, improperly ventilated water heaters and gas stoves, and blocked or poorly maintained chimney flues. CO interferes with the ability of the blood to carry oxygen. The result is headache, nausea, convulsions, and finally death by asphyxiation.


Carbon monoxide, sometimes called coal gas, has been known as a toxic substance since the third century B.C. It was used for executions and suicides in early Rome. Today it is the leading cause of accidental poisoning in the United States. According to the Journal of the American Medical Association, 2,000 Americans die each year from accidental exposure to CO, and another 2,300 from intentional exposure (suicide). An additional 10,000 people seek medical attention after exposure to CO. The Consumer Products Safety Commission eported in 2004 that about 64% of unintentional CO poisoning deaths occur in the home.
Anyone who is exposed to CO will become sick, and the entire body is involved in CO poisoning. A developing fetus can also be poisoned if a pregnant woman breathes CO gas. Infants, people with heart or lung disease, or those with anemia may be more seriously affected. People such as underground parking garage attendants who are exposed to car exhausts in a confined area are more likely to be poisoned by CO. Firemen also run a higher risk of inhaling CO.

Causes and symptoms

Normally when a person breathes fresh air into the lungs, the oxygen in the air binds with a molecule called hemoglobin (Hb) that is found in red blood cells. This allows oxygen to be moved from the lungs to every part of the body. When the oxygen/hemoglobin complex reaches a muscle where it is needed, the oxygen is released. Because the oxygen binding process is reversible, hemoglobin can be used over and over again to pick up oxygen and move it throughout the body.
Inhaling carbon monoxide gas interferes with this oxygen transport system. In the lungs, CO competes with oxygen to bind with the hemoglobin molecule. Hemoglobin prefers CO to oxygen and accepts it more than 200 times more readily than it accepts oxygen. Not only does the hemoglobin prefer CO, it holds on to the CO much more tightly, forming a complex called carboxyhemoglobin (COHb). As a person breathes CO contaminated air, more and more oxygen transportation sites on the hemoglobin molecules become blocked by CO. Gradually, there are fewer and fewer sites available for oxygen. All cells need oxygen to live. When they don't get enough oxygen, cellular metabolism is disrupted and eventually cells begin to die.
The symptoms of CO poisoning and the speed with which they appear depend on the concentration of CO in the air and the rate and efficiency with which a person breathes. Heavy smokers can start off with up to 9% of their hemoglobin already bound to CO, which they regularly inhale in cigarette smoke. This makes them much more susceptible to environmental CO. The Occupational Safety and Health Administration (OSHA) has established a maximum permissible exposure level of 50 parts per million (ppm) over eight hours.
With exposure to 200 ppm for two to three hours, a person begins to experience headache, fatigue, nausea, and dizziness. These symptoms correspond to 15-25% COHb in the blood. When the concentration of COHb reaches 50% or more, death results in a very short time. Emergency room physicians have the most experience diagnosing and treating CO poisoning.
The symptoms of CO poisoning in order of increasing severity include:
  • headache
  • shortness of breath
  • dizziness
  • fatigue
  • mental confusion and difficulty thinking
  • loss of fine hand-eye coordination
  • nausea and vomiting
  • rapid heart rate
  • hallucinations
  • inability to execute voluntary movements accurately
  • collapse
  • lowered body temperature (hypothermia)
  • coma
  • convulsions
  • seriously low blood pressure
  • cardiac and respiratory failure
  • death
In some cases, the skin, mucous membranes, and nails of a person with CO poisoning are cherry red or bright pink. Because the color change doesn't always occur, it is an unreliable symptom to rely on for diagnosis.
Although most CO poisoning is acute, or sudden, it is possible to suffer from chronic CO poisoning. This condition exists when a person is exposed to low levels of the gas over a period of days to months. Symptoms are often vague and include (in order of frequency) fatigue, headache, dizziness, sleep disturbances, cardiac symptoms, apathy, nausea, and memory disturbances. Little is known about chronic CO poisoning, and it is often misdiagnosed.


The main reason to suspect CO poisoning is evidence that fuel is being burned in a confined area, for example a car running inside a closed garage, a charcoal grill burning indoors, or an unvented kerosene heater in a workshop. Under these circumstances, one or more persons suffering from the symptoms listed above strongly suggests CO poisoning. In the absence of some concrete reason to suspect CO poisoning, the disorder is often misdiagnosed as migraine headache, stroke, psychiatric illness, food poisoning, alcohol poisoning, or heart disease.
Concrete confirmation of CO poisoning comes from a carboxyhemoglobin test. This blood test measures the amount of CO that is bound to hemoglobin in the body. Blood is drawn as soon after suspected exposure to CO as possible.
Other tests that are useful in determining the extent of CO poisoning include measurement of other arterial blood gases and pH; a complete blood count; measurement of other blood components such as sodium, potassium, bicarbonate, urea nitrogen, and lactic acid; an electrocardiogram (ECG); and a chest x ray.


Immediate treatment for CO poisoning is to remove the victim from the source of carbon monoxide gas and get him or her into fresh air. If the victim is not breathing and has no pulse, cardiopulmonary resuscitation (CPR) should be started. Depending on the severity of the poisoning, 100% oxygen may be given with a tight fitting mask as soon as it is available.
Taken with other symptoms of CO poisoning, COHb levels of over 25% in healthy individuals, over 15% in patients with a history of heart or lung disease, and over 10% in pregnant women usually indicate the need for hospitalization. In the hospital, fluids and electrolytes are given to correct any imbalances that have arisen from the breakdown of cellular metabolism.
In severe cases of CO poisoning, patients are given hyperbaric oxygen therapy. This treatment involves placing the patient in a chamber breathing 100% oxygen at a pressure of more than one atmosphere (the normal pressure the atmosphere exerts at sea level). The increased pressure forces more oxygen into the blood. Hyperbaric facilities are specialized, and are usually available only at larger hospitals.


The speed and degree of recovery from CO poisoning depends on the length and duration of exposure to the gas. The half-life of CO in normal room air is four to five hours. This means that, in four to five hours, half of the CO bound to hemoglobin will be replaced with oxygen. At normal atmospheric pressures, but breathing 100% oxygen, the half-life for the elimination of CO from the body is 50-70 minutes. In hyperbaric therapy at three atmospheres of pressure, the half-life is reduced to 20-25 minutes.
Although the symptoms of CO poisoning may subside in a few hours, some patients show memory problems, fatigue, confusion, and mood changes for two to four weeks after their exposure to the gas.


Carbon monoxide poisoning is preventable. Particular care should be paid to situations where fuel is burned in a confined area. Portable and permanently installed carbon monoxide detectors that sound a warning similar to smoke detectors are available for less than $50. Specific actions that will prevent CO poisoning include:
  • stopping smoking. Smokers have less tolerance to environmental CO
  • having heating systems and appliances installed by a qualified contractor to assure that they are properly vented and meet local building codes
  • inspecting and properly maintaining heating systems, chimneys, and appliances
  • not using a gas oven or stove to heat the home
  • not burning charcoal indoors
  • making sure there is good ventilation if using a kerosene heater indoors
  • not leaving cars or trucks running inside the garage
  • keeping car windows rolled up when stuck in heavy traffic, especially if inside a tunnel



"Silencing the Silent Killer." USA Today Magazine March 2004: 77.


American Lung Association. 1740 Broadway, New York, NY 10019. (800) 586-4872.


"Carbon Monoxide Headquarters." Wayne State University School of Medicine. 〈〉.

Key terms

Carboxyhemoglobin (COHb) — Hemoglobin that is bound to carbon monoxide instead of oxygen.
Hemoglobin (Hb) — A molecule that normally binds to oxygen in order to carry it to our cells, where it is required for life.
Hypothermia — Development of a subnormal body temperature.
pH — A measurement of the acidity or alkalinity of a fluid. A neutral fluid, neither acid nor alkali, has a pH of 7.

carbon monoxide

a colorless, odorless, tasteless gas, CO, formed by burning carbon or organic fuels with a scanty supply of oxygen; it is the number one cause of unintentional poisoning around the world (see carbon monoxide poisoning). Inhalation causes central nervous system damage and asphyxiation. Carbon monoxide is present in the exhaust of gasoline engines, in the smoke of wood and coal fires, in manufactured gas such as that used in the household, and wherever carbon burns without a sufficient supply of oxygen.
carbon monoxide poisoning poisoning by carbon monoxide, the most common type of gas poisoning around the world. When the gas is inhaled and comes in contact with the blood, it combines more readily with hemoglobin than oxygen does. Thus it takes the place of oxygen in the erythrocytes, and the tissues are deprived of their normal oxygen supply. The symptoms of carbon monoxide poisoning begin with dizziness, headache, weakness, shortness of breath, and sometimes nausea; the skin and mucous membranes become cherry red in color. Unconsciousness follows, with death from asphyxia if a large enough quantity is inhaled.
Treatment. The victim of acute carbon monoxide poisoning should be moved immediately to an open area with fresh air. Administration of 100 per cent oxygen or hyperbaric oxygen via face mask may be indicated.
Prevention. Cases of carbon monoxide poisoning are usually accidental. It should be remembered that carbon monoxide has no odor and its presence may not be detected unless other gases, such as exhaust fumes from an automobile motor, are also escaping. Care should be taken to ensure proper ventilation of working and sleeping areas. It is extremely dangerous to leave an automobile motor running in a closed garage. Stoves and furnaces should be kept in good repair. Burners using gas, especially in a bedroom, should have a ventilator pipe to carry the exhaust to the outside.

car·bon mon·ox·ide poi·son·ing

a potentially fatal acute or chronic intoxication caused by inhalation of carbon monoxide gas, which has an affinity 210 times that of oxygen for binding with hemoglobin (carboxyhemoglobinemia) and thus interferes with the transportation of oxygen and carbon dioxide by the blood.

carbon monoxide poisoning

a toxic condition in which carbon monoxide gas has been inhaled and binds to hemoglobin molecules, thus displacing oxygen from the red blood cells and decreasing the capacity of the blood to carry oxygen to the cells of the body. Characteristically, headache, dyspnea, drowsiness, confusion, cherry-pink skin, unconsciousness, and apnea occur in sequence as the level of carbon monoxide in the blood increases. Cherry-red skin is a late sign most commonly noted in fatalities. The most common source of carbon monoxide in cases of poisoning is exhaust fumes from an automobile.

carbon monoxide poisoning

Intoxication due to excess carbon monoxide (CO) in ambient air, from accidental or suicidal inhalation. CO levels in normal non-smokers = 0.25–2.1%; smoking and certain industrial exposures can result in levels up to 10%.
Types, carbon monoxide poisoning
Suicidal (more common); accidental due to incomplete combustion of fuel; structural defects in fume venting in older buildings.
Clinical findings
Acute symptoms occur at 20% concentration (of CO in blood); severe symptoms at 30%; headache and confusion at 40–50%; unconciousness and seizures at 60–70%; ≥60% can be fatal. The skin of someone dying from carbon monoxide, especially in dependent areas of hypostasis, is classically described as having a cherry-pink colour, which is not seen below 30%.

Hyperbaric oxygen.

Carbon monoxide poisoning (effect of CO concentrations in ambient air)
0.08%—Dizziness, nausea, convulsions in 45 minutes; loss of consciousness in 2 hours.

0.64%—Headache, dizziness in 1–2 minutes; convulsions, respiratory arrest, death in < 20 minutes.

1.28%—Unconsciousness after 2–3 breaths; death in < 3 minutes.

carbon monoxide poisoning

Emergency medicine Intoxication caused by excess of carbon monoxide in ambient air, due to either smoke inhalation or suicide attempts Clinical Acute Sx occur at 20% concentration–of CO in blood, severe symptoms at 30%, headache and confusion at 40–50%, unconciousness and seizures as 60–70%, and ≥60% can be fatal; levels in normal nonsmokers = 0.25–2.1%, with smokers and certain industrial-exposed individuals having up to 10% Management Hyperbaric oxygen. See Hyperbaric oxygen therapy.

car·bon mon·ox·ide poi·son·ing

(kahr'bŏn mŏ-noks'īd poy'zŏn-ing)
A potentially fatal acute or chronic intoxication caused by inhalation of carbon monoxide gas, which competes favorably with oxygen for binding with hemoglobin (carboxyhemoglobinemia) and thus interferes with the transportation of oxygen and carbon dioxide by the blood.

car·bon mon·ox·ide poi·son·ing

(kahr'bŏn mŏ-noks'īd poy'zŏn-ing)
Potentially fatal acute or chronic intoxication caused by inhalation of carbon monoxide gas.

carbon monoxide

a colorless, odorless, tasteless gas, CO, formed by burning carbon or organic fuels with a scanty supply of oxygen; inhalation causes central nervous system damage and asphyxiation. Carbon monoxide is present in the exhaust of petrol engines, in the smoke of wood and coal fires, in manufactured gas such as that used in the household, and wherever carbon burns without a sufficient supply of oxygen. Used as a euthanizing agent for dogs and laboratory animals.

carbon monoxide poisoning
poisoning by carbon monoxide; one of the most common types of gas poisoning. When carbon monoxide is inhaled, it comes in contact with the blood and combines with hemoglobin. Since carbon monoxide combines more readily with hemoglobin than does oxygen, it takes the place of oxygen in the erythrocytes, and the tissues are thus deprived of their normal oxygen supply. Death from asphyxia results if a large enough quantity of carbon monoxide is inhaled. Because death is very sudden, carbon monoxide has been used as a euthanatizing agent for dogs in large numbers. It is not widely used because of the danger to human attendants and the difficulty in maintaining a CO generator in good condition for long periods.
References in periodicals archive ?
Work-up for suspected CO poisoning includes ABG, COHb level, CBC, basic metabolic panel, EKG, cardiac enzymes, and chest radiography, as well as other laboratory tests as deemed appropriate.
Berry said the effects of CO poisoning are cumulative and produce flu-like symptoms.
In the UK, there are more than 4,000 visits to accident and emergency for treatment of CO poisoning - which can often lead to lasting neurological damage.
Methods to confirm CO poisoning in the body require specialist equipment that is frequently used long after the patient has stopped being exposed to CO, making it much more difficult to determine if a person has been exposed since CO can be rapidly eliminated from the body.
Gas Safe Register is therefore sharing the following barbecue safety tips and urging people to keep themselves safe by learning the symptoms of CO poisoning.
The cardiac effects of CO poisoning include angina, arrhythmia, cardiomyopathy, cardiogenic shock, and even sudden death (1).
CO poisoning mortality and morbidity surveillance is a collaboration between the Air Pollution and Respiratory Health Branch (APRHB) and the Environmental Health Tracking Branch.
For more on the symptoms of CO poisoning or what to do if you suspect a gas leak, see: http://www.
Sami Ulus Maternity, Children's Health and Diseases Training and Research Hospital, Department of Pediatric Emergency Medicine with CO poisoning between January 2005 and 2013 were retrospectively analyzed.
A case of CO poisoning was defined as a blood COHb level >5.
In the United States, unintentional CO poisoning is responsible for approximately 15,000 emergency department (ED) visits and nearly 500 deaths annually.
6) The incidence of CO poisoning is higher during the winter months and after natural disasters.