Carbon monoxide poisoning

Definition

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 wood-burning 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.

Description

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.

Anyone who is exposed to CO becomes 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.

Demographics

Carbon monoxide is the leading cause of accidental poisoning in the United States. Experts estimate that 1,500 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 and recover.

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 process 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 do not 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 percent 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 to 25 percent COHb in the blood. When the concentration of COHb reaches 50 percent 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 the following:

• 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 does not always occur, it is an unreliable symptom to count 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.

When to call the doctor

A healthcare professional should be consulted whenever more than passing exposure to carbon monoxide is suspected. While waiting for help to arrive, a potentially affected person should be moved outdoors.

Diagnosis

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.

Treatment

Immediate treatment for CO poisoning is to remove the victim from the source of carbon monoxide gas and 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 percent 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 percent in healthy individuals, over 15 percent in people with a history of heart or lung disease, and over 10 percent in pregnant women usually indicate the need for hospitalization . In the hospital, fluids and electrolytes are given to correct imbalances that have arisen from the breakdown of cellular metabolism.

In severe cases of CO poisoning, individuals are given hyperbaric oxygen therapy. This treatment involves placing the person in a chamber in which the person breathes 100 percent 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.

Prognosis

The speed and degree of recovery from CO poisoning depends on the length of exposure to the gas and the concentration of carbon monoxide. The half-life of CO in normal room air is four to five hours, which 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 percent oxygen, the half-life for the elimination of CO from the body is 50 to 70 minutes. In hyperbaric therapy at three atmospheres of pressure, the half-life is reduced to between 20 and 25 minutes.

Although the symptoms of CO poisoning may subside in a few hours, some affected persons show memory problems, fatigue, confusion, and mood changes for two to four weeks after their exposure to the gas.

Prevention

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 under $50. Specific actions that prevent CO poisoning include the following:

• Stop smoking . Smokers have less tolerance to environmental CO.
• Have heating systems and appliances installed by a qualified contractor to assure that they are properly vented and meet local building codes.
• Inspect and properly maintain heating systems, chimneys, and appliances.
• Do not use a gas oven or stove to heat the home.
• Do not burn charcoal indoors.
• Make sure there is good ventilation if using a kerosene heater indoors.
• Do not leave cars or trucks running inside the garage.
• Keep car windows rolled up when stuck in heavy traffic, especially if inside a tunnel.

Parental concerns

Parents should not allow children to play in areas heated by kerosene space heaters or to use charcoal grills of any kind indoors.

KEY TERMS

Carboxyhemoglobin —Hemoglobin that is bound to carbon monoxide instead of oxygen.

Hemoglobin —An iron-containing pigment of red blood cells composed of four amino acid chains (alpha, beta, gamma, delta) that delivers oxygen from the lungs to the cells of the body and carries carbon dioxide from the cells to the lungs.

Hypothermia —A serious condition in which body temperature falls below 95°F (35 °C). It is usually caused by prolonged exposure to the cold.pH —A measurement of the acidity or alkalinity of a solution. Based on a scale of 14, a pH of 7.0 is neutral. A pH below 7.0 is an acid; the lower the number, the stronger the acid. A pH above 7.0 is a base; the higher the number, the stronger the base. Blood pH is slightly alkaline (basic) with a normal range of 7.36–7.44.

Resources

BOOKS

Braunwald, Eugene, et al, eds. "Hypoxia and Cyanosis." In Harrison's Principles of Internal Medicine, 15th ed. New York: McGraw Hill, 2001, pp. 214–6.

Carbon Monoxide Poisoning: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. San Diego, CA: Icon Health Publications, 2004.

Penney, David G. Carbon Monoxide Toxicity. Lakeland, FL: CRC Press, 2000.

Robertson, William O. "Chronic Poisoning: Trace Metals and Others." In Cecil Textbook of Medicine, 22nd ed. Edited by Lee Goldman, et al. Philadelphia: Saunders, 2003, pp. 91–9.

PERIODICALS

Harper A., and J. Croft-Baker. "Carbon monoxide poisoning: undetected by both patients and their doctors." Age and Ageing 33, no. 2 (2004): 105–9.

Huffman, S. M. "Exposure to carbon monoxide from material handling equipment." Journal of Occupational and Environmental Hygiene 1, no. 5 (2004): D54–6.

Piantadosi C. A. "Carbon monoxide poisoning." Undersea and Hyperbaric Medicine 31, no. 1 (2004): 167–77.

Thomassen, O., G. Brattebo, M. Rostrup. "Carbon monoxide poisoning while using a small cooking stove in a tent." American Journal of Emergency Medicine 22, no. 3 (2004): 204–6.

Vacchiano, G., and R. Torino. "Carbon-monoxide poisoning, behavioral changes and suicide: an unusual industrial accident." Journal of Clinical Forensic Medicine 8, no. 2 (2004): 86–92.

ORGANIZATIONS

American Academy of Clinical Toxicology. 777 East Park Drive, PO Box 8820, Harrisburg, PA 17105–8820. Web site: <www.clintox.org/index.html>.

American Academy of Emergency Medicine. 611 East Wells Street, Milwaukee, WI 53202. Web site: <www.aaem.org/>.

American Academy of Family Physicians. 11400 Tomahawk Creek Parkway, Leawood, KS 66211–2672. Web site: <www.aafp.org/>.

American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 60007–1098. Web site: <www.aap.org/default.htm>.

American Association of Poison Control Centers. 3201 New Mexico Avenue NW, Washington, DC 20016. Web site: <www.aapcc.org/>.

American College of Emergency Physicians. PO Box 619911, Dallas, TX 75261–9911. Web site: <www.acep.org/>.

American College of Hyperbaric Medicine. PO Box 25914–130, Houston, Texas 77265. Web site: <www.hyperbaricmedicine.org/>.

American College of Occupational and Environmental Medicine. 55 West Seegers Road, Arlington Heights, IL 60005. Web site: <www.acoem.org/>.

American College of Osteopathic Emergency Physicians. 142 E. Ontario Street, Suite 550, Chicago, IL 60611. Web site: <www.acoep.org/>.

International Congress on Hyperbaric Medicine. 1592 Union Street, San Francisco, CA 94123. Web site: <www.ichm.net/>.

Undersea and Hyperbaric Medical Society. 10531 Metropolitan Ave, Kensington, MD 20895. Web site: <www.uhms.org/>.

WEB SITES

"A Guide to Prevent Carbon Monoxide Poisoning." Industry Trade Group. Available online at <www.carbonmonoxide-poisoning.com/> (accessed November 2, 2004).

"Carbon Monoxide Poisoning." Centers for Disease Control and Prevention. Available online at <www.cdc.gov/nceh/airpollution/carbonmonoxide/default.htm> (accessed November 2, 2004).

"Carbon Monoxide Poisoning." National Library of Medicine. Available online at <www.nlm.nih.gov/medlineplus/carbonmonoxidepoisoning.html> (accessed November 2, 2004).

OTHER

Carbon Monoxide Headquarters. Wayne State University School of Medicine. <www.phymac.med.wayne.edu/FacultyProfile/penney/COHQ/co1.htm> (accessed November 2, 2004).

L. Fleming Fallon Jr., MD, DrPH

Carbon Monoxide Poisoning

Definition

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 of fossil fuels. It is found in automobile exhaust fumes, faulty stoves and heating systems, fires, and cigarette smoke. Other sources include wood-burning stoves, kerosene heaters, improperly ventilated water heaters and gas stoves, and blocked or poorly maintained fireplace chimney flues. CO interferes with the ability of the blood to carry oxygen. The result is headache, nausea, convulsions, and finally death by asphyxiation.

Description

Carbon monoxide, sometimes called coal gas, has been known to be 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, 1,500 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 and recover after exposure to CO.

Anyone who is exposed to CO will become sick, and the entire body is involved in CO poisoning. A developing fetus can 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 than otherwise healthy adults. 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. Firefighters also have an elevated occupational 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 repeatedly to pick up oxygen and move it throughout the body. After oxygen is released, carbon dioxide binds to hemoglobin and is transported back to the lungs.

Inhaling carbon monoxide gas interferes with this oxygen-transport system. In the lungs, CO competes with oxygen to bind with a hemoglobin molecule. Hemoglobin and CO bind more than 200 times more readily than do Hb and oxygen. The hemoglobin 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. This creates a condition called carboxyhemoglobinemia. All cells need oxygen to live. When they do not get enough oxygen, cellular metabolism is disrupted and eventually cells begin to die.

The symptoms of CO poisoning and the speed with which molecules of carboxyhemoglobin appear depend on the concentration of CO in the air and the rate and efficiency with which a person breathes. Heavy smokers may live 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 environmental exposure level of 50 parts per million (ppm) of CO 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 follows in a very short time. Emergency room physicians usually have the most experience diagnosing and treating CO poisoning, though occupational and environmental health professionals may also see multiple cases.

The symptoms of CO poisoning in order of increasing severity include:

• headache
• shortness of breath (dyspnea)
• dizziness fatigue
• fatigue
• mental confusion and difficulty thinking (disorientation)
• loss of fine hand-eye coordination
• nausea and vomiting
• rapid heart rate (tachycardia)
• hallucinations
• inability to accurately execute voluntary movements
• collapse
• lowered body temperature (hypothermia)
• coma (unconsciousness)
• convulsions (seizures)
• seriously low blood pressure (critical hypotension)
• cardiac and respiratory failure
• death

In some cases, the skin, nose, mucous membranes, or nails of a person with CO poisoning are cherry red or bright pink. Because the color change does not always occur, it is an unreliable symptom on which to base a diagnosis.

Although most CO poisoning is acute (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 or 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.

Diagnosis

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.

Confirmation of CO poisoning comes from a carboxyhemoglobin test. This blood test measures the amount of CO 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.

Treatment

The most immediate treatment for CO poisoning is to remove a person from the source of carbon monoxide gas and expose the individual to fresh air. If breathing has stopped or there is 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 over an airway as soon as it is available.

Taken with other symptoms of CO poisoning, COHb levels over 25% in otherwise 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 chemical imbalances that may have arisen from the breakdown of cellular metabolism.

In severe cases of CO poisoning, patients are given hyperbaric oxygen therapy. This treatment involves placing a person in a special chamber where he or she breathes 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 or regional trauma centers.

Prognosis

The speed and degree of recovery from CO poisoning depends on the duration and concentration 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 people may show residual memory problems, fatigue, confusion, and mood changes for two to four weeks after their exposure to the gas.

KEY TERMS

Carboxyhemoglobin (COHb)— Hemoglobin that is bound to carbon monoxide instead of oxygen.

Carboxyhemoglobinemia— A condition characterized by blood saturated with carboxyhemoglobin molecules.

Hemoglobin (Hb)— A molecule of red blood cells that normally binds to oxygen to transport it to cells, where it is required for life.

Hypothermia— Development of a subnormal body temperature, usually less than 96°F (37°C).

pH— A measurement of the acidity or alkalinity of a fluid. A neutral fluid, neither acid nor alkali, has a pH of 7.0.

Health care team roles

Trained persons may initiate first aid and CPR. Emergency medical technicians or paramedics may continue such treatment and initiate oxygen therapy while transporting a patient to a hospital. A physician provides treatment in the emergency department. A physician also supervises treatment in a hyperbaric chamber. A therapist may provide counseling after recovery from CO exposure.

Prevention

Carbon monoxide poisoning is preventable. Particular care should be paid to situations where fuel is burned in a confined area, or where heating equipment is old and in need of replacement. Portable and permanently installed carbon monoxide detectors that sound a warning similar to smoke detectors are available for under $50. Specific actions that will prevent CO poisoning include:

• Stop smoking. Smokers have less tolerance to environmental CO.
• Have heating systems and appliances installed by a qualified contractor to ensure they are properly vented and meet local building codes.
• Inspect and properly maintain heating systems, chimneys, and appliances.
• Do not use a gas oven or stove to heat the home.
• Do not burn charcoal indoors.
• Make sure there is good ventilation if using a kerosene heater indoors.
• Do not leave cars or trucks running inside a garage.
• Keep car windows rolled up when stuck in heavy traffic, especially when inside a tunnel.

Resources

BOOKS

Braunwald, Eugene. "Hypoxia, Polycythemia and Cyanosis." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. 14th ed. New York: McGraw-Hill, 1998, pp. 205-210.

Haddad, Lester M. "Acute Poisoning." In Cecil Textbook of Medicine, edited by Lee Goldman, and J. Claude Bennett. 21st ed. Philadelphia: W.B. Saunders, 2000, pp. 515-522.

Klaassen, Curtis D. Casarett & Doull's Toxicology: The Basic Science of Poisons. New York, McGraw-Hill, 2001.

Martin, T.G., and J.L. Burgess. Dreisbach's Handbook of Poisoning. 13th ed. Pearl River, NY: Parthenon Publishing, 2001.

PERIODICALS

Bourgeois, J.A. "Amnesia After Carbon Monoxide Poisoning." American Journal of Psychiatry, vol. 157, no. 11 (2000): 1884-1885.

Brakey, M.R. "Myths & Facts About Carbon Monoxide Poisoning." Nursing, vol. 30, no. 12, (2000): 26-28.

Etzel, R.A. "The 'Fatal Four' Indoor Air Pollutants." Pediatric Annals, vol. 29, no. 6 (2000): 344-350.

Ralston, J.D., and N.B. Hampson. "Incidence of Severe Unintentional Carbon Monoxide Poisoning Differs Across Racial/Ethnic Categories." Public Health Reports, vol. 115, no. 1 (2000): 46-51.

Shimazu, T. "Half-life of Blood Carboxyhemoglobin." Chest, vol. 119, no. 2 (2001): 661-663.

Takeuchi, A. "A Simple 'New' Method to Accelerate Clearance of Carbon Monoxide." American Journal of Respiratory and Critical Care Medicine, vol. 161, no. 6 (2000): 1816-1819.

ORGANIZATIONS

American Academy of Emergency Medicine, 611 East Wells Street, Milwaukee, WI 53202. (800) 884-2236. Fax: (414) 276-3349. 〈http://www.aaem.org〉.

American Association for Respiratory Care, 11030 Ables Lane, Dallas, TX 75229. 〈http://www.aarc.org〉

American Association of Nurse Anesthetists, 222 S. Prosper Avenue, Park Ridge, IL 60068. Tel: 847-692-7050. 〈http://www.aana.com〉.

American Lung Association, 1740 Broadway, NY, NY 10019. (212)-315-8700. 〈http://www.lungusa.org/diseases/lungtb.html〉. info@lungusa.org.

OTHER

Chimney Safety Institute of America. 〈http://www.csia.org/home/cohazard.html〉.

National Institute of Occupational Safety and Health. 〈http://www.cdc.gov/niosh/carbon2.html〉.

U.S. Environmental Protection Agency. 〈http://www.epa.gov/iaq/pubs/coftsht.html〉.

Carbon Monoxide Poisoning

Definition

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.

Description

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.

Diagnosis

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.

Treatment

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.

Prognosis

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.

Prevention

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

Resources

PERIODICALS

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

ORGANIZATIONS

American Lung Association. 1740 Broadway, New York, NY 10019. (800) 586-4872. 〈http://www.lungusa.org〉.

OTHER

"Carbon Monoxide Headquarters." Wayne State University School of Medicine. 〈http://www.phypc.-med.wayne.edu/〉.

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 Poisoning

A Close Call

What is Carbon Monoxide (CO) Poisoning?

Carbon Monoxide and the Environment

How is CO Poisoning Treated?

Can CO Poisoning Be Prevented?

Resources

Carbon monoxide is a colorless, tasteless, odorless gas that results from incomplete burning of solid, liquid, and gaseous fuels. This gas can cause dizziness, nausea, coma, or death if breathed in sufficient amounts.

KEYWORDS

for searching the Internet and other reference sources

Anoxia

Environmental health

Hypoxia

Hyperbaric oxygen

Toxicology

A Close Call

The neighbors could set a clock by Dr. Smith’s morning routine. He turned off the porch light at 6:00 a.m., picked up the newspaper from the driveway at 6:15, and took the dog for a walk at 6:30. One winter morning, Dr. Smith’s next-door neighbor noticed that none of these things had happened. He knew the Smiths were home, but they did not answer the doorbell or the telephone.

The neighbor called the police, who broke into the house and found four unconscious people. The gas heater had shut off during the night and had been giving off carbon monoxide gas for many hours. The Smiths were rushed to the hospital and treated for carbon monoxide poisoning. Dr. Smith and his wife and children were lucky; they were found in time and recovered completely after several weeks.

What is Carbon Monoxide (CO) Poisoning?

Carbon monoxide (CO) is a chemical created when some fuels, such as coal and gas, are burned. CO is toxic because it reduces the amount of oxygen received by the body’s cells. Red blood cells contain a protein called hemoglobin that carries oxygen to the body’s cells. Because CO binds much more easily and tightly to hemoglobin than does oxygen, CO will replace oxygen in the bloodstream when inhaled. When that happens, the cells that need lots of oxygen, such as those of the heart, skeletal muscles, and central nervous system, cannot function properly.

Acute CO poisoning

Dr. Smith and his family suffered acute* CO poisoning, in which a large amount of CO was breathed at one time. This kind of poisoning can lead to death: it kills 25 to 40 percent of those exposed. Survivors may feel symptoms for days, months, or years.

* acute

means sudden.

Chronic CO poisoning

CO poisoning also can be chronic*. A small amount of CO inhaled continuously or frequently over a long period of time does not kill, but it does impair oxygen flow to the brain and may cause long-term nervous system problems, such as headaches, dizziness, weakness, sleepiness, nausea, and vomiting. Low-level chronic exposure to CO is especially serious for people with heart, lung, or circulatory problems, and for infants and older adults. Developing fetuses also can be affected by CO poisoning.

* chronic

(KRON-ik) means continuing for a long period of time.

Carbon Monoxide and the Environment

CO is one of the most prevalent poisons in the environment. It can get into buildings, homes, and vehicles in many ways. Sources of CO include car exhaust, gas or oil furnaces, kerosene lamps, space heaters, improperly installed appliances, wood stoves, wood-burning fireplaces, and tobacco smoke. CO poisoning most often occurs during winter months, when people use heaters and fireplaces.

How is CO Poisoning Treated?

A person with acute CO poisoning requires extra oxygen as soon as possible. The individual may be given pure oxygen to breathe. A hyperbaric (hy-per-BARE-ik) oxygen chamber also may be used to treat CO poisoning. This is a large chamber that holds the patient, and sometimes the medical team. The chamber is filled with 100 percent oxygen, and the pressure is increased to three atmospheres (three times the pressure of the air near the earths surface, or the pressure the body feels about 90 feet under water). Pressure and pure oxygen help the oxygen molecules displace the CO attached to hemoglobin. Diagnosis and treatment of chronic CO poisoning may be more difficult, because its symptoms are similar to flu and many other conditions.

Can CO Poisoning Be Prevented?

CO poisoning is usually preventable. Basic safety guidelines include:

• Never burning charcoal in a tent or camper to keep warm.
• Installing water heaters and gas appliances properly and checking them often to make sure they are operating correctly.
• Keeping chimneys and wood-burning fireplaces clean.
• Never letting a car idle inside a garage, especially if the garage is attached to the house.
• Installing commercial CO detectors (similar in design to smoke detectors) for the home.

See also

Environmental Diseases

Resources

The U.S. National Center for Environmental Health at the Centers for Disease Control and Prevention (CDC) posts a Checklist for the Prevention of Carbon Monoxide (CO) Poisoning at its website. http://www.cdc.gov/nceh/programs/heeh/monxide/cocklst.htm

The U.S. National Institute of Neurological Disorders and Stroke posts a fact sheet at its website about anoxia and hypoxia from carbon monoxide inhalation and other causes. http://www.ninds.nih.gov/patients/Disorder/anoxia/anoxia.htm

Carbon Monoxide Poisoning

Carbon monoxide, with chemical formula CO, is a compound of carbon (C) and oxygen (O₂). It is a colorless, odorless, and tasteless gas that in appropriate amounts is poisonous to human beings and, for that matter, to all warm-blooded animals and many other life forms on Earth. Carbon monoxide is poisonous when, as a result of being inhaled into the lungs, it combines with the blood's hemoglobin , which then prevents the absorption of oxygen into the respiratory system of the body. Carbon monoxide poisoning results when the human body is consistently denied essential oxygen. A person without sufficient oxygen in the blood stream will initially feel dizziness, fatigue, headaches, nausea, and shortness of breath, which will eventually lead to unconsciousness and eventually to asphyxiation and death.

Carbon monoxide is a component of air pollution, both as an intentional or accidental side product, that results from many natural and artificial products, materials, and processes such as gasoline-powered vehicles, furnaces, manufacturing plants, and forest fires. The identification of carbon monoxide poisoning is important to forensic scientists because carbon monoxide can be the primary or secondary cause of such investigations as accidents, homicides, and suicides, or can be used as a deceptive tactic by criminals to hide other causes of crimes. For example, a forensic investigator might examine three unrelated dead bodies inside automobiles within three different closed garages and find (1) one body with carbon monoxide in the blood stream, but without any other suspicious evidence (which indicates a suicide), (2) another body with carbon monoxide in the blood, but with greasy fingers and clothing (which indicates an accidental death), and (3) a third body with blunt injuries to the head and only a small amount of carbon monoxide in the body (which indicates a homicide).

In order to determine the level of carbon monoxide within the blood stream of a deceased person, the accurate measurement of the blood pigment carboxyhemoglobin is required. Carboxyhemoglobin is hemoglobin that is saturated with carbon monoxide. Several detection methods are used for the measurement of carbon monoxide including CO-Oximeter, flame ionization, infrared spectrophotometry, syringe capillary, thermal conductivity, ultraviolet spectrophotometry, and Van Slyke. In ultraviolet spectrophotometry, for example, carbon monoxide is expelled from the blood stream and is then measured when exposed to ultraviolet radiation.

see also Asphyxiation (signs of); Hemoglobin; Poison and antidote actions; Toxicological analysis; Toxicology.