Home > Encyclopedia of Nursing & Allied Health > 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 undergroundparking 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
• 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 doesn't 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 sub- side 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.

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 environ- mental 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.

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KEY TERMS

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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.

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L. Fleming Fallon, Jr., MD, DrPH