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Am Fam Physician. 1999;59(5):1300-1308

About 600 accidental deaths from carbon monoxide poisoning occur each year, making it one of the most common causes of morbidity from poisoning in the United States. About five to 10 times as many intentional deaths from carbon monoxide are reported. Exposure occurs from a variety of sources, particularly motor vehicle exhaust. The number of accidental deaths caused by carbon monoxide poisoning from motor vehicle exhaust is higher in the North and peaks during the winter months. Ernst and Zibrak reviewed the clinical aspects of carbon monoxide poisoning, including signs and symptoms, diagnostic tests, treatment and prevention strategies.

The clinical signs and symptoms of carbon monoxide poisoning are nonspecific (see the accompanying table) and are often mistaken for a simple viral illness. Patients typically present with tachycardia and tachypnea, and may complain of headache, nausea and vomiting. However, patients rarely have the classic findings of cyanosis, retinal hemorrhage and cherry-red lips.

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Symptom severity ranges from mild (constitutional symptoms) to severe (coma, respiratory depression and hypotension) and is not associated with serum levels of carboxyhemoglobin, although duration of exposure is an important factor. Not all patients exhibit signs and symptoms immediately after exposure. In some patients, neuropsychiatric symptoms, including cognitive and personality changes, may develop anywhere from three days to eight months after exposure. The mechanism for these conditions is unknown, but hypoxia alone is not sufficient to explain the observed clinical manifestations.

Because carbon monoxide poisoning has no pathognomonic signs or symptoms, a high level of suspicion is needed to confirm the diagnosis. Measuring the level of carbon monoxide in the exhaled air of a patient can be diagnostic, but a blood sample should be obtained to measure carboxyhemoglobin levels and any coexisting acidosis. A detailed neurologic examination, including psychologic testing, is recommended to document any abnormal findings, which are often subtle. The Carbon Monoxide Neuropsychological Screening Battery is a frequently used tool that takes about 30 minutes to administer and helps to establish a baseline for assessing the patient's mental status.

The most important steps in treatment are removing the patient from the source of poisoning and administering 100 percent oxygen. Oxygen should be given until the patient's carboxyhemoglobin level returns to normal. Hospitalization should also be considered for patients with severe poisoning or serious underlying medical problems. Indications for hyperbaric oxygen therapy are not clear, except that it is undisputedly indicated in unconscious patients.

The authors conclude that public awareness of the dangers of carbon monoxide is key to decreasing morbidity and mortality from carbon monoxide poisoning. Carbon monoxide detectors are inexpensive and widely available, but there are no standard recommendations regarding their use in the home or the workplace.

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Copyright © 1999 by the American Academy of Family Physicians.

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