Carbon monoxide poisoning (acute)
Carbon monoxide is an odourless, colourless gas, and poisoning causes hypoxia, cell damage, and death. Diagnosis of carbon monoxide poisoning: Exposure to carbon monoxide is measured either directly from blood samples and expressed as a percentage of carboxyhaemoglobin, or indirectly using the carbon monoxide in expired breath. Carboxyhaemoglobin percentage is the most frequently used biomarker of carbon monoxide exposure. Although the diagnosis of carbon monoxide poisoning can be confirmed by detecting elevated levels of carboxyhaemoglobin in the blood, the presence of clinical signs and symptoms after known exposure to carbon monoxide should not be ignored. The signs and symptoms of carbon monoxide poisoning are mainly associated with the brain and heart, which are most sensitive to hypoxia. The symptoms of carbon monoxide poisoning are non-specific and varied, and include headache, fatigue, malaise, “trouble thinking”, confusion, nausea, dizziness, visual disturbances, chest pain, shortness of breath, loss of consciousness, and seizures. In people suffering from co-morbidities, symptoms such as shortness of breath or chest pain may be more evident. The classical signs of carbon monoxide poisoning — described as cherry-red lips, peripheral cyanosis, and retinal haemorrhages — are rarely seen. Interpretation of carboxyhaemoglobin levels: Non-smokers living away from urban areas have carboxyhaemoglobin levels of 0.4–1.0%, reflecting endogenous carbon monoxide production, whereas levels of up to 5% may be considered normal in a busy urban or industrial setting. Smokers are exposed to increased levels of carbon monoxide in cigarettes, and otherwise healthy heavy smokers can tolerate levels of carboxyhaemoglobin of up to 15%. The use of carboxyhaemoglobin percentage as a measure of severity of carbon monoxide poisoning, or to predict treatment options, is limited because carboxyhaemoglobin levels are affected by removal from the source of carbon monoxide and any oxygen treatment given before measurement of percentage carboxyhaemoglobin. Additionally, people with co-morbidities that make them more sensitive to the hypoxia associated with carbon monoxide can present with symptoms of poisoning at carboxyhaemoglobin levels that are either low or within the normal range. Attempts have been made in the literature to equate symptoms and signs to different carboxyhaemoglobin levels, but it is accepted that carboxyhaemoglobin levels in an acutely poisoned person only roughly correlate with clinical signs and symptoms, especially those relating to neurological function. Earlier studies attempted to differentiate between smokers and non-smokers. Attempts have also been made in the literature to divide carbon monoxide poisoning into mild, moderate, and severe based on carboxyhaemoglobin percentage levels and clinical symptoms, but there is no clear clinical consensus or agreement on this issue. The degrees of poisoning have been described as mild carbon monoxide poisoning: a carboxyhaemoglobin level of over 10% without clinical signs or symptoms of carbon monoxide poisoning; moderate carbon monoxide poisoning: a carboxyhaemoglobin level of over 10%, but under 20–25%, with minor clinical signs and symptoms of poisoning, such as headache, lethargy, or fatigue; and severe carbon monoxide poisoning: a carboxyhaemoglobin level of over 20–25%, loss of consciousness, and confusion or signs of cardiac ischaemia, or both. ...read more.
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