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Carbon Monoxide Poisoning
Diagnosis of CO Poisoning
Nonspecific symptoms or metabolic acidosis in at-risk patients Venous carboxyhemoglobin level Because symptoms can be vague, nonspecific, and variable, the diagnosis of carbon monoxide (CO) poisoning is easily missed. Many cases of mild poisoning with nonspecific symptoms are mistaken for viral syndromes. Physicians must maintain a high level of suspicion. If people from the same dwelling, particularly a heated dwelling, experience nonspecific flu-like symptoms, CO exposure should be considered. If CO poisoning is suspected, the carboxyhemoglobin level in the blood is measured with a CO-oximeter; venous samples can be used because arteriovenous differences are trivial. Arterial blood gases (ABGs) are not measured routinely. ABGs and pulse oximetry, alone or combined, are inadequate for diagnosis of CO poisoning because oxygen saturation reported in ABGs represents dissolved oxygen and is thus unaffected by carboxyhemoglobin concentration; furthermore, the pulse oximeter cannot differentiate normal hemoglobin from carboxyhemoglobin and thus provides a falsely elevated oxyhemoglobin reading. Noninvasive CO detectors have not been shown to be accurate or useful in the diagnosis of CO exposure or toxicity. Although elevated carboxyhemoglobin levels are clear evidence of poisoning, levels may be falsely low because they decrease rapidly after CO exposure ends, particularly in patients treated with supplemental oxygen (eg, in an ambulance). Metabolic Acidosis can be a clue to the diagnosis. Other tests may help evaluate specific symptoms (eg, electrocardiography for chest pain, CT, and MRI for neurologic symptoms). 