Snapshot A 35-year-old painter presents to the emergency room for nausea, vomiting, and a headache. He reports that a large vat of paint thinner had spilled, and he had spent the afternoon cleaning it up. While at the time he felt fine, an hour after he finished, he started experiencing these symptoms. On physical exam, he is oriented to self and place but not the year. He is tachycardic with a pulse of 112/min. Pulse oximetry reveals an oxygen saturation of 96% on room air. A CO-oximetry shows carboxyhemoglobin levels of 23%. He is started on 100% oxygen. A lactic acid level is drawn to assess for concomitant cyanide poisoning. Introduction Clinical definition carbon monoxide (CO) poisoning results from exposure to CO resulting in hypoxia ETIOLOGY Pathogenesis mechanism displaces oxygen from hemoglobin causes left-shift of oxygen-hemoglobin curve, leading to decreased delivery of oxygen to tissues binds to cytochrome oxidase disrupts electron transport chain increases lipid peroxidation in the central nervous system Associated conditions cyanide poisoning Epidemiology Incidence leading cause of death from unintentional poisoning common in industrialized patients Risk factors use of charcoal, gas, or petroleum wood-burning heaters cooking in poorly ventilated areas building fires smoke inhalation motor vehicle exhaust exposure to methylene chloride (paint thinners) metabolized into CO delayed CO poisoning Presentation Symptoms headache lightheadedness nausea and vomiting improvement when removed from the exposure Physical exam normal pulse oximetry tachycardia dyspnea altered mental status confusion cherry-red skin late finding of CO poisoning Studies Diagnostic testing studies pulse oximetry normal oxygen saturation level ↑ carboxyhemoglobin (COHb) levels must be assessed before supplemental oxygen is administered arterial blood gas venous blood gas portable CO-oximetry devices (not regular pulse oximetry) > 3% for nonsmokers > 9% for smokers ↑ lactic acid decreased delivery of oxygen to tissues ↑ troponin CO poisoning may cause myocardial injury due to relative hypoxemia Differential Cyanide poisoning distinguishing factor ↑ lactic acid does not respond to oxygen therapy DIAGNOSIS Making the diagnosis based on clinical presentation and laboratory studies carboxyhemoglobin levels > 20% Treatment Management approach remove all sources of CO from the patient 100% or hyperbaric oxygen First-line 100% oxygen to displace CO from hemoglobin decreases half-life of CO in most patients from 4-5 hours to 1 hour decreases half-life of CO from methylene chloride from 13 hours to 6 hours Second-line hyperbaric oxygen indication neurological deficits pregnant women children elderly significantly elevated COHb levels methylene chloride as cause of CO poisoning Complications Myocarditis Acute respiratory distress syndrome Prognosis Worse with very young or very old age Worse with prolonged or intentional exposures