A 35-year-old woman is brought to the emergency department after being rescued from inside a burning building by firefighters. She had a brief tonic-clonic seizure en route to the hospital. Her past medical history is unknown. She is confused and mildly agitated. Her temperature is 37 C (98.6 F), blood pressure is 100/60 mm Hg, pulse is 115/min, and respirations are 24/min. Her oxygen saturation is 96% on room air as measured by standard pulse oximetry. Physical examination shows no burns, and her skin color is normal. There are symmetric breath sounds bilaterally with scattered end-expiratory wheezes. Neurologic examination shows no abnormalities apart from confusion. The abdomen is soft and nontender. Which of the following is the best initial treatment for this patient?
Carbon monoxide poisoning | |
Epidemiology |
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Manifestations | Mild-moderate
Severe
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Diagnosis |
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Treatment |
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ABG = arterial blood gas. | |
This patient presents with confusion, wheezing, and a seizure following smoke inhalation; this clinical picture suggests carbon monoxide (CO) poisoning. CO is a tasteless, colorless, and odorless gas produced by incomplete combustion of carbon-containing compounds. CO poisoning should be considered in all patients exposed to smoke in a closed space. The affinity of CO for binding hemoglobin (Hb) is >200 times that of oxygen; once bound to Hb, CO forms carboxyhemoglobin, which impairs oxygen delivery to tissue by shifting the Hb-oxygen dissociation curve to the left.
Manifestations of mild to moderate CO toxicity include headache, nausea, dyspnea, malaise, altered mentation, and dizziness. Severe CO poisoning can present with seizures, coma, syncope, heart failure, or arrhythmias. Bright cherry lips can be a sign of CO poisoning (not specific). The diagnosis is confirmed clinically and by documenting an elevated carboxyhemoglobin level (eg, >3% in nonsmokers, >10% in smokers). A standard pulse oxymetry is unreliable and may appear normal because it cannot differentiate carboxyhemoglobin from oxyhemoglobin (as seen in this patient).
The treatment of CO poisoning involves administration of 100% oxygen via nonrebreather facemask to compete with CO binding to Hb and to decrease the half-life of CO (from ~5 hours on room air to 1-2 hours on 100% oxygen). Patients should then be monitored (for >4 hours) and hospitalized if their condition has not improved. Hyperbaric oxygen is sometimes used in severe cases that are unresponsive to facemask-administered oxygen.
(Choice A) A bolus of 50% dextrose can be given for suspected hypoglycemia in an unconscious patient. Intravenous thiamine can be given for suspected Wernicke encephalopathy (delirium, oculomotor abnormalities, ataxia). This patient's presentation after being inside a burning building is more concerning for CO poisoning.
(Choices C and E) Intravenous lorazepam and phenytoin are treatment options if the patient continues to have seizures or develops status epilepticus.
(Choice D) Intravenous naloxone is indicated to reverse (suspected) opioid toxicity with respiratory depression, but this patient's respiratory rate of 24/min makes this less likely.
Educational objective:
All patients with smoke inhalation should be suspected to have acute carbon monoxide (CO) poisoning and treated with 100% oxygen via a nonrebreather facemask. Early symptoms of CO poisoning are typically neurological and include agitation, confusion, and somnolence.