A 44-year-old man is rescued from a house fire and brought to the emergency department with nausea, headache, and altered mental status. The fire likely began due to the stove accidently being left on overnight. He has no chronic medical problems and takes no medications. The patient had smoked a pack of cigarettes a day for 10 years but quit several years ago. He does not use illicit drugs. Temperature is 36.7 C (98 F), blood pressure is 110/70 mm Hg, pulse is 112/min, and respirations are 28/min. Pulse oximetry is 97% on room air. The patient has soot around the mouth and oropharynx, flushed cheeks, pink palmar skin, and breath that smells strongly of smoke. He is lethargic but has spontaneous movement in all extremities. Cardiopulmonary auscultation reveals clear lung fields and normal heart sounds with occasional ectopic beats. Laboratory results are as follows: Chest-x ray reveals no infiltrates. ECG shows T-wave inversions in leads I, aVL, V5, and V6 that were not present on previous ECGs. Which of the following is most likely to confirm the underlying diagnosis?

Question

A 44-year-old man is rescued from a house fire and brought to the emergency department with nausea, headache, and altered mental status.  The fire likely began due to the stove accidently being left on overnight.  He has no chronic medical problems and takes no medications.  The patient had smoked a pack of cigarettes a day for 10 years but quit several years ago.  He does not use illicit drugs.  Temperature is 36.7 C (98 F), blood pressure is 110/70 mm Hg, pulse is 112/min, and respirations are 28/min.  Pulse oximetry is 97% on room air.  The patient has soot around the mouth and oropharynx, flushed cheeks, pink palmar skin, and breath that smells strongly of smoke.  He is lethargic but has spontaneous movement in all extremities.  Cardiopulmonary auscultation reveals clear lung fields and normal heart sounds with occasional ectopic beats.  Laboratory results are as follows:  Chest-x ray reveals no infiltrates.  ECG shows T-wave inversions in leads I, aVL, V5, and V6 that were not present on previous ECGs.  Which of the following is most likely to confirm the underlying diagnosis?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c199_b84d_8f63_8f1b1c79018b_MD0005_00 This patient who was rescued from a burning house has headache, nausea, altered mental status, and significant lactic acidosis suggesting carbon monoxide (CO) poisoning. CO binds heme with a much greater affinity than oxygen, forming carboxyhemoglobin. As carboxyhemoglobin levels increase above 10%-15%, impaired peripheral oxygen delivery and peripheral oxygen use may lead to acute symptoms. Mild cases manifest with headache, malaise, nausea, and dizziness; more severe cases often present with seizure, syncope, coma, and/or myocardial ischemia. Significant lactic acidosis and elevated cardiac enzymes are frequently present. Pulse oxymetry cannot differentiate carboxyhemoglobin from oxyhemoglobin and is typically normal. Diagnosis requires arterial blood gas analysis with measurement of carboxyhemoglobin level by co-oximetry. Mild cases are typically treated with high-flow 100% oxygen; more severe cases may require mechanical ventilation or hyperbaric oxygen therapy. (Choice A) Coronary artery catheterization can diagnose coronary atherosclerosis and is often used in patients thought to have acute coronary ischemia from an unstable atherosclerotic plaque. Although this patient has evidence of cardiac ischemia (troponinemia, ECG abnormalities), the underlying etiology is almost certainly CO poisoning (not atherosclerosis). (Choice B) Arterial blood PO₂ reflects the amount of oxygen dissolved in blood and is typically unchanged by CO exposure (unlike oxyhemoglobin, which is severely reduced). (Choice D) Methemoglobinemia is due to the oxidation of iron molecules in hemoglobin, which prevents oxygen binding. The most common causes are medications (eg, dapsone, benzocaine) and toxins (eg, aniline dyes). Manifestations are due to impaired oxygen delivery and include headache, nausea, lethargy, and cyanosis. This patient who was rescued from a burning house is far more likely to have CO poisoning. (Choice E) Urine toxicology may be useful for patients with alterations in mental state following suspected drug exposure, and some illicit stimulants (eg, cocaine) can cause altered mental status and ischemia. However, this patient who was rescued from a burning house is far more likely to have CO poisoning. Educational objective: Acute carbon monoxide poisoning often causes headache, malaise, nausea, and dizziness; more severe cases may present with seizure, syncope, coma, and/or myocardial ischemia. Diagnosis requires arterial blood gas analysis with carboxyhemoglobin level measured by co-oximetry. Pulse oxymetry cannot diagnose carbon monoxide poisoning (no differentiation between carboxyhemoglobin and oxyhemoglobin). References: Carboxyhemoglobin levels in carbon monoxide poisoning: do they correlate with the clinical picture? (http://www.ncbi.nlm.nih.gov/pubmed/18606318)

A 44-Year-Old Man Is Rescued from a House Fire and Brought