A 16-year-old girl is being evaluated in the emergency department because of lethargy and headache for the past one hour. Her pulse is 115/min and respirations are 12/min. she had a peritonsillar abscess and a topical anesthetic was applied for incision and drainage. Physical examination shows bluish discoloration of the lips and nail beds. A venous blood sample appears chocolate-colored and does not change color when exposed to oxygen. Which of the following is the most likely cause of this patient's hypoxemia?

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Eductional Objective: Acquired methemoglobinemia can be precipitated by benzocaine and result in the conversion of Fe²⁺ to Fe³⁺, which results in functional anemia and a left shift of the oxygen dissociation curve. Patients have cyanosis that does not improve with supplemental oxygenn

A 16-Year-Old Girl Is Being Evaluated in the Emergency Department