Methemoglobinemia as a Rare Complication During a Transesophageal Echocardiogram
A transesophageal echocardiogram was performed on a 44-year-old patient to rule out endocarditis. After local benzocaine spray was applied to the throat and intravenous sedation was administered, the pulsoximeter showed a drop in oxygen saturation to 84% on room air, not responding to supplemental oxygen. Despite the use of flumazenil and naloxone for benzodiazepine (midazolam) and opiate (meperidine) reversal, respectively, the patient was still drowsy and cyanotic. The blood sample withdrawn from the femoral artery was very dark in color, “chocolate brown” compared with his blood after recovery (Figure, right and left tubes). It showed an oxygen saturation of 99%; constituting a “saturation gap” of 15% between the pulsoximeter and the blood sample readings. Methemoglobinemia was suspected and later confirmed by blood levels. Methylene blue (70 mg) in a solution given intravenously over 15 minutes was used for reversal with excellent results. (The recommended dose is 1 to 2 mg/kg intravenously administered over several minutes.) This is believed to be a reaction to the local anesthetic spray, 20% benzocaine.