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Methemoglobinemia and transesophageal echo.

Methemoglobin (MHb) is the oxidized form of Hemoglobin (Hb) containing iron in its ferric (Fe3+) rather than ferrous (Fe2+) state. Under physiologic conditions, diaphorase II accounts for only a small percentage of the red blood cell reducing capacity but can be pharmacologically activated by exogenous cofactors. Methemoglobinemia is an abnormal elevation of MHb levels resulting in impaired oxygen delivery to tissues as well as a left shift of the oxygen-Hb dissociation curve. We present the case of a 56-year-old female patient who underwent transesophageal echocardiography (TEE) prior to elective cardioversion. Prep for TEE included use of Hurricane spray. Twenty min after receipt, the patient's O2 saturation by pulse oximetry dropped from 100% to 86%; heart rate and blood pressure were unchanged. Physical exam revealed pallor, perioralcyanosis and acrocyanosis without tachypnea, respiratory distress, or jugular venous distension. A 100% non-rebreather mask provided no improvement. MHb was suspected and arterial blood gasses were drawn which was dark chocolate in appearance. Methylene Blue at 1 mg/kg over 5 minutes was administered empirically. ABG results were: pH 7.44/ CO2 40/ O2 315/ HCO2 26/ O2 sat 69%; MHb levels were 30.1% confirming the diagnosis of methemoglobinemia. This condition resolved within minutes. Though uncommon, MHb is the most Sported adverse event associated with topical benzocaine use. Untreated, it can lead to significant cardiopulmonary compromise, neurologic sequelae, and even death. Prompt recognition of this potentially life-threatening side-effect is essential in order to provide opportune treatment.

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