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Introduction: Sudden onset of hypoxia and dyspnea in a hospital setting requires prompt evaluation and treatment. When these symptoms are followed by cyanosis, methemoglobinemia should be on the differential as it requires special management. The prompt suspicion and treatment of this condition is crucial for patient recovery.

Case presentation: Patient is a 68-year-old man with COPD, OSA, and CAD who was admitted to the hospital for an episode of dyspnea after an elective septoplasty cauterization with inferior turbinate tonsillectomy and uvulopalatopharyngoplasty to treat OSA. He presented with new-onset dyspnea, followed by cyanosis, and severe hypoxia not resolved after 100% oxygen administration. Troponin and ECG were normal. A methemoglobin level was obtained and was 24.8%. He was given methylene blue and his symptoms, including his cyanosis, subsided less than 10 minutes after the initial dose. Talking with the patient after the event, he revealed to us that he was using the 20% benzocaine spray (Hurricane) for throat pain at least 20 times a day in the hospital even though it was prescribed to be used only three times daily as needed. Patient was discharged home the next day with no sequelae, asymptomatic.

Discussion: Methemoglobinemia can be either inherited or acquired. Inherited methemoglobinemia is a rare disorder. A wide variety of agents are known to induce methemoglobinemia, including benzocaine. In patients with multiple comorbidities, especially lung and heart disorders, the diagnosis is a challenge. Cyanosis not reverted after 100% oxygen is an important clue to define the disease.

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