Cyanosis in the Pre-op Area

Abstract Case Presentation Pulmonology was consulted for a patient who developed acute hypoxic respiratory failure in the pre-op area. A 47-year-old female presenting for a tonsillar biopsy was noted to have an oxygen saturation of 91% in pre-op which subsequently decreased to 75%. She was given nebulizers and supplemental oxygen. Upon arrival to the bedside, the patient's oxygen saturation was in the 80s and her face was cyanotic. She denied dyspnea, headache, nausea or dizziness. Chest x-ray was negative for effusion or a consolidative process. Bedside ultrasound was negative for right heart strain, pericardial effusion, B lines, and pleural effusion. The patient interview revealed recent use of benzocaine containing spray and mouthwash which raised concern for methemoglobinemia. Labs drawn showed a methemoglobin of level of 6% (reference range < 1%). By this time, her cyanosis and oxygenation were improving. Given the short half-life of benzocaine, improvement in symptoms, and rule out of an acute cardiopulmonary process, she proceeded with her biopsy. Anesthesia had methylene blue available should it be needed during her procedure. Discussion Methemoglobinemia is caused by an elevated level of blood methemoglobin, which is formed when ferrous iron in hemoglobin is oxidized to ferric iron. As ferric iron does not bind oxygen, methemoglobinemia results in diminished oxygen carrying capacity of blood (1). Methemoglobinemia is rare with a prevalence 0.035% (1,4). Acquired methemoglobinemia from drug or chemical exposure is the most common etiology (1). Dapsone is the most common medication (3). Benzocaine topical anesthetics are also common. (1,2). Other medications include lidocaine and nitrate vasodilators (1). The severity of presentation of methemoglobinemia correlates with blood levels of methemoglobin (1). Methemoglobin <10% is often asymptomatic with low pulse oximetry readings and possible cyanosis (1). As levels increase, symptoms may include confusion, palpitations, headache, and fatigue; levels of 70% and greater can be fatal (1). Given the short half-life of benzocaine, this patient likely had a higher methemoglobin level prior to when her labs were drawn (5). Methylene blue, which reduces methemoglobin to hemoglobin, is the drug of choice for drug-induced methemoglobinemia (1,3). Conclusion This case of benzocaine-associated methemoglobinemia demonstrates a typical presentation of the disorder. It highlights the importance of using caution with benzocaine containing medications and of maintaining a high degree of suspicion when included in the patient's history.