(1732) Methemoglobinemia: A Case Report

Introduction: Methemoglobinemia is potentially life-threatening. Acquired methemoglobinemia results from exposure to substances that cause oxidation of the hemoglobin. This results in the production of methemoglobin that exceeds capacity to convert iron within the hemoglobin back to its ferrous state. The most common agent that causes acquired methemoglobinemia is benzocaine. Patients may become symptomatic at a level of 10% and levels of ≥ 70% are often fatal.

Description: A 52 y/o female presented to our ED after being the restrained driver of an MVC and suffering injuries to her lower extremities. Primary history includes systemic lupus erythematosus, ethanol, and tobacco use. Of note, the patient had recently undergone removal of her teeth due to dental disease. She underwent surgery for her lower extremity injuries and a left popliteal bypass with fasciotomies. She was transferred to the STICU. On day two, the patient was resting and had recently eaten when she acutely desaturated to SpO2 87% refractory to administration of NRB oxygen. She was cyanotic, tachycardic, and hypotensive. She denied dyspnea. A CXR was done which was normal. POCUS was performed to evaluate heart function which was unremarkable. An ABG was performed via the right brachial artery. The sample appeared “brown”. Results were normal except for oxyhemoglobin: 47.7% and methemoglobin: 49.8%. Upon recognizing that there was significant methemoglobinemia, the patient was given 2mg/kg methylene blue. Because of the blue color, the SpO2 dropped to 28% during administration. One hour after methylene blue was given, the methemoglobin level decreased to 6.7%. In a debrief after recognition of methemoglobinemia, it was discovered that before the patient desaturated, 20% benzocaine gel was applied to her dentures, and replaced so that she could eat.

Discussion: High levels of methemoglobin can be fatal, but early recognition and intervention reduces the chances significantly. Our patient exhibited classical signs such as low SpO2 despite refractory to high FIO2, chocolate colored arterial blood, tachycardia, and cyanosis. Notably, her lupus erythematosus is managed with hydroxychloroquine, which is also associated with methemoglobinemia.