Silent Hypoxia From Benzocaine-Induced Methemoglobinemia Following Transesophageal Echocardiogram

Methemoglobinemia is a rare but potentially life-threatening cause of hypoxia, often presenting with cyanosis and low oxygen saturation unresponsive to supplemental oxygen. We report the case of a 32-year-old woman with a complex medical history including morbid obesity, asthma, type 2 diabetes mellitus, and hypertension, who was admitted with MRSA bacteremia and septic pulmonary emboli. After a nondiagnostic transthoracic echocardiogram, she underwent a transesophageal echocardiogram (TEE), during which topical benzocaine spray was administered for oro-esophageal anesthesia. Following the procedure, she developed asymptomatic but profound hypoxemia, requiring rapid escalation from room air to 100% oxygen via non-rebreather mask, despite denying dyspnea. Arterial blood gas analysis revealed a methemoglobin level of 31.8%, confirming benzocaine-induced methemoglobinemia. She was promptly treated with methylene blue, resulting in rapid clinical improvement and return to room air the next morning. This case underscores the importance of recognizing silent hypoxia following TEE, particularly when benzocaine-containing anesthetics are used. Early recognition and treatment are essential to prevent unnecessary escalation of care and potential morbidity.