Abstract Introduction Methemoglobinemia is a rare, potentially life-threatening condition caused by oxidation of ferrous (Fe²+) to ferric (Fe³+) iron in hemoglobin, impairing oxygen delivery to tissues. It can be congenital or acquired from oxidizing drugs such as local anesthetics. Benzocaine remains a well-recognized cause of acquired methemoglobinemia. This report describes a case of severe benzocaine-induced methemoglobinemia presenting as acute hypoxemia in a postoperative patient. Case Presentation A 37-year-old female with asthma, nicotine dependence, anxiety, and recent perforated diverticulitis with abscess formation status post proctosigmoidectomy presented with severe diffuse abdominal pain and nausea. CT imaging showed bowel perforation with retroperitoneal fluid and free air. She underwent emergent exploratory laparotomy revealing purulent peritonitis and multiple intra-abdominopelvic abscesses. A Jackson-Pratt drain and nasogastric tube were placed, and she remained NPO until bowel function returned.Her postoperative course was initially stable until postoperative day five, when a rapid response was called for sustained tachycardia and SpO2 of 74%. Examination revealed cyanotic lips, pale mucous membranes, and a tender, rigid abdomen. She denied dyspnea while on a non-rebreather mask. An arterial blood gas showed dark “chocolate-colored” blood. Review of bedside medications revealed frequent self-administration of benzocaine oral spray every 1-2 hours for nasogastric discomfort. ABG confirmed methemoglobinemia with a level of 61.9%. The patient received methylene blue 1 mg/kg IV over 10 minutes and was transferred to the ICU. Serial ABGs demonstrated rapid improvement (61.9 → 22.6 → 17.7 → 9.0 → 0.3%). Her condition stabilized, and she was discharged without further complications. Discussion Benzocaine-induced methemoglobinemia is uncommon but can cause profound hypoxemia unresponsive to oxygen therapy. Typical clues include cyanosis with normal PaO2 and chocolate-colored blood. Diagnosis is confirmed by co-oximetry demonstrating elevated methemoglobin levels. Management requires immediate discontinuation of the offending agent and prompt administration of methylene blue, which reduces methemoglobin via the NADPH-dependent pathway.This case highlights the importance of considering methemoglobinemia in the differential diagnosis of unexplained postoperative hypoxemia, particularly in patients using topical anesthetics. Early recognition and treatment are critical to prevent life-threatening complications. Figure 1: ABG sample with characteristic chocolate-brown hue. This abstract is funded by: None
Jarri et al. (Fri,) studied this question.