1907 Methemoglobinemia: A Life-Threatening Complication of Topical Pharyngeal Anesthetics

Abstract

INTRODUCTION: Topical pharyngeal anesthetics such as benzocaine are used in conjunction with moderate sedation to increase patient comfort during esophagogastroduodenoscopy (EGD). Topical pharyngeal anesthetics can cause methemoglobinemia, which is a rare and life-threatening complication. We want to highlight the potential complication with the use of topical pharyngeal benzocaine through this case presentation. CASE DESCRIPTION/METHODS: A 22-year-old female presented with odynophagia after swallowing a piece of meat. She underwent inpatient EGD and received topical pharyngeal benzocaine spray along with moderate sedation. EGD was unremarkable, but during recovery, the patient became dyspneic, cyanotic, and her oxygen saturation (SaO2) dropped to 85% on room air. On chest examination, she had no wheezing, rhonchi, or crackles. Arterial blood gas showed pH 7.50, partial pressure of carbon dioxide 21 mmHg, partial pressure of oxygen 409 mmHg, and SaO2 99%. Blood work showed a methemoglobin level of 27.8%. She was transferred to the Intensive Care Unit and was given supplemental oxygen through facemask and IV ascorbic acid, which resolved her cyanosis and hypoxemia. Repeat methemoglobin level was 8.3% with normal oxygen saturation on room air. Upon stabilization, she was discharged home 48 hours after her initial presentation. DISCUSSION: Methemoglobinemia is the oxidation of ferrous to ferric iron within hemoglobin, impairing its ability to transport oxygen, leading to tissue hypoxemia and death. The etiologies of methemoglobinemia are hemoglobinopathy (hemoglobin M), hereditary nicotinamide adenine dinucleotide reductase (NADH) enzyme deficiency and drug induced. Drug-induced methemoglobinemia should be considered in patients with cyanosis and hypoxemia following topical pharyngeal anesthetic use. Despite the rare incidence, most cases of topical-anesthesia-induced methemoglobinemia are secondary to benzocaine. If the use of topical pharyngeal anesthetics is deemed necessary during an EGD, topical viscous lidocaine should be preferred over benzocaine to avoid this potentially life-threatening complication. There is insufficient evidence for methemoglobinemia caused by topical pharyngeal lidocaine alone and reported cases of lidocaine associated methemoglobinemia occurred in patients with either cardiorespiratory diseases or with the use of other anesthetic agents.