An Atypical Case of Methemoglobinemia due to Self-Administered Benzocaine

Abstract

Acquired methemoglobinemia is an uncommon hemoglobinopathy that results from exposure to oxidizing agents, such as chemicals or medications. Although, as reported in the adult population, it happens most often due to prescribed medication or procedural anesthesia and not due to easily accessed over-the-counter medications, the authors will describe an otherwise healthy male adult with no known medical history and no prescribed medications, who presented to the emergency department reporting generalized weakness, shortness of breath, headache, dizziness, and pale gray skin. In addition, the patient reported that he also had a severe toothache for several days, which he had been self-treating with an over-the-counter oral benzocaine gel. Ultimately, the diagnosis of methemoglobinemia was made by clinical history, physical examination, and the appearance of chocolate-colored blood and arterial blood gas (ABG) with cooximetry. After 2 mg/kg of intravenous methylene blue was administered, the patient had complete resolution of all signs and symptoms. This case illustrates that emergency physicians should be keenly aware of the potential of toxic hemoglobinopathy secondary to over-the-counter, nonprescribed medications. Discussion with patients regarding the dangers of inappropriate use of these medicines is imperative, as such warnings are typically not evident on product labels.

A Case Report of Acute Transient Encephalopathy Following a Trans-esophageal Echocardiography

“…Traditional pulse oximetry is unreliable in diagnosing methemoglobinemia. It cannot distinguish oxyhemoglobin from abnormal hemoglobin like methemoglobin, sulfhemoglobin, and carboxyhemoglobin which bind and carry oxygen to varying extents but do not release it to the tissues [2,8].…”

“…Traditional pulse oximetry is unreliable in diagnosing methemoglobinemia. It cannot distinguish oxyhemoglobin from abnormal hemoglobin like methemoglobin, sulfhemoglobin, and carboxyhemoglobin which bind and carry oxygen to varying extents but do not release it to the tissues [ 2 , 8 ]. Oxygen saturation gap (difference between oxygen saturation measured by pulse oximeter and saturations by blood gas analysis) >5% indicates the presence of abnormal hemoglobin [ 9 ].…”

Oral Chronic Graft-Versus-Host Disease

“…Studies in oral mucositis patients have shown low systemic absorption and risk is low with oral application when used as directed [104]. Methemoglobinemia has been described after application to large mucosal surfaces (e.g., bronchoscopy) and with excessive oral use [105][106][107][108].…”

Anemia That Presented with Desaturation: A Focus on Core Concepts

“… Oxygen saturation. ceHb (effective haemoglobin) excludes the fractions of carboxy‐ and methemoglobin, which a blood gas analyzer cannot quantify accurately [ 18 ]. …”