Abstract
Methemoglobinemia is life-threatening and bears pathognomonic signs difficult to diagnose in real time. Local anesthetics are widely used and are known for eliciting this condition. We report a case of methemoglobinemia secondary to self-administered use of benzocaine spray. A 27-year-old woman was found to be in respiratory distress during postoperative recovery. After desaturation persisted, arterial blood gas yielded a methemoglobin level of 47%. The patient was successfully treated with intravenous methylene blue. Review of the events revealed self-administered doses of benzocaine spray to alleviate discomfort from a nasogastric tube. We review this case in detail in addition to discussing methemoglobinemia and its relevant biochemistry, pathophysiology, clinical presentation, and medical management. Given the recognized risk of methemoglobinemia associated with benzocaine use, we recommend its removal from the market in favor of safer alternatives.
Highlights
Methemoglobin arises when the ferrous (Fe2+) iron moiety of the heme group within hemoglobin is converted to the ferric (Fe3+) state
The methemoglobinemia that arises leads to functional anemia and inadequate tissue oxygen delivery can result in symptoms observable even in the setting of modest increases in percent methemoglobin
If methemoglobinemia is allowed to continue unrecognized by cooximetry or arterial blood gas and untreated by methylene blue, significant morbidity and mortality can result from tissue hypoxia
Summary
Methemoglobin arises when the ferrous (Fe2+) iron moiety of the heme group within hemoglobin is converted to the ferric (Fe3+) state This occurs in the setting of oxidative stress and converts the heme group into a non-oxygen binding state. The methemoglobinemia that arises leads to functional anemia and inadequate tissue oxygen delivery can result in symptoms observable even in the setting of modest increases in percent methemoglobin. If methemoglobinemia is allowed to continue unrecognized by cooximetry or arterial blood gas and untreated by methylene blue, significant morbidity and mortality can result from tissue hypoxia. This requires a heightened index of suspicion when relevant exogenous substances like local anesthetics are incorporated into therapy. We report an episode of methemoglobinemia in which clinical diagnosis was challenging given lack of cues pointing towards a diagnosis
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