Topical Benzocaine (Hurricaine®) Induced Methemoglobinemia during Endoscopic Procedures in Gastric Bypass Patients

Background: Methemoglobinemia results from oxidation of ferrous to ferric iron in hemoglobin. In addition to a functional anemia, methhemoglobinemia causes the O₂-binding affinity of the remaining O₂ sites in the hemoglobin tetramer to increase; essentially shifting the oxyhemoglobin dissociation curve to the left and decreasing O₂ delivery. Patients develop profound cyanosis unresponsive to O₂ when methemoglobin (MHb) levels exceed 10%. It can be lethal if levels exceed 70%. Benzocaine 20% (Hurricaine®) spray, commonly used in endoscopy (EGD) can cause methemoglobinemia. We report our experience. Methods: Two patients out of >1,000 EGDs in 4 yrs developed methemoglobinemia. Results: Patient 1 : 34 F, BMI 46, open distal gastric bypass. Patient 2 : 26 F, BMI 49, laparoscopic proximal gastric bypass. Both had nausea and vomiting from stomal stenosis requiring EGD for which benzocaine 20% spray was used. Severe cyanosis (despite pulse oximetry readings of 86% and 89%), dyspnea and tachycardia, were seen within 13 and 7 minutes. They were unresponsive to O₂, despite being awake and conversant after complete reversal of sedatives. MHb levels were 35.6% and 18.8% (normal <1%). Patients dramatically improved after 1% methylene blue at 1-2 mg/kg IV over 5 minutes. MHb levels dropped to 2.3% and 0.8 % within 150 and 110 minutes. Neither patient had any evidence of pulmonary embolism or DVT or G6PD deficiency. Conclusion: Topical benzocaine 20% (Hurricane®) spray used in EGDs gets absorbed and can cause methemoglobinemia. Sprays should be limited to 1 second. Prompt treatment with 1% methylene blue IV can be life-saving.