Introduction: Topical anesthetics such as benzocaine, although generally well tolerated, a rare but life-threatening methemoglobinemia reaction has been associated with their use. Case reports and studies have described benzocaine induced methemoglobinemia, however, no case studies have detailed the occurrence of methemoglobinemia following benzocaine spray for nasogastric tube (NGT) placement.
Description: A 68-year-old female with hypertension was admitted to the intensive care unit following lumbar spine decompression and fusion. Her postoperative period was complicated by restrictions to supine position, encephalopathy; subsequently requiring NGT enteral nutrition. Prior to placement, 1 spray of HurriCaine Spray with 20% benzocaine was administered. 15 minutes after administration, the patient began desaturating to 86% with no response to oxygen. Physical exam showed no evidence of respiratory distress, however there was obvious perioral and peripheral cyanosis. Bedside echocardiogram and thoracic ultrasound showed no signs of pneumothorax, pulmonary edema or abnormal heart function. Noninvasive ventilation with BiPAP initiated and arterial blood gas (ABG) was obtained. As ABG was drawn, there was a distinct chocolate-brown discoloration prompting concern for methemoglobinemia, likely secondary to benzocaine administration. ABG showed pH 7.479, PCO2 47.7, PO2 457, HCO3 30.9, HBO2 42.0 and methemoglobin 58.1. We administered methylene blue 2 mg/kg (100 mg) IV push over 5 minutes and ascorbic acid 10 g IV over 5 hours due to unknown history of G6PD deficiency. ABG at 60 minutes showed an increase in HBO2 to 68.1 and decrease in methemoglobin 31.3. Additional dose of methylene blue at 1 mg/kg given. Final ABG 12 hours from onset showed full clearance of methemoglobin and patient was titrated off supplemental oxygen.
Discussion: Hypoxia and cyanosis unresponsive to oxygen with recent exposure to topical anesthetics should prompt consideration of methemoglobinemia. Providers and staff should discuss this potential complication before administering topical anesthetics, ensuring proper monitoring and early recognition. Rapid recognition and administration of methylene blue and/or considering ascorbic acid is paramount to prevent tissue hypoxia and ultimately death.
