A 55-year-old male was admitted to the hospital with pneumonia. During an intubation procedure, the patient received an application of endobronchial lidocaine (4% gel). Within 2 h of intubation, the patient developed worsening hypoxia, and investigation of arterial blood gasses revealed a pH of 7.21, carbon dioxide partial pressure (PaCO2) of 3.3 kPa, oxygen partial pressure (PaO2) of 55.1 kPa, and measured oxygen saturation of 49%. Co-oximetry of this sample returned a methemoglobin level of 53%. Intravenous methylthioninium chloride (1% solution at 1 mg/kg) was delivered, and subsequent arterial blood gasses, at 30 min and 1 h post administration, showed methemoglobin levels of 12 and 9%, respectively, with return of oxygen saturation to > 90%.