Epidermal growth factor receptor mutation-positive advanced lung adenocarcinoma presenting with acute respiratory failure diagnosed by thin bronchoscope through transnasal route under high-concentration oxygen mask.

A 59-year-old woman complained of continuous dyspnea. Computed tomography revealed multiple pulmonary nodules, mildly small enlarged mediastinal lymph nodes and a nodule in the liver segment 8. Her dyspnea worsened with respiratory failure 4 days after presentation. Liver biopsy was not possible as she could not hold her breath; thus, we performed bronchoscopy. For biopsy, the pulmonary nodules with a positive bronchus sign were preferred over the mildly small enlarged mediastinal lymph nodes. Bronchoscopy under non-invasive positive pressure ventilation (NPPV) or high-flow nasal cannula (HFNC) was impossible because of the lack of equipment. Therefore, we biopsied via thin bronchoscope through nasal cavity under a high-concentration oxygen mask. Pathological findings revealed epidermal growth factor receptor mutation-positive lung adenocarcinoma. For patients with respiratory failure who cannot undergo bronchoscopy under NPPV or HFNC, thin bronchoscopy through the nasal cavity under a high-concentration oxygen mask may be clinically useful to prevent hypoxaemia during the procedure.