This single-centre, single-blind, randomised controlled study with parallel-group design was conducted in Yun Ling, Taiwan between May 2019 and August 2019. Participants were randomly allocated to an intervention (mouth care using 0.12% CHX before intubation) or control (standard care) group on a 1:1 basis. This study was approved by the institutional review board of National Taiwan University Hospital, Taiwan (IRB No.201806086RINB). Each participant completed written informed consent after explanation of this study and advised that they could withdraw anytime.

Participants were recruited at the operation room of a teaching hospital. Participants were included if they met the following criteria: 18-80 years of age, American Society of Anesthesiologists, ASA) class 1-3, scheduled for surgery under endotracheal tube intubation general anesthesia. Patients were excluded if they were diagnosed with upper or lower respiratory tract disease, including COPD, cold, had oral ulcer, scheduled to have a respiratory-related surgical procedure, had endotracheal tube intubated.

Inclusion Criteria:

• 18-80 years of age, American Society of Anesthesiologists, ASA) class 1-3, scheduled for surgery under endotracheal tube intubation general anesthesia.

Exclusion Criteria:

• Patients were excluded if they were diagnosed with upper or lower respiratory tract disease, including COPD, cold, had oral ulcer, scheduled to have a respiratory-related surgical procedure, had endotracheal tube intubated, >1 during anesthesia processes,