Randomization and blinding
Randomization was conducted using computer-generated random numbers sealed in opaque envelopes. Patients were randomly allocated into two groups by the corresponding envelope. Knowing the group task, the anesthesiologist was responsible for the intervention, and the other researchers, blinded to the random allocation, participated in the follow-up visit and data analysis. Chest EIT and lung ultrasonography were performed by the relevant technicians and analyzed by a researcher.