Randomization and blinding
Group allocation was concealed in sequentially numbered, opaque, sealed envelopes that were opened by trained study personnel. Each envelope contained the group allocation and instructions for the attending anaesthesiologist. Weiwei Cai generated the random allocation sequence, Huanhuan Ni enrolled participants, and Longde Zhao assigned participants to interventions. Weiwei Cai was blinded after assignment to interventions and performed the second lung ultrasound examination. Finally 46 children were randomly divided into spontaneous breathing group (