This single-center randomized controlled trial will evaluate whether real-time visual feedback from electrical impedance tomography (EIT) improves the immediate distribution of lung ventilation during incentive spirometry in adults with postoperative atelectasis. Approximately 60 participants will be randomized 1:1 to receive either EIT-guided visual feedback or standardized verbal guidance during one session of 30 incentive-spirometry breaths. The primary outcome is the change in dorsal ventilation fraction from before training to 5 minutes after training. Secondary outcomes include inspiratory capacity, ventilation homogeneity, dependent silent spaces, end-expiratory lung impedance, oxygenation, in-hospital intubation or reintubation, and intervention-related adverse events.

Eligible adults recovering from major thoracic or upper-abdominal surgery will be screened using bedside lung ultrasound and baseline EIT. Participants must be spontaneously breathing, clinically stable, able to follow instructions, and have a baseline dorsal ventilation fraction below 50%.

After a 2-minute baseline EIT recording in a 30- to 45-degree semi-recumbent position, participants will be randomized through a central randomization system using stratified variable blocks based on baseline dorsal ventilation fraction. Both groups will complete three sets of 10 incentive-spirometry breaths. In the experimental group, the EIT screen will be visible and trained staff will provide real-time, target-directed feedback intended to increase ventilation in dependent dorsal lung regions. In the control group, the EIT screen will be concealed and participants will receive standardized verbal instructions without imaging feedback.

After training, participants will rest for 5 minutes and undergo a second 2-minute EIT recording under stable oxygen-therapy conditions. EIT outcomes will be calculated offline by assessors blinded to group assignment. Respiratory-support outcomes will be recorded through hospital discharge. Intervention-related adverse events will be recorded from the start of the single intervention session through 24 hours after completion of the session.

Inclusion Criteria:

1. Age 18 years or older.
2. Admitted to an intensive care unit or postoperative monitoring unit after major thoracic or upper-abdominal surgery; tracheal tube removed; spontaneously breathing; and clinically stable.
3. Alert and able to understand and follow incentive-spirometry and EIT instructions.
4. Bedside lung ultrasound shows atelectasis or markedly reduced aeration in dorsal or posterolateral lung regions, with the lung-ultrasound assessment recorded.
5. Baseline EIT during quiet breathing in a semi-recumbent position shows insufficient dorsal ventilation with potential for improvement; dorsal ventilation fraction below 50%.
6. Written informed consent provided by the participant or legally authorized representative according to the ethics-approved process, with participant re-consent when decision-making capacity returns.

Exclusion Criteria:

1. Ongoing invasive mechanical ventilation or noninvasive ventilation, or high-flow nasal oxygen when study conditions cannot be maintained stably.
2. Hemodynamic instability or inability to tolerate a semi-recumbent position.
3. Inability to cooperate with training or impaired consciousness.
4. Unsuitable for EIT monitoring, including an implanted pacemaker or defibrillator incompatible with the device, severe skin disease at the electrode-belt site, or known relevant allergy.
5. Severe underlying pulmonary disease likely to substantially affect ventilation distribution and obscure the intervention effect.
6. Chest-wall deformity or severe scoliosis affecting EIT image quality.
7. Body mass index greater than 35 kg/m2.
8. Pregnancy or breastfeeding.
9. Current participation in another interventional clinical trial that could interfere with study outcomes.
10. Any other condition that, in the investigator's judgment, makes participation inappropriate.

Participants and bedside intervention staff cannot be masked because the experimental group views the EIT screen. EIT data analysts and outcome assessors remain blinded to group assignment.