BACKGROUND: Lung expansion therapy is often ordered after surgery to improve alveolar ventilation and reduce risks of postoperative pulmonary complications. The impact of lung expansion therapy at altering ventilation in patients who are not intubated has not been described. The primary purpose of this study was to determine if there is a difference in dorsal redistribution of ventilation and incidences of postoperative pulmonary complications when comparing incentive spirometry (IS) with Ez-PAP lung expansion therapy after upper abdominal surgery. Our a priori null hypothesis was that there are no differences. METHODS: This randomized controlled trial enrolled adult human subjects after upper-abdominal surgery from January 2017 to November 2018. The subjects were allocated to receive IS or EzPAP 3 times a day on postoperative days 1-5. An electrical impedance tomography device was connected to the subjects for a single lung expansion therapy session on postoperative days 1, 3, and 5 to measure the change in post-lung expansion therapy dorsal end-expiratory lung impedance (⌬EELI%). Lung expansion therapy sessions with electrical impedance tomography included 2 min of normal breathing, 3 cycles of 10 breaths, and 2 min of normal breathing after cycle 3. Postoperative pulmonary complications were screened until hospital discharge. Mann-Whitney, chi-square, and Fisher exact tests were applied. Data were reported as count (n), percentage, and median (interquartile range) for primary and secondary outcomes. Alpha (2-tailed) was < 0.05. RESULTS: A total of 112 subjects were enrolled to receive IS (n ‫؍‬ 56) or EzPAP (n ‫؍‬ 56). Baseline characteristics were equal. Post-lung expansion therapy dorsal ⌬EELI% increased for both groups, but the dorsal ⌬EELI% for IS versus EzPAP on postoperative day 1 (16% versus 12%, P ‫؍‬ .39), postoperative day 3 (6% versus 6%, P ‫؍‬ .68), and postoperative day 5 (9% versus 6%, P ‫؍‬ .46) was not significantly different. Hospital length of stay (4 d; P ‫؍‬ .30) and incidence of postoperative pulmonary complications (3.6% versus 7.1%, P ‫؍‬ .19) were similar. CONCLUSIONS: There was no significant post-lung expansion therapy dorsal ⌬EELI% or postoperative pulmonary complications among the adults who received IS or EzPAP 3 times a day after upper abdominal surgery. (ClinicalTrials.gov registration NCT02892773.)Dräger provided an electrical impedance tomography device and electrode belts.