Highlights • The role of FiO 2 in reducing postoperative pulmonary complications (PPCs) is unclear. • Mortality within 7 postoperative days did not differ between groups. • Mean length of hospital stay did not differ between the two groups. • There was no difference between 30% and 80% FiO₂ regarding the reduction of PPCs. • However, 30% FiO₂ resulted in less severe pulmonary complications.