Effect of Different Oxygen Concentrations Before Extubation After General Anesthesia on Hypoxemia After Extubation in Post-anesthesia Care Unit

Before extubation during the anesthesia recovery period, 100% oxygen is routinely inhaled to increase the oxygen reserves, maximizing the time window for anesthesiologists to adjust strategies when they encounter hypoxemia after extubation. However, even inhaling a short period of pure oxygen can cause absorptive atelectasis, and may even impair the effectiveness of intraoperative protective ventilation measures continuing to post-operative period. The purpose of this study is to determine whether 30% oxygen before extubation after abdominal surgery could reduce hypoxemia incidence after extubation during the recovery period or not, compared to 100% oxygen. 590 patients scheduled to abdominal surgeries, will be randomly assigned to receive 30% or 100% oxygen concentration from the end of surgery to extubation after general anesthesia in the post-anesthesia care unit. The incidence of hypoxemia (SpO2 \< 90%) from extubation to leaving the post-anesthesia care unit (PACU) is the primary outcome.