“…20,21 In the subjects after surgical aortic valve replacement, age, COPD, congestive heart failure, and bleeding disorders were associated with 30-d re-intubation. 22 Similarly, in subjects after thoracic surgery, American Society of Anesthesiology physical status classification of $ III, surgery duration > 80 min, fluid balance during operation > 4,000 mL were found to be independent risk factors of postoperative hypoxemia. [23][24][25][26][27][28] During abdominal surgery, including hepatectomy, upper or upper and lower (vs lower) abdominal incision, multiple procedures (vs one), crystalloid replacement > 6 L, and total surgery duration > 5 h were found to be risk factors.…”