Inclusion Criteria:  enrollment of patients aged 18 years or above； Eligible adult patients had an American Society of Anesthesiologists (ASA) physical status classification of I to IV undergoing elective or expedited nonurgent, noncardiac surgery with general anesthesia  Exclusion Criteria:  patient refusal; morbid obesity (BMI >40 kg/ m²); American Society of Anesthesiologists (ASA) physical status categories IV-V; previous intrathoracic procedure; severechronic obstructive pulmonary disease (forced expiratory volume in 1 s <30% of the predicted value; a contraindication to radial artery cannulation.