Inclusion Criteria:  Age ≥65 years old, ASA scoreⅠ-Ⅲ, Scheduled to undergo a 2-hour-or-longer elective major abdominal surgeries  Exclusion Criteria:  Urological surgery or procedure related to renal tissue may be performed during surgeries. Nephrectomy or partial nephrectomy was performed before surgeries. Preoperative glomerular filtration rate<30ml/1.73m2, or end-stage renal disease or renal transplant. Poor hearing or vision and language barrier impeding postoperative assessment. Skin condition incompatible with the adhesive oximetry probe. Refuse to participate in the trial.