Figure 1 Patient flow diagram of this study. Studies have found that preoperative rSO2 value less than 60% is closely related to the occurrence of postoperative mental state dysfunction in elderly patients, therefore, patients with baseline rSO2 value <60% before anesthesia induction were removed from the trial. MV – conventional mechanical ventilation; LPV – lung-protective ventilation; rSO2 – cerebral oxygen saturation.