Results
postoperative pulmonary complications
Of 57 patients assessed for eligibility, 4 patients did not meet the inclusion criteria, so 53 patients were randomized into two groups and received the intended interventions. One patient was excluded because he returned to the intensive care unit (ICU) with a tracheal tube after the operation in the titration group, and 1 patient was excluded due to technique problems in EIT in the control group. Finally, 51 patients were enrolled in the analyses (Fig. 
Flow diagram of patients undergoing elective supratentorial craniotomy. BMI, body mass index; PEEP, positive end-expiratory pressure; EIT, electrical impedance tomography; ICU, intensive care unit
Demographics and surgery characteristicsData are presented as mean(standard deviation) or a frequency with proportion(%). The standardized mean difference(SMD) with 95% confidence interval (95% CI) is calculated for the data. BMI body mass index, ASA American Society of AnesthesiologistsDP in the titration group was significantly lower than in the control group, with a median (IQR [range]) of 10 (9–12 [7–13]) cmHThe GI in the titration group showed a tendency to fall immediately after extubation compared with baseline but did not differ between different time points. The differences between the two groups were not significant (
Global inhomogeneity index obtained from electrical impedance tomography and lung ultrasonography scores at different time points Captions: *, p < 0.05; ***, p < 0.001 compared to baselineIn both groups, there was an increase in the LUSs immediately after extubation and 1 h after extubation (
Representative lung ultrasonography images at different time pointsThe first group is the control group, and the second group is the titration group. The titration group showed better respiratory system parameters than the control group. The compliance in the titration group was higher than that in the control group at 1 h after intubation and at the end of surgery (The changes in the PaO
Patient ventilatory mechanics and gas analysisimmediately afterintubationimmediately afterintubationimmediately afterintubationimmediately afterextubationimmediately afterextubationimmediately afterextubationData are presented as the Median (IQR).Ppeak, airway peak pressure; Pplat, airway plateau pressure. PaCOAt the 3-day follow-up, no PPCs, defined as those with an MGS-2 of at least 4, occurred in either group. During the entire surgical period, the number of patients using vasopressors and requiring crystalloid fluid infusion did not differ between groups(Table 
Surgery and postoperative characteristics2 (8)0 (0)Data are presented as the Median (IQR) or a frequency with proportion(%). RR, respiratory rate; VAS, visual analog scale; PPCs, postoperative pulmonary complications