<qa>  What was the NIBP monitor?Approval from Ethical Committee of Faculty of Medicine University of Indonesia was acquired prior conducting the study. Subjects were given informed consent before enrolling the study. Non-invasive blood pressure NIBP monitor, electrocardiogram ECG and pulse-oximeter was set on the subjects in the operation room. Anesthesia procedure was epidural regional block. After given premedication midazolam 0.05 mgkgBW and fentanyl 1-2 ugkgBW, induced with propofol, 1-2 mgkgbb, endotracheal tube intubation was done facilitated by atracurium 0.5 mgkgbb. Mechanical ventilation was set up with volume control mode, Positive End Expiratory Pressure PEEP 5cmH2O 5 centimeters of water, O2 fraction FiO2 30-50, target carbondioxide CO2 35-45. Volume tidal was given according to the group 6 mLkgBW or 10 mlkgBW. Hemodynamic, ventilation parameter, Electrical Impedance Tomography EIT parameter were recorded. If desaturation happened intraoperatively will be managed by increasing FiO2 and recruitment maneuver until oxygen saturation SpO2 95. Data was analyzed using Statistical Program for Social Sciences SPSS, for numeric data using unpaired T-test or Mann-Whitney-U test, for categorical data using Chi-square or Fisher Exact Test. Significant value is p0.05. 