Method:18-65 yo, ASA2-3 status, 60 MO patients which planned SLG under general anesthesia were included.Two patient in Group 5 PEEP were excluded because of the haemodynamic instability during procedure. Patients were divided into 2 groups which was ventilated with no PEEP (Group ZEEP)(n=30) and 5 cmH2O PEEP levels (Group5 PEEP)(n=28). All patients were use right hand dominant. Near infrared spectroscopy probes were applied to both frontal cerebral area of all patiens and measured rSO2 values. IAP were measured transvesically in all groups. Datas were recorded as basal, after induction of anesthesia, 5 minute before insuflation(5BI), 5 minute after insuflation(5BA), 15, 30, 45, 60 minute after induction, 5 minute before desuflation(5BD) and 5 minute after desuflation(5AD) time periods. Invasive arterial pressures, serebral oxymeter values, 5 lead electrocardiography, peripheral oxygen saturation, end tidal carbondioxide, peak inspiratory pressures, IAP, were recorded time periods in all groups. Arterial blood sample analysed on 5BI,5AI, 5AD periods.