A total of 40 ASA (American Society of Anesthesiology) physical status I-III who underwent lumbar disc hernia repair for one or two levels were included in this prospective study. A standard anesthesia protocol was performed in all patients. Routine intraoperative monitoring consisted of electrocardiography, automatic noninvasive arterial blood pressure, pulse oximetry, capnography, and cerebral tissue oxygen saturation through NIRS.Patients' demographics such as age, gender, height, weight, BMI, smoking status and pre-existing medical conditions were recorded.The patients were allocated equally to two groups according to BMI as Group I: BMI ≥30kg/m2,Group II <30 kg/m2.

Routine intraoperative monitoring consisted of electrocardiography, automatic noninvasive arterial blood pressure, pulse oximetry, capnography, and cerebral tissue oxygen saturation through NIRS.Frontal lobe oxygenation was monitored continuously and recorded every 5 minutes.Before positioning patients on the operating table, a Foley catheter was placed. IAP was measured in the following positions in all patients: 1) in the supine position after intubation 2) in the prone position before the skin incision.All patients were placed into the prone position on the silicone pads after general anesthesia.Before statistical analysis, the 40 patients were allocated equally to two groups according to the World Health Organization Guideline of BMI: Group I: BMI ≥30kg/m2, Group II <30 kg/m2

Inclusion Criteria:

• Age 18-70 years
• ASA physical status I - III patients undergoing lumbar disc hernia repair for two or less levels

Exclusion Criteria:

• Age smaller than 18 or older than 70 years,
• ASA physical status more than III,
• Patients with a history of carotid artery stenosis, prior neck surgery, cervical canal stenosis, stroke, neurological deficit, myocardial infarction, spinal cord injury and sudden vision loss

40 ASA physical status I - III patients undergoing lumbar disc hernia repair for two or less levels. The ethical committee approval for the study was taken from the Abdurrahman Yurtaslan Oncology Training and Research Hospital (2014-2182). The informed consent was obtained for all the patients that were included in the study