It is difficult to measure the several levels of intracranial pressure during abdominal surgery, and direct monitoring with intracranial devices is often impossible. Measurement of optic nerve sheath diameter (ONSD) via ultrasonography has been developed as an alternative method for evaluating intracranial pressure. Increased intracranial pressure may cause in expanding of the optic nerve sheath and may increase the diameter. Therefore, measuring the diameter of the optic nerve sheath via ultrasonography is considered as a non-invasive, easy-to-apply and reliable method to evaluate intracranial pressure.

The peritoneum is inflated with carbon dioxide (insufflation) and head-down position is performed (Trendelenburg) during laparoscopic colon and gynecologic surgeries. Intracranial pressure (ICP) may be affected by positive intraabdominal pressure due to pneumoperitoneum. The Trendelenburg position (usually at a degree of 25-400) causes increasing in the pressure of cerebrospinal fluid during surgery. Therefore, cerebral edema and an increasing in ICP may occur. It is difficult to measure the several levels of intracranial pressure during abdominal surgery, and direct monitoring with intracranial devices is often impossible. Measurement of optic nerve sheath diameter (ONSD) via ultrasonography has been developed as an alternative method for evaluating intracranial pressure. The optic nerve is an extension of the central nervous system, surrounded by cerebrospinal fluid (CSF) and continues with the nerve sheath. Increased intracranial pressure may cause in expanding of the optic nerve sheath and may increase the diameter. Therefore, measuring the diameter of the optic nerve sheath via ultrasonography is considered as a non-invasive, easy-to-apply and reliable method to evaluate intracranial pressure.

In this study, we aimed to evaluate the changes of optic nerve sheath diameter in patients who will undergo laparoscopic colon and gynecologic surgery during trendelenburg position. Our primary goal is to compare the optic nerve sheath diameters via ultrasonography, and our secondary aim is to evaluate the effect of this change on intracranial pressure.

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) classification I-II
• Scheduled for laparoscopic colon and gynecologic surgeries under general anesthesia

Exclusion Criteria:

• use of beta blocker or diuretic drugs
• severe heart failure
• diabetes with ocular or neurologic complications
• history of cardiac, eye, intracranial, and thoracic surgery
• history of hydrocephalus, glocoma, intracranial tumor, cerebrovascular disease

Laparoscopic colon and gynecologic surgery patients aged between 18-75 years with ASA I and ASA II status will be included in this randomized prospective study.

We will not plan to share IPD data