As a result of COVID-19 pandemics

Positive end-expiratory pressure (PEEP) is sometimes used during perioperative period, as it has favourable effects on lung mechanics. Unfortunately, it has some negative effects on the patients, like increased intraabdominal, intrathoracic, intracranial and intraocular pressures. In this study the investigators aimed to investigate the effects of different PEEP levels on the patients' intraocular and intracranial pressures. Intraocular pressure will be measured by ocular tonometry, and intracranial pressure will be estimated by optic nerve sheath diameter measurement. The measurements will be performed in the operating room in the patients undergoing laparotomic surgery.

Inclusion Criteria:

• Patients undergoing laparotomy for gastrointestinal surgery
• American Society of Anesthesiologists (ASA) 1 or 2 physical status
• Elective surgery

Exclusion Criteria:

• Patients with glaucoma
• ASA 3 or over physical status
• Emergency surgery