The aim of this clinical trial is to determine the effect of minimal low-flow versus high-flow anesthesia on intraocular pressure (IOP) by non-contact tonometry, optic nerve sheath diameter (ONSD) by USG and optic perfusion pressure (OPP) in percutaneous nephrolithotomy operations. He will also learn about the effect on hemodynamic responses and arterial oxygenation. The main questions it aims to answer are: What are the effects of low-flow anesthesia combined with prone position on intraocular pressure (IOP), optic nerve sheath diameter (ONSD) and optic perfusion pressure (OPP)? Which anesthesia flow type has optimal eye-protective results? The investigators will compare minimal low-flow and high-flow anesthesia. Participants: The study will include patients between the ages of 18-60 years with ASA (American Society of Anesthesiologists) risk classification I-II-III, who are scheduled for unilateral percutaneous nephrolithotomy (PCNL) operation in the Urology Clinic under elective conditions and who have given informed consent.
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Optic nerve sheath diameter (ONSD) measurements
Timeframe: Measurements will be performed serially after induction of anesthesia (T0), 1 min after intubation (T1), 30 min after supine position (T2), supine from prone position (T3) and 5 min after extubation (T4).