The aim of this study is to evaluate the effect of internal jugular vein catheterization on intracranial pressure in intubated patients in the intensive care unit using optic nerve sheath diameter

Before central venous catheter insertion, the baseline ONSD value will be determined by measuring the optic nerve sheath diameter in the supine and Trendelenburg positions (15 degrees head down).

Immediately after central venous catheter insertion, the measurement will be taken while the patient is still in the Trendelenburg position. The measurement will be repeated at 5, 15, and 30 minutes after the patient is placed in the supine position.

Transorbital optic nerve sheath diameter measurements will be performed using the linear probe of the ultrasound device routinely used in our clinic. The ultrasound linear probe will be gently placed on the eyelid over the closed eye, ensuring no pressure is applied to the patient's eye. The length of the line representing the optic nerve sheath diameter, which intersects the line drawn 3 mm downwards from the lower edge of the eyeball seen on the ultrasound, will be measured and recorded. The optic nerve sheath diameter will be measured transorbitally vertically once from each eye during the first measurement, and the average will be taken.

Inclusion Criteria:

• The study will include adult patients over 18 years of age who are on mechanical ventilation support and monitored in the intensive care unit.

Exclusion Criteria:

• patients with intracranial tumors
• patients with acute traumatic brain injury
• patients diagnosed with acute or chronic eye diseases
• hypercarbic patients
• Patients receiving inotropic support
• patients using medications that affect intraocular pressure

Intubated intensive care unit patients who receive internal jugular vein catheterization