This prospective observational study aims to evaluate the effect of internal jugular vein catheterization on intracranial pressure using optic nerve sheath diameter (ONSD) measurements and carotid artery Doppler ultrasonography in adult patients undergoing surgery under general anesthesia.

ONSD will be measured noninvasively using transorbital ultrasonography, and carotid Doppler parameters will be assessed at two time points: after endotracheal intubation and approximately 5 minutes after catheterization. The primary objective is to assess short-term changes in ONSD following catheterization.

Secondary objectives include evaluating changes in carotid Doppler measurements and their relationship with ONSD, as well as associations with physiological parameters such as blood pressure, heart rate, oxygen saturation, and end-tidal carbon dioxide.

This prospective observational study is designed to investigate the effect of internal jugular vein catheterization on intracranial pressure using noninvasive ultrasonographic methods in adult patients undergoing elective surgery.

Internal jugular vein catheterization will be performed as part of routine clinical care in patients requiring central venous access. The study does not introduce any additional intervention beyond standard clinical practice.

Intracranial pressure will be indirectly assessed by measuring optic nerve sheath diameter (ONSD) using transorbital ultrasonography with a high-frequency linear probe. Measurements will be obtained at a standardized depth of 3 mm posterior to the optic disc.

In addition, carotid artery Doppler ultrasonography will be performed to assess hemodynamic parameters, including flow velocities and derived indices.

All ultrasonographic measurements will be performed at two predefined time points: after endotracheal intubation and approximately 5 minutes following internal jugular vein catheterization. Measurements will be obtained from the side of catheterization.

The primary outcome is the change in ONSD following internal jugular vein catheterization. Secondary outcomes include changes in carotid Doppler parameters and their relationship with ONSD, as well as associations with physiological variables such as blood pressure, heart rate, oxygen saturation, and end-tidal carbon dioxide.

Ultrasonographic assessments are noninvasive and considered safe, with no known risk to participants. All data will be collected prospectively and analyzed to evaluate short-term physiological changes associated with the procedure.

Inclusion Criteria:

• Age ≥18 years
• Patients undergoing surgery under general anesthesia
• Patients requiring internal jugular vein catheterization as part of routine clinical care
• Ability to obtain optic nerve sheath diameter measurements using transorbital ultrasonography
• Provision of informed consent

Exclusion Criteria:

• Known intracranial pathology affecting intracranial pressure
• Ocular conditions preventing accurate ultrasonographic measurement (e.g., orbital trauma, ocular surgery, infection)
• Hemodynamic instability
• Contraindication to internal jugular vein catheterization
• Inability to obtain adequate ultrasound images

Adult patients undergoing surgical procedures under general anesthesia at a tertiary care hospital, in whom internal jugular vein catheterization is performed as part of routine clinical care.

Individual participant data (IPD) will not be shared due to institutional policies and concerns regarding patient confidentiality and data privacy. Data may be available from the corresponding author upon reasonable request and with appropriate ethical approvals.