Effect of Internal Jugular Vein Catheterization on Intracranial Pressure and Intracranial Blood Flow

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.

• Internal Jugular Vein Catheterization (Procedure): Internal jugular vein catheterization is performed in patients undergoing major surgical procedures when clinically indicated as part of routine perioperative care. The procedure is not assigned by the study. Additional non-invasive ultrasound measurements, including optic nerve sheath diameter assessment, are obtained to evaluate physiological changes associated with catheterization without altering standard clinical management. Ultrasonography is a non-invasive and safe imaging method routinely used in clinical practice.

Primary outcomes

• Change in Optic Nerve Sheath Diameter (mm) Following Internal Jugular Vein Catheterization [Baseline (immediately after endotracheal intubation) and 5 minutes after internal jugular vein catheterization]: Optic nerve sheath diameter (ONSD) will be measured in millimeters using transorbital ultrasonography at 3 mm posterior to the optic disc on the side of catheterization. The outcome is defined as the difference between measurements obtained immediately after endotracheal intubation (baseline) and 5 minutes after internal jugular vein catheterization. Higher values indicate increased optic nerve sheath diameter.

Secondary outcomes

• Change in Internal Carotid Artery Peak Systolic Velocity (PSV) Following Internal Jugular Vein Catheterization [Baseline (immediately after endotracheal intubation) and 5 minutes after internal jugular vein catheterization]: Peak systolic velocity (PSV) of the internal carotid artery will be measured in cm/s using Doppler ultrasonography. The outcome is defined as the difference between post-intubation (baseline) and post-catheterization values.
• Change in Internal Carotid Artery End-Diastolic Velocity (EDV) Following Internal Jugular Vein Catheterization [Baseline and 5 minutes after internal jugular vein catheterization]: End-diastolic velocity (EDV) of the internal carotid artery will be measured in cm/s using Doppler ultrasonography. The outcome is defined as the difference between post-intubation and post-catheterization values.
• Change in Internal Carotid Artery Time-Averaged Maximum Velocity (TAMAX) Following Internal Jugular Vein Catheterization [Baseline and 5 minutes after internal jugular vein catheterization]: Time-averaged maximum velocity (TAMAX) will be measured in cm/s using Doppler ultrasonography. The outcome is defined as the difference between post-intubation and post-catheterization values.
• Change in Internal Carotid Artery Pulsatility Index (PI) Following Internal Jugular Vein Catheterization [Baseline and 5 minutes after internal jugular vein catheterization]: Pulsatility index (PI) will be calculated from Doppler measurements (unitless). The outcome is defined as the difference between post-intubation and post-catheterization values.
• Change in Internal Carotid Artery Systolic/Diastolic Ratio (S/D) Following Internal Jugular Vein Catheterization [Baseline and 5 minutes after internal jugular vein catheterization]: The systolic/diastolic (S/D) ratio will be calculated from Doppler measurements (unitless). The outcome is defined as the difference between post-intubation and post-catheterization values.
• Change in Mean Arterial Pressure (MAP) [Baseline and 5 minutes after internal jugular vein catheterization]: Mean arterial pressure (MAP) will be measured in mmHg. The outcome is defined as the difference between post-intubation (baseline) and post-catheterization values.
• Change in Heart Rate [Baseline and 5 minutes after internal jugular vein catheterization]: Heart rate will be measured in beats per minute (bpm). The outcome is defined as the difference between post-intubation and post-catheterization values.
• Change in End-Tidal Carbon Dioxide (EtCO₂) [Baseline and 5 minutes after internal jugular vein catheterization]: End-tidal carbon dioxide (EtCO₂) will be measured in mmHg. The outcome is defined as the difference between post-intubation and post-catheterization values.

Sex: All, ages: 18 Years to any

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

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