Acute brain injury (ABI) is a serious condition that can cause a dangerous increase in pressure inside the skull (called intracranial pressure, or ICP), which can harm the brain. Patients with ABI often need a central venous catheter (CVC) - a small, flexible tube placed into a large neck vein - to receive medications, fluids, and to monitor their circulation. However, placing this catheter might temporarily affect brain pressure, either because of the patient's head position during the procedure or the procedure itself. The effect size and duration are not yet known.

The purpose of this observational study is to understand how placing a CVC in the neck (internal jugular vein) affects brain pressure in patients with acute brain injury. The study will closely monitor changes in brain pressure, blood flow, and oxygen levels in the brain during and immediately after the procedure. The study will also examine whether the brain's ability to regulate its own blood flow (called cerebral autoregulation) influences these changes.

This prospective, observational study will enroll approximately 100-120 adult patients with ABI who are in the Intensive Care Unit (ICU) and need a CVC as part of their regular medical care. The study will be conducted in two large hospitals in China. There is no experimental treatment or intervention; only observation and data recording during the standard medical procedure will be performed.

The main goal is to measure how brain pressure changes during CVC insertion. The study will also look at how long any changes last and whether the brain's blood flow regulation is affected. The results will help doctors better understand the risks of this common procedure and guide safer management of ABI patients in the ICU.

Study Design This is a prospective, multicenter, observational cohort study. The study will be conducted in two intensive care units (ICUs) in China: Beijing Tiantan Hospital (primary center) and Guiyang Second People's Hospital (collaborating center). No experimental intervention is administered; all procedures are part of routine clinical care.

Population and Enrollment A total of 100-120 adult patients (≥18 years) with acute brain injury who require invasive intracranial pressure (ICP) monitoring and are scheduled for percutaneous internal jugular vein catheterization (central venous catheter, CVC) will be enrolled. Enrollment is expected to take 24 months (from March 2026 to February 2028). (Specific etiologies are not listed here as they are detailed in the Eligibility Criteria section.)

Exposure The exposure of interest is the performance of percutaneous internal jugular vein catheterization using the Seldinger technique. The procedure is performed by the patient's primary medical team according to institutional standards, with the patient lying supine, head turned to the contralateral side, and a shoulder roll placed if needed. Ultrasound guidance may be used at the operator's discretion.

Multimodal Monitoring

All enrolled patients already have an ICP monitor in place as part of clinical management (Codman microtransducer or external ventricular drain). Additionally, the following neuromonitoring parameters will be recorded continuously before, during, and after the CVC procedure:

Intracranial pressure (ICP) and derived cerebral perfusion pressure (CPP = MAP - ICP)

Cerebral autoregulation: assessed by pressure reactivity index (PRx) in Beijing Tiantan Hospital, or by transient hyperemic response test (THRT) using transcranial Doppler in Guiyang Second People's Hospital

Regional cerebral oxygen saturation (rSO₂): using near-infrared spectroscopy (EGOS-600A)

Bispectral index (BIS) as an indicator of sedation level

End-tidal CO₂ (EtCO₂) and ventilator parameters (for mechanically ventilated patients)

Hemodynamics: heart rate, systolic/diastolic/mean arterial pressure

All data are collected from existing clinical monitors and recorded at baseline, during catheterization, and up to 30 minutes after the procedure.

Data Collection and Quality Control Data will be collected by trained ICU physicians using standardized case report forms. Two independent data entries will be performed, with discrepancies resolved by consensus with a senior investigator. All personal identifiers will be removed, and a unique study ID will be assigned to each participant. Data will be stored in a password-protected database.

Statistical Analysis Continuous variables will be compared using paired t-test or repeated-measures ANOVA (for normally distributed data) or Wilcoxon signed-rank test / Friedman test (for non-normal data). The relationship between ICP changes and patient/procedural factors will be analyzed using linear mixed-effects models or generalized estimating equations. A subgroup analysis will compare patients with intact versus impaired cerebral autoregulation. All tests will be two-sided with α = 0.05. Sample size was calculated to detect a clinically relevant change in the primary ICP parameter, with 80% power and accounting for a 15% dropout rate; the target enrollment is 100-120 patients to allow for subgroup analyses.

Ethics and Consent The study protocol has been approved by the Institutional Review Board of Beijing Tiantan Hospital, Capital Medical University (approval number: KY 2021-006-02). Written informed consent will be obtained from each patient or their legally authorized representative prior to enrollment. The study is registered at ClinicalTrials.gov (NCT number to be assigned). All procedures are conducted in accordance with the Declaration of Helsinki.

Inclusion Criteria:

• Age ≥ 18 years
• Admitted to the ICU with acute brain injury (including traumatic brain injury, spontaneous intracerebral hemorrhage, large hemispheric infarction, or aneurysmal subarachnoid hemorrhage) and ICU stay ≥ 24 hours
• Invasive intracranial pressure (ICP) monitoring in place as part of clinical care
• Scheduled to undergo percutaneous internal jugular vein catheterization (central venous catheter) as determined by the treating physician
• Written informed consent obtained from the patient or legally authorized representative

Exclusion Criteria:

• Informed consent not obtained
• Intracranial pressure (ICP) > 22 mmHg within the past 48 hours
• Any contraindication to internal jugular catheterization exists (severe coagulopathy with INR > 1.5 or platelets < 50×10⁹/L; neck infection, tumor, prior surgery or anatomical abnormality on either side; or bilateral jugular veins already catheterized)
• Pregnancy or breastfeeding

Adult patients (≥18 years) with acute brain injury (including traumatic brain injury, spontaneous intracerebral hemorrhage, large hemispheric infarction, and aneurysmal subarachnoid hemorrhage) who require invasive intracranial pressure monitoring and are scheduled for clinically indicated percutaneous internal jugular vein catheterization. Patients with ICP >22 mmHg within 48 hours prior to the procedure, contraindications to jugular catheterization (e.g., severe coagulopathy, local neck pathology, bilateral catheters already in place), or who are pregnant/breastfeeding are excluded. The study population is recruited from two ICUs in China (Beijing Tiantan Hospital and Guiyang Second People's Hospital).