This is a single-center, prospective, observational, self-controlled clinical study conducted at the Neurosurgical Intensive Care Unit of Xijing Hospital, The First Affiliated Hospital of Air Force Military Medical University. The study aims to evaluate whether non-invasive Electrical Impedance Tomography (EIT) can reliably assess cerebral blood flow autoregulation in neurocritically ill participants, by comparing EIT-derived parameters with the current gold-standard invasive index PRx.

Cerebral blood flow autoregulation helps maintain stable brain perfusion in critically ill neurological patients. Impaired autoregulation raises the risk of secondary brain injury. The current standard evaluation requires invasive intracranial pressure monitoring, which carries risks of infection, bleeding, and tissue damage. EIT is a non-invasive, radiation-free bedside monitoring technique that uses scalp electrodes to measure real-time changes related to cerebral blood flow, with no additional harm to participants.

Adult participants admitted to the neurosurgical intensive care unit who require routine invasive intracranial pressure monitoring will be enrolled, with informed consent provided by legal guardians. All participants receive standard clinical care as prescribed by current medical guidelines; no extra experimental treatments, drugs, or invasive procedures are applied for this study.

During the study, invasive monitoring data and non-invasive EIT brain monitoring data will be collected simultaneously. Researchers will analyze the correlation and consistency between EIT-derived parameters and the gold-standard index.

This study has received ethical approval from the Medical Ethics Committee of The First Affiliated Hospital, Air Force Military Medical University. All participant information is anonymized to protect privacy, and adverse events will be recorded and reported in accordance with regulatory requirements. The results are expected to support a safe, non-invasive monitoring method for cerebral blood flow autoregulation in neurocritical care.

Background and Rationale Cerebral autoregulation (CA) is the ability of the cerebrovascular system to maintain relatively constant cerebral blood flow when cerebral perfusion pressure is extremely high or low. In neurocritical patients with acute intracerebral hemorrhage, subarachnoid hemorrhage, or ischemic stroke, impaired CA is closely associated with secondary brain injury, intracranial hypertension, neurological deterioration, and poor outcomes. The pressure reactivity index (PRx), calculated as the moving Pearson correlation between invasively measured intracranial pressure (ICP) and mean arterial pressure (MAP), is the current gold standard for bedside assessment of CA. However, invasive ICP monitoring requires surgical placement of an intraventricular or intraparenchymal catheter, which carries risks of infection, hemorrhage, cerebrospinal fluid leakage, and tissue damage, and requires specialized expertise and intensive care resources, limiting widespread use.

Electrical impedance tomography (EIT) is a non-invasive, radiation-free, real-time biomedical imaging technique that measures regional changes in bioimpedance, which reflect variations in cerebral blood volume and tissue perfusion. A custom-built cerebral EIT system (EC100-PRO) has been developed by the research team. It uses 16 scalp electrodes placed in a ring configuration to continuously acquire impedance signals. Through standardized signal processing and image reconstruction algorithms, EIT-derived parameters that track cardiac-synchronous cerebral blood volume pulsations are generated. Preclinical and pilot clinical data indicate that these EIT-derived parameters correlate with changes in cerebral perfusion and autoregulatory status. This study aims to validate the agreement between EIT-derived parameters and the reference standard PRx, thereby establishing a non-invasive, continuous alternative for CA monitoring in neurocritical care.

Study Design and Technical Framework This is a single-center, prospective, observational, self-controlled clinical study conducted in the Neurosurgical Intensive Care Unit (NICU) of Xijing Hospital, The First Affiliated Hospital of Air Force Military Medical University. The study is observational: EIT monitoring serves only as an additional non-invasive signal acquisition and does not interfere with, terminate, or affect the patient's original clinical diagnosis and treatment plan. It is self-controlled because invasive ICP/ABP data and non-invasive EIT data are collected synchronously from the same patient, using the patient's own invasive standard (PRx) to verify the accuracy of the non-invasive index.

All participants receive standard clinical care according to current international neurocritical care guidelines (including blood pressure management per the 2024 Chinese Expert Consensus on Hypertension Management in Stroke Patients, sedation, analgesia, and ICP-directed therapy). No experimental drugs, additional surgical procedures, or treatment modifications are applied for research purposes. EIT monitoring is add-on only and does not interrupt routine care.

Continuous synchronous multimodal data acquisition is performed during the participant's NICU stay. Invasive MAP (via femoral arterial catheter) and ICP (via intraventricular catheter) are measured as standard of care. The EIT system applies a 1 mA, 50 kHz alternating current through 16 Ag/AgCl electrodes placed equidistantly around the scalp at the level of the upper border of the eyebrow arch to the external occipital protuberance. Electrode-skin impedance is kept below 5 kΩ. EIT data are acquired at 40 frames per second.

Signal preprocessing includes low-pass filtering at 0.05 Hz to remove respiratory and high-frequency artifacts and resampling to 10-second averages. The reference index PRx is calculated as the Pearson correlation between MAP and ICP within a 300-second sliding window (step 60 seconds). From the EIT image sequence, a parameter reflecting cardiac-synchronous cerebral blood volume pulsation is extracted. Within the same 300-second sliding window, the correlation between MAP and this EIT-derived parameter (called the EIT-CA index) is computed. Data segments with electrode contact impedance >5 kΩ or motion artifacts exceeding 10% of the recording duration are excluded. At least 2 hours of continuous valid data per participant are required for analysis.

Study Design and Technical Framework This is a single-center, prospective, observational, self-controlled clinical study conducted in the Neurosurgical Intensive Care Unit (NICU) of Xijing Hospital, The First Affiliated Hospital of Air Force Military Medical University. The study is observational: EIT monitoring serves only as an additional non-invasive signal acquisition and does not interfere with, terminate, or affect the patient's original clinical diagnosis and treatment plan. It is self-controlled because invasive ICP/ABP data and non-invasive EIT data are collected synchronously from the same patient, using the patient's own invasive standard (PRx) to verify the accuracy of the non-invasive index.

All participants receive standard clinical care according to current international neurocritical care guidelines (including blood pressure management per the 2024 Chinese Expert Consensus on Hypertension Management in Stroke Patients, sedation, analgesia, and ICP-directed therapy). No experimental drugs, additional surgical procedures, or treatment modifications are applied for research purposes. EIT monitoring is add-on only and does not interrupt routine care.

Continuous synchronous multimodal data acquisition is performed during the participant's NICU stay. Invasive MAP (via femoral arterial catheter) and ICP (via intraventricular catheter) are measured as standard of care. The EIT system applies a 1 mA, 50 kHz alternating current through 16 Ag/AgCl electrodes placed equidistantly around the scalp at the level of the upper border of the eyebrow arch to the external occipital protuberance. Electrode-skin impedance is kept below 5 kΩ. EIT data are acquired at 40 frames per second.

Signal preprocessing includes low-pass filtering at 0.05 Hz to remove respiratory and high-frequency artifacts and resampling to 10-second averages. The reference index PRx is calculated as the Pearson correlation between MAP and ICP within a 300-second sliding window (step 60 seconds). From the EIT image sequence, a parameter reflecting cardiac-synchronous cerebral blood volume pulsation is extracted. Within the same 300-second sliding window, the correlation between MAP and this EIT-derived parameter (called the EIT-CA index) is computed. Data segments with electrode contact impedance >5 kΩ or motion artifacts exceeding 10% of the recording duration are excluded. At least 2 hours of continuous valid data per participant are required for analysis.

Inclusion Criteria:

• Aged ≥18 years old
• Diagnosed with acute intracerebral hemorrhage, subarachnoid hemorrhage or ischemic stroke, admitted to the Neurosurgical Intensive Care Unit
• Receiving routine invasive monitoring of intracranial pressure (ICP) and mean arterial pressure (MAP)
• Written informed consent obtained from the legally authorized representative

Exclusion Criteria:

• Severe scalp damage, infection or skull defect affecting electrode placement
• Craniotomy history with metal implants interfering with EIT signal acquisition Pregnancy
• Terminal critical illness with estimated survival <24 hours
• Severe coagulation dysfunction or confirmed allergy to electrode materials
• Unavailable for ≥2-hour continuous valid monitoring data collection

The study population consists of adult neurocritical care inpatients admitted to the Neurosurgical Intensive Care Unit (NICU) of Xijing Hospital, the First Affiliated Hospital of Air Force Military Medical University. Eligible participants are patients aged ≥18 years with severe acute cerebrovascular diseases, severe traumatic brain injury and other critical central nervous system disorders who require NICU admission and routine invasive intracranial pressure and mean arterial pressure monitoring, forming a single-center prospective observational cohort with consecutive enrollment.

Individual participant data (IPD) will not be shared with external researchers due to privacy protection and institutional data security regulations. Aggregated statistical results will be published in peer-reviewed journals.