Investigator's aim in this study is to compare the more accessible and low-cost Carotid Doppler USG measurements, which are relatively more difficult to access, costly, and have technical disadvantages, and to demonstrate their superiority over each other in the evaluation of cerebral perfusion in liver transplantation surgeries, without any invasive intervention to the patient.

Liver transplant surgeries cause intraoperative problems that are difficult to manage from hemodynamic, respiratory, neurological, hematological, and metabolic perspectives due to the nature of liver failure, which affects many organs and systems. Particularly during the anhepatic period, when the healthy graft is integrated into the recipient's vascular system, clamping of the inferior vena cava, one of the two main veins of the hepatic veins, is often required for its connection. This means that a sudden interruption occurs in the blood volume returning to the heart from the lower part of the body, which constitutes half of the total cardiac output.

Cerebral perfusion is also affected during the anhepatic period, and previous studies have observed impaired cerebral perfusion using cerebral oximetry. However, not every clinic has a cerebral oximetry device, and there are factors that limit its use. Some of these factors include high cost, hyperbilirubinemia, variables that disrupt regional blood flow, diabetes, hypertension, and low hemoglobin.

Ultrasound devices are more commonly available in large clinical centers that perform liver transplant surgeries, even for other purposes. It is possible to evaluate the blood flow to the brain using carotid Doppler ultrasonography. The aim of this study is to measure patients' carotid peak systolic and end-diastolic flow and carotid peak systolic flow variability using carotid Doppler ultrasonography and to compare these measurements with cerebral oximetry measurements.

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Inclusion Criteria:

• Adult patients aged 18-65 years scheduled for elective liver transplantation
• Written informed consent obtained prior to participation

Exclusion Criteria:

• Fulminant hepatic failure
• Hepatic encephalopathy
• Hepatorenal or hepatopulmonary syndrome
• Pre-existing cerebrovascular disease or carotid stenosis
• Severe cardiopulmonary comorbidity
• Refusal to participate

Eligibility is based on biological sex. Both male and female adult patients undergoing liver transplantation are eligible for inclusion. No restrictions are applied based on gender identity.

The study population consists of adult patients aged 18-65 years who underwent elective liver transplantation at Inonu University Turgut Ozal Medical Center. All participants had end-stage liver disease and were monitored intraoperatively for cerebral perfusion using carotid Doppler ultrasonography and near-infrared spectroscopy (NIRS). The study was conducted as a single-center, prospective observational study.

Individual participant data (IPD) will not be shared due to ethical restrictions and institutional data protection policies. Only aggregated anonymized results will be available upon reasonable request.