Early allograft dysfunction (EAD) remains one of the most important complications following orthotopic liver transplantation (OLT). Currently, there is no established intraoperative biomarker that reliably predicts graft dysfunction at an early stage. Near-infrared spectroscopy (NIRS) combined with the vascular occlusion test (VOT) is a non-invasive method for assessing tissue oxygenation and microcirculatory reserve. This prospective observational study aims to investigate whether VOT-derived parameters, including desaturation slope, recovery slope and post-ischemic hyperemic area under the curve (AUC-H), can predict EAD in liver transplant recipients. Measurements will be performed at four predefined intraoperative timepoints: after induction of anesthesia, during the anhepatic phase, during the neohepatic phase and at the end of surgery. The primary outcome is the occurrence of EAD according to Olthoff criteria.

Orthotopic liver transplantation (OLT) is the treatment of choice for patients with end-stage liver disease and acute liver failure. Despite advances in surgical technique and perioperative management, early allograft dysfunction (EAD) remains a common postoperative complication associated with increased morbidity, prolonged intensive care unit stay and reduced graft survival.

Increasing evidence suggests that microcirculatory dysfunction may play a pivotal role in the pathophysiology of ischemia-reperfusion injury and graft dysfunction after OLT. In contrast to conventional macrocirculatory monitoring, microcirculatory assessment provides direct information regarding tissue oxygenation, endothelial function and the adequacy of oxygen delivery at the cellular level.

Near-infrared spectroscopy (NIRS) combined with the vascular occlusion test (VOT) is a non-invasive and well-established technique for evaluating microvascular reactivity. During VOT, transient arterial occlusion is induced using a pneumatic cuff, while tissue oxygen saturation (StO₂) is continuously recorded. Parameters derived from the test include the desaturation slope (downslope), the recovery slope (upslope) and the area under the post-ischemic hyperemic curve (AUC-H), reflecting tissue oxygen consumption, endothelial function and microvascular reserve, respectively.

The present study is a prospective, single-center observational cohort study aiming to investigate the prognostic value of VOT-derived parameters in liver transplant recipients. VOT measurements will be performed at four predefined intraoperative timepoints: following induction of anesthesia (baseline), during the anhepatic phase, during the neohepatic phase after graft reperfusion, and at the end of surgery.

The primary endpoint is the occurrence of early allograft dysfunction according to the Olthoff criteria. Secondary outcomes include intensive care unit length of stay, hospital length of stay, duration of mechanical ventilation and established liver transplant outcome scores including L-GrAFT, EASE and EASIX.

In addition, exploratory analyses will investigate the relationship between VOT-derived parameters normalized to oxygen delivery (DO₂ and DO₂I) and postoperative outcomes, aiming to determine whether microcirculatory reserve adjusted for systemic oxygen transport provides superior prognostic information.

Inclusion Criteria:

• Adult patients aged 18 years or older
• Patients scheduled to undergo orthotopic liver transplantation
• Ability to obtain intraoperative Near-Infrared Spectroscopy measurements
• Written informed consent obtained before enrollment

Exclusion Criteria:

• Age younger than 18 years
• Refusal or inability to provide informed consent
• Emergency liver transplantation without sufficient time for enrollment
• Inability to perform the Vascular Occlusion Test or obtain reliable NIRS measurements
• Severe peripheral vascular disease or local upper-limb conditions interfering with monitoring

The study population will consist of adult patients undergoing orthotopic liver transplantation at the participating center. Eligible patients will be enrolled before surgery and monitored intraoperatively using Near-Infrared Spectroscopy during standardized Vascular Occlusion Tests. The cohort will include liver transplant recipients managed according to standard institutional anesthetic, surgical and postoperative care protocols