The goal of this clinical trial is to compare the effects of somatostatin and terlipressin on lowering portal pressure in patients with portal hypertension undergoing liver transplantation, and to investigate whether there are differences in clinical outcomes between the two drugs. The study will evaluate the decrease in portal pressure from baseline following drug administration at defined time points. It will also compare the effects of these drugs on hemodynamics, bleeding, and transfusion requirements. After baseline intraoperative direct portal pressure measurement, a bolus dose of the study drug will be administered, followed by continuous intravenous infusion intraoperatively and for 24 hours postoperatively. Direct portal pressure will be measured again 5 minutes after the bolus dose, after the portal vein anastomosis, after the hepatic artery anastomosis, and, if performed after splenic artery ligation. Hemodynamic parameters will be recorded, and the drugs will be compared in terms of their intraoperative hemodynamic effects. As elevated portal pressure is associated with increased bleeding, intraoperative blood loss and transfusion needs will also be assessed between the groups. Patients will be followed for 7 days postoperatively for clinical and laboratory outcomes.

It is well known that elevated portal pressure during liver resection is associated with increased bleeding, greater surgical difficulty, impaired splanchnic perfusion, a higher incidence of postoperative kidney injury, and increased need for blood transfusion. Somatostatin, a peptide hormone used to reduce portal pressure, lowers portal venous pressure by altering splanchnic blood flow. It is frequently administered in patients with end-stage liver disease for indications such as controlling variceal bleeding and reducing intraoperative portal pressure. Terlipressin, a vasopressin analog, induces vasoconstriction, thereby decreasing portal inflow and venous congestion in the splanchnic circulation. By lowering portal pressure and exerting favorable systemic effects, it is often used intraoperatively in patients with impaired renal function. It has been associated with reduced surgical bleeding and improved renal perfusion.

Following baseline portal pressure measurement from the portal vein (PVP0), patients will receive treatment according to their study group. In the somatostatin (SS) group, a bolus dose of 250 mcg will be administered over 2 minutes, followed by a maintenance infusion at 2.5 mcg/kg/hour. In the terlipressin (TRP) group, a bolus dose of 1 mg will be given over 2 minutes, followed by a maintenance infusion at 2 mcg/kg/hour. Five minutes after completion of the bolus dose, portal pressure will be measured again and recorded with the corresponding time point (PVP1).

Once the hepatic and portal vein anastomoses are completed and graft reperfusion is achieved, the third portal pressure measurement will be taken (PVP2), and right after completion of the arterial anastomosis, the fourth portal pressure measurement will be performed (PVP3). If PVP exceeds 20 mmHg or Hepatic Venous Pressure Gradient (HVPG) exceeds 15 mmHg, splenic artery ligation will be performed to modify portal inflow and prevent small-for-size syndrome. If performed, this intervention will be recorded, and subsequent measurements will be repeated (PVP4)

Intraoperative ultrasound routinely performed by radiology will be used to measure arterial (peak systolic velocity, resistive index, acceleration time) and portal (flow volume) flow parameters, which will be documented. Hemodynamic data will be recorded throughout all measurements. The study drugs will be administered as continuous infusion for at least 24 hours, and if portal pressure remains elevated, the infusion may be extended up to a maximum of 5 days.

Inclusion Criteria:

Patients scheduled for right lobe living donor liver transplantation with clinically significant portal hypertension (esophageal varices, thrombocytopenia (<100,000), ascites, encephalopathy; Child-Turcotte-Pugh class B-C)

Exclusion Criteria:

• Allergy to any of the medications to be used
• Portal vein thrombosis
• Being treated with terlipressin with a diagnosis of hepatorenal syndrome
• Portopulmonary hypertension
• Acute on chronic liver failure
• Chronic renal failure (glomerular filtration rate ≤ 30%)
• Myocardial ischemia
• Uncontrolled hypertension
• Arrhythmia
• Multiple solid organ transplantation

The investigators will not share individual patient data (IPD).

The surgeons performing the portal pressure measurements and the participants will be blinded to group allocation. The study drugs will be prepared and labeled by an independent anesthesiologist/pharmacist not involved in outcome assessment.