Chronic thromboembolic pulmonary hypertension (CTEPH), one of the leading causes of pulmonary hypertension (PH), is caused by the chronic obstruction of the pulmonary arteries following episode of pulmonary embolism. It is the only cause of PH which is accessible to a potential curative surgical treatment: the pulmonary endarterectomy (PEA). Because of their underlying disease (pulmonary hypertension and potential right heart dysfunction), anesthesia should be performed cautiously. Perioperative hemodynamic management often requires the administration of a vasopressor to maintain the arterial pressure above a specific threshold of 65 mmHg.

Low dose of vasopressin increases systemic arterial pressure with minimal effects on the pulmonary circulation. This profile suggests that vasopressin may be an ideal agent for vasopressor support in the high-risk population of patients with pulmonary hypertension.

To date, there is no data on the use of vasopressin in patient undergoing PEA surgery. The interesting properties of vasopressin - specifically, its ability to increase systemic arterial resistance while having a low impact on pulmonary resistance and offering potential renal protective effects - are highly advantageous in the specific subset of patient scheduled for PEA.

The investigators aim to conduct a randomized single center open label study to compare the effect of vasopressin compared to norepinephrine on mean pulmonary artery pressure after PEA surgery.

The primary objective of this study is to determine whether the use of vasopressin compared to norepinephrine decrease the mean pulmonary artery pressure after PEA surgery.

Participation to the study involves follow up at day 30 following surgery.

Inclusion Criteria:

• Age ≥18 years;
• Patient scheduled for pulmonary endarterectomy surgery;
• In women of childbearing potential: negative serum pregnancy test and use of adequate contraception;
• Affiliation to the French social care service;
• Patient able to understand and sign a written informed consent form.

Exclusion Criteria:

• Emergency surgery;
• Mesenteric ischemia and/or acute coronary syndrome within the month preceding the intervention;
• Patients with documented mesenteric artery stenosis;
• Impossibility to insert the pulmonary artery catheter (anatomical or technical issue);
• Preoperative administration of norepinephrine and/or inotropic drugs (dobutamine, isoproterenol, epinephrine) or patients assisted by veno-venous or veno-arterial ECMO before surgery;
• Known allergy to the active substance vasopressin or to any of its excipients;
• Concomitant coronary bypass procedure or other combined surgery (i.e. valve replacement);
• mPAP<25 mmHg on preoperative right heart catheterization;
• Patient with preoperative natremia below 130 mol/L;
• Patient participating to another interventional clinical trial;
• For females only: documented pregnancy or lactation;
• Patient under tutorship, curatorship or legal protection;
• Patient deprived of liberty.