In patients with septic shock, vasopressin is increasingly used in combination with norepinephrine, but its timing of initiation remains heterogeneous and its clinical hemodynamic effects are still insufficiently characterized. Available data suggest variable responses, which may depend on the hemodynamic phenotype at the time of treatment initiation. In particular, the effects of vasopressin may differ according to the presence of preload dependency, baseline cardiac output, impaired systolic function, or baseline diastolic arterial pressure, reflecting the degree of vasoplegia. In this context, the VASO-PHENO study aims to provide a detailed and dynamic description of the early hemodynamic and clinical effects of vasopressin initiation in septic shock.

To date, no clinical study has systematically and dynamically evaluated the effects of vasopressin on central and peripheral hemodynamic parameters according to the hemodynamic profile at the time of its initiation. Describing these effects appears essential to better understand the variability in clinical responses and to contribute to a more rational and personalized approach to vasopressor escalation in septic shock.

In patients with septic shock, hemodynamic profiles are highly heterogeneous. From a pathophysiological perspective, three main hemodynamic phenotypic components may contribute to the septic shock state:

• preload dependency;
• impaired myocardial function, leading to a cardiac output that is inadequate to meet oxygen demand;
• vasoplegia.

In some of these contexts, the introduction of vasopressin, as a pure vasoconstrictor, may be inappropriate or even harmful, by impairing cardiac output or exposing the patient to excessive vasoconstriction and a subsequent risk of ischemia.

Thus:

• In the presence of impaired myocardial function, defined by reduced cardiac output and/or impaired left ventricular ejection fraction, vasopressin initiation may lead to a decrease in cardiac output;
• In the presence of vasoplegia, the effects of vasopressin on mean arterial pressure and microcirculatory indices, such as capillary refill time, mottling, and urine output, may vary according to the severity of the initial vasoplegia, notably reflected by diastolic arterial pressure;
• In the presence of persistent preload dependency, the initiation of a pure vasoconstrictor may either increase cardiac output by increasing venous return, or worsen microcirculatory alterations by enhancing vasoconstriction in a context of hypovolemia.

To date, no study has precisely described the effects of vasopressin on macrocirculatory hemodynamic parameters, including arterial pressure, cardiac output, and central venous pressure, and on routinely assessable microcirculatory parameters, including capillary refill time, mottling, and urine output, according to the different hemodynamic phenotypic components present at the time of vasopressin initiation.

Describing the evolution of these parameters appears essential to better understand the variability in clinical responses and associated outcomes. Such an approach could help identify at-risk profiles and provide objective elements to support a more rational and personalized escalation of vasopressor therapy in septic shock.

Inclusion Criteria:

• Age ≥ 18 years;
• Hospitalized in an intensive care unit;
• Presenting with septic shock according to Sepsis-3 criteria;
• For whom the treating clinician wishes to initiate vasopressin as second-line therapy as part of routine care;
• Undergoing hemodynamic monitoring with a PiCCO2 device (Pulsion Medical Systems, Getinge, Feldkirchen, Germany) or pulmonary artery catheterization as part of routine care.

Exclusion Criteria:

• Patient already receiving vasopressin;
• Pregnancy;
• Patient under legal protection;
• Patient unwilling to participate in the study.

Adult patients hospitalized in the intensive care unit for septic shock and with use of vasopressin