To manage the treatment in the intensive care unit for patients with septic shock, central venous oxygen saturation (scvO2) is used as a macrocirculatory indicator, with a target value of 70% or higher being recommended. Tissue oxygenation (stO2) measurement can be implemented to assess the microcirculation in these patients, but a specific target value has not been established yet. The investigators believe that guiding the treatment of septic shock patients based on the measurement of microcirculation using stO2 and evaluating its correlation with scvO2 can reduce mortality.

This study aims to investigate the independent impact of high-dose norepinephrine on microvascular reactivity assessed by NIRS-VOT in patients with septic shock, while also examining how these microcirculatory indices relate to the macrocirculatory marker ScvO₂.

Inclusion Criteria:

• Age 18 years or older
• Diagnosis of septic shock
• Receiving vasopressor and mechanical ventilation therapy
• Presence of a central venous catheter that allows ScvO₂ sampling
• Ability to obtain tissue oxygenation (stO₂) measurements using a NIRS probe placed on the thenar eminence
• Written informed consent obtained from patient or legal representative

Exclusion Criteria:

• Local infection, wound, or skin lesion at the planned NIRS probe application site
• Mean arterial pressure (MAP) < 60 mmHg despite vasopressor therapy
• Pregnancy
• Inability to safely perform the vascular occlusion test (as judged by treating clinician)
• Any condition preventing safe blood sampling or reliable stO₂ measurement