This prospective, non-interventional study aims to investigate the relationship between early oxygen exposure and oxidative stress in adult intensive care unit (ICU) patients diagnosed with sepsis or septic shock. Fraction of inspired oxygen (FiO₂) levels administered during the first 24 hours of ICU admission will be evaluated in relation to changes in the uric acid/albumin ratio (UAR), a biochemical marker reflecting oxidative burden and inflammation. Serum uric acid and albumin levels will be measured at ICU admission and at 24 hours, and the percentage change in UAR (ΔUAR%) will be calculated. Associations between FiO₂ exposure parameters and ΔUAR% will be analyzed, along with secondary outcomes including 28-day mortality and oxygenation indices. The findings may help clarify whether excessive oxygen therapy contributes to oxidative stress and whether UAR can serve as an accessible biomarker of oxygen-related oxidative injury in septic ICU patients.

Inclusion Criteria:

• Adult patients aged 18 years or older
• Admission to the intensive care unit with a diagnosis of sepsis according to Sepsis-3 criteria
• Receipt of oxygen therapy with FiO₂ ≥ 0.3 during ICU stay
• Availability of serum uric acid, albumin, and lactate measurements and calculated SOFA scores at ICU admission
• Availability of serum uric acid and albumin levels both at ICU admission (baseline) and at 24 hours
• Provision of informed consent by the patient or a legally authorized representative

Exclusion Criteria:

• Age younger than 18 years
• Pregnant or breastfeeding women
• Chronic kidney disease or receipt of renal replacement therapy
• Advanced liver failure (Child-Pugh class C)
• Receipt of albumin infusion within the previous 24 hours
• Use of medications that affect uric acid metabolism (e.g., allopurinol, febuxostat, rasburicase)
• History of active gout attack or malignancy-related hyperuricemia
• Missing serum uric acid or albumin measurements at baseline or 24 hours
• Inability to obtain informed consent from the patient or a legally authorized representative

The study population consists of adult patients aged 18 years and older who are admitted to a tertiary-level intensive care unit with a diagnosis of sepsis or septic shock according to Sepsis-3 criteria. All included patients receive oxygen therapy as part of standard clinical care, with a fraction of inspired oxygen (FiO₂) of at least 0.3 during the early phase of ICU admission. The population represents critically ill patients requiring close monitoring, respiratory support, and comprehensive laboratory evaluation. Patients with conditions or treatments that may independently affect uric acid or albumin metabolism are excluded to allow a clearer assessment of the relationship between oxygen exposure and changes in the uric acid/albumin ratio.