The aim of the study was to assess the effect of intraoperative oxygen (O2), which was applied at 30% and 50% concentrations on patients who had undergone septoplasty surgery, on Total Oxidant Status (TOS), Total Antioxidant Status (TAS), and Oxidative Stress Index (OSI).

Inclusion Criteria:

• patients aged between 18-60 years,
• ASA I-II risk class with a minimum operative time of 1.5 hour(s) for whom septoplasty operation under elective conditions

Exclusion Criteria:

• metabolic, endocrine, hepatic, cardiac, or renal diseases,
• malignancies and who used a drug with antioxidant properties such as vitamin E-C
• acetylcysteine in the last 48 hours,
• patients requiring intraoperative 100% O2 inhalation