130 patients aged between 18 and 70 with ASA I-II will be included in the study. Patients will be assigned to one of the two study groups in equal numbers using a computerized random numbers table.

In the 1st group (Group DA), the patients will be taken to the operating table. The standard consisting of electrocardiogram (ECG), peripheral oxygen saturation (Spo2), and non-invasive blood pressure will be monitored. Prior to induction, the first blood sample (To) will be drawn for COHB and biochemistry analysis. After induction of anesthesia with propofol and rocuronium, he will be intubated orotracheal. Anesthesia will be maintained with desflurane (MAC:1), oxygen (50%), air (50%). After a high flow phase of 4 l/min for 10 min, the fresh gas flow will be reduced to 0.6 L/min (low flow anaesthesia) and fentanyl and rocuronium will be administered intermittently. Patients will be ventilated with a ring system ventilator with a newly changed absorber at a constant tidal volume (body weight kg x 6 mL) and respiratory rate (12/min). At the 1st hour of low flow anesthesia maintenance, a second blood sample (T1) will be taken for COHB and biochemistry analysis. Patients will be awakened at the end of the case. After the recovery room, it will be transferred to the relevant service. A third blood sample (T2) will be taken from the patients at the postoperative 24th hour in the service for COHB and biochemistry analysis. Blood carboxyhemoglobin (COHB), total antioxidant status (TAS), total oxidant status (TOS), Hypoxia-inducible factor 1α (HIF-1α) values will be calculated.

Patients in group 2 (Group NA) will be taken to the operating table. The standard consisting of electrocardiogram (ECG), peripheral oxygen saturation (Spo2), and non-invasive blood pressure will be monitored. Prior to induction, the first blood sample (To) will be drawn for COHB and biochemistry analysis. After induction of anesthesia with propofol and rocuronium, he will be intubated orotracheal. Anesthesia will be maintained with desflurane (MAC:1), oxygen (50%), air (50%). After a high flow phase of 4 l/min for 10 min, the fresh gas flow will be reduced to 2.0 L/min (normal flow anaesthesia) and fentanyl and rocuronium will be administered intermittently. Patients will be ventilated with a ring system ventilator with a newly changed absorber at a constant tidal volume (body weight kg x 6 mL) and respiratory rate (12/min). A second blood sample (T1) will be taken for COHB and biochemistry analysis at the 1st hour of normal flow anesthesia maintenance. Patients will be awakened at the end of the case. After the recovery room, it will be transferred to the relevant service. A third blood sample (T2) will be taken from the patients at the postoperative 24th hour in the service for COHB and biochemistry analysis. Blood carboxyhemoglobin (COHB), total antioxidant status (TAS), total oxidant status (TOS), Hypoxia-inducible factor 1α (HIF-1α) values will be calculated.

SPSS 25.0 (IBM Corporation, Armonk, New York, United States) program will be used in the statistical analysis of the variables obtained as a result of the study. The conformity of the data to the normal distribution will be evaluated with the Shapiro-Wilk test and the homogeneity of variance with the Levene test. Independent sample t test and Mann Whitney u test will be used to compare two groups with each other according to quantitative data. In order to examine the correlations of the variables with each other, appropriate ones from Pearson Correlation, Kendall's tau-b and Spearman's rho tests will be used considering the distribution of the data. According to the results of the correlation analysis, it will be supported by regression analysis when necessary. Pearson Chi-Square and Fisher Exact tests will be used to compare categorical variables with each other. Quantitative variables will be shown in the tables as mean (standard deviation) and median (Maximum-Minimum), and categorical variables as n(%). Variables will be analyzed at 95% confidence level and p value less than 0.05 will be considered significant.