Oxygen therapy is the most common treatment modality for patients with hypoxemia, but target values for normoxemia are not clearly defined. Therefore, iatrogenic hyperoxemia is a very common situation. Even though there are many side effects reported related to hyperoxemia and hyperoxemia is shown to be related to worse outcome than expected; clinicians still observe hyperoxemia frequently.

Oxygen reserve index (ORi™) (Masimo Corp., Irvine, USA) can guide clinicians in detection of hyperoxia. ORi is a parameter which can evaluate partial pressure of oxygen (PaO2) rating from 0 to 1. There are growing evidences in ORi that it might be helpful to reduce hyperoxia in general anesthesia. Continuous ORi monitoring can be used for detecting and preventing hyperoxia. The ability to perform FiO2 titration with ORi may be an appropriate monitoring management to prevent the harmful effects of hyperoxia.In this study, in patients who underwent major abdominal surgery; It was aimed to investigate the effectiveness of ORi-guided FiO2 titration in preventing hyperoxia.

Inclusion Criteria:

1. Patients older than 18,
2. Patients scheduled for major abdominal surgery that are expected to last longer than 2 hours
3. Patients that have invasive arterial monitorization
4. American Society of Anesthesiologists physical class I, II or III.

Exclusion Criteria:

1. Patients younger than 18
2. Patients that need to be treated with high doses of vasopressors,
3. Patients having peripheric hypoperfusion,
4. Hemodynamically unstable patients,
5. Patients with hemoglobinopathy,
6. Pregnancy,
7. Morbid obesity (bmi>40 kg/m2),
8. Patients with arrythmia that can result in hemodynamic instability, patients with acute coronary syndrome
9. Acute respiratory failure or ARDS.