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.

The definition of elderly by the World Health Organization is individuals aged 65 and older. As the average life expectancy continues to increase, the number of surgical procedures performed in the geriatric population is also increasing.

Postoperative delirium is a complication that occurs after surgery and is characterized by sudden-onset confusion, fluctuating mental status, and attention deficits. Its incidence increases in elderly patients and is higher in those with pre-existing mild cognitive impairment. The etiology encompasses multiple factors such as age, presence of additional comorbidities, metabolic disorders, hypoxia, polypharmacy, pain, hypothermia, and may be associated with the depth of anesthesia during surgery.

Early recognition and prevention of delirium will become more prominent in the future due to reduced hospitalization durations, postoperative complications, and mortality rates.

Various methods are available to detect hyperoxemia during surgery. Hyperoxemia can be detected using noninvasive finger pulse oximetry with the oxygen reserve index parameter. Oxygen levels can be noninvasively assessed during operations using routine oxygen saturation and oxygen reserve index measurements.

Delirium can be evaluated in both intensive care and ward patients. The gold standard for diagnosis is the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria. DSM-5 criteria require psychiatric evaluation and are conducted by someone with psychiatric training. Additionally, the Confusion Assessment Method (CAM) is used for diagnosis and can be evaluated as CAM-ICU for intubated patients in intensive care units.

Inclusion Criteria:

1. Patients aged 65 and older
2. Patients expected to have surgery lasting more than 2 hours
3. Patients with ASA (American Society of Anesthesiologists) classification 1-2-3-4
4. Patients planned to have at least 2 days of postoperative hospitalization

Exclusion Criteria:

1. Patients with preoperative central nervous system disorders or dementia
2. Patients with MMSE (Mini-Mental State Examination) scores of 23 or below
3. Patients unable to communicate
4. Emergency surgeries
5. Patients who refuse to participate in the study
6. Patients using high-dose vasopressors
7. Patients with peripheral hypoperfusion
8. Hemodynamically unstable patients

Patients aged 65 and older. Geriatric patients