In obese patients, the risk of perioperative complications such as rapid desaturation, atelectasis, difficult mask ventilation, difficult intubation, and hypoxia is higher compared to the normal population. Therefore, preoxygenation is even more critical in the obese patient group. In clinical practice, ETO2 is used as a practical indicator to evaluate sufficient oxygenation during preoxygenation. The Oxygen Reserve Index (ORiⓇ) is a new oxygenation monitoring parameter that is continuously and non-invasively measured by a specialized pulse oximetry device (Masimo, Irvine, CA).The primary objective of the investigators was to observe the correlation between ORIⓇ monitoring and ETO₂ during preoxygenation in obese patients.The secondary objective of the investigators was to evaluate the correlation of ORIⓇ with SpO₂ and PaO₂ in this patient population.

Obesity is a chronic, progressive, and recurrent disease characterized by abnormal fat accumulation that adversely affects health and increases morbidity and mortality.

According to World Health Organization (WHO) data, the prevalence of obesity among adults aged 18 years and older is reported to be 16%.

Obese patients have an increased risk of perioperative complications compared to the general population, including rapid desaturation, atelectasis, difficult mask ventilation, difficult intubation, and hypoxia.

Therefore, preoxygenation is particularly important in obese patient populations.

The goal of preoxygenation is to maximize the duration during which the patient can tolerate apnea, thereby providing the anesthesiologist with crucial time to secure the airway in cases of planned or unanticipated "cannot ventilate, cannot intubate" scenarios.

In clinical practice, end-tidal oxygen concentration (ETO₂) is frequently used as a practical indicator to evaluate the adequacy of preoxygenation.

However, achieving a tight-fitting face mask and obtaining accurate ETO₂ measurements can sometimes be challenging.

Thus, alternative monitoring parameters may be needed to evaluate the effectiveness of preoxygenation.

The Oxygen Reserve Index (ORIⓇ) is a novel, continuous, and non-invasive oxygenation monitoring parameter provided by a specialized pulse oximeter (Masimo, Irvine, CA).

While SpO₂ is useful in assessing hypoxia and normoxia, and PaO₂ can evaluate a wide range of oxygenation states, arterial blood gas (ABG) analysis is limited due to its intermittent and invasive nature.

ORIⓇ offers real-time visibility into moderate hyperoxic states (PaO₂ between 100-200 mmHg), which SpO₂ cannot detect.

Several studies have investigated the use of ORIⓇ monitoring to evaluate preoxygenation efficacy in various patient populations.

It has been reported in the literature that ORIⓇ may serve as an early warning indicator of hypoxia and help predict unwanted hyperoxic episodes.

The primary objective of the investigators was to observe the correlation between ORIⓇ monitoring and ETO₂ during preoxygenation in obese patients.The secondary objective of the investigators was to evaluate the correlation of ORIⓇ with SpO₂ and PaO₂ in this patient population.

Inclusion Criteria:

• Patients with a body mass index (BMI) >35 kg/m² scheduled for elective surgery
• ASA (American Society of Anesthesiologists) physical status classification I-III
• Patients aged 18 years and older

Exclusion Criteria:

• Patients with ASA physical status classification IV-V,
• Psychiatric disorders
• Severe cardiac arrhythmias
• Patients with an ejection fraction below 30%
• Chronic obstructive pulmonary disease (COPD)
• Those receiving home oxygen therapy
• Patients requiring supraglottic airway devices, and emergency cases

Between February 2024 and July 2024, 60 patients aged 18 to 75 years, with an ASA physical status classification of II-III, a body mass index (BMI) greater than 35 kg/m², and scheduled for elective surgery under general anesthesia, were included in our study after obtaining verbal and written informed consent.