Oxygen Reserve Index and Prevention of Hyperoxemia

In patients under general anesthesia, the oxygen level (FiO2) used in inspiration is usually adjusted by monitoring the peripheral oxygen saturation level (SpO2). As a non-invasive method, SpO2 monitoring is known as one of the required methods that can be used to adjust FiO2 and detect and treat hypoxemia. While SpO2 approaching 100% matches the value of 128 mmHg in arterial partial oxygen pressure (PaO2), in cases where PaO2 increases more, the investigators cannot follow this situation with SpO2 and cannot prevent hyperoxemia.

As stated in the literature, hyperoxemia has positive effects in general anesthesia and intensive care, as well as negative effects such as increased inflammation, oxidative stress and ischemia-reperfusion. In addition, acute lung injury, development of atelectasis, increased mortality, and critical illness rates have been associated with hyperoxemia in many publications. The only way the investigators can use to measure the level of hyperoxemia seems to be arterial blood gas analysis, and this method limits the investigators use because it is invasive. The Oxygen Reserve Index (ORi™) (Masimo Corp., Irvine, CA, USA) is a variable related to real-time oxygenation reserve status in the mildly hyperoxemic range (approximately 100 - 200 mmHg PaO2). ORi can be defined as a multi-wavelength, noninvasive pulse co-oximetry sensor. ORi is a dimensionless index ranging from 0.00 (no reserve) to 1.00 (maximum reserve) depending on the oxygenation reserve status.

There are very few studies in the literature using ORi to detect hyperoxemia. The investigators thought that if FiO2 levels used in preoxygenation, anesthesia maintenance and recovery stages in day surgeries were correlated with ORi levels, a threshold value could be determined for FiO2 levels during anesthesia stages in cases where invasive arterial blood gas could not be followed.

This study aims to determine the relationship between SpO2, FiO2 and ORi during general anesthesia, to investigate the usefulness of ORi in determining the FiO2 threshold value during anesthesia stages as an indicator of hyperoxemia, and to investigate the effects of these values on the hemodynamics, recovery, agitation and nausea-vomiting states of the patients.