Hyperoxemia and Oxygen Reserve Index During Neurointerventional Anesthesia

The goal of this observational study is to learn how often high blood oxygen levels (hyperoxemia) occur in adults receiving general anesthesia for planned (elective) neurointerventional procedures, such as brain aneurysm coiling or other catheter-based treatments of brain vessels. It will also look at how well a non-invasive finger sensor measurement called the Oxygen Reserve Index (ORi) reflects arterial oxygen levels. The main questions it aims to answer are: * How often is the arterial oxygen pressure (PaO2) 150 mmHg or higher in blood gas samples taken as part of routine care during these procedures? * How does ORi relate to PaO2, and can ORi help identify high oxygen levels? Participants will: * Receive anesthesia and their procedure exactly as planned by their care team; the study does not change any treatment, oxygen setting, or ventilator setting. * Have a painless ORi sensor placed on a finger, similar to a standard pulse oximeter, during anesthesia. * Have their routine monitoring values and the results of arterial blood gas samples taken for routine clinical care recorded. No extra blood samples will be taken for the study, and ORi values will not be used to guide care.