This prospective observational study aims to evaluate the effectiveness of Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) compared to standard nasal cannula (SNC) oxygen supplementation in patients undergoing elective diagnostic gastroscopy under propofol sedation. The primary outcome is the incidence of hypoxemia (SpO₂ \<93% for ≥20 seconds) during the procedure. Secondary outcomes include the need for airway intervention, Oxygen Reserve Index (ORi) values, peripheral oxygen saturation (SpO₂) levels, and hemodynamic parameters recorded throughout the procedure. Oxygen delivery method was selected by the attending anesthesia provider independent of the study team.