This prospective randomized controlled trial aims to compare the effectiveness of High-Flow Nasal Cannula (HFNC) versus Tight Face Mask (TFM) in maintaining oxygenation during rapid sequence induction (RSI) for endotracheal intubation in adult patients. Participants will be randomly assigned in a 1:1 ratio to receive either HFNC or TFM for preoxygenation before induction of anesthesia. The primary outcome is the lowest peripheral oxygen saturation (SpO₂) recorded from induction until successful endotracheal intubation. Secondary outcomes include the incidence of oxygen desaturation (\<90%), duration of apnea, duration of laryngoscopy, intubation time, number of intubation attempts, and peri-intubation complications. The study will determine whether HFNC provides superior oxygenation compared with conventional face mask preoxygenation during RSI and may contribute to improving airway management protocols and patient safety.