This prospective, multicenter observational study aims to evaluate the effect of different flow rates of high-flow nasal oxygen (HFNO) on the quality of the laryngoscopic view during videolaryngoscopy in adult patients undergoing general anesthesia. Each patient will serve as their own control, with repeated measurements obtained at three different HFNO flow settings (0, 40, and 60 L/min). The study will assess objective and subjective parameters of glottic visualization using standardized scoring systems.

Anaesthetic management Anaesthesia induction and airway management will be standardized as far as clinically feasible. Standard monitoring will be applied according to institutional practice. Preoxygenation will be performed using high-flow nasal oxygen (HFNO). General anaesthesia will be induced using standard intravenous agents, followed by administration of neuromuscular blockade to facilitate laryngoscopy. Mask ventilation will be performed as clinically indicated.

Videolaryngoscopy will be performed using a standardized device and blade type whenever possible. All procedures will be performed by anesthesiologists experienced in videolaryngoscopy.

Study procedure

After induction of anaesthesia and achievement of adequate conditions for laryngoscopy, videolaryngoscopy will be performed. During a single laryngoscopic sequence, images of the laryngeal view will be obtained under three predefined HFNO flow conditions:

• 0 L/min
• 40 L/min
• 60 L/min At each flow level, once a stable laryngeal view will be achieved, a still image will be captured using the videolaryngoscope recording system. The laryngoscope position will be maintained as stable as possible during acquisition of all three images. No attempt at tracheal intubation will be made during image acquisition.

After completion of the image capture protocol, tracheal intubation will be performed according to standard clinical practice.

All images will be anonymized and stored for subsequent offline analysis. Image assessment Captured images will be evaluated offline by an independent anesthesiologist blinded to HFNO flow rates and patient identity. Where applicable, evaluation will be performed by more than one assessor to allow assessment of inter-rater agreement.

Each image will be assessed using predefined objective and subjective measures (Percentage of Glottic Opening, Likert scale).

Inclusion Criteria:

• Age ≥18 years
• Scheduled for endotracheal intubation under general anesthesia
• Use of videolaryngoscopy

Exclusion Criteria:

• Anticipated difficult airway
• Emergency intubation
• Contraindications to HFNO
• Inability to obtain adequate video recording

Adult patients undergoing elective surgical procedures requiring endotracheal intubation under general anesthesia.