This study aims to investigate two oxygenation methods (high flow nasal oxygen and supraglottic, superimposed high-frequency jet ventilation) for tubeless laryngotracheal surgeries concerning their safety and efficiency.

Eligible adult patients will be prepared for intubation according to the local SOPs of the anesthesia departments. Mandatory monitoring will consist of: SpO2, HR, NIBP, tcCO2, EEG, TOF and EIT.

Induction of anesthesia: Patients will be preoxygenated before induction of anesthesia for at least one minute through face-mask with FiO2 1.0 until etO2 reaches 0.9. The induction of anesthesia will be performed using a combination of sedative/hypnotic drugs, opioids and muscle relaxant.

The following medications will be mandatory as per protocol:

• A neuromuscular blocking agent (NMBA): Rocuronium 0.5-1 mg/kg
• Propofol 1-3 mg/kg
• Opioid: Fentanyl 1-3mcg/kg, Remifentanyl 1-3mcg/kg

After induction of anesthesia and the administration of a NMBA, bag-mask ventilation with FiO2 1.0 will be performed for at least 60 seconds or until the muscle relaxant is working. Full neuromuscular blockade will be assessed by train-of-four (TOF) monitoring. Anaesthesia will be given total intravenously with Propofol and Remifentanil under EEG guidance. Tracheal tube will be placed recruitment manoeuver (RM) will be performed before surgical disinfection. The RM consists of recruitment pressure of 30 cmH2O during 30 seconds. PEEP level will be set at 10cmH20.

Thereafter placement of the surgical laryngoscope will be performed by the ENT-surgeon and the oxygenation device according to randomization will be installed. The patient will be extubated and the intervention start.

Jet ventilation Group (intervention-group): Patients will receive supraglottic superimposed high frequency jet ventilation using the Monsoon 4 (Thora Tech GmbH, Giessen, Germany), that will be directly attached to the operative suspension laryngoscope with a Luer-lock. Before use, pressure safety limits of the device will be tested. Initially FiO2 will remain at 1.0, FiO2 will be reduced to 0.3 during laser interventions. Frequency and pressure will be set according to the local standards.

High-Flow Oxygen Group (control-group): Patients will receive high-flow oxygen (up to 70 L/min FiO2 1.0) via nasal cannula with the Optiflow (Fisher & Paykel Healthcare, Auckland, New Zealand). FiO2 will remain at 1.0, FiO2 will be reduced to 0.3 during laser interventions.

If the measured SpO2 falls below 80%, or if the measured tcCO2 rises above 70mmHg, surgical procedures will be interrupted. Additionally, if deemed necessary, rescue strategies will be performed at the discretion of the attending anesthesiologist, even if the predefined thresholds are not crossed. Rescue oxygenation or decarboxylation will be provided, this may include increasing the FiO2 to 100% or performing tracheal tube placement by the surgeon, determined by the anaesthesiologist in charge. If this change in airway strategy remains unsuccessful, the local difficult airway algorithm will be followed according to the SOP.

If the rescue airway management was successful and respiratory parameters return to baseline levels, the initial airway device according to randomisation will be reapplied. A permanent switch of airway strategy leads to study termination.

EIT will be measured using PulmoVista® 500 by Dräger, Lübeck, Germany, to visualize possible atelectasis formation and its progression over time. EIT is a non-invasive, radiation-free technique for the assessment of spatial and temporal ventilation distribution based on the changes in electrical properties of the tissue during the respiratory cycle. EIT measurements will be performed using a commercially available setup (PulmoVista 500, Draeger, Germany). A loose-fitting belt with 16 evenly spaced electrodes will be placed around the participant's chest in thoracic median plane. Small electrical currents are injected through adjacent electrodes in a rotating mode. Resulting potential differences are measured, and impedance distribution sampled at 30 Hz will be calculated by an automated linearized newton-raphson reconstruction algorithm. The device is suitable for assessment of jet ventilation and high flow.

Thoracic electrical impedance tomography measurements (each measurement will last 1 min) will be performed at the following time points: before induction of the anaesthesia; before the surgical procedure when the induction is terminated and recruitment manoeuvers have been performed; after the termination of the surgical procedure; before transport to the Post anaesthesia Care Unit (PACU); before the discharge from the PACU after 2 hours of monitoring. Relative change in poorly ventilated lung. regions (silent spaces) and end-expiratory lung impedance (EELI) and measures of ventilation inhomogeneity such as the global inhomogeneity index will be calculated as described previously, using customised code (Matlab R2021a, The MathWorks, Nattick, Massachusetts, USA).

Inclusion Criteria:

• Written informed consent
• Patients aged ≥18 years
• Patients requiring elective tubeless laryngotracheal surgery

Exclusion Criteria:

• Patients <18 years
• High risk of aspiration which concludes the consideration of using a tube in order to prevent aspiration.