Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) denotes the use of high-flow humidified nasal oxygen system (for example Optiflow®) as an alternative ventilation modality for an anesthetized patient without spontaneous respiration. This method requires only basic airway management manoeuvres to keep the airway open and provides both stable longterm oxygenation as well as apneic ventialtion.

We plan to evaluate this methods physiological performance under standardized conditions of airway management by frequent, repeated arterial blood gas analyses.

THRIVE is previously shown feasible as sole mode of ventilation in selected patients during general anaesthesia for minor laryngeal surgery for a limited time up to 30 minutes, where direct laryngoscopy was required and applied throughout the procedure. A stable oxygenation and a degree of ventilation was observed. However, a slowly developed respiratory acidosis was also observed over time.

Existing physiologic studies on high flow humidified nasal oxygen suggest that closed mouth breathing enhance the effects of the high flows of oxygen levels applied by increasing the airway pressures and thereby enhance gas exchange in the lungs. Currently, it is unclear whether the efficiency of THRIVE depends on the particular circumstances of airway management. Physiologic characterization of THRIVE performance under standardized conditions of airway management and under close monitoring by systematic analysis of blood gas dynamics over time during general anesthesia is needed.

We plan to study the blood gas dynamics during THRIVE apnea ventilation during general anesthesia, where the airway is managed only by jaw-thrust for up to 60 minutes. The patients will be closely monitored by repetitive arterial blood gasses to evaluate blood gas dynamics and development of respiratory acidosis. Desaturation or respiratory acidosis with pH under 7.15 and/or PaCO2-rise > 12 kPa will lead to cessation of THRIVE.

Inclusion Criteria:

1. Adult (age over 18 years)
2. Elective surgery where intubation is not mandatory
3. The patient can understand the information about the study and give their informed written consent of participation

Exclusion Criteria:

1. ASA (American Society of Anaesthesiologists class) > 3
2. NYHA (New York Heart Association class) > 2
3. BMI > 30 kg/m2
4. Symptomatic respiratory disease
5. Symptomatic cardiac disease
6. Evidence of arteriosclerotic disease
7. Neuromuscular disease
8. Pregnancy
9. Presumed or predicted difficult airway (SARI - Simplified Airway Risk Index score > 4)
10. Known or suspected nasal congestion/stenosis or catharalia

Patients presenting for non-laryngeal surgery in general anesthesia, where intubation is not mandatory.