Physiological Effects of Different Preoxygenation Strategies

Hypoxemia is a frequent and potentially life-threatening complication during advanced airway management, associated with adverse outcomes such as hypoxic brain injury, cardiovascular collapse, and death. Effective preoxygenation is essential to increase oxygen reserves and prolong safe apnea time during intubation. Although several devices are routinely used for preoxygenation, including non-rebreather masks (NRM) and bag-valve masks (BVM) with or without positive end-expiratory pressure (PEEP), important uncertainties remain regarding their actual performance and physiological effects.

Current evidence suggests that techniques providing PEEP may improve oxygenation by increasing functional residual capacity, enhancing ventilation of dependent lung regions, and reducing ventilation-perfusion mismatch. However, the relative contribution of FiO₂ delivery versus PEEP, as well as the physiological effects on respiratory mechanics and cardiovascular function, are not fully understood. In addition, it remains unclear whether BVM devices without a dedicated PEEP valve can generate measurable PEEP, and whether patients can generate sufficient inspiratory effort to effectively operate BVM valves without assisted ventilation. Data in pediatric populations are particularly limited.

This randomized crossover study is designed to systematically evaluate the performance of commonly used preoxygenation devices under controlled conditions in healthy adult and pediatric volunteers. By comparing NRM, BVM without PEEP, and BVM with PEEP-with and without supplemental oxygen via nasal cannula-the study aims to characterize differences in oxygen delivery, airway pressure generation, inspiratory effort, and their physiological impact.

The study will focus on key physiological domains, including oxygenation (FiO₂), respiratory mechanics (tidal volume, airway pressures, and diaphragm activity), lung aeration (with particular attention to dependent lung regions), and cardiovascular responses (including right ventricular dimensions and function). Measurements will be obtained using non-invasive monitoring techniques, including gas analysis and ultrasound.

The crossover design allows within-subject comparisons across all study conditions, minimizing inter-individual variability and enabling precise assessment of device-related effects. The findings of this study are expected to improve understanding of the mechanisms and physiological consequences of preoxygenation strategies, with potential implications for optimizing airway management practices in both adult and pediatric populations.

• Nasal cannula (NC) (Device): Preoxygenation performed using a nasal cannula delivering supplemental oxygen at a flow rate of 15 L/min, without the use of an additional mask or ventilation device, during spontaneous breathing.
• Non-rebreather mask (NRM) (Device): Preoxygenation performed using a non-rebreather mask with reservoir, delivering oxygen at a flow rate of 15 L/min. The mask is fitted to ensure an optimal seal, and participants breathe spontaneously without assisted ventilation.
• Non-rebreather mask (NRM) plus Nasal cannula (NC) (Device): Preoxygenation performed using a non-rebreather mask with reservoir, delivering oxygen at a flow rate of 15 L/min, combined with a nasal cannula delivering supplemental oxygen at 15 L/min. The mask is fitted to ensure an optimal seal, and participants breathe spontaneously without assisted ventilation.
• Bag-valve mask (BVM) without PEEP (Device): Preoxygenation performed using a bag-valve mask without a PEEP valve, delivering oxygen at a flow rate of 15 L/min. The mask is held with a two-handed technique to ensure an airtight seal, without providing assisted ventilation, allowing spontaneous breathing.
• Bag-valve mask (BVM) without PEEP + nasal cannula (NC) (Device): Preoxygenation performed using a bag-valve mask without a PEEP valve, delivering oxygen at a flow rate of 15 L/min, combined with a nasal cannula delivering supplemental oxygen at 15 L/min. The mask is held with a two-handed technique to ensure an airtight seal, without providing assisted ventilation, allowing spontaneous breathing.
• Bag-valve mask (BVM) with PEEP (Device): Preoxygenation performed using a bag-valve mask equipped with a PEEP valve set at 10 cmH₂O, delivering oxygen at a flow rate of 15 L/min. The mask is held with a two-handed technique to ensure an airtight seal, without assisted ventilation, during spontaneous breathing.
• Bag-valve mask (BVM) with PEEP + nasal cannula (NC) (Device): Preoxygenation performed using a bag-valve mask equipped with a PEEP valve set at 10 cmH₂O, delivering oxygen at a flow rate of 15 L/min, combined with a nasal cannula delivering supplemental oxygen at 15 L/min. The mask is held with a two-handed technique to ensure an airtight seal, without assisted ventilation, during spontaneous breathing.

Primary outcomes

• Difference in fraction of inspired oxygen (FiO₂) between preoxygenation devices [During each 3-minute preoxygenation session]: Fraction of inspired oxygen (FiO₂) delivered during preoxygenation will be continuously measured at the airway opening using a gas analyzer. FiO₂ values will be recorded breath-by-breath during each 3-minute preoxygenation session under all study conditions. The primary outcome is the difference in mean FiO₂ achieved between the different preoxygenation devices (non-rebreather mask, bag-valve mask without PEEP, and bag-valve mask with PEEP), with and without supplemental oxygen via nasal cannula.

Secondary outcomes

• Positive end-expiratory pressure (PEEP) generated during preoxygenation [During each 3-minute preoxygenation session]: Airway pressures will be continuously measured to quantify the presence and magnitude of PEEP generated during preoxygenation with bag-valve mask (BVM) with and without a dedicated PEEP valve, with and without nasal cannula oxygen supplementation.
• Inspiratory effort required to open the BVM valve [During each 3-minute preoxygenation session]: The negative pressure required to open the BVM valve will be measured using airway pressure monitoring, and diaphragm ultrasound parameters (thickening fraction and excursion) will be used as surrogate markers of inspiratory effort.
• Cardiac output [Baseline and at the end of each 3-minute preoxygenation session]: Changes in cardiac output (l/min/m²) will be assessed using echocardiography before and after preoxygenation to evaluate the hemodynamic effects of different devices and PEEP.
• Changes in right ventricular dimensions [Baseline and at the end of each 3-minute preoxygenation session]: Changes in right ventricular dimensions (mm) will be assessed using echocardiography before and after preoxygenation to evaluate the hemodynamic effects of different devices and PEEP.
• Right ventricular strain [Baseline and at the end of each 3-minute preoxygenation session]: Changes in right ventricular strain (%) will be assessed using echocardiography before and after preoxygenation to evaluate the hemodynamic effects of different devices and PEEP.
• Ventilation of dependent lung regions [During each 3-minute preoxygenation session]: Lung ultrasound will be used to assess regional ventilation of dependent lung areas, with findings quantified using a validated scoring system to compare the effects of preoxygenation with and without PEEP.
• Correlation between FiO₂ and tidal volume [During each 3-minute preoxygenation session]: The relationship between fraction of inspired oxygen (FiO₂) and tidal volume during preoxygenation will be assessed using continuous, breath-by-breath measurements.

Other outcomes

• Airway pressure during breath-holding maneuver [Immediately following the preoxygenation session with bag-valve mask (with or without PEEP)]: Airway pressure generated during a brief voluntary breath-holding maneuver will be measured when oxygen is delivered via nasal cannula under a bag-valve mask (with or without PEEP), to assess potential continuous positive airway pressure generation.

Sex: All, ages: 5 Years to 75 Years, accepts healthy volunteers

Inclusion Criteria:

* Adults with an American Society of Anesthesiologists (ASA) physical status score ≤ 2
* Children aged 5 to 12 years with an ASA physical status score ≤ 2
* Ability (or legal guardian ability) to provide written informed consent

Exclusion Criteria:

* Children aged < 5 years or 13 to 18 years
* ASA physical status score > 2
* Body mass index (BMI) ≥ 30 kg/m²
* Known airway pathology or anatomical abnormality that could affect mask fit, ventilation, or oxygenation
* Presence of an active airway infection at the time of the study
* Pregnancy
* Refusal or inability to provide informed consent

• Roveri G, Camporesi A, Hofer A, Kahlen S, Breidt F, Rauch S. Preoxygenation With and Without Positive End-Expiratory Pressure in Lung-Healthy Volunteers: A Randomized Clinical Trial. JAMA Netw Open. 2025 May 1;8(5):e2511569. doi: 10.1001/jamanetworkopen.2025.11569. PMID 40392551
• Rauch S, Pietsch U, Roveri G. Preoxygenation in prehospital critical care: a survey of HEMS practices in eight European countries. Emerg Med J. 2026 Aug 20;43(9):588-589. doi: 10.1136/emermed-2025-215335. No abstract available. PMID 41545175

• Simon Rauch, Principal investigator, Eurac research, Institute of mountain emergency medicine