Comparison of the preoxygenation efficacy of tidal volume breathing using three different preoxygenation techniques which are available to providers in the prehospital environment.

Prospective randomised interventional study.

Healthy volunteers will be positioned supine and undergo preoxygenation by tidal volume breathing for 3 minutes using each technique in turn. The sequence of techniques for each volunteer will be randomised in advance. Investigators will be instructed to ensure a good mask seal throughout the testing period. At the end of a 3 minute preoxygenation period, after a brief breath hold, the volunteer will exhale into reservoir tubing, allowing the fractional expired oxygen concentration (FeO2) to be determined (primary outcome) using a calibrated gas analyser.

The techniques being assessed have been chosen from methods of preoxygenation commonly available to clinicians in the prehospital environment:

1. Continuous Positive Airway Pressure mode with fractional inspired oxygen concentration (FiO2) 100% using a portable ventilator.
2. Bag-valve-mask device (BVM) with 15 l/min oxygen flow.
3. Non-rebreather mask (NRM) device with 15 l/min oxygen flow.

Volunteers will also be asked to indicate the subjective ease of breathing for each technique (secondary outcome) using a visual analogue scale (VAS).

Inclusion Criteria:

• Adult volunteers

Exclusion Criteria:

• Pregnancy
• Respiratory disease
• Bearded
• Facial abnormality
• Edentulous