This study compares two methods of gas delivery in a dental setting: 1) demand-driven (DD) and 2) free-flow (FF).

Nitrous oxide and oxygen sedation (NOS) is a common form of minimal sedation for adult and paediatric patients undergoing dental procedures. In order for NOS devices to be utilized during dental treatment, dentists must be able to provide gas flow to the patient, and subsequently scavenge used and unused gasses. Gas delivery is via a nasal mask, since the oral cavity must be accessible to the dentist throughout treatment.

Current devices for NOS in the dental setting utilize a free-flow gas method, where nitrous oxide and oxygen are released continuously from their tanks. The flow rate is set by the dentist according to the patient's minute ventilation needs, and unused and exhaled gasses are scavenged via the nasal mask. The demand-driven gas flow method, where inspiration triggers gas flow, has been used successfully in other medical settings, such as in obstetrics, medical emergencies, and for patients with chronic obstructive pulmonary disease. However, in these settings the mask used covers both the nose and mouth, and patients can trigger the demand-driven method through inspiration of the nose or mouth. The demand-driven gas flow method has a significant gas-sparing advantage over the free-flow method. With a demand-driven method, the patient dictates the flow rate and gas is only delivered when they are inspiring, compared to the free-flow method which provide gas flow throughout inspiration and expiration. However, the demand-driven method have not been studied in a dental setting where flow can only be triggered through the nose. It is therefore unknown whether it is feasible or comfortable for patients to trigger a demand-driven method nasally when their mouth is open during dental treatment.

This study will aim to assess the feasibility and comfort of a nasal demand-driven gas delivery method utilizing 100% oxygen in healthy, adult participants in a simulated dental setting. If the device is feasible and comfortable with 100% oxygen in a simulated dental setting, future research can be conducted to assess its use for NOS for dental treatment.

The study design is a within-subjects, single-blinded, randomized control trial. Participants will be randomzied to inspire 100% oxygen through their nose utilizing a demand-driven (DD) gas delivery method and a free-flow (FF) gas delivery method for 2 minutes each in a simulated dental setting.

The study will take place at the University of Toronto's Faculty of Dentistry Children's Clinic. Participants will be positioned supine in the dental chair. A child size, rubber bite block will be inserted with an attached capnography device to measure end-tidal carbon dioxide at the mouth. A double-mask nasal hood with disposable insert will be placed on the participant's nose. The participant will be instructed to breathe through their mouth for 1 minute. Baseline respiratory rate and presence/absence of end tidal carbon dioxide at the mouth will be obtained through the capnograph and recorded. The presence of carbon dioxide at baseline during mouth breathing will confirm that the capnograph is able to measure end-tidal carbon dioxide at the mouth.

The researcher will then open the envelope with the randomization plan for the participant and will indicate whether they will receive the FF or DD gas delivery method first. The gas delivery device will be attached to the nasal hood, and set to either DD or FF gas delivery method. Once the device is connected, the participant will be instructed to breathe through their nose for 2 minutes. During this time, respiratory rate, presence/absence of end tidal carbon dioxide at the mouth, and oxygen flow rate per minute will be observed and recorded. The absence of end-tidal carbon dioxide at the mouth during this testing phase will provide a verifiable measure that patients are breathing through their nose. After 2 minutes, the flow will be stopped and the bite block removed. The participant will be instructed to breathe through their mouth. The participant will then complete the VAS on comfort of breathing through their nose during the first gas flow delivery method. The bite block will then be reinserted, and the flow resumed using the second gas flow delivery method for 2 minutes. During this time, respiratory rate, presence/absence of end tidal carbon dioxide at the mouth, and oxygen flow rate per minute will be observed and recorded. After 2 minutes, the gas flow will once again be stopped and the bite block removed. The participant will be instructed to complete the VAS on comfort of breathing through their nose. The nasal hood will be removed. The participant will be debriefed to the order of gas flow received (DD or FF first) and the participant will then be dismissed.

Inclusion Criteria:

1. Participants must be adults, 18 years of age or older.
2. Participants must be ASA I (a normal, healthy patient) or ASA II (a patient with mild systemic disease).

Exclusion Criteria:

1. Participants who are ASA III (a patient with a severe systemic disease that is not life-threatening) or higher.
2. Participants who indicate they are claustrophobic.
3. Participants with nasal obstruction of both nostrils.

Participants will not be told the order the gas flow delivery method (DD or FF) they will be receive. To assist with masking participants, the same device and nasal hood will be used throughout, they will be told to face forward away from the device and device display, which indicates the setting of the gas flow. It will not be feasible to blind the researcher as the researcher will need to change the device setting (FF or DD).