The main goal of this study is to determine if supplemental oxygen given only when the patient is inspiring (demand delivery) is more effective than constant-flow oxygen given during all phases of the breath regardless if the patient is breathing it in. A previous study in volunteers (NCT02886312) showed that the oxygen saturation in the blood and the concentration of oxygen breathed out from the lungs (end-tidal oxygen) was higher when given in demand (inhalation only) mode. A secondary goal is to determine in patients, whether turning oxygen delivery off during expiration improves the accuracy of end-tidal CO2 (Carbon Dioxide) monitoring. This was found to be the case in the previous volunteer study.

The investigators want to determine if these improvements are also observable in relatively healthy patients undergoing procedural sedation and analgesia. The efficacy of the demand mode will be determined by measuring the resulting difference in oxygen saturation and end-tidal oxygen levels. The investigators will alternate between traditional oxygen delivery (continuous flow) and demand delivery (flow only during inhalation) for two minutes in each mode after which oxygen saturation and end-tidal oxygen will be measured. End-tidal CO2 measurement will be compared with those during the brief time when O2 flow is stopped.

Inclusion Criteria:

• ASA class I-III

Exclusion Criteria:

• Procedures scheduled for a lime less than 20 minutes
• Age < 18 years
• Baseline SpO2 (arterial oxygen saturation as measured by pulse oximetry) < 93% on room air
• ARDS (Acute respiratory distress syndrome), lung disease, cardiovascular disease
• ASA class IV or above
• Pregnant women.

There is no plan to share individual participant data.