This study is a randomized controlled trial comparing oxygen delivery by nasal mask with continuous positive airway pressure versus standard care (nasal cannula or standard facemask) during propofol-based sedation for gastrointestinal endoscopy procedures to reduce the incidence of hypoxia. The primary outcome will be the rate of oxygen desaturation below 90% for ≥15 seconds.

This study is a randomized controlled trial comparing oxygen delivery by nasal mask with continuous positive airway pressure versus standard care (nasal cannula or standard facemask) during propofol-based sedation for gastrointestinal endoscopy procedures to reduce the incidence of hypoxia. The primary outcome will be the rate of oxygen desaturation below 90% for ≥15 seconds. In addition, secondary measures will include evaluation of mechanism and degree of respiratory depression associated with hypoxia and hypoventilation by characterizing changes in minute ventilation, tidal volume, and respiratory rate as well as the rate and degree of airway obstruction. The investigators hypothesize that the addition of nasal continuous positive airway pressure in the intervention arm will lead to decreased obstruction as positive pressure will stent open the obstructed airway. Depth of anesthesia will be monitored by Bispectral Index and investigators hypothesize that the degree of hypoventilation, obstruction, and will be significantly lower in the intervention arm compared to the control arm. Further, the depth of anesthesia will be independent of total propofol dose received. While the primary outcome in this study is hypoxia, investigators also seek to marry end tidal carbon dioxide with minute ventilation and transcutaneous carbon dioxide measurement to better understand the total effects of sedation on respiration. Thus the study will also serve to evaluate which mode(s) of respiratory monitoring might be the best possible intervention to enhance safety during procedural sedation in the future. Further, investigators suspect that the amplitude of end tidal carbon dioxide will not predict the degree of respiratory depression seen with other monitors. In addition, investigators will measure serum short chain fatty acid concentrations as a predictor and possible mechanism for differences in individual variability in anesthesia induced respiratory depression.

Inclusion Criteria:

• Adult patients (≥ 18 years of age) undergoing colonoscopy, endoscopic gastroduodenoscopy, and endoscopic gastroduodenoscopy with biopsy and/or ultrasound, or combined upper and lower endoscopy procedure anticipated to last longer than 10 minutes in the Endoscopy Suite at the Johns Hopkins Hospital when the anesthetic plan is monitored anesthesia care with propofol-based anesthesia with a natural airway.

Exclusion Criteria:

• Left ventricular Assist Device
• Severe Pulmonary Hypertension
• Ejection fraction less than 35 percent
• Active Congestive Heart Failure Exacerbation
• Planned procedure is Balloon Enteroscopy or Endoscopic Retrograde Duodenoscopy.
• Topical lidocaine administration
• Pregnancy
• Previous enrollment in this study

Discharge from endoscopy unit, up to 1 week.

Any untoward or unfavorable medical occurrence in a participant, including any abnormal sign (for example, abnormal physical exam or laboratory finding), symptom, or disease, temporally associated with the participant's participation in the research, whether or not considered related to the participant's participation in the research.