The purpose of this study is to investigate if high flow nasal cannula (HFNC), as compared to conventional nasal cannula, improves oxygenation and prevents desaturation events in obese patients undergoing colonoscopy.

Intravenous sedation during colonoscopy has become the standard practice in United States given its higher patient satisfaction and procedural quality. The most common used short acting sedative agent is propofol. Although possessing safe and rapidly reversed pharmacokinetic properties, propofol intravenous infusion can lead to respiratory depression and hypoxemia. In one prospective study, hypoxemia events, defined by oxygen saturation less than 90 percent was found in 20 percent of patients receiving colonoscopy using propofol sedation. The mechanism of hypoxemia is mainly hypoventilation, airway collapse, and carbon dioxide (CO2) retention. When it comes to gastrointestinal procedures, using oxygen devices for augmenting ventilation is usually avoided, ex: positive pressure ventilation, since it can lead to bowel distention and affect quality of procedures. Therefore most hospitals in United States still use nasal cannula of oxygen therapy during gastrointestinal procedures, and there is lack of available options of oxygen therapy which can improve hypoventilation and prevent hypoxemia.

High flow nasal cannula (HFNC) is a new generation of oxygen therapy. It provides constant high flow oxygen delivery with heated and humidified air. Moreover, it has been studied that high velocity of airflow can create the effect of "positive end expiratory pressure" thus assist ventilation and work of breathing. Compared to conventional nasal cannula and face mask, HFNC has demonstrated superior performance in oxygenation, work of breathing and patient comfort in many studies. Since its invention, HFNC has been studied in post-cardiac surgery, post-extubation, bronchoscopy and dental procedures and all of them show equal to better oxygen performance in comparison of nasal cannula.

While capnographic monitoring has been studied to prevent hypoxemia during sedation, no studies have been done to evaluate the clinical utility of new generation oxygen therapy. Obesity is associated with increased frequency of sedation related complications especially hypoxemia during propofol mediated sedation for advanced endoscopic procedures. The Investigators hypothesized that HFNC may improve oxygen performance compared to conventional nasal cannula for obese patients receiving colonoscopy under intravenous sedation.

Inclusion Criteria:

• BMI ≥ 30.
• Age ≥ 18 years.
• ASA classification II and III.
• Scheduled for colonoscopy.
• Able to provide written informed consent.

Exclusion Criteria:

• Allergic to propofol and any of its contents.
• Baseline SpO2 less than 93%.
• Patients who require intubation for airway protection based on anesthesiologist discretion.