Endoscopic retrograde cholangio-pancreatography (ERCP) is commonly performed under deep sedation to provide amnesia, comfort, and optimal procedural conditions. However, anesthetic drugs commonly used such as midazolam and/or propofol and opioids for sedative endoscopy in clinical practice may depress normal ventilation by blunting central chemoreceptor responsiveness to CO2, and alveolar hypoventilation and predispose patients to upper airway obstruction; all of that can result in hypoxemia, hypercarbia, respiratory acidosis, hypotension, and, in rare cases, brain injury or death.(1-3)

The incidence of hypoxia during ERCP with sedation has been reported to range from 16.2 to 39.2% (4) may be because ERCP procedures can be lengthy and are often performed in the prone position.(5) Hypoxemia is the most common adverse cardiopulmonary complication during sedated endoscopy and is caused by respiratory depression, airway obstruction, and decreased chest wall compliance. (2)

Obese patients are particularly at risk of upper airway obstruction and hypoxemia under sedation and may benefit from Conventional CPAP, applied nasally to improve ventilation and oxygenation during spontaneous ventilation in patients under deep sedation through maintenance of upper airway patency.(6) Recently novel techniques have been shown to be more effectively help ventilation than conventional low flow nasal oxygen. High flow nasal oxygen (HFNO) has been utilized in the intensive care setting for over 15 years. Its use in anaesthesia is rapidly increasing, providing an alternative to low flow oxygen devices during sedation for procedures such as gastroenterology, non-invasive cardiological, radiological, emergency medicine and persistent pain procedures.(1) Multiple mechanisms account for the therapeutic effects of HFNO, including a reduction in dead space, increased positive end-expiratory pressure, increased functional residual capacity, and delivery of higher inspired oxygen concentrations to the distal airways.(7) Moreover the heated and humidified HFNO provides adequate oxygenation with less drying of the upper airway mucosa, thereby improving patient comfort.(8) The use of HFNO in the gastroenterological suite had reduced critical incidents by providing high-inspired oxygen and slowing carbon dioxide rises related to respiratory depression.

Maintaining patient safety while successfully completing the procedures under sedation requires careful monitoring. Australian and New Zealand College of Anaesthetists (ANZCA) Guidelines on Monitoring during Anaesthesia, the Association of Anaesthetists of Great Britain & Ireland (AAGBI) and the American Society of Anesthesiologists Standards for Basic Anesthetic Monitoring had all emphasized the importance of monitoring exhaled Co2 during moderate to deep sedation to improve patients' safety. (9) Monitoring EtCO2 for the anesthesiologist is more superior to the pulse oximeter for immediately detecting an obstructed airway, opiate-induced apnea, or other airway problems that only much later may be detected by the pulse oximeter.(9) Unfortunately, it would be expected that the high oxygen flow rates during HFNO would severely dilute expired carbon dioxide and make sampling impossible.

Inclusion Criteria:

• patients undergoing elective ERCP with deep sedation will be enrolled
• age 18 - 70 years old
• obesity (BMI 30-35 kg/m2)
• American Society of Anaesthesiologists' physical status classification of 1 to 3
• Anticipated duration of the procedure is > 15 minutes.

Exclusion Criteria:

• • BMI >35 kg/m2

  • Simple procedures of < 15 minutes duration.
  • untreated or unstable cardiac conditions
  • Nasal or oral disease resulting in difficulty of either nasal breathing or mouth breathing.
  • Acute or chronic respiratory disorders as asthma and chronic obstructive pulmonary disease.
  • Pregnant patients and patients having procedures with planned endotracheal intubation
  • Expected difficult intubation patients.