The purpose of this study is to compare the effect of mandibular advancement bite block to standard bite block for prevention of hypoxemia, intervention events and adverse effects during endoscopic examinations.

During endoscopic examinations, especially upper gastrointestinal, bile duct, or bronchoscopic examinations, the endoscope need to be placed through the mouth. A bite block is used to protect vulnerable endoscope and protect patient's teeth. During sedative endoscopic exams, respiratory depression, apnea or upper airway obstruction will occur under the influence of the sedative medications. Serious adverse events may occur such as hypoxemia. A nasal airway, Larson's maneuver, jaw thrust or chin lift may be needed to open airways.

Mandibular advancement devices has been widely used in treating obstructive sleep apnea. A modified bite block that provides mandibular advancement could provide entry inlet of endoscope as well as provide mandibular advancement to provide patent airway during sedative endoscopy. In this study, we group the patients into test group using mandibular advancement bite block and a control group using standard bite block. After anesthetic induction, gastric endoscopy was performed. Degree of upper airway obstruction will be evaluated and recorded. Differences between the two groups will be evaluated.

Inclusion Criteria:

• American Society of Anesthesiologist class I or II
• Patients undergoing routine upper gastrointestinal endoscopy under sedation

Exclusion Criteria:

• Baseline oxygen saturation < 90%
• Known difficult airway
• Oral or facial surgery history
• BMI > 35
• patients with gastroparesis or gastrointestinal bleeding
• anticipated exam time > 30 minutes

ASA class I or II patients admitted for routine upper gastrointestinal endoscopy