In the use of the second supraglottic airway device- i-gel in the laparoscopic pneumoperitoneum and Trendelenburg (LPT) surgical positioning, our data reported that the leak fraction in the i-gel group was higher than in the endotracheal tube group.1 These air leak may be gone into the GI tract and cause the gastric distension resulting in the increasing risk of aspiration. Few studies investigated whether the risk of occurrence of the gastroesophageal reflux (GER), the changes of the lower esophageal sphincter (LES) while the GER occurred, and the stomach fullness in the i-gel group than in the endotracheal tube group.

We aim to observe the changes of gastroesophageal function parameters by esophageal manometry, pH impedance, and intra-abdominal pressure before and after laparoscopic pneumoperitoneum during anesthesia, all via the second SADs.

Background: In the use of the second supraglottic airway device- i-gel in the laparoscopic pneumoperitoneum and Trendelenburg (LPT) surgical positioning, our data reported that the leak fraction in the i-gel group was higher than in the endotracheal tube group.1 These air leak may be gone into the GI tract and cause the gastric distension resulting in the increasing risk of aspiration. Few studies investigated whether the risk of occurrence of the gastroesophageal reflux (GER), the changes of the lower esophageal sphincter (LES) while the GER occurred, and the stomach fullness in the i-gel group than in the endotracheal tube group. The LES is the important physiological mechanisms that prevent regurgitation and aspiration. The previous study has been investigated that LES would have adaptive response in using the endotracheal tube in the LPT setting. However, the change of LES pressure and gastroesophageal reflux during the LPT surgical settings using the i-gel is still unknown.

The esophageal manometry has pressure sensor to measure the LES pressure. The combined esophageal multichannel intraluminal impedance and pH monitoring (MII -pH) could not only detect the acidic reflux or weakly acidic reflux, but also the height of the regurgitant. We also used the abdominal echo in check the gastric volume before and after the surgery.

Objectives: we aimed to compare the changes of lower esophageal sphincter pressure (LESP) and the occurrence of the GER during the LPT setting by esophageal manometry and MII-pH monitor between the endotracheal tube (ETT) and the i-gel group. The gastric volume before and after surgery has been checked by abdominal echo. We also observed the respiratory parameters changes while the GER occurred.

Patients and methods: Consecutive patients who will receive scheduled laparoscopic surgery under general anesthesia and aged from 20 to 80 years old will be enrolled. All subjects provide basic demographic data. The patients have been randomized into the i-gel or ETT group by sealing envelope. After induction, the MII-pH monitor has been pre-attached to the esophageal manometry. Then they will be inserted into the esophagus. The patients have received the ETT or i-gel. Then the respiratory parameters were collected by the GE S/5 Compact Anesthesia Monitor (GE Healthcare, Helsinki, Finland) with a spirometry tube (GE Healthcare, Helsinki, Finland) and D-lite sensor (GE Healthcare, Helsinki, Finland). The data have been continuous recorded. There were four time point of the LESP measured: (1)T1, after induction (without muscle relaxant) (2)T2, ETT or i-gel intubation (3)T3, after LPT setting (4) T4, off LPT setting.

Expected result: We will compared the difference between the patients receiving the i-gel or ETT group about the (1) the changes of LESP in the above four time point (2) the occurrence of the GER and the relationship between the LES and GER (3) gastric volume before and after surgery.

Inclusion Criteria:

• Patients who will receive scheduled surgery with laparoscopic pneumoperitoneum and Trendelenburg (LPT) setting under general anesthesia
• Aged from 20-80 years old

Exclusion Criteria:

• Major systemic disease, such as congestive heart failure, liver cirrhosis, end stage renal disease and malignancy.
• Patients who have the risk of difficult ventilation or intubation.
• pregnant women
• coagulopathy

due to the privacy of the individual participant data of our patients, we cannot share their data to other researchers.

The raw data will be kept very carefully in our research team.