Effect of Position and Pneumoperitoneum on Respiratory Mechanics and Transpulmonary Pressure During Laparoscopic Surgery

The study is a prospective observational study. Following approval by the Institutional Review Board, the study will be performed in a prospective, longitudinal cohort manner. Patients scheduled for elective laparoscopic surgery aged between 20 and 60 years will be included. Each participant signed an informed consent. Exclusion criteria included respiratory pathology, a body mass index lower than 18 or higher than 40 kg/m2, esophageal pathology and previous esophageal or pulmonary operation.

Following induction of anesthesia using fentanyl 2-5 microgram/kg, propofol 1-3 mg/kg and muscle relaxation with rocuronium 0.6-0.8 mg/kg, the trachea will be intubated using a 7-8 mm ID endotracheal tube. Mechanical ventilation in a volume controlled mode with a tidal volume 6-8 ml/kg and a PEEP of 5 cm of water will be initiated at a rate of 12-16 breaths per minute using an anesthesia machine (Fabius GS Premium, Drägerwerk AG \& Co. KGaA, Lübeck, Germany). Balanced general anesthesia will be maintained by sevoflurane and fentanyl.

Esophageal balloon catheter will be placed according to manufacturer instructions 9. In brief, the stomach will be decompressed and suctioned with an 18 F orogastric tube. This tube will be also utilized to estimate the depth of the lower esophageal sphincter, a measure that will be corroborated with external simulation of the approximate distance from the gastric opening to the nares. A lubricated 86 cm long closed-tip catheter with a 9.5 cm long balloon catheter at its distal end will be gently inserted via one nostril and advanced into the esophagus. The calculated depth aiding in positioning the balloon at the lower third of the thoracic cavity at about 10 cm above the lower esophageal sphincter, as guided by catheter markings, will be the product of patient height x 0.288. This location had been verified by the external measurements at described above. An extension tubing will be attached to the Y piece at the proximal ending of the catheter and connected to a syringe and a pre-calibrated pressure transducer via a 3-way stopcock. One ml of air will be injected into the balloon so that it became semi inflated, and the tracing on the pressure monitor will be adjusted with additional small amounts of air until no flattening or damping will be noted in the pressure waveform. When properly positioned, the catheter will be secured with tape to prevent movement or extubation.

Esophageal pressure will be continuously measured via a calibrated pressure transducer system (Art-Line ,BioMetrix, Kiryat Mada, Jerusalem, Israel) connected to a patient monitor (Datex AS/3, Datex Ohmeda Medical Equipment, GE Healthcare, USA) and recorded using a designated computer software.

Esophageal pressure will be documented with the patient at horizontal position, and with the head up, operating table elevated 20 cm (anti Trendelenburg position) and head down, operating table lowill bed 20 cm (Trendelenburg position).

Following peritoneal access and trocar insertion, the peritoneal cavity will be gradually inflated with carbon dioxide by a laparoscopy insufflator (UHI-4 High Flow Insufflation Unit, Olympus Corporation Inc., Center Valley, PA, USA) and esophageal pressure will be recorded at a stable peritoneal pressure of 5, 10 and 15 mmHg. Following complete peritoneal inflation, the esophageal balloon catheter will be removed and recording terminated.