Intraoperative lung protective ventilation strategies using standardized tidal volumes based on predicted body weight have proven beneficial, but attempts to standardize positive end expiratory pressure (PEEP) settings have not robustly accounted for body habitus or dynamic surgical conditions. Laparoscopic abdominal surgery in Trendelenburg (head-down) is an increasingly common surgical modality that presents a unique physiological challenge to the pulmonary system. In order to delineate the impact of body habitus, pneumoperitoneum, and surgical positioning on intraoperative pulmonary mechanics we conducted an observational study of patients undergoing robotic assisted laparoscopic abdominal surgery in Trendelenburg position. Using esophageal manometry, we partitioned the mechanical properties of the respiratory system into its lung and chest wall components and evaluated the effects of pneumoperitoneum, surgical position, and body mass index (BMI) on transpulmonary pressures, airway and transpulmonary driving pressures, and lung elastance. We hypothesized that increasing BMI would be associated with evidence of increasing atelectasis, increased driving pressures, and elevated lung elastance and that these changes would be exacerbated by pneumoperitoneum and Trendelenburg positioning.

Inclusion Criteria:

• Inclusion criteria were presentation for robotic assisted laparoscopic abdominal surgery in the supine position, age ≥ 18 years, and ability to provide informed consent

Exclusion Criteria:

• Exclusion criteria included intrinsic lung disease, ≥ 20 pack year smoking history, reactive airways disease, home oxygen requirement, inability to provide informed consent, emergent surgery, or esophageal pathology (i.e., strictures, varices, history of esophageal dilatation or surgery).

Patients undergoing robotic assisted laparoscopic abdominal surgery at the University of Vermont Medical Center