An Observational Study to Determine Feasibility and Validity of Esophageal and Transpulmonary Pressure Measurements During One Lung Ventilation

In this prospective cohort study, the investigators will assess the feasibility of esophageal pressure measurements during general anesthesia with one-lung ventilation in patients undergoing non-cardiac intrathoracic surgery, which is typically conducted in the lateral position. The investigators will measure esophageal pressure with an esophageal balloon catheter. The investigators will compare esophageal pressure measurements to lung collapse estimated by Electrical Impedance Tomography (EIT).

Patients will be equipped with the EIT belt before induction of anesthesia, and a one-minute EIT recording during spontaneous breathing will be conducted. Anesthesia will be induced as to institutional standards and upon the discretion of the attending anesthesiologist. After placement of a double-lumen endotracheal tube, the esophageal balloon catheter will be placed.

• After placement of the esophageal catheter, esophageal pressure, transpulmonary pressure, airway pressure and flow and EIT signal will be recorded ("baseline").
• When the patient has been positioned for surgery (typically in the lateral position), a second recording of the above parameters is conducted ("lateral"). One-lung ventilation will then be initiated and a third measurement ("OLV") is made.
• During the third measurement, a decremental positive end-expiratory pressure trial will be conducted to correlate the measured esophageal pressure to the positive end-expiratory pressure where lung collapse is detected from EIT.
• Before surgery, the EIT belt is opened and removed from the surgical field to avoid interference.
• If feasible, when surgery is finished, before reversal of neuromuscular blockade and extubation, a final recording of EIT, esophageal pressure, transpulmonary pressure, airway pressure and flow will be conducted.