The purpose of this clinical trial is to determine whether different types of ventilator settings during surgery change the relationship between the pressures in the lungs and the function of the heart.

In this study, patients will be randomly assigned (like flipping a coin) to receive either standard or individualized (research) lung protective ventilator settings.

Before surgery, patients will be given an 8-item verbal questionnaire about any respiratory symptoms. After patients are asleep for surgery, an ultrasound probe will be inserted into the esophagus (food pipe) and stomach to examine the heart and lungs and take ultrasound pictures. The ultrasound probe is then removed. Next, a small balloon catheter (a narrow tube smaller in diameter than a pencil lead) will be placed in the esophagus, where it will be used to measure the pressures in the chest and lungs.

For patients who are assigned to standard ventilator settings, the ventilator settings and pressures during surgery will be recorded.

For patients assigned to individualized (research) ventilator settings, the pressures from the balloon catheter will be used to adjust the ventilator settings every 30 minutes during surgery.

A second ultrasound pictures of the heart and lungs will be obtained at the point at which the patient is placed into the Trendelenburg position. At the end of surgery and before the patient is awake, the balloon catheter will be removed, the ultrasound probe will be inserted, a third set of ultrasound pictures of the heart and lungs will be obtained, and the ultrasound probe then removed.

Patients will be telephoned 30 days after surgery to ask about their recovery. The 8-item respiratory symptom questionnaire will be repeated at this time.

This study builds on the concepts and techniques used successfully in the study "Changes in Transpulmonary Pressures During Varying Surgical Conditions," CHRMS 18-0048, which demonstrated that obese patients have significantly worse lung mechanics than lean patients during robotic-assisted laparoscopic surgery. (This is a type of minimally invasive surgery in which the patient is tilted head downward on the operating table (the Trendelenburg position), and the abdomen is inflated with carbon dioxide; both of these steps allow more room in the abdomen for surgical instruments, and allow a better field of vision for the surgeon). In that study, which is ongoing, we use a balloon catheter in the patient's esophagus as a way to measure the pressures experienced by the lung: With each breath, the lungs push on the esophagus; the balloon catheter is attached to an external pressure transducer, which allows us to record the lung pressures during surgery.

During surgery with general anesthesia (and sometimes in the ICU), the patient's breathing is controlled by a mechanical ventilator. Under physiologically stressful conditions, such as acute respiratory distress syndrome (ARDS), or mechanically stressful conditions, such as surgery in Trendelenburg position, setting the ventilator can become a balancing act between what is safe for the lungs and the effects on other organ systems, such as the heart.

In this study, we hypothesize that obesity in combination with inflation of the abdomen and steep Trendelenburg positioning are associated with elevated right heart strain, and that the use of lung pressure measurements to guide ventilation may ameliorate the increased strain. We will conduct an ultrasound exam of the heart and lungs at three points during the surgical procedure: The first will occur after the patient is anesthetized, but before the surgical incision has been made; the second will be while the patient is in steep Trendelenburg position; and the third will take place near the end of surgery, just before desufflation of the abdomen. The ultrasound exam is done by inserting a probe through the patient's mouth into their esophagus and stomach, because that provides a close view of the heart and lungs; this type of exam is typically done on cardiac surgery patients.

This study is a randomized controlled trial of ventilation in lean and obese subjects undergoing robotic abdominal surgery. Subjects will be randomized to receive either standard lung-protective ventilation or transpulmonary pressure-guided ventilation using the esophageal balloon catheter.

Objective 1: To determine the effect of obesity and surgical conditions on right heart function. We will compare ultrasound measurements of the right ventricle of the heart between lean and obese subjects immediately after intubation, while in steep Trendelenburg position, and again just before desufflation of the abdomen.

Objective 2: To determine if intraoperative transpulmonary pressure-guided ventilation alters right heart function. We will compare ultrasound measurements of the right ventricle of the heart between subjects randomized to standard ventilation or transpulmonary pressure-guided ventilation.

Procedures: In the preoperative area, measurement of the patient's waist size and weight. Once in the operating room, after general anesthesia is induced, the first ultrasound exam will be conducted. The ultrasound probe will be inserted into the esophagus and stomach to examine the heart and lungs, and images will be saved. Each exam will take 5-10 minutes, and will not extend the length of your surgery. A plastic tooth guard will be used to protect the patient's teeth. The ultrasound will be removed after the exam is over.

Next, a small balloon catheter (smaller in diameter than a pencil lead) will be placed in the esophagus. We will record the pressures and gas flows from the ventilator and in the balloon catheter for the entire surgery.

Patients will be randomly assigned (like flipping a coin) to receive either standard or individualized ventilation. If you assigned to standard lung-protective ventilation, we will use national anesthesiology guidelines to set and maintain the ventilator during surgery. If assigned to individualized ventilation, we will use the same national guidelines to set the ventilator but then adjust the pressures at the end of each breath using the measurements from the balloon catheter. We will make this adjustment every 30 minutes during the surgery.

The second ultrasound exam will be performed after the patient is tilted into the Trendelenburg position. At the end of surgery before the third ultrasound, we will remove the catheter the esophagus, and then perform the third ultrasound exam.

Inclusion Criteria:

• Patients undergoing robotic-assisted laparoscopic surgery at University of Vermont Medical Center in Trendelenburg position
• Age ≥ 18 years
• Signed consent form

Exclusion Criteria:

• Inability to sign consent form
• Inability to speak English
• Emergent surgery
• Current smoker
• Smoking history ≥20 pack years
• Esophageal pathology: Strictures, varices, history of esophageal dilatation or surgery
• Intrinsic lung disease (e.g. asthma, COPD, emphysema, interstitial lung disease, lung cancer)
• Impaired cardiac function (e.g. decreased ejection fraction, wall motion abnormalities, or cardiomyopathy).
• Any other co-morbid condition that, in the opinion of the study investigators, may interfere with study participation.