The goal of this study is to compare two continuous positive airway pressure (CPAP) settings on heart and lung function in patients with severe obesity after anesthesia. The main questions it aims to answer are:

1. Does a recruitment maneuver and CPAP set to intrathoracic pressure (ITP) improve cardiopulmonary function compared to standard CPAP settings in patients with severe obesity after anesthesia?
2. Does the location of adipose tissue influence the response to CPAP settings in patients with severe obesity after anesthesia?

Participants will undergo monitoring of their intrathoracic pressure using an esophageal catheter. In the recovery area after anesthesia, participants will receive two CPAP settings, each for 20 minutes.

• Intervention 1: Recruitment maneuver and CPAP will set to the level of intrathoracic pressure
• Intervention 2: CPAP set to home settings (if OSA is present) or between 8-10 cmH20 (if OSA is not present).

The current proposed crossover study is a single center, open-label clinical trial in patients who have severe obesity (defined by body mass index greater than or equal to 40 kg/m2) and are recovering from anesthesia. The primary aim is to describe the difference cardiopulmonary function between two settings for continuous positive airway pressure (CPAP), using electrical impedance tomography (EIT), transthoracic echocardiography, and esophageal pressure monitoring to measure response. The secondary aim is to determine whether the location of adipose tissue modifies responses to CPAP settings.

The study protocol consists of placing an esophageal catheter to monitor intrathoracic pressure in the operating room when the participant is under anesthesia. In the post-anesthesia care unit, participants will receive two CPAP settings, in random order, for 20 minutes each. One setting is a recruitment maneuver and CPAP set to the level of end-expiratory pressure (intrathoracic pressure). Another setting is a CPAP set to home levels (if known) or 8-10 cmH20 if not on home CPAP. There will be a 10 minute washout period between interventions. Investigators will monitor airway and esophageal pressure, ventilation with electrical impedance tomography, right heart function with transthoracic echocardiography, and abdominal muscle contraction with ultrasound. Waist and hip circumference will be measured prior to CPAP.

Inclusion Criteria:

1. Adult patients (≥ 18 years old) scheduled for elective non-cardiothoracic surgery requiring general anesthesia with an endotracheal tube

2. Planned admission to the post-anesthesia care unit (PACU) after surgery

3. BMI ≥ 40 kg/m2

4. At the time of baseline measurements in the PACU, patients meet the following criteria:

   • Receiving ≤ 6 liters of supplemental nasal cannula oxygen
   • Alert as defined by a Richmond Agitation Sedation Scale of 0 or -1
   • Oriented to person, place, and time

Exclusion Criteria:

1. Pregnancy, suspected pregnancy or less than six weeks postpartum Known or current pneumothorax

2. Hemodynamic instability at the time of study assessment in the PACU defined as:

   • systolic blood pressure <90 mmHg or >180 mmHg
   • mean blood pressure <60 or >130 mmHg
   • Any use of intravenous vasoactive agent
   • heart rate < 50 or > 120 beats per minute

3. Respiratory insufficiency in PACU defined as:

   • Respiratory rate > 30
   • Oxygen saturation < 92%
   • Receiving > 6 liters of supplemental oxygen

4. Known chronic lung disease requiring supplemental oxygen at home

5. Known systolic heart dysfunction (left ventricular ejection fraction ≤ 30%)

6. Contraindication for esophageal catheter placement:

   • Known esophageal varices
   • Known bacterial sinusitis
   • Recent esophageal, nasopharyngeal, or laryngeal trauma or surgery
   • Known coagulopathy: including history of thrombocytopenia defined as platelet count <50,000; presence of hemophilia; known genetic disorder of coagulation (e.g.,deficits of protein C, protein S, von Willebrand factor) or oral and subcutaneous anticoagulation treatment (e.g., heparin, warfarin, and or other oral anticoagulants)

7. Contraindication for electrical impedance tomograph belt placement:

   • Pacemaker and/or internal cardiac defibrillator
   • Chest skin injury

8. Concern for study inclusion by the perioperative nurse or anesthesia team

All data analysis codes developed for this project in MATLAB (for electrical impedance tomography) or R will be thoroughly documented and made openly accessible on GitHub. We will make de-identified data available via the vivli platform (http://vivli.org/), non-profit clinical research data sharing platform. All data will be shared publicly under a data use agreement through a managed access process.

Individual participant data and supporting information will be available after data analysis and manuscript publication.

Individual participant data can be accessed from a data use agreement once data is uploaded on vivil