The objective of this study is to investigate the hemodynamic effects of two strategies of alveolar recruitment maneuver in patients undergoing major abdominal surgery in the operating room

In practice, after induction of general anesthesia and intubation, patients will be conditioned with the recommended monitoring (arterial catheter, central venous catheter, and transpulmonary thermodilution).

Once conditioning is complete, optimization of blood volume will be performed with volumetric expansions (250 mL of Ringer lactate) to achieve a change in stroke volume of less than 10%, as recommended (RFE SFAR 2013 - Perioperative Vascular Filling Strategy). The patient will then be randomized to one of the following groups: [ extended sigh then CPAP ] or [ CPAP then extended sigh ] (random order of ARMs - each patient becoming their own control). In order to homogenize the settings, the mechanical ventilation will be standardized with in particular the use of a PEEP of 6 cmH2O before inclusion and between the ARMs (for a duration of at least 10 minutes in each case).

Hemodynamic values will be recorded during the last 10 seconds of each procedure. Once the two ARMs have been performed, the rest of the management will then be left to the discretion of the practitioner in charge of the patient.

The included patient will be managed according to the recommendations at the time of the study.

Inclusion Criteria:

• patient over 18 years old
• patient under general anesthesia
• patient intubated under controlled invasive mechanical ventilation
• patient with invasive hemodynamic monitoring (transpulmonary thermodilution)
• patient sedated (BIS between 40 and 60) and/or curarized with TOF monitoring to avoid inspiratory effort
• patient optimized on the hemodynamic level, in particular with regard to blood volume, following the hemodynamic monitoring data and the recommendations of the French Society of Anesthesia and Resuscitation (RFE SFAR 2013 - Perioperative vascular filling strategy)
• patient covered by a Social Security plan
• patient consent to participate in the study

Exclusion Criteria:

• contraindication to the use of cardiac output measurement
• cardiac arrhythmia
• pace-maker/implantable defibrillator
• severe valvulopathy
• contraindication to the use of the tomographic electroimpedancemetry technique
• thoracic lesions, thoracic dressing
• left ventricular ejection fraction (LVEF) < 45% and/or right ventricular failure.
• history of pulmonary lobectomy and/or pneumonectomy and/or known emphysema
• patient with restrictive or obstructive lung disease
• body mass index (BMI) < 16.5 or > 30 kg.m-2
• pregnancy
• intracranial hypertension or suspected intracranial hypertension
• patient under limitation of care
• patient under legal protection (guardianship, curatorship, safeguard of justice)