The purpose of this multicenter, randomized controlled trial (ULTRASVENT-2) is to evaluate the effect of different positive end-expiratory pressure (PEEP) levels on postoperative oxygenation and lung aeration in adult patients undergoing elective non-cardiac and non-thoracic surgery under general anesthesia. Moving away from traditional binary outcomes, this study utilizes a continuous functional metric, the non-invasive oxygenation index SpO2/FiO2 (S/F ratio), as the primary endpoint to precisely capture the degree of respiratory function preservation.
Patients will be stratified into four distinct surgical cohorts based on the type and aggressiveness of the procedure: non-abdominal surgery, major open abdominal surgery, major laparoscopic abdominal surgery, and low-trauma laparoscopic surgery. This adaptive design aims to investigate how protective PEEP strategies interact with varying degrees of surgical trauma and intraoperative pneumoperitoneum, allowing the optimization of mechanical ventilation parameters for routine clinical practice.
Age greater than or equal to 18 years.
Planned elective non-cardiac and non-thoracic surgical intervention requiring general anesthesia with mechanical ventilation.
Airway protection utilizing an endotracheal tube.
Assignment to one of the four specific surgical strata: non-abdominal, major open abdominal, major laparoscopic abdominal, or low-trauma laparoscopic surgery.
Planned cardiac or thoracic surgery (e.g., coronary artery bypass grafting, valve replacement, heart transplantation, lung resection, esophageal surgery).
Pneumothorax diagnosed before or during the surgical procedure.
Inability to adequately visualize the target dorsal-basal lung zones by ultrasound due to physical limitations (e.g., morbid obesity, massive surgical dressings, anatomical anomalies, or dermatological lesions in the scanning area).
Presence of hydrothorax detected on the baseline preoperative ultrasound.
Parallel
Intraoperative Positive End-Expiratory Pressure (PEEP) Regulation
Procedure/SurgeryApplication of fixed PEEP levels calculated according to surgical aggressiveness and the presence of pneumoperitoneum. Standard PEEP arm utilizes PEEP values of 5 cm H2O. Higher PEEP arm utilizes protective PEEP values of 8 or 12 cm H2O. The assigned PEEP strategy is initiated immediately following endotracheal intubation and maintained continuously until extubation.
Non-invasive oxygenation index (SpO2/FiO2 ratio)
The primary functional outcome is the SpO2/FiO2 (S/F) ratio, a continuous metric indicating the degree of lung oxygenation. The S/F ratio is calculated by dividing the peripheral capillary oxygen saturation (SpO2) by the fraction of inspired oxygen (FiO2). To ensure standardization, postoperative measurements are performed on room air in a supine position. Measurements are recorded strictly when the patient achieves full wakefulness, which is verified using the modified Post Anesthesia Recovery Score (PARS) as a readiness criteria. The PARS scale ranges from a minimum of 0 to a maximum of 10, where higher scores indicate a better clinical recovery. Note: The reported outcome is solely the S/F ratio value; the PARS score is used exclusively as a clinical condition to initiate the S/F measurement and is not aggregated into the final outcome value.
Incidence of Postoperative Pulmonary Complications (PPCs)
The composite clinical outcome evaluates the total percentage of patients developing at least one severe respiratory adverse event in the postoperative period. PPCs are strictly defined as the presence of one or more of the following: confirmed hospital-acquired pneumonia, prolonged requirement for supplemental oxygen therapy lasting longer than 24 hours, or the onset of refractory hypoxemia necessitating unexpected transfer to the Intensive Care Unit for non-invasive or invasive mechanical ventilation.
Postoperative lung ultrasound score and aeration patterns
Evaluation of the absolute postoperative Lung Ultrasound (LUS) score to assess anesthesia-induced alveolar collapse. A differentiated protocol is used based on surgical strata. Strata 1 and 4 use a 2-zone express protocol targeting dorsal-basal sectors (total scale range: minimum 0 to maximum 6). Strata 2 and 3 use a comprehensive 12-zone panoramic thoracic mapping protocol (total scale range: minimum 0 to maximum 36). For both LUS scales, higher scores indicate a worse outcome (more severe loss of lung aeration and atelectasis). Specific qualitative acoustic patterns (e.g., multiple B-lines, subpleural consolidations, or static bronchograms) are also recorded to validate the numerical LUS score.
Incidence of Intraoperative Hemodynamic Instability
Frequency of intraoperative hemodynamic instability episodes directly related to mechanical ventilation settings, specifically measured as the requirement for the initiation or dose increase of vasopressor support (ephedrine, phenylephrine, or norepinephrine) to maintain a mean arterial pressure (MAP) greater than 65 mm Hg.
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