The goal of this clinical trial is to compare the effects of flow-controlled ventilation (FCV) and volume-controlled ventilation (VCV) on hemodynamic and respiratory parameters in obese patients undergoing elective laparoscopic bariatric surgery. The main questions it aims to answer are:

Does FCV provide better intraoperative hemodynamic and respiratory stability compared to VCV during laparoscopic bariatric surgery? Is FCV a safe and feasible ventilation strategy under high intraabdominal pressure and position changes required in bariatric surgery?

Researchers will compare FCV group to VCV group to see if FCV improves intraoperative respiratory mechanics and hemodynamic parameters.

Participants will:

Undergo elective laparoscopic bariatric surgery with BMI >40 kg/m² (ASA I-III) Receive either flow-controlled or volume-controlled ventilation with individualized PEEP and tidal volume of 6-8 ml/kg predicted body weight Have intraoperative hemodynamic and respiratory parameters monitored at regular intervals, including arterial blood gas analysis Be followed postoperatively for oxygen therapy requirement and intensive care need

Laparoscopic surgery is associated with significant physiological changes due to pneumoperitoneum, which adversely affects hemodynamic and respiratory parameters, thereby complicating intraoperative anesthetic management. These challenges are particularly pronounced in obese patients, who present with reduced functional residual capacity and other physiological alterations that impact both intraoperative and postoperative outcomes.

Although bariatric surgery has conventionally been managed with volume-controlled ventilation (VCV), recent studies have highlighted the potential benefits of flow-controlled ventilation (FCV) in terms of safety and contribution to lung-protective ventilation strategies.

This study primarily aims to compare the effects of FCV and VCV on intraoperative hemodynamic and respiratory function dynamics in patients undergoing bariatric surgery. Secondarily, the study evaluates the clinical feasibility and safety of FCV under the high intraabdominal pressures and position changes required during bariatric procedures.

Study Design:

This study includes 34 patients with BMI >40 kg/m² classified as ASA I-III scheduled for elective laparoscopic bariatric surgery. Seventeen patients were prospectively managed with FCV, while data from 17 patients managed with VCV were retrospectively reviewed. All patients received standard monitoring plus intra-arterial blood pressure monitoring. Anesthesia induction and maintenance protocols were identical across both groups.

Ventilation Protocol:

In the FCV group, a tidal volume (VT) of 6-8 ml/kg predicted body weight was targeted, and positive end-expiratory pressure (PEEP) was individualized based on compliance following CO₂ insufflation. The same tidal volume strategy was applied in the VCV group with PEEP titration performed in eligible patients.

Measurements:

The following parameters were recorded after intubation, after insufflation, and at 30-minute intervals intraoperatively: mean arterial pressure (MAP), heart rate, peripheral oxygen saturation (SpO₂), plateau airway pressure (Pplat), peak airway pressure (Ppeak), driving pressure, end-tidal CO₂ (EtCO₂), minute volume, respiratory rate (RR), airway resistance (Raw), and static compliance (Cstatic) calculated as VT/(Pplat-PEEP). Arterial blood gas parameters including pH, PaCO₂, PaO₂, SaO₂, hemoglobin, and lactate were also recorded. Postoperative oxygen therapy requirement and intensive care unit admission were monitored.

Inclusion Criteria:

• Age between 18 and 65 years American Society of Anesthesiologists (ASA) physical status I, II, or III Body Mass Index (BMI) ≥ 40 kg/m² Scheduled for elective laparoscopic bariatric surgery Willing to participate in the study

Exclusion Criteria:

• ASA physical status IV or V Emergency surgical procedures Pregnant patients Patients requiring vasopressor support to maintain mean arterial pressure above 65 mmHg intraoperatively Patients with advanced pulmonary disease Patients who decline to participate in the study

Adult morbidly obese patients (BMI ≥40 kg/m²) aged 18-65 years, classified as ASA I-III, scheduled for elective laparoscopic bariatric surgery at Ankara Training and Research Hospital.

Individual participant data will be shared upon reasonable request.

Beginning 6 months after publication and ending 5 years following article publication

Individual participant data will be available upon reasonable request to the corresponding author.