Flow-Controlled vs. Pressure-Controlled Ventilation in CABG: Effects on Lung Aeration and Diaphragm Function

Comparison of Flow-Controlled Ventilation and Pressure-Controlled Ventilation on Lung Aeration and Diaphragm Function in Patients Undergoing Elective Isolated On-Pump Coronary Artery Bypass Graft Surgery: A Single-Centre Prospective Randomised Controlled Trial

Pulmonary atelectasis and loss of lung aeration are common complications following cardiac surgery with cardiopulmonary bypass (CPB) and are associated with impaired oxygenation and prolonged mechanical ventilation. Diaphragm dysfunction occurring in the perioperative period may further delay extubation and prolong intensive care unit (ICU) stay. Flow-Controlled Ventilation (FCV) is a novel ventilation modality that provides continuous, flow-based delivery of tidal breaths with a triangular flow profile, potentially offering superior dynamic compliance optimisation compared to conventional Pressure-Controlled Ventilation (PCV).

This single-centre, prospective, 1:1 randomised parallel-group controlled trial will compare intraoperative FCV with PCV in adults undergoing elective isolated on-pump coronary artery bypass graft (CABG) surgery. The primary outcome is total lung ultrasound (LUS) score change (0-36 scale) from baseline (T0) to 24 hours postoperatively (T2). Secondary outcomes include diaphragm thickening fraction (TFdi), diaphragm excursion, PaO₂/FiO₂ ratio, extubation time, and ICU/hospital length of stay. Lung and diaphragm ultrasonography will be performed by an assessor blinded to group allocation at three time points: preoperatively (T0), at end of surgery while intubated (T1), and at 24 hours postoperatively after extubation (T2).

Inclusion Criteria:

• Age ≥18 years
• Planned elective isolated on-pump coronary artery bypass graft (CABG) surgery
• ASA Physical Status Classification II-IV
• Written informed consent obtained
• Technically adequate acoustic window for lung and diaphragm ultrasonography

Exclusion Criteria:

• Emergency surgery
• Combined surgical procedures (e.g., valve repair/replacement + CABG)
• Preoperative requirement for invasive or non-invasive mechanical ventilation
• Known diaphragm paralysis or neuromuscular disease
• Severe COPD exacerbation or active pneumonia at time of surgery
• Body mass index ≥40 kg/m²
• Inability to obtain standard lung or diaphragm ultrasound images due to pleural effusion, thoracic deformity, or prior thoracic surgery