Morbidly obese patients undergoing open heart surgery are at increased risk of breathing problems after removal of the breathing tube due to reduced lung function and chest wall restriction following surgery. These complications may result in poor oxygenation, respiratory failure, and prolonged ICU stay.
Airway Pressure Release Ventilation (APRV) is a mechanical ventilation mode that improves lung recruitment and oxygenation. This study aims to evaluate whether the prophylactic use of APRV after ICU admission, compared with conventional lung-protective mechanical ventilation, improves oxygenation, lung function, and ICU outcomes in morbidly obese patients undergoing elective cardiac surgery.
Patients will be randomly assigned to receive either APRV or conventional ventilation during postoperative mechanical ventilation, followed by standard weaning and extubation. Outcomes include oxygenation index, lung ultrasound findings, need for reintubation, and ICU clinical outcomes.
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Parallel
Airway Pressure Release Ventilation (APRV)
DevicePatients will be ventilated using the Airway Pressure Release Ventilation (APRV) mode immediately upon ICU admission. This mode will be maintained throughout the postoperative period until the patient meets the clinical criteria for extubation. with the following standardized steps: Initial APRV Settings * P High: 20-25 cm H₂O * P Low: 0 cm H₂O * T High: 4.0-6.0 seconds * T Low: 0.5-0.8 seconds * FiO₂: Adjusted to maintain SpO₂ \>92% Note: P High may be titrated according to patient tolerance, Mean airway pressure (MAP), and plateau pressures. T Low is set to terminate expiratory flow at 50-75% to preserve lung recruitment. Weaning/Transition from APRV to Extubation Once oxygenation and ventilation criteria are met: * T High will be gradually increased (to ≥8 sec) and P High decreased (to 10-15 cm H₂O) * Then transition to CPAP/PS for 15-30 minutes Final decision for extubation will be based on successful spontaneous breathing trial (SBT) (RSBI \< 105) and clinical readiness
Conventional Lung-Protective Mechanical Ventilation
DevicePatients will be ventilated using the SIMV Volume-Controlled mode with lung-protective strategies: * Tidal volume: 6-8 mL/kg of Ideal Body Weight (IBW) * PEEP: Set at 8-12 cm H₂O, individualized based on oxygenation status * Respiratory rate: Adjusted to maintain normocapnia, typically starting from 12-18 breaths per minute * FiO₂: Titrated to maintain SpO₂ \> 92% * Also transition to CPAP/PS for 15-30 minutes as a transition before extubation will be applied.
Oxygenation Index (OI)
The oxygenation index will be used as a quantitative measure of pulmonary oxygenation efficiency. It will be calculated using the formula: OI = (Mean Airway Pressure × FiO₂ × 100) / PaO₂. Changes in oxygenation index will be assessed to compare the effect of prophylactic APRV versus conventional lung-protective ventilation on pulmonary function in morbidly obese patients after elective cardiac surgery.
Lung Ultrasound Score (LUS)
Lung aeration will be assessed using lung ultrasound scoring across standardized thoracic zones. Each zone will be graded based on the presence of A-lines, B-lines, or consolidation, with higher scores indicating worse aeration. The lung ultrasound score will be used to evaluate postoperative lung recruitment and aeration in both study groups.
PaO₂/FiO₂ Ratio
The PaO₂/FiO₂ ratio will be measured as an indicator of oxygenation efficiency and gas exchange. Higher values indicate improved pulmonary oxygenation.
Reintubation Rate
Reintubation will be defined as the need for endotracheal intubation within 48 hours following planned extubation due to predefined clinical criteria including hypoxemia, hypercapnia, respiratory distress, altered mental status, or hemodynamic instability.
Duration of Mechanical Ventilation
Total duration of invasive mechanical ventilation from ICU admission until successful extubation.
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