The Effectiveness of Two Distinct Ventilation Strategies Escalating Positive End Expiratory Pressure (PEEP) and Lung Recruitment Maneuvers in Improving Oxygenation

1. Preoperative settings :

• Written informed consent will be obtained from all participants prior to the study.
• Pre-operative optimisation of patients include cessation of smoking, improvement of pulmonary functions using bronchodilators and steroids, pre-operative chest physiotherapy and training of patient with lung expansion manuoevers. Reversible components of COPD such as bronchospasm, infections, and pulmonary oedema should be actively looked for and treated aggressively 9.
• Detection of severity of COPD by using The Global Initiative for Chronic Obstructive Lung Disease (GOLD) system categorizes airflow limitation into stages. In patients with FEV₁/FVC <0.7:
• GOLD 1 - mild: FEV₁ ≥80% predicted
• GOLD 2 - moderate: 50% ≤ FEV₁ <80% predicted
• GOLD 3 - severe: 30% ≤ FEV₁ <50% predicted
• GOLD 4 - very severe: FEV₁ <30% predicted 10.
• Preoperative assessment evaluates lung mechanics, parenchymal function, and cardiopulmonary reserve to determine a patient's suitability for surgery. Lung mechanics, including forced expiratory volume in 1 second (FEV1), maximum voluntary ventilation, forced vital capacity, and residual volume/total lung capacity (RV/TLC) ratio, provide insights into respiratory function. An FEV1 greater than 60% indicates potential tolerance for anatomic lobe resection. An FEV1 of less than 30% suggests postoperative ventilator or supplemental oxygen dependence. In FEV1s less than 60%, a ventilation-perfusion scan (VQ scan) may calculate a postoperative FEV1, with values above 35% (and up to 40%), suggesting adequate postoperative pulmonary reserve. DLCO, measuring gas diffusion, ideally exceeds 40% for surgery. Cardiopulmonary exercise testing assesses overall reserve, with a maximum rate of oxygen (O2) your body can use during exercise (VO2) greater than 10 mL/min/kg, indicating suitability for surgery 2.
• Preoperative assessment for VATS also involves evaluating blood counts for indications of polycythemia or infection. Chest x-rays and CT scans provide anatomical details for surgical planning. Arterial blood gases identify patients at risk for postoperative complications; a partial pressure of carbon dioxide (CO2) more than 50 mm Hg or a partial pressure of O2 less than 60 mm Hg indicates vulnerability 2.

1. Intraoperative settings:

Electrocardiogram (ECG), non-invasive blood pressure (NIBP), pulse oximeter (SpO2) will be applied, and baseline readings will be taken before induction.

Anaesthesia will be induced after a period of preoxygenation with 100% oxygen for 2-3 minutes with intravenous injection of fentanyl 2 µg/kg, propofol 2 mg/kg and a muscle relaxant (Atracurium) 0.5 mg/kg after loss of patient consciousness. Lung isolation is achieved using a double-lumen endotracheal tube, Fiberoptic bronchoscopy is typically used to guide and confirm the placement and positioning of the tube 11.

Patients often requires the placement of invasive monitoring devices, such as invasive blood pressure (IBP) lines and central venous lines (CVL).

Anaesthesia will be maintained by 1-2 % of isoflurane in 50% oxygen/air mixture according to oxygen state and 0.1 mg/kg atracurium, ventilation parameters that maintain normocapnia (CO2 between 35- 40 mmHg). Fluids as crystalloids used by a fluid chart for the deficit and maintenance as needed.

The surgery typically begins with the patient positioned in a full lateral decubitus posture tailored to the side of the operation or in a supine position with appropriate support to access the chest.

Ventilatory setting:

Typically, an initial PEEP of 5 cm H₂O is used in all patients,

Group A:

PEEP is typically increased in 2-3 cm H₂O increments while monitoring the patient's response (oxygenation, hemodynamics, and lung compliance).

Group B:

A sustained inflation:

Set the ventilator to CPAP mode and increase the pressure to 30 cm H2O for 30 s.

1. Postoperative settings:

Follow up patients in recovery room whether transferred to ICU or to Ward, data will be recorded at the following times 1 h, 2 h, 6 h, 12 h, and 24 h. Both groups will be compared to each other according to the following variables:

• Hypoxemia
• The Need for mechanical ventilation