Comparative Study of Escalating PEEP (Positive End Expiratory Pressure) Vs. Lung Recruitment by Sustained Inflation Strategies for Managing Hypoxemia in COPD Patients Undergoing Video-Assisted Thoracoscopic Surgery (VATS)

A) 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.

B) Intraoperative settings:

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