Early Postoperative Physiotherapy to Prevent Respiratory Insufficiency After Elective Heart Surgery

Inclusion Criteria: * Adults aged 18-80 years * Male and female participants * Elective coronary artery bypass grafting (CABG) * Body mass index (BMI) \< 30 kg/m² * Left ventricular ejection fraction (EF) \> 25% * Extubated on postoperative day 0 (POD 0) * Able and willing to provide written informed consent * Able to perform spirometry and follow study instructions Exclusion Criteria: * Refusal or inability to provide informed consent * Emergency CABG surgery * Previous cardiac surgery * Severe cardiac arrhythmias (e.g., ventricular tachycardia/fibrillation, third-degree atrioventricular block) * Previous stroke * Motor impairment of upper or lower extremities due to neurological or musculoskeletal disease * Dyskinesia * Not extubated on POD 0 * Significant postoperative neurological complications * Peripheral arterial disease of the lower extremities or previous lower-limb amputation * Acute or chronic pulmonary disease * Preoperative FEV1 \<30% of predicted (greater than 70% reduction) * Inability to perform spirometry correctly * Cancelled surgery after preoperative assessment * Extubation later than 24 hours after surgery * Requirement for continuous positive airway pressure (CPAP) after extubation SpO₂ \<90% one hour after extubation despite oxygen supplementation (4 L/min by nasal cannula) * Return to the operating room after the initial CABG procedure * Requirement for dialysis (acute or chronic)