This prospective observational study evaluates the association between intraoperative mechanical power (MP) - a composite measure of the total energy delivered to the lungs during mechanical ventilation - and postoperative pulmonary complications (PPCs) and prolonged mechanical ventilation in adult patients undergoing elective coronary artery bypass graft (CABG) surgery with cardiopulmonary bypass (CPB). Intraoperative ventilatory parameters including tidal volume, respiratory rate, airway pressures, and PEEP will be recorded and used to calculate MP and driving pressure (DP). No additional interventions will be applied beyond standard clinical care.

This single-center prospective observational study enrolls adult patients undergoing elective first-time isolated coronary artery bypass graft (CABG) surgery with cardiopulmonary bypass (CPB).

Mechanical power (MP) will be calculated as: MP = 0.098 × RR

× VT × [PIP - 0.5 × (Pplat - PEEP)], normalized to predicted body weight (norMP = MP/PBW). Male PBW (kg) = 50 + 0.91 × [height (cm) - 152.4]; female PBW (kg) = 45.5 + 0.91 × [height (cm) - 152.4]. Driving pressure (DP) = Pplat - PEEP.

Ventilatory parameters (VT, RR, peak pressure, plateau pressure, PEEP, FiO2, EtCO2) and arterial blood gases (PaO2/FiO2, PaCO2, lactate) will be recorded at four standardized time points: T1 (post-intubation), T2 (post- sternotomy), T3 (pre-bypass), and T4 (post-bypass). No additional interventions beyond standard clinical care will be applied.

Postoperative outcomes including atelectasis, pneumonia, pleural effusion, prolonged oxygen requirement, need for non-invasive ventilation, re-intubation, duration of mechanical ventilation, and ICU length of stay will be assessed within the first 48 hours.

Sample size: 110 patients (α=0.05, power=80%, expected PPC incidence 35% vs 65% in low vs high MP groups, 20% dropout allowance). Statistical analysis will include Mann-Whitney U or t-test, chi-square or Fisher exact test, and logistic regression. Significance: p<0.05 (two-tailed).

Inclusion Criteria:

• Age 18 years or older
• Scheduled for elective, first-time isolated CABG surgery
• Use of cardiopulmonary bypass (CPB)
• Intraoperative mechanical ventilation applied under general anesthesia with recordable ventilator data
• Provision of written informed consent

Exclusion Criteria:

• Emergency cardiac surgery
• Off-pump CABG (without CPB)
• Preoperative requirement for invasive mechanical ventilation
• Advanced chronic lung disease
• Incomplete or unreliable intraoperative ventilatory data
• Intraoperative use of advanced non-standard support (ECMO)

Adult patients undergoing elective isolated CABG surgery with cardiopulmonary bypass at a single tertiary cardiac surgery center

Individual participant data will not be shared. This is a single-center observational study conducted at a public hospital. Data sharing is not planned due to institutional privacy regulations and the absence of external funding requiring data sharing.