The goal of this clinical trial is to evaluate whether low tidal volume (LTV) ventilation during cardiopulmonary bypass (CPB) surgery helps preserve diaphragmatic excursion in adult patients undergoing coronary artery bypass grafting (CABG). The study will also assess the relationship between LTV ventilation and postoperative pulmonary complications, such as atelectasis, pleural effusion, and pneumonia.

The main questions this trial aims to answer are:

Does LTV ventilation better preserve diaphragmatic motion compared to apnea during CPB?

Are postoperative pulmonary complications less frequent in patients receiving LTV?

Does LTV contribute to shorter extubation times and ICU stays?

Researchers will compare LTV ventilation with apnea (standard care) during CPB to assess its effects on diaphragmatic excursion, measured via ultrasound, and postoperative respiratory outcomes.

Participants will:

Undergo elective CABG surgery under general anesthesia

Be randomly assigned to receive either LTV ventilation or apnea during CPB

Have diaphragmatic excursion measured by ultrasound before surgery, before extubation, and 24 hours after surgery

Be monitored for postoperative pulmonary complications (atelectasis, effusion, pneumonia), extubation time, and ICU length of stay

Ultrasound will be used to measure diaphragmatic excursion (DE) in quiet and deep breathing. DE below 10 mm will be considered as diaphragmatic paralysis. Postoperative respiratory assessments will include blood gas analysis (PaO₂/FiO₂ ratio), clinical respiratory parameters, and imaging findings.

This is a prospective, single-center, assessor-blinded randomized controlled trial. Patients and outcome assessors will be blinded to group allocation. The study will be conducted at the Anesthesiology Clinic of Konya City Hospital and is expected to enroll 60 patients.

oronary artery bypass grafting (CABG) surgery performed under cardiopulmonary bypass (CPB) is a complex procedure frequently associated with postoperative pulmonary complications (PPCs). During CPB, mechanical ventilation is usually paused (apnea), which leads to temporary diaphragmatic inactivity. The diaphragm, being a rhythmically contracting muscle under normal physiological conditions, may experience transient dysfunction or even paralysis due to this intraoperative inactivity. Several mechanisms, including loss of neuromechanical coupling, disrupted neuromuscular signaling, altered venous return, and impaired diaphragmatic oxygenation and metabolism, are thought to contribute to this process.

Reduced diaphragmatic motion can create a favorable condition for atelectasis, impair oxygenation, and increase the risk of infection in the postoperative period. The resulting transient diaphragmatic dysfunction is considered a potential contributor to the development of PPCs such as pneumonia, pleural effusion, and prolonged mechanical ventilation.

Recent research has focused on the protective effects of low tidal volume (LTV) ventilation in surgical and critical care settings. However, limited studies have evaluated its direct impact on diaphragmatic function during CPB, particularly in the context of CABG surgery. There is a need to investigate whether intraoperative application of LTV ventilation during CPB can help preserve diaphragmatic excursion (DE) and reduce PPCs.

Inclusion Criteria:

Age over 18 years

Male or female patients

American Society of Anesthesiologists (ASA) physical status class II or III

Scheduled for elective coronary artery bypass graft (CABG) surgery with cardiopulmonary bypass (CPB)

Provided written informed consent to participate in the study -

Exclusion Criteria:

History of neuromuscular disease

History of thoracic surgery

History of pneumothorax or ascites

Chronic respiratory failure

Pulmonary hypertension or right ventricular failure

Emergency surgery

Inability to perform diaphragm ultrasonographic measurements

Refusal to participate in the study

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The plan to share individual participant data has not been determined. No data will be shared at this stage due to institutional policy and ethical concerns.

Only participants and outcome assessors are masked in this study. No additional masked parties beyond those listed.