The investigators designed this prospective observational study with the theory that alkalosis caused by decreased CO2 solubility due to temperature increase during the rewarming period of the Cardiopulmonary Bypass could be prevented by reducing the sweep gas flow during the rewarming period.

Inclusion Criteria:

• Patients over 18 years of age
• Elective CPB surgery

Exclusion Criteria:

• Patients undergoing minimally invasive surgery
• Patients undergoing robotic cardiac surgery,
• Patients undergoing deep hypothermia,
• Patients undergoing total circulatory arrest,
• Patients whose FiO2 requirement is high that cannot be applied to target gas flow

Patients over 18 years of age scheduled for elective CPB surgery