Mixed venous oxygen saturation is known to reflect oxygen delivery and, thus, is frequently monitored in patients undergoing cardiac surgery. Factors that affect mixed venous oxygen saturation include hemoglobin level, arterial oxygen saturation and arterial oxygen partial pressure. Among them, arterial oxygen partial pressure is known to have minimal effect on oxygen delivery compared to hemoglobin and arterial oxygen saturation. However, some argues that in certain clinical setting, such as anemia which is very common in cardiac surgery patients, the contribution of plasma (arterial oxygen partial pressure in this case) to oxygen delivery becomes more significant. Therefore, we planned to perform a pilot clinical trial to observe the change of oxygen delivery, which would be reflected in mixed venous oxygen saturation and cerebral regional oxygen saturation, according to hemoglobin level.

Inclusion Criteria:

• Patients that scheduled to undergo cardiac surgery using cardiopulmonary bypass.

Exclusion Criteria:

• Emergent surgery
• Symptomatic carotid artery stenosis or carotid artery stenosis of ≥50%
• Preoperative oxygen therapy that is equivalent to the inspired oxygen fraction of 0.5.