Femoro-femoral cardiopulmonary bypass with retrograde perfusion is needed for totally thoracoscopic cardiac surgery. one of the major complication of retrograde perfusion is organ hypoperfusion.

Arterial blood gas analysis can help to detect hypoperfusion or hypoxia during retrograde perfusion. However,whether the arterial oxygenation status from different parts of the body are the same in the condition of retrograde perfusion have not been studied.

The present study is aimed to determine if there is difference in the arterial oxygenation between peripheral arterial and aortic root during the period of retrograde perfusion.In addition, the impact of artificial ventilation on the difference of arterial oxygenation will also be investigated.

All patients included will be assigned into two different groups according to the surgical approach,one group is named "NP" with normal perfusion,and the other is named "RP" with retrograde perfusion.

For all the patients,we will obtain 0.5ml blood from both peripheral arterial and aortic root for blood gas analysis at some specific time points.

We will focus on the differences of arterial oxygenation between peripheral arterial and aortic root at each group.At the same time,we will analyse the impact of artificial ventilation on it.

Inclusion Criteria:

• age > 18 years old
• undergoing totally thoracoscopic cardiac surgery with cardiopulmonary bypass

Exclusion Criteria:

• without informed consent
• pregnancy

patient undergoing totally thoracoscopic cardiac surgery with cardiopulmonary bypass