During CPB, the main source of mediastinal blood is which?

• A. Coronary arteries
• B. Pulmonary arteries
• C. Non coronary collaterals
• D. Systemic venous channels

Answer: (C)

During CPB the heart is bypassed and the mediastinal tissues rely on arterial flow from systemic collateral vessels rather than the coronary arteries. The coronary arteries are dedicated to perfusing the myocardium, especially when the heart is stopped and cardioplegia is used. The pulmonary arteries feed the lungs, not the mediastinal chest structures, and systemic venous channels return blood to the heart rather than supply arterial inflow to the mediastinum. The arteries that branch off the systemic circulation—non coronary collaterals such as bronchial and other mediastinal arteries—are the main source of mediastinal blood during bypass.