Which organ in the thoracic region is not perfused during cardiopulmonary bypass?

During cardiopulmonary bypass (CPB), blood flow is redirected through a heart-lung machine, which takes over the function of the heart and lungs, allowing for controlled perfusion of vital organs. While the kidneys, head, and pancreas receive blood flow during this process, the lungs are not perfused in the same manner. This is due to the fact that the function of the heart-lung machine facilitates oxygenation of blood outside of the body, meaning that oxygenation typically achieved by the lungs does not occur through normal pulmonary functions during CPB.

In typical situations, blood is oxygenated by the heart-lung machine and then distributed to the body's organs without passing through the lungs. This is particularly important in surgeries involving the heart, as it allows for a bloodless and dry surgical field while still ensuring that other essential organs receive adequate blood flow.

Thus, the lungs are effectively excluded from the perfusion circuit during cardiopulmonary bypass, making them the organ in the thoracic region that is not directly perfused in this scenario.