Cardiopulmonary Bypass

The problem with operating on the heart is that it is very difficult to do surgery on a moving organ, especially when that organ is nonnegotiable and there is no margin for error. But to stop the heart would be fatal to the body without another means by carrying blood and oxygen to the organs and removing waste products from them. Furthermore, even if a surgeon could operate on the beating heart (which is done occasionally as "off-pump coronary artery bypass grafts"), if the surgery requires entering any of the heart's chambers, then the heart must be still.

Cardiopulmonary bypass changes everything. In the most simplistic description, a surgeon puts in a catheter into the aorta (occasionally the femoral artery) and into the vena cava or right atrium (occasionally the femoral vein). The blood is thinned with heparin to prevent clotting as it leaves the body. Blood is withdrawn from the vena cava or right atrium before it can enter the heart. It goes to the machine where it is oxygenated, filtered, and warmed or cooled. Then it returns to the body into the aorta where it perfuses the organs. In this way, the heart and lungs are completely bypassed, giving the surgeon a bloodless field in which to work.

What impresses me is that the first successful case of this occurred in 1953. Although technology has certainly improved since then, there are still a lot of risks and complications associated with cardiopulmonary bypass. A lot of trauma occurs to the blood components and there is a high risk of bleeding afterwards. The body mounts an inflammatory response leading to leaky vessels, changes in mentation, difficulty maintaining a blood pressure. As a result, we try to limit time on the pump to reduce the effects of cardiopulmonary bypass.

Image of cardiopulmonary bypass is in the public domain, from Wikipedia.