When a patient is connected to a heart-lung machine during bypass surgery, the surgeon places a clamp on the aorta. This manipulation increases the risk of stroke. Performing the surgery without the heart-lung machine eliminates the need to clamp the aorta, thereby reducing the risk of stroke by 50 percent. Conversely, surgery without the pump decreases blood loss and patients benefit from a reduced need for blood transfusions. There haven't been a lot of studies done on this, but patients who have traditional bypass surgery often have trouble reading a book or doing a crossword puzzle after the surgery.
Simple tasks are more difficult because concentration is reduced.
A report published in a recent issue of the New England Journal of Medicine confirms the relatively high prevalence and persistence of cognitive decline after traditional bypass surgery. The heart-lung machine may be responsible for some of this decline. Doctors suspect that air bubbles the machine produces may block blood flow through vessels in the skull, killing brain cells. Or the surgical site may release small drops of fat, which the pump could circulate to the brain, causing the same problem that air bubbles cause. Another possibility is that, when surgeons place the clamp on the aorta, fatty deposits could break off and travel to the head, blocking blood flow.