“Retrograde priming” generally means the same thing as “retrograde autologous priming” which means allowing a heart surgery patient’s arterial blood to replace some of the “priming fluid” in the pump (“heart-lung machine”) that circulates blood during surgery.

During heart surgery the surgeon may need the heart and lungs to be motionless. A mechanical pump must then be connected to receive venous blood from the body and pump it back into the arteries. This pump must keep the circulation and composition of the blood as close to normal as possible so that it can support the health of the body and organs during surgery. The blood in the patient’s body is diluted by the “priming fluid” that fills the tubing in the pump at the start of surgery. Some dilution may be helpful but too much dilution creates problems. So the surgical team may need a way to decrease the amount of priming fluid in the pump.

One way to reduce the amount of “priming fluid” in the pump is to replace it with the patient’s own blood right before starting up the pump. If the patient’s venous blood is allowed to flow into the pump to replace some of this fluid (which is drained off as the blood flows in), then the blood is flowing in its natural direction and this is called “anterograde priming”. If the patient’s arterial blood is allowed to flow backwards into the pump to replace some of this fluid, this is called “retrograde priming” because the direction of flow is opposite to the direction it will be flowing when the pump is started.
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Cincinnati Children's Hospital Medical Center . (2010, March). Cardiopulmonary Bypass: Procedure and Risk. Retrieved June 27, 2010, from Cincinnati Children's Hospital Medical Center : http://www.cincinnatichildrens.org/health/heart-encyclopedia/treat/surg/bypass.htm

Ghosh, S., Falter, F., & Cook, D. J. (2009). Cardiopulmonary Bypass. New York, NY: Cambridge University Press.
http://books.google.com/books?id=DJNBae1Kx6gC&pg=PA37&lpg=PA37&dq=%22RETROGRADE+PRIMING%22&source=bl&ots=7qTrD12xEi&sig=Arz8_1910YeHEgk8WJUQNsaRcPo&hl=en&ei=CaIlTP_9GoT78AaVxqT3Dw&sa=X&oi=book_result&ct=result&resnum=8&ved=0CDoQ6AEwBw#v=onepage&q=%22RETROGRADE%20PRIMING%22&f=false