Retrograde autologous priming

Retrograde Autologous Priming (RAP) is a technique used in cardiopulmonary bypass (CPB) procedures to reduce the need for blood transfusions by minimizing the amount of hemodilution. This method involves the displacement of a portion of the prime volume of the CPB circuit with the patient's own blood prior to the initiation of bypass. This process is aimed at reducing the total volume of foreign fluid introduced into the patient's system, thereby preserving the patient's hematocrit level and reducing the potential for transfusion-related complications.

Overview

During a CPB procedure, it is necessary to replace a portion of the patient's blood volume with a priming solution to initiate the bypass circuit. Traditionally, this priming solution is a crystalloid or colloid solution, which can significantly dilute the patient's blood, leading to a decrease in hematocrit and potentially necessitating blood transfusions. RAP is implemented as a strategy to mitigate this dilution by using the patient's blood to displace some of the priming solution, thus maintaining a higher hematocrit level.

Procedure

The RAP procedure begins with the cannulation of the patient, where tubes are inserted into the arteries and veins to connect the patient's circulatory system to the CPB machine. Before the start of CPB, a controlled amount of the priming solution is removed from the circuit and replaced with the patient's blood, drawn retrograde through the venous line. This process reduces the volume of foreign fluid in the circuit and increases the concentration of red blood cells, which can improve oxygen delivery and reduce the need for allogeneic blood transfusions.

Benefits

The primary benefit of RAP is the reduction in the need for blood transfusions, which are associated with risks such as transfusion reactions, transmission of infections, and immunomodulation. By maintaining a higher hematocrit level, RAP can also improve oxygen delivery to tissues during CPB, potentially improving patient outcomes. Additionally, the use of RAP can lead to a decrease in the total cost of the procedure by reducing the use of blood products.

Risks and Considerations

While RAP offers several benefits, there are also risks and considerations. The technique requires careful management to avoid air embolism and ensure adequate de-airing of the CPB circuit. There is also a risk of hemodilution if the volume of blood displaced does not adequately compensate for the dilutive effects of the remaining priming solution. Furthermore, the effectiveness of RAP may be limited in patients with low blood volumes or anemia.

Conclusion

Retrograde Autologous Priming is a valuable technique in the field of cardiac surgery, offering a means to reduce the reliance on blood transfusions and improve patient outcomes. As with any medical procedure, the implementation of RAP requires careful consideration of the potential benefits and risks, tailored to the individual patient's condition.