PRINCIPLES OF CARDIOPULMONARY BYPASS MECHANISM (CPB)

What is CPB? It is a technique by which the mechanical function of the heart and respiratory function of the lungs are replaced by a pump oxygenator that is connected to the arterial and venous circulation of the patient.

Purposes

Provide a bloodless field while the surgeon is enabled to operate on the heart under direct vision and maintain homeostatis at the same time.

Principles

1. Function of heart and lung is taken over by a machine. 
2. Protect the myocardium, while it is paralysed. 
3. Prevent hemolysis and air or particular embolism. 
4. Reduce the metabolic needs of the body. 
5. Increase the renal perfusion. 

Now we will see how these principles are taken care of while the surgeon is provided a bloodless field and non-beating heart. There are specially trained perfusionist who performs the CPB in cardiac operation theatre. Having a basic understanding of the mechanism is important for nurses for the pre, peri and post operative management of cardiac surgical patients.
The perfusionist assembles the circuit of the CPB. The air is expelled from the tubing using isotonic saline. Then a priming solution is used for hemodilutin. Hemodilution is a method of increasing the volume of blood plasma, which results in reduced concentration of red blood cells. The shortage of donor bank blood and high incidence of blood-borne diseases has led to the widespread use of hernodilution for cardiopulmonary bypass. The patient's blood is collected in specialized transfusion bags and reserved during surgery. Donated blood is added to the circuit if needed.