Cardiopulmonary Bypass Procedure: Recent Advances
Cardiopulmonary bypass (CPB) is a technique that provides a motionless and bloodless surgical field that makes complex cardiac surgeries possible in the current era. It consists of an extracorporeal circuit that is designed to provide both respiratory and circulatory support. The circuit usually includes a pump, cannulae, reservoir, heat exchanger, oxygenator, and arterial line filter.
During CPB, blood is drained by the force of gravity from the heart and lungs to a reservoir through venous cannulation and tubing and then returned by a pump after oxygenation using an artificial lung (gas exchanger or oxygenator).
Modern machines include systems to monitor temperature, pressure, oxygen saturation, blood gases, hemoglobin, and electrolytes. Additionally, safety features such as oxygen sensor, bubble detector, and an alarm that detects low-level in the reservoir have been incorporated. Advancements in the field of cardiac surgery have been possible as a result of the development of CPB. In the last two decades, rapid improvements in the CPB technique have occurred because of advances in biomaterials, electronics, computer microsystem technology, and manufacturing. CPB has undergone a lot of modifications over a period of time, and these include novel defoaming agents, miniaturized circuit design, heparin-coated circuitry, ultrafiltration, and integrated arterial filters with an oxygenator. However, side-effects and complications do occur and current research aims towards developing strategies that minimize these and provide better outcomes.
How Do Newer Materials Help Reduce Common Complications with the CPB Technique?
The use of CPB during cardiac surgery often causes a systemic inflammatory response syndrome, and in order to reduce these unwanted effects, biocompatible coatings are being used. CPB is associated with significant morbidity following cardiac surgery, which is mainly because of contact of blood with various foreign surfaces in the CPB circuit.
Centrifugal Pumps: Centrifugal pumps have been developed to reduce damage to the blood elements such as RBCs, platelets, and plasma proteins that result when conventional roller pumps are used. These pumps are non-occlusive and thus avoid excess pressure build-up in the extracorporeal circuit and its rupture.
Surface-coated circuit: The use of biocompatible coatings such as heparin helps reduce the inflammatory response caused by the contact between the blood and foreign substances in the CPB circuit. This coating also makes the CPB circuits hydrophilic and protein resistant. The major advantage of heparin coating is increased thromboresistance, which allows the reduction of systemic anticoagulation that will be used. This, in turn, reduces postoperative bleeding and the need for blood transfusion. Similarly, phosphorylcholine coating reduces platelet activation and postoperative loss of blood. This coating tries to mimic the natural cell membrane and reduces the interaction between the internal surface and plasma proteins.
Heparin-coated Oxygenator: Currently, the membrane oxygenator is used frequently and has replaced the bubble and disc types. This allows the exchange of gases through a membrane that helps reduce the blood trauma caused by direct-contact oxygenators. Heparin-coated oxygenator mimics the endothelial lining of the vessels. Studies show improved overall biocompatibility and reduced adhesion of plasma proteins, which lead to elevated postoperative platelet count and reduced chance of lung atelectasis.
Minimal extracorporeal circulation: The mini-bypass system is made up of an integrated venous bubble trap, heat exchanger, oxygenator, and centrifugal pump. It was designed for use with an autotransfusion/cell saving system for sequestration of aspiration blood. It differs from conventional CPB in that it lacks a reservoir and cardiotomy suction, which leads to significantly shortened length of tubing and reduced priming volume. This is a closed circuit which means that there is little or no blood-air contact. This concept of mini-bypass was developed to combine significantly reduced circuit prime volume and suction blood separation. This could lead to improved homeostasis, decreased hemodilution, and reduced morbidity following on-pump cardiac surgery. Studies have shown evidence of decreased postoperative bleeding and improvements in postoperative renal functions.
At Marina Del Ray Hospital, our cardiothoracic surgeons treat the most complex cardiac disorders with advanced techniques and attention to the patient’s comfort.