Ann Thorac Surg 1997;63:1339
© 1997 The Society of Thoracic Surgeons
Invited Commentary
Invited Commentary
Robert H. Bartlett, MD
Department of Surgery, University of Michigan Medical Center, 1500 E Medical Center Dr, Ann Arbor, MI 48109-0331
See also page 1333.
This article by Pedersen and colleagues is very important for anyone involved with blood perfusion because it clearly shows that: (1) centrifugal pumps cause hemolysis, (2) the hemolysis is caused by the generation of negative pressure, (3) this hemolysis leads to or is associated with other blood cellular injury, (4) blood cellular injury is associated with renal failure, and (5) hemolysis and renal failure can be prevented by preventing negative pressure generation during centrifugal pumping. The fact that unmodified centrifugal pumps cause hemolysis and renal failure is well known in extracorporeal life support centers, where servo-regulated roller pumps are used, almost exclusively, to eliminate these problems. However, there is still a misperception that centrifugal pumps are less hemolytic than roller pumps, leading to the (dangerous) use of centrifugal pumps for extracorporeal membrane oxygenation or acute cardiopulmonary support in inexperienced centers. This valuable report demonstrates why centrifugal pumps cause hemolysis and how that problem can be minimized.
Positive pressure applied to blood rarely causes hemolysis; negative pressure usually causes hemolysis. During cardiopulmonary bypass for cardiac operations, the pump is fed by a large venous reservoir, and negative pressure never occurs unless the perfusionist clamps the line between the venous reservoir and the pump. Consequently, neither centrifugal nor roller pumps cause substantial hemolysis during cardiopulmonary bypass. (Hemolysis during cardiac operations is caused by the negative pressure associated with aspiration of blood from the operative field.) During extracorporeal membrane oxygenation or cardiopulmonary support, however, the pump is usually attached directly to the venous drainage line, and venous drainage is frequently interrupted by catheter kinking, patient position, patient activity, increased intrathoracic pressure, or hypovolemia. When roller pumps are used in this application, they are always combined with a servo regulation system, which senses negative pressure and turns the pump off whenever venous drainage is impaired. When unmodified centrifugal pumps are used in this application, negative pressure as high as -700 mm Hg is generated transiently whenever venous drainage is impaired. The cavitation associated with this phenomenon is usually visible as micro bubbles in the pump chamber. Because these bubbles are mostly oxygen and carbon dioxide, they disappear immediately as soon as venous drainage is reestablished. However, the small amount of blood exposed to this cavitation hemolyzes every time this phenomenon takes place. Therefore, extracorporeal membrane oxygenation is used with servo regulated roller pumps, or with very careful monitoring of negative pressure with centrifugal pumps, to attempt to avoid this problem. In this research, Pedersen and colleagues demonstrated that even low levels of negative pressure, when applied continuously to flowing blood, cause pronounced hemolysis. Moreover, they showed that the hemolysis and associated renal failure caused by unmodified centrifugal pumps can be prevented using a simple servo regulation system similar to that used with roller pumps during prolonged extracorporeal support.
The ideal pumps for prolonged blood perfusion have yet to be invented. Servo-regulated roller pumps are safe, reliable, and nonhemolytic but subject to raceway and high-pressure blowout. The hemolysis caused by centrifugal pumps can be controlled using this servo regulation system to eliminate negative pressure surges, but there are still problems of heat generation, thrombus formation, and broken seals when centrifugal pumps are used for several days. We are indebted to Pedersen and colleagues for documenting the problem, the cause, and the solution of hemolysis caused by centrifugal pumps.
Related Article
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Extracorporeal Membrane Oxygenation Using a Centrifugal Pump and a Servo Regulator to Prevent Negative Inlet Pressure
- Thore H. Pedersen, Vibeke Videm, Jan L. Svennevig, Harald Karlsen, Randi Wolden Østbakk, Øystein Jensen, and Tom Eirik Mollnes
Ann. Thorac. Surg. 1997 63: 1333-1339.
[Abstract]
[Full Text]
