Miniaturized cardiopulmonary bypass in coronary artery bypass surgery: marginal impact on inflammation and coagulation but loss of safety margins
Nollert G, Schwabenland I, Maktav D, Kur F, Christ F, Fraunberger P, Reichart B, Vicol C. Ann Thorac Surg
Reviewer: Mark A. Chaney, MD
University of Chicago
Abstract: Inflammation and coagulation disturbances are common consequences of cardiopulmonary bypass(CPB). Recently, miniaturized closed CPB circuits without cardiotomy suction and venous reservoir have been proposed to reduce complication rates. The authors compared outcomes with conventional (CCPB) and miniaturized cardiopulmonary bypass (MCPB) after coronary artery bypass operations (CABG) with respect to inflammation and coagulation. Thirty patients were prospectively, randomly assigned to undergo isolated CABG with CCPB or MCPB. CCPB had a pump prime of 1600mL.MCPB consisted of a centrifugal pump, arterial filter, heparinized tubing, and oxygenator, with a priming volume of 800 mL. Shed blood was removed by a cell-saving device and reinfused. Measurements included interleukin (IL)-2 receptor, IL-6, IL-10, tumor necrosis factor receptor 55 and 75, C reactive protein, leukocyte differentiation, d-dimers, fibrinogen, and thrombocytes at six time points. In both groups, no major complications occurred. However, two dangerous air leaks occurred in the closed MCPB circuit, demonstrating the narrow safety margins. Operative handling was also more difficult owing to limitations in venting and fluid management. International normalized ratio (p=0.03) and antithrombin III (p=0.04) levels were elevated during CPB in the CCPB group, most likely owing to differences regarding intraoperative anticoagulation management. Repeated measures analysis revealed that not a single parameter of inflammation or clinical outcome showed significant differences among groups. The authors conclude that use of a MCPB affected inflammation and coagulation variables only marginally and did not lead to clinically relevant changes as assessed by blood loss, need for blood products, and intensive care unit and clinical stays. However, safety margins for volume loss, air emboli, and weaning from CPB decrease, because of the closed MCPB circuit.
Comments: CPB exposes blood to large areas of synthetic materials that trigger the production and release of numerous chemotactic and vasoactive substances. This ensuing abnormal whole-body inflammatory response can complicate the postoperative period by causing major organ dysfunction. The basic physiologic insults caused by CPB have been associated with major postoperative morbidity, including neurologic dysfunction, cardiac dysfunction,pulmonarydysfunction,renaldysfunction,and/orhematologic abnormalities. MCPB systems have been developed in order to potentially avoid the detrimental physiologic effects of CCPB. The authors compared the inflammatory response and clinical outcome among patients undergoing CABG with CCPB or MCPB.
Theoretical advantages of a MCPB system include avoidance of a cardiotomy sucker, reduced prime volume, use of heparin-coated tubing/oxygenators, and use of centrifugal pumps. However, the authors were unable to demonstrate any significant benefit for patients operated on with the MCPB system (although very sensitive laboratory parameters of inflammation and coagulation were used as endpoints). Most importantly, the study was prematurely discontinued because of concerns regarding safety. Air entered the closed MCPB system in 2 of 15 cases, demonstrating low safety margins of such systems. In one case, the volume status of the patient was low and the negative pressure generated around the atrial cannula sucked bubbles into the venous cannula (resolved with cannula ligation). In the second case, the right ventricular cavity was opened unintentionally, air was sucked into the circuit, and the pump immediately stopped. After meticulous deairing and closure of the right ventricular defect, the pump was started again. The authors also note that volume management was more challenging in the MCPB group. The results of this clinical investigation clearly show that the modifications required to make the MCPB system physiologically "safer" substantially decrease safety margins. This article once again reminds us as clinicians and researchers to carefully balance the risks and benefits before embarking on innovative adventures.