Do We Need Heparin Coating for Extracorporeal Membrane Oxygenation? New Concepts and Controversial Positions About Coating Surfaces of Extracorporeal Circuits

Blood contact with surfaces of the extracorporeal circuit provokes the activation of the coagulation system. To improve biocompatibility of the extracorporeal circuit without increasing the risk of bleeding, coatings of artificial surfaces were designed; many of them involve the use of heparin. Data in the literature show that heparin‐induced thrombocytopenia is a major issue in the extracorporeal membrane oxygenation scenario, and no relevant benefits have been shown comparing heparin and no‐heparin coating.     

Extracorporeal carbon dioxide removal performed with surface-heparinized equipment in patients with ARDS

To avoid the drawbacks of systemic anticoagulation during prolonged extracorporeal circulation in patients with adult respiratory distress syndrome (ARDS) a heparinization technique has been developed by which partially degraded heparin can be covalently end-point attached to the surface of the equipment constituting the extracorporeal circuit (Carmeda Bio-Active Surface, CBAS) thereby localizing the anticoagulatory effect. Since 1986 we have used extracorporeal circuits and membrane lungs coated with the CBAS for extracorporeal lung assistance (ECLA) in 14 patients suffering from ARDS. The patients were on ECLA for 3 to 55 days with a survival rate of 43%. Our experience so far is that by using equipment coated with CBAS it is possible to perform long-term extracorporeal circulation with a minimum of intravenously administered heparin, thus avoiding the risk of major coagulation defects.     

Heparin-coated circuits reduce the formation of TNFα during cardiopulmonary bypass

Background: Cardiopulmonary bypass (CPB) causes a systemic intlammatory response. TNFα, which is a major inflammatory mediator, has been found in the circulation during and after CPB. Although previous studies have shown that heparin coating of the extracorporeal circuits reduces complement and granulocyte activation, and the inflammatory response, the possible effect of heparin coating on TNFα formation and the inflammatory response has not been fully investigated.
Methods: Eighteen patients scheduled for coronary artery bypass grafting were divided randomly into two groups. One group of patients had extracorporeal perfusion using heparin coated circuits (HC group, n = 9). The other group had extra-corporeal perfusion using an identical circuit that was not coated (UC group, n = 9). Blood samples were drawn before, during, and after CPB for measurement of plasma TNFα, plasma IL-8, neutrophil count, and neutrophil elastase.
Results: Plasma levels of TNFα increased during CPB in the UC group but not in the HC group. Plasma concentrations of IL-8 increased similarly during and after CPB in both groups. Coating the circuits with heparin did not affect the levels of IL-8. In both groups, the neutrophil count increased after the release of the aortic cross clamp and remained elevated for three days. In the HC group, however, the increase of neutrophil count was significantly lower compared with the UC group. Plasma concentrations of neutrophil elastase were significantly increased during and after CPB in both groups. However, the levels of elastase were significantly lower at certain time points in the HC group.
Conclusion: From these observations, we conclude that heparin coating of the extracorporeal circuits reduces the TNFα formation during CPB, which may reduce neutrophil activation.     

Coating of extracorporeal circuit with heparin does not prevent sequestration of propofol in vitro

Propofol is sequestered in extracorporeal circuits, but the factors responsible for the phenomenon are mostly unknown. We have compared two extracorporeal circuits (oxygenators, reservoirs and tubings) coated with heparin with two corresponding uncoated circuits for their capacity to sequester propofol in vitro. Three experiments were conducted with each circuit. The circuit was primed with a mixture of Ringer's acetate solution and whole blood, and the study conditions (pump flow, temperature, pH) were standardized. Propofol was added to the solution to achieve a concentration of 2 micrograms ml-1. These studies were followed with concentrations of 10- and 100-fold to assess possible saturation of propofol binding. Serial samples were obtained from the circulating solution for measurement of propofol concentration. Propofol concentrations decreased to 22-32% of the initial predicted concentration of 2 micrograms ml-1 in the circuits (no significant difference between circuits). With greater concentrations, the circuits did not become saturated with propofol, even with the highest predicted concentration of 200 micrograms ml-1. We conclude that propofol was sequestered in extracorporeal circuits in vitro, irrespective of coating the circuit with heparin.      

A heparin-coated circuit reduces complement activation and the release of leukocyte inflammatory mediators during extracorporeal circulation in a rabbit

Heparin coating modifies complement activation during extracorporeal circulation much more effectively than systemically administered heparin. This rabbit study was undertaken to address possible mechanisms responsible for this difference. We evaluated the effect of heparin coating on complement activation and subsequently the release of leukocyte inflammatory mediators during extracorporeal circulation through a simplified circuit. We found in the heparin-coated group a significantly reduced complement hemolytic activity (CH50), remaining higher leukocyte numbers, significantly decreased release of beta-glucuronidase, and most strikingly a complete prevention of tumor necrosis factor (TNF) formation. The significantly reduced CH50 activity in the heparin-coated groups indicates the reduction of one or more native classical complement products. This could be explained by the absorption of complement components by the circuit, which results in reduced activity of the complement cascade. We conclude therefore that heparin coating reduces complement activation and consequently reduces the release of leukocyte inflammatory mediators.     

Modified surface coatings and their effect on drug adsorption within the extracorporeal life support circuit

A recently completed study quantified the percent of fentanyl or morphine sulfate lost to uncoated polyvinylchloride (PVC) tubing or to one of two hollow fiber oxygenators within the extracorporeal life support (ECLS) circuit. The results demonstrated the majority of drug loss was due to adsorption by the PVC tubing. The purpose of this study was to determine if a tubing coating process affects fentanyl or morphine Sulfate adsorption. The goal was to quantify fentanyl or morphine sulfate lost due to adhesion within surface modified tubing. The following surface modifications were studied: 1) Maquet Safeline (synthetic immobilized albumin); 2) Maquet Softline (a heparin free biopassive polymer); 3) Maquet Bioline (recombinant human albumin + heparin) (Maquet Cardiopulmonary AG, Hirrlingen, Germany); 4) Terumo X Coating (poly2methoxylacrylate)) (Terumo Cardiovascular Systems Corporation, Ann Arbor, MI); 5) Medtronic Carmeda (covalently bonded heparin); and 6) Medtronic Trillium (covalently bonded heparin) (Medtronic, Minneapolis, MN). A total of 36 individual circuits were built from the above six available modified surface coatings, for a total of six individual circuits of each coating type. Blood samples were drawn at 5 minutes, 120 minutes, and 360 minutes followed by High-Performance Liquid Chromatography to determine available circulating levels of either fentanyl or morphine sulfate. Fentanyl concentrations decreased to an average final available concentration of 35% (+/- 5%) within the 18 circuits. Morphine sulfate however, decreased to a final available concentration of 57% (+ 1%) in all Maquet tubing and the Medtronic Trillium tubing, while it decreased to a final concentration of 35% (+ 1%) in the Medtronic Carmeda coated tubing and in the Terumo X Coating tubing. Biocompatible ECLS circuit surface coatings affected drug-adsorption and availability. Further evaluation is necessary to understand the adsorptive loss of other drugs administered to our patients while on modified surface coated ECLS circuits.     

Extracorporeal Circulation, Hemocompatibility, and Biomaterials

Background. Performance of a majority of cardiac surgical procedures requires the use of extracorporeal circulation. Contact of the patients' blood with the nonendothelial surface of the cardiopulmonary bypass circuit is responsible for several, potentially harmful systemic reactions.

Methods. The patients' response to extracorporeal circulation is reviewed briefly. The interactions between patient and circuit are discussed not only as they relate to blood-material contact, but also from a mechanical and rheologic standpoint. The theoretic benefits of the newer, more hemocompatible materials are presented, along with a review of published clinical experience with heparinized cardiopulmonary bypass circuits.

Results. The response to extracorporeal circulation extends far beyond a simple derangement of hemostasis. This inflammatory response is strongly influenced by the rheologic design of the circuit and by the physical and chemical properties of the surface. Heparinized circuits decrease inflammation, but the clinical benefits of this reduction remain unclear, except for extended cardiopulmonary support. The safe use of these circuits requires full heparinization and does not reduce allogeneic transfusions.

Conclusions. Clinicians are still in the search of the ideal material and the ideal extracorporeal circuit design. Newer, heparinized materials offer real but limited clinical benefits.     

Immobilized Heparin Inhibits the Increase in Leukocyte Surface Expression of Adhesion Molecules

Abstract: The effect of heparin coating of artificial materials on the surface expression of leukocyte surface molecules was assessed in blood from 9 donors in an experimental model of extracorporeal circulation. The leukocyte surface molecules CD11b, complement receptor type 3 (CR3). and CD45. leukocyte common antigen (LCA), on granulo-cytes and monocytes exposed to unmodified polyvinyl chloride tubes increased significantly compared with unmanipu-lated controls (p < 0.001) whereas a very modest and nonsignificant increase was observed in blood circulated in heparin-coated tubes. Accordingly, a highly significant reduction in expression of the 2 molecules was achieved by heparin coating (p < 0.001). The expression of CD11b and CD4.5 correlated with the degree of complement activation in plasma (rho = 0.6, p = 0.003). The expression of CD14 (endotoxin receptor) and CD16 (Fcy III receptor) was increased to the same extent in blood from unmodified and heparin-coated tubes (p < 0.02), and no correlation to complement activation was seen (rho = -0.27.5, p = 0.17 and rho = -0.004, p = 1, respectively). In conclusion, heparin coating of artificial surfaces has a substantial effect, reducing the expression of molecules involved in cellular adhesion and activation (CD11b and CD45), and the increase of these molecules by unmodified surfaces is complement dependent. In contrast, up-regulation of other surface molecules (CD14 and CD16) seems to be independent of heparin coating and complement activation and, thus, might be regulated by other mechanisms.     

肝素涂层与非肝素涂层动脉过滤器的临床对比观察

目的　对肝素涂层和非肝素涂层动脉过滤器在体外循环术中的应用结果进行对比观察。　方法　 80例体外循环心脏直视手术患者随机分为两组 ,每组 40例。 A组 :用肝素涂层动脉过滤器 ,B组 :用非肝素涂层动脉过滤器 ;并于不同的时间点观察血小板计数、血红蛋白、红细胞压积、激活凝血时间和过滤器内网在电子显微镜下的改变。结果　转流 6 0分钟和结束时血小板计数 ,A组高于 B组 (P<0 .0 5 )。电子显微镜示 A组网眼清晰 ,边缘清楚 ,偶见有块状过滤物 ,B组滤网有絮状物 ,散在分布于网眼边缘 ,模糊不清 ,堵塞网眼 ,表明有纤维蛋白聚集 ,血小板粘附 ,脱落形成血小板碎片。　结论　肝素涂层动脉过滤器能改善其生物相容性     

The protein C system in patients undergoing cardiopulmonary bypass

Fifteen men undergoing extracorporeal circulation for aorta-coronary bypass grafting were investigated for alterations of the plasma levels of cross-linked fibrin degradation products, protein C, free protein S, coagulation factor II, immunoglobulin G, and albumin. Although all patients were given heparin, a progressive increase of cross-linked fibrin degradation products was recorded during extracorporeal circulation, which indicates an activation of the plasmatic coagulation system. This increase was most pronounced in the late phase of extracorporeal circulation after reperfusion of the lung and in the early postoperative period. The levels of all other investigated plasma proteins decreased drastically after the patient was connected to the bypass circuit, which was primed with saline solution. These levels increased after termination of extracorporeal circulation and administration of fresh-frozen plasma. To study the consumption of protein C, protein S, and factor II during extracorporeal circulation, we formed ratios of the values of these parameters to the value of immunoglobulin G. After this volume correction, protein C was found to decrease significantly in the late phase of extracorporeal circulation, remaining low in the early postoperative period; protein S increased significantly soon after the onset of extracorporeal circulation and decreased after termination of extracorporeal circulation; factor II was unaffected by extracorporeal circulation, showing only a slight, insignificant increase in the postoperative phase. These results suggest a disturbance of the protein C system by extracorporeal circulation, which is possibly linked to the reported high bleeding tendency in patients undergoing operations with extracorporeal circulation.     

Pharmacological inhibition of plasma coagulation and platelet activation during experimental long-term perfusion

OBJECTIVE: During extracorporeal circulation, initial contact between blood and the artificial surface of the circuit induces an overall activation of the hemostatic system. The objective of this study was to investigate the combined effect of epoprostenol (PGI (2) ), nitric oxide (NO) and nafamostat mesilate (FUT-175, a serine protease inhibitor), on plasma coagulation and platelet activation during experimental long-term perfusion. DESIGN: Two identical extracorporeal life support (ECLS) circuits were primed with fresh, heparinized human blood, and circulated for 24 h. FUT was given with a bolus dose of 85 mg/l blood at the initiation of the experiment and thereafter as a continuous infusion of 14 mg/l/h. PGI (2), at a rate of 2.4 microg/l/h, was also administered to the experimental circuit, and 120 ppm NO gas was added to the oxygenator sweep gas. The other circuit was used as a control. RESULTS: Higher platelet count and platelet membrane expression of GPIb were found in the experimental circuits as compared with control circuits. The levels of thrombin/antithrombin III complex (TAT) and prothrombin fragment 1 + 2 (F1 + 2) increased significantly over time in the control circuits but remained low in the experimental circuits. Plasma levels of plasminogen activator inhibitor 1 (PAI-1) decreased rapidly in both circuits but were higher in the control circuits at each time point studied. CONCLUSION: The activation of platelets and of the coagulation system encountered during extracorporeal perfusion is consistently inhibited by a combination of PGI (2), NO and FUT-175. The combination of these drugs appears to be more effective than each drug separately.     

Synthetic protein treated versus heparin coated cardiopulmonary bypass surfaces: similar clinical results and minor biochemical differences.

OBJECTIVE: Complications associated with cardiopulmonary bypass (CPB) have gained more attention due to increased interest in coronary artery bypass grafting without CPB. The impact of heparin coating of CPB circuits has been discussed controversially. The present study examines if the treatment of the oxygenator surface with a synthetic protein may serve as an alternative to a completely heparin coated circuit. METHODS: Fifty-eight patients undergoing coronary artery bypass grafting with CPB were randomly assigned to completely heparin coated circuits or synthetic protein treated oxygenators in a double blind protocol, focussing on the inflammatory reaction resulting in membrane damage, coagulation changes and markers of cerebral injury or dysfunction. Treatment groups did not differ as to preoperative demographics, and intraoperative clinical data. Patients with any neurologic disease or risk factors for cerebral dysfunction were not included in the study. RESULTS: Postoperative clinical data did not differ between groups. Both surface treatments resulted in similar coagulation activation, hyperfibrinolysis and disseminated intravascular coagulation. Platelet count displayed a difference in favour of the heparin coated group (P = 0.029). Increased leukocyte activation reflected by rising myeloperoxidase concentrations on CPB was present in both synthetic protein and heparin coating groups. Interleukins 6 and 8 reacted similarly, but interleukin 8 increased significantly more (P = 0.0061) at the end of surgery in patients treated with protein treated oxygenators. The same pattern was observed for complement activation as determined by total complement complex (P = 0.006). Both surface changes resulted in moderately increased S-100B protein and neuron specific enolase, without difference between groups. Both markers did not reach concentrations associated with clinical manifestation of cerebral injury. CONCLUSIONS: These results in routine patients with short bypass time, imply that protein treated oxygenators are associated with a limited increase of biochemical markers similar to heparin coating. However, significantly lower interleukin 8 release and complement activation can be achieved by heparin coating. The protein treatment is a standard feature of the oxygenator examined in both groups. It is not associated with additional cost and therefore appropriate for use in routine patients.     

Activated leukocytes adsorbed on the surface of an extracorporeal circuit

Biocompatibility of extracorporeal circuits has mostly been investigated by sampling blood in circulation. However, a proportion of activated leukocytes leave circulation by sticking to the circuits, and might affect the circuit biocompatibility. To reveal these characteristics, we eluted the adsorbed leukocytes from circuits used for 6 patients by washing with ethylenediaminetetraacetic acid (EDTA)-HEPES buffer. 1.3 x 109 leukocytes, representing 5 to 10% of the circulating leukocytes, were collected. Most were neutrophils expressing CD11b antigens as high as those in circulation during cardiopulmonary bypass. Adsorbed monocytes expressed tissue factor higher than those in circulation (P < 0.05). An elution procedure by EDTA itself induced only a minimal activation of the leukocytes. These results indicate that extracorporeal circuits adsorb a large number of activated neutrophils and a small number of highly thrombogenic monocytes during their use. Although our data is limited, this elution procedure appears useful to investigate the biocompatibility of extracorporeal circuits.     

Pharmacological inhibition of plasma coagulation and platelet activation during experimental long-term perfusion

Objective --During extracorporeal circulation, initial contact between blood and the artificial surface of the circuit induces an overall activation of the hemostatic system. The objective of this study was to investigate the combined effect of epoprostenol (PGI 2 ), nitric oxide (NO) and nafamostat mesilate (FUT-175, a serine protease inhibitor), on plasma coagulation and platelet activation during experimental long-term perfusion. Design --Two identical extracorporeal life support (ECLS) circuits were primed with fresh, heparinized human blood, and circulated for 24 &#114 h. FUT was given with a bolus dose of 85 &#114 mg/l blood at the initiation of the experiment and thereafter as a continuous infusion of 14 &#114 mg/l/h. PGI 2 , at a rate of 2.4 &#114 &#55 g/l/h, was also administered to the experimental circuit, and 120 &#114 ppm NO gas was added to the oxygenator sweep gas. The other circuit was used as a control. Results --Higher platelet count and platelet membrane expression of GPIb were found in the experimental circuits as compared with control circuits. The levels of thrombin/antithrombin III complex (TAT) and prothrombin fragment 1 &#114 + &#114 2 (F1 &#114 + &#114 2) increased significantly over time in the control circuits but remained low in the experimental circuits. Plasma levels of plasminogen activator inhibitor 1 (PAI-1) decreased rapidly in both circuits but were higher in the control circuits at each time point studied. Conclusion --The activation of platelets and of the coagulation system encountered during extracorporeal perfusion is consistently inhibited by a combination of PGI 2 , NO and FUT-175. The combination of these drugs appears to be more effective than each drug separately.     

Pulsatile Augmentation Device for Extracorporeal Circulation

Abstract: A device has been designed, constructed, and tested to provide pulsatile pressure/flow to a standard extracorporeal bypass circuit. The pulsatile augmentation device is pneumatically driven similar to an artificial heart ventricle except that there are no valves. It is constructed of polyurethane by vacuum forming and high frequency welding. Drivers used are a modified Arrow-Kontron in-traaortic balloon pump or the Utah artificial heart driver. In vitro testing with fresh bovine blood demonstrated acceptable blood compatibility and hemodynamic function. In vivo testing for 4 h in a right and left heart extracorporeal bypass circuit showed good pulse augmentation in pulmonary and systemic bypass circuits. The device shows promise for adding pulse to standard cardiopulmonary bypass and to extracorporeal right heart circulatory assist circuits.     

Combined treatment with nafamostat mesilate and aspirin prevents heparin-induced thrombocytopenia in a hemodialysis patient

We report on the management of a 36-year-old hemodialysis patient with heparin-induced thrombocytopenia (HIT, type II) and clot formation in extracorporeal circulation. Platelet aggregation test and measurement of anti-platelet factor 4/heparin complex antibody by enzyme-linked immunosorbent assay revealed to us that our patient had developed HIT. Instead of heparin, we used nafamostat mesilate (NM) as an anticoagulant during hemodialysis, but could not completely prevent HIT-induced thrombocytopenia or clot formation in the extracorporeal circuit. Combined use of NM and aspirin completely inhibited platelet aggregation, decrease in platelet count and clot formation in the extracorporeal circuit.     

Comparative study of biocompatibility between the open circuit and closed circuit in cardiopulmonary bypass.

The theoretical benefit of a centrifugal pump or heparin coating demonstrated through in vitro or in vivo studies is not recognizable in cardiopulmonary bypass (CPB) during chemical open heart surgery. The objective of this study was to investigate the influence of the interface of air and blood in current CPB with an open circuit system and its relative significance in relationship to the heparin dose and heparin coating. Using the same oxygenator and circuit, an open circuit and closed circuit CPB with the same priming volume were prepared for a 4 h perfusion experiment using diluted and heparinized (3.6 U/ml) fresh human blood. In these experiments, both heparin-coated and noncoated circuits were examined. Blood was sampled before and 2, 30, 60, 120, and 240 min after the start of perfusion, and the platelet and white blood cell counts and beta-thromboglobulin (beta-TG) and C3a levels were measured. The amount of adsorbed protein in the hollow fibers was also measured after retrieval. Although the results demonstrated significantly better biocompatibility of the heparin-coated circuit than the noncoated circuit, the difference between the open and closed circuits was unexpectedly small and insignificant with either the heparin-coated circuit or noncoated circuit. In contrast, the C3a level was higher in the closed circuit than the open circuit. However, the amount of adsorbed protein was markedly lower in the closed circuit (0.7 microgram/cm2) than in the open circuit (11.1 micrograms/cm2). An immunoblot of the adsorbed protein showed a higher density of fibrinogen bands and conversion to fibrin in the open circuit. We speculate that the lower blood C3a level in the open circuit suggests that C3a was taken in by the adsorbed protein. In conclusion, analysis of the adsorbed protein indicates the lower biocompatibility of the open circuit. Similar experiments with less heparin use and more severe conditions will be necessary to elucidate the essential benefit of making a CPB closed circuit.     

Formation of C5a during cardiopulmonary bypass: inhibition by precoating with heparin

A novel enzyme immunoassay based on direct detection of C5a by a monoclonal antibody (C17/5) specific for a neoepitope exposed in C5a/C5adesArg was used to measure in vivo and in vitro C5a formation during cardiopulmonary bypass. In vivo, we observed a significant threefold to fourfold increase in patient plasma C5a/C5adesArg levels from baseline values (5.6; 1.6 to 12.9 ng/mL) (median and range) up to 42 hours postoperatively (17.5; 6.5 to 46.0 ng/mL) when two different uncoated cardiopulmonary bypass circuits were used. Coating of the extracorporeal circuit with end-point-attached heparin completely abolished C5a formation in vitro during circulation of blood through the circuit for 120 minutes. The C5a concentration (median and range) was 3.2 (2.6 to 15.9) ng/mL at the start and 3.1 (2.7 to 15.0) ng/mL at the end of the experiment. In the uncoated setups the corresponding C5a concentrations were 10.1 (6.2 to 17.5) and 19.7 (13.1 to 24.3) ng/mL. Finally, heparin-coated cardiopulmonary bypass circuits were examined in vivo. C5a levels did not increase significantly during the cardiopulmonary bypass period in the heparin-coated group in contrast to the uncoated group, but the postoperative increase in C5a levels was similar in the two groups. We conclude that heparin coating improves biocompatibility by completely abolishing C5a formation in vitro. The discrepancy between the in vitro and the in vivo findings is probably related to the complicated biological turnover of C5a.     

Arterial-venous perfusion without anticoagulation: the impeller centrifugal pump

A study was designed to test the effects of the absence of anticoagulation in the extracorporeal circuit. Five swine were subjected to this experiment utilizing the impeller centrifugal pump during which neither heparin nor any other anticoagulant was used. The extracorporeal circuit consisted of polyvinylchloride tubing, a Centri-Med pump and an external stainless steel heat exchanger that was primed with albuminized Ringer's solution. An arterial-venous circuit was employed with oxygenation supplied from the subject's lungs. A series of blood aliquots were analyzed for coagulation at various times throughout the procedure. Following total body cooling using topically applied ice water, the subjects were rewarmed utilizing bypass. Within 10 minutes after the initiation of bypass, the circuits became clotted, rendering perfusion and subsequent warming ineffective. The lab values indicated that intrinsically activated coagulation occurred upon exposure to the extracorporeal apparatus. Flow visualization studies revealed a source of stagnant blood flow in the area around the hub of the pump head. Blood clot was similarly located in this area, with clot extension throughout the return circuit being realized. It is imperative that areas of stagnation be eliminated from extracorporeal circuits, since they may be potential sites for clot formation.     

Cellular aggregation and destruction during blood circulation and oxygenation.

Platelet and leucocyte aggregation and severe haemolysis may occur in blood during the preparation of an extracorporeal circuit for open-heart surgery. Experiments with dog blood showed that both processes result from bubble oxygenation but not from circulation of diluted blood and that they appear to be inhibited by the presence of acid citrate dextrose and heparin, or citrate phosphate dextrose and heparin, but not by heparin alone.