The effects of Carmeda Bioactive Surface on human blood components during simulated extracorporeal circulation

Extracorporeal life support without systemic anticoagulation: a nitric oxide-based non-thrombogenic circuit for the artificial placenta in an ovine model

BACKGROUND

Clinical translation of the extracorporeal artificial placenta (AP) is impeded by the high risk for intracranial hemorrhage in extremely premature newborns. The Nitric Oxide Surface Anticoagulation (NOSA) system is a novel non-thrombogenic extracorporeal circuit. This study aims to test the NOSA system in the AP without systemic anticoagulation.

METHODS

Ten extremely premature lambs were delivered and connected to the AP. For the NOSA group, the circuit was coated with DBHD-N2O2/argatroban, 100 ppm nitric oxide was blended into the sweep gas, and no systemic anticoagulation was given. For the Heparin control group, a non-coated circuit was used and systemic anticoagulation was administered.

RESULTS

Animals survived 6.8 ± 0.6 days with normal hemodynamics and gas exchange. Neither group had any hemorrhagic or thrombotic complications. ACT (194 ± 53 vs. 261 ± 86 s; p < 0.001) and aPTT (39 ± 7 vs. 69 ± 23 s; p < 0.001) were significantly lower in the NOSA group than the Heparin group. Platelet and leukocyte activation did not differ significantly from baseline in the NOSA group. Methemoglobin was 3.2 ± 1.1% in the NOSA group compared to 1.6 ± 0.6% in the Heparin group (p < 0.001).

CONCLUSIONS

The AP with the NOSA system successfully supported extremely premature lambs for 7 days without significant bleeding or thrombosis.

IMPACT

The Nitric Oxide Surface Anticoagulation (NOSA) system provides effective circuit-based anticoagulation in a fetal sheep model of the extracorporeal artificial placenta (AP) for 7 days. The NOSA system is the first non-thrombogenic circuit to consistently obviate the need for systemic anticoagulation in an extracorporeal circuit for up to 7 days. The NOSA system may allow the AP to be implemented clinically without systemic anticoagulation, thus greatly reducing the intracranial hemorrhage risk for extremely low gestational age newborns. The NOSA system could potentially be applied to any form of extracorporeal life support to reduce or avoid systemic anticoagulation.

Unravelling Surface Modification Strategies for Preventing Medical Device-Induced Thrombosis

The use of biomaterials in implanted medical devices remains hampered by platelet adhesion and blood coagulation. Thrombus formation is a prevalent cause of failure of these blood-contacting devices. Although systemic anticoagulant can be used to support materials and devices with poor blood compatibility, its negative effects such as an increased chance of bleeding, make materials with superior hemocompatibility extremely attractive, especially for long-term applications. This review examines blood-surface interactions, the pathogenesis of clotting on blood-contacting medical devices, popular surface modification techniques, mechanisms of action of anticoagulant coatings, and discusses future directions in biomaterial research for preventing thrombosis. In addition, this paper comprehensively reviews several novel methods that either entirely prevent interaction between material surfaces and blood components or regulate the reaction of the coagulation cascade, thrombocytes, and leukocytes.

Anticoagulation in Neonatal ECMO: An Enigma Despite a Lot of Effort!

Extracorporeal membrane oxygenation (ECMO) is a valuable modality used to support neonates, children, and adults with cardiorespiratory failure refractory to conventional therapy. It requires use of anticoagulation to prevent clotting in the extracorporeal circuit. Balancing bleeding from excessive anticoagulation with thrombotic risk remains a difficult aspect of ECMO care. Despite many advances in ECMO technology, better understanding of the coagulation cascade and new monitoring schemes to adjust anticoagulation, bleeding and thrombosis remain the most frequent complications in ECMO and are associated with morbidity and mortality. In neonates, ECMO is also complicated by the immature hemostatic system, laboratory testing norms which are not specific for neonates, lack of uniformity in management, and paucity of high-quality evidence to determine best practices. Traditional anticoagulation focuses on the use of unfractionated heparin. Direct thrombin inhibitors are also used but have not been well-studied in the neonatal ECMO population. Anticoagulation monitoring is complex and currently available assays do not take into account thrombin generation or platelet contribution to clot formation. Global assays may add valuable information to guide therapy. This review provides an overview of hemostatic alterations, anticoagulation, monitoring and management, novel anticoagulant use, and circuit modifications for neonatal ECMO. Future considerations are also presented.

Novel Surfaces in Extracorporeal Membrane Oxygenation Circuits

The balance between systemic anticoagulation and clotting is challenging. In normal hemostasis, the endothelium regulates the balance between anticoagulant and prothrombotic systems. It becomes particularly more challenging to maintain this physiologic hemostasis when we are faced with extracorporeal life support therapies, where blood is continuously in contact with a foreign extracorporeal circuit surface predisposing a prothrombotic state. The blood-surface interaction during extracorporeal life support therapies requires the use of systemic anticoagulation to decrease the risk of clotting. Unfractionated heparin is the most common anticoagulant agent widely used in this setting. New trends include the use of direct thrombin inhibitor agents for systemic anticoagulation; and surface modifications that aim to overcome the blood-biomaterial surface interaction by modifying the hydrophilicity or hydrophobicity of the polymer surface; and coating the circuit with substances that will mimic the endothelium or anti-thrombotic agents. To improve hemocompatibility in an extracorporeal circuit, replication of the anti-thrombotic and anti-inflammatory properties of the endothelium is ideal. Surface modifications can be classified into three major groups: biomimetic surfaces (heparin, nitric oxide, and direct thrombin inhibitors); biopassive surfaces [phosphorylcholine, albumin, and poly- 2-methoxyethylacrylate]; and endothelialization of blood contacting surface. The focus of this paper will be to review both present and future novel surface modifications that can obviate the need for systemic anticoagulation during extracorporeal life support therapies.

Trillium™ Biopassive Surface: A New Biocompatible Treatment for Extracorporeal Circulation Circuits

139 patients undergoing cardiac surgery were included in a prospective, randomized trial. Patients were randomly allocated to receive cardiopulmonary bypass (CPB) with Trillium™ Biopassive Surface (TBS Group) coated oxygenators or conventional circuits (control group).

112 patients were studied with respect to postoperative biochemical profile; a subgroup of 27 patients was studied with respect to perioperative complement (C3a) activation.

Patients in the TBS group demonstrated a significantly lower white blood cell count at the end of the operation (p=0.036) and a significantly higher platelet count the day after the operation (p=0.023) when compared to the control group. C3a was significantly higher (p=0.02) in the TBS group after 30 minutes of CPB, but the C3a increase after protamine administration was significantly less pronounced in the TBS group vs. the control group.

Further studies involving platelet and leukocyte activation are required to better elucidate the action of this new coating in the setting of routine CPB.

VV extracorporeal life support for the Third Millennium: will we need anticoagulation?

Since the late 1600's medicine and science have entertained the idea of extracorporeal circulation. With this technology to allow for cardiac and pulmonary support came the development of anticoagulation. Although this advanced the technology and capabilities of extracorporeal life support, it was not without complications and risks. The most common complications in extracorporeal life support (ECLS) present day are related to hemorrhage and thrombus due to the need for systemic anticoagulation and the challenges associated with it. This review focuses on present day techniques for anticoagulation for ECLS and what future surface modifications may do to obviate the use of systemic anticoagulation entirely.

Heparin coatings for improving blood compatibility of medical devices

Blood contact with biomaterials triggers activation of multiple reactive mechanisms that can impair the performance of implantable medical devices and potentially cause serious adverse clinical events. This includes thrombosis and thromboembolic complications due to activation of platelets and the coagulation cascade, activation of the complement system, and inflammation. Numerous surface coatings have been developed to improve blood compatibility of biomaterials. For more than thirty years, the anticoagulant drug heparin has been employed as a covalently immobilized surface coating on a variety of medical devices. This review describes the fundamental principles of non-eluting heparin coatings, mechanisms of action, and clinical applications with focus on those technologies which have been commercialized. Because of its extensive publication history, there is emphasis on the CARMEDA^® BioActive Surface (CBAS^® Heparin Surface), a widely used commercialized technology for the covalent bonding of heparin.

Significantly reduced adsorption and activation of blood components in a membrane oxygenator system coated with crosslinkable zwitterionic copolymer

A crosslinkable zwitterionic copolymer PMBT was coated onto the surfaces of polypropylene hollow fiber membrane (PP-HFM) oxygenator and its connecting tubes. The PMBT copolymer coating on the oxygenator circuit formed a cell outer membrane mimetic surface with excellent stability. The hemocompatibility of the PMBT copolymer coated PP-HFM oxygenator circuit was evaluated by animal extracorporeal circulation. The concentrations of clotting components fibrinogen and platelet in the blood were almost unchanged during the circulation through the PMBT copolymer coated oxygenator circuits. By contrast, the concentrations of fibrinogen and platelet were significantly reduced to 52% and 56% respectively in the uncoated oxygenator group due to adsorption and thrombogenesis of the blood during 2h circulation. Moreover, concentration of activation marker beta-thromboglobulin for platelet in the blood was remarkably lower in the PMBT group than the uncoated control group (p<0.01). All the results strongly supported that the hemocompatibility of the PP-HFM oxygenator circuit could be improved significantly by coating a stable and densely assembled zwitterionic polymer film. This simple, stable and highly effective cell membrane mimetic coating strategy may be applicable in developing advanced oxygenator systems and other artificial organs.

STATEMENT OF SIGNIFICANCE

Although a number of studies have reported the fabrication of zwitterionic phosphorylcholine coated oxygenators to resist the adsorption and activation of blood components and eliminate heparin-induced thrombocytopenia, none of them have fabricated stable and densely assembled film, especially with crosslinkable amphiphilic random copolymer described in our manuscript. The novel features of our work include.

Ex vivo simulation of cardiopulmonary bypass with human blood for hemocompatibility testing

OBJECT

Experimental circuits for biomaterial surface testing are frequently limited by the tested blood volume, composition of the circuit, flow conditions and the use of animal blood. This report describes an ex vivo set-up for simulated cardiopulmonary bypass with human blood perfusion. We investigated the clinical generalizability of the observed effects on hematological and metabolic parameters and the hemocompatibility of the system.

METHODS

The simulated cardiopulmonary bypass circuit consisted of a heparin-coated tubing system connected to an oxygenator and a venous reservoir. Normothermic flow of blood obtained from healthy donors was maintained at 2.4 L/min/m(2) by a roller pump. Heparin was dosed to obtain a target activated clotting time (ACT) ⩾500 s. Blood was drawn at baseline and 0, 10, 60 and 120 minutes following the initiation of blood flow to determine hematological and metabolic parameters and the hemocompatibility of the extracorporeal system. Data were analyzed using repeated measures ANOVA.

RESULTS

Two hours of blood perfusion resulted in a small, but clinically unimportant reduction in hematocrit, whereas hemoglobin levels and red blood cell, platelet and leukocyte counts remained stable. There was a significant increase in ACT throughout the experiment. While pO2 levels and the pH remained unaltered during the experiment, pCO2 values decreased from 51 ± 6 mmHg at T0 to 41 ± 3 mmHg at T120 (p<0.001). Simulated cardiopulmonary bypass induced a two-fold increase in C3a (p=0.001) while tissue factor was decreased from 44 ± 14 pg/mL at T0 to 38 ± 13 pg/mL at T120 (p=0.009). Levels of CD40L, prothrombin fragment 1+2, β-thromboglobulin and factor VIIa remained stable over time.

CONCLUSION

The ex vivo set-up for simulated cardiopulmonary bypass mimicked the clinical cardiosurgical setting. Exposure of fresh donor blood to the extracorporeal circuit showed a good hemocompatibility, indicated by maintained hematological parameters and a mild immune response.

Research approaches for studying flow-induced thromboembolic complications in blood recirculating devices

The advent of implantable blood recirculating devices has provided life-saving solutions to patients with severe cardiovascular diseases. Recently it has been reported that ventricular assist devices are superior to drug therapy. The implantable total artificial heart is showing promise as a potential solution to the chronic shortage of available heart transplants. Prosthetic heart valves are routinely used for replacing diseased heart valves. However, all of these devices share a common problem--significant complications such as hemolysis and thromboembolism often arise after their implantation. Elevated flow stresses that are present in the nonphysiologic geometries of blood recirculating devices, enhance their propensity to initiate thromboembolism by chronically activating the blood platelets. This, rather than hemolysis, appears to be the salient aspect of blood trauma in devices. Limitations in characterizing and controlling relevant aspects of the flow-induced mechanical stimuli and the platelet response, hampers our ability to achieve design optimization for these devices. The main objective of this article is to describe state-of-the-art numerical, experimental, and in vivo tools, that facilitate elucidation of flow-induced mechanisms leading to thromboembolism in prosthetic devices. Such techniques are giving rise to an accountable model for flow-induced thrombogenicity, and to a methodology that has the potential to transform current device design and testing practices. It might lead to substantial time and cost savings during the research and development phase, and has the potential to reduce the risks that patients implanted with these devices face, lower the ensuing healthcare costs, and offer viable long-term solutions for these patients.

DEHP and its active metabolites: leaching from different tubing types, impact on proinflammatory cytokines and adhesion molecule expression. Is there a subsumable context?

Introduction: Di(2-ethylhexyl)phthalate (DEHP) is suspected to be toxic for several reasons. During contact with a lipophilic medium, DEHP leaks from polyvinylchloride (PVC), but its influence on inflammatory reactions remains unknown. We examined specific DEHP leaching out of different tubing types, the possibly modulated liberation of proinflammatory cytokines and the induction of adhesion molecule expression in primary endothelial cells.

Materials and Methods: Blood samples were circulated in traditional PVC, nodioctyl phthalate (DOP) PVC and heparin-coated PVC tubing within a Chandler loop model. The blood was tested for the concentration of DEHP and its active metabolites as well as the liberation of the proinflammatory cytokines TNFα and IL1ß. Furthermore, we exposed human endothelial cells to circulated blood and analysed them for the expression of the adhesion molecules ICAM-1, VCAM-1 and E-selectin.

Results: In contrast to the other tubing, PVC tubing showed significantly elevated DEHP levels, but no alteration was observed concerning a potential up-regulation of the cytokines or activation of the endothelial adhesion molecule receptors.

Conclusions: Our data conclude that there is no correlation between DEHP leaching and the inflammatory response after ECC support, but this study showed that even DEHP-free material is leaching DEHP and its toxic metabolites.

Effect of biopassive and bioactive surface-coatings on the hemocompatibility of membrane oxygenators

Postoperative complications associated with cardiopulmonary bypass (CPB) surgery and extracorporeal circulation (ECC) procedures are still a major clinical issue. Improving the hemocompatibility of blood contacting devices used for ECC procedures may ameliorate various postpump syndromes. In a simulated CPB model using human blood, we investigated the hemocompatibility, fibrinogen adsorption, and platelet receptor (GPIIb-IIIa) binding capacity of surface-modified membrane oxygenators (Jostra Quadrox). Three groups were compared: (i) biopassive protein coatings (SafeLine), (ii) bioactive heparin coatings (BioLine), and (iii) noncoated controls. During the 2 h recirculation period, plasma concentrations of activation markers for platelets (beta-thromboglobulin), inflammation (elastase), complement (C5a), and coagulation (prothrombin fragment 1+2, thrombin-antithrombin III) were lower in the groups with biopassive and bioactive coatings compared to the noncoated group (p < 0.01). These parameters did not significantly differ between the two surface-coated groups, except for complement activation: C5a levels were higher in the biopassive group compared to the bioactive group (p < 0.01). Moreover, surface-coated oxygenators showed less fibrinogen adsorption, GPIIb-IIIa binding, and platelet/leukocyte adhesion (p < 0.01). We assume that fewer fibrinogen and platelet receptor molecules bound to the surface-coated oxygenator surfaces results in fewer platelet adhesion and activation, which will significantly contribute to the improved hemocompatibility of the biopassive and bioactive oxygenators. Our results suggest that the application of bioactive oxygenators (BioLine) during CPB surgery may reduce postoperative complications for the patient more effectively than biopassive oxygenators (SafeLine).

Differential Effect of Heparin Coating and Complement Inhibition on Artificial Surface-Induced Eicosanoid Production

BACKGROUND

Contact between blood and artificial surfaces induces an inflammatory response including activation of leukocytes and platelets, as well as complement and other plasma cascade systems. In the present study we investigated the roles of complement and surface modification in polyvinyl chloride-induced synthesis of eicosanoids (arachidonic acid metabolites).

METHODS

Human whole blood was incubated in rotating loops of polyvinyl chloride or heparin-coated polyvinyl chloride tubing for 4 hours. Plasma concentrations of the eicosanoids leukotriene B4, prostaglandin E2 and thromboxane B2 were quantified.

RESULTS

Polyvinyl chloride induced a substantial increase in leukotriene B4, prostaglandin E2, and thromboxane B2. Inhibition of complement activation by the complement factor 3 binding peptide compstatin or blockade of the complement factor 5a receptor with a specific antagonist significantly and specifically inhibited the synthesis of leukotriene B4, whereas thromboxane B2 and prostaglandin E2 synthesis were apparently complement independent. The increase in all three mediators was significantly reduced by the heparin coating. Indomethacin abolished the increase of the cyclooxygenase products prostaglandin E2 and thromboxane B2, but had no effect on the increase of the lipoxygenase product leukotriene B4, consistent with the specificity of indomethacin for the cyclooxygenase and confirming the specificity of complement inhibition.

CONCLUSIONS

Polyvinyl chloride-induced increase in all three eicosanoids was attenuated by heparin coating, whereas complement inhibition selectively reduced the synthesis of leukotriene B4.

Off-pump CABG reduces complement activation but does not significantly affect peripheral endothelial function: a prospective randomized study

OBJECTIVE

Cardiac surgery initiates a systemic inflammatory response, which may affect endothelial function. The aim of this study was to investigate if off-pump CABG (OPCAB) reduces the postoperative inflammatory response and affects endothelial function less than conventional on-pump CABG.

DESIGN

Fifty-two patients submitted for elective CABG were included in a prospective, randomized study. Twenty-six patients were operated with, and 26 without cardiopulmonary bypass (CPB). Plasma levels of complement (C3a), cytokines (IL-8, TNF-alpha), endothelin-1 and neopterin were measured before and during surgery and 2 and 24 h after surgery. Endothelial function was assessed by forearm plethysmography and acetylcholine infusion in 30 patients 2-4 h after surgery.

RESULTS

C3a and neopterin concentrations were significantly higher during and early after surgery in the CPB group while TNF-alpha and IL-8 tended to be higher in the CPB group but the difference did not reach statistical significance. Endothelial function did not differ significantly between the two groups.

CONCLUSION

OPCAB reduces complement activation compared with on-pump CABG but does not significantly affect TNF-alpha and IL-8 release or endothelial function.

Protective effect of heparin-coated circuits on the platelets during cardiopulmonary bypass

To observe the protective effect of heparin-coated circuits (HCC) on the platelet function during cardiopulmonary bypass (CPB), 23 patients with heart valve replacement were studied. The system heparin dose was 3 mg/kg in the control group (n = 15) and heparin-coated circuits in the HCC group (n = 8). Platelet count, alpha-granule membrane protein-140 (GMP-140) concentrations were determined before CPB, at 60 min of CPB, 30 and 60 min after protamine administration, first 12 h after CPB, respectively. At end of CPB the arterial filters in the circuits were observed by electron microscopy. The amount of first 12-h postoperative blood loss was measured. There was significant reduction in platelet loss during and after CPB in the HCC group in contrast to the control group during CPB (P<0.05). During the first 12 h, postoperative blood loss was reduced in the HCC group as compared with that in the control group (218+/-61 ml, vs. 332+/-118 ml, P<0.05). Electron microscopy showed that in the HCC group the filter meshes and their fringes were clear and fragments of floccules were occasionally seen, without adherent cells or only few adherent cells on their surfaces, whereas several cellular and fibrous components were found to adhere to the surfaces of the filter meshes in the control group. This study indicates that heparin-coated circuits might reduce the platelet loss and activation during CPB and improve hemocompatibility of cardiopulmonary bypass equipment.

Thrombin generation during cardiopulmonary bypass: the possible role of retransfusion of blood aspirated from the surgical field

BACKGROUND: In spite of using heparin-coated extracorporeal circuits, cardiopulmonary bypass (CPB) is still associated with an extensive thrombin generation, which is only partially suppressed by the use of high dosages of heparin. Recent studies have focused on the origins of this thrombotic stimulus and the possible role of retransfused suctioned blood from the thoracic cavities on the activation of the extrinsic coagulation pathway. The present study was designed to find during CPB an association between retransfusion of suctioned blood from the pericardium and pleural space, containing activated factor VIIa and systemic thrombin generation. METHODS: Blood samples taken from 12 consenting patients who had elective cardiac surgery were assayed for plasma factor VIIa, prothrombin fragment 1+2 (F1+2), and thrombin-antithrombin (TAT) concentrations. Blood aspirated from the pericardium and pleural space was collected separately, assayed for F1+2, TAT, and factor VIIa and retransfused to the patient after the aorta occlusion. RESULTS: After systemic heparinization and during CPB thrombin generation was minimal, as indicated by the lower than base line plasma levels of F1+2, and TAT after correction for hemodilution. In contrast, blood aspirated from the thoracic cavities had significantly higher levels of factor VIIa, F1+2, and TAT compared to the simultaneous samples from the blood circulation (P < 0.05). Furthermore, after retransfusion of the suctioned blood (range, 200-1600 mL) circulating levels of F1+2, and TAT rose significantly from 1.6 to 2.9 nmol/L (P = 0.002) and from 5.1 to 37.5 μg/L (P = 0.01), respectively. The increase in both F1+2, and TAT levels correlated significantly with the amount of retransfused suctioned blood (r = 0.68, P = 0.021 and r = 0.90, P = 0.001, respectively). However, the circulating factor VIIa levels did not correlate with TAT and F1+2 levels. CONCLUSIONS: These data suggest that blood aspirated from the thoracic cavities during CPB is highly thrombogenic. Retransfusion of this blood may, therefore, promote further systemic thrombin generation during CPB.

Heparin-coated versus uncoated extracorporeal circuit in patients undergoing coronary artery bypass graft surgery

OBJECTIVE

To assess the effect of heparin-coated circuits on bleeding, transfusion, and platelet count in patients undergoing primary coronary artery bypass grafting with full heparinization.

DESIGN

Randomized, double-blind study.

SETTING

Tertiary-care academic medical center.

PARTICIPANTS

Eighty-eight patients undergoing coronary artery bypass grafting requiring cardiopulmonary bypass (CPB) without previous sternotomy.

INTERVENTIONS

Subjects received either a heparin-coated or an uncoated extracorporeal circuit for CPB. Heparin, 300 micro/kg, was administered, and supplemental amounts were administered to maintain an activated coagulation time of greater than 480 seconds. Platelet counts were determined during CPB. Mediastinal chest tube drainage was collected in the intensive care unit for 24 hours.

MEASUREMENTS AND MAIN RESULTS

The mean platelet counts were similar between the groups during CPB. There was no significant difference in 24-hour mediastinal chest tube drainage (mean +/- standard deviation; median) between the heparin-coated (n = 44, 1096 +/- 401, 1015 mL) and uncoated group (n = 44, 1150 +/- 548, 1040 mL; p = 0.91). The heparin-coated group received less allogeneic packed red blood cells (0.9 +/- 1.6, 0.0 v 1.5 +/- 1.8, 1.0 U; p = 0.04).

CONCLUSIONS

The use of a heparin-coated or uncoated cardiopulmonary bypass circuit and full heparinization marginally reduced only red blood cell transfusion but was not associated with platelet sparing or reduced perioperative bleeding.

Duroflo II heparin bonding does not attenuate cytokine release or improve pulmonary function

BACKGROUND

Comparison of the cytokine generation and leukocyte activation properties of Duroflo II heparin bonded bypass circuit (Baxter Healthcare Corp, Compton, UK) and the conventional cardiopulmonary bypass circuit. Attempt to correlate these to pulmonary dysfunction postoperatively.

METHODS

Forty patients undergoing elective, isolated coronary artery bypass grafting were randomly allocated to have either plain extracorporeal circuits (group C) or heparin bonded extracorporeal circuits (group H). Full systemic heparinization was used in all patients. The inflammatory response was assessed by measuring plasma levels of interleukin-6, interleukin-8, interleukin-10, and polymorphonuclear elastase. Gas exchange was assessed by measuring the PaO2/FIO2 ratio.

RESULTS

Significant impairment of oxygenation was seen in both groups with the lowest values at the end of the operation before a gradual return to normal during the next 6 hours. There were no differences between the groups in gas exchange or times to extubation. There were significant elevations in all the cytokines, with interleukin-6 levels peaking at 4 hours in group H and 24 hours in group C, before starting to return to normal at 48 hours. The patterns of interleukin-8 and interleukin-10 rise were identical in the two groups. Polymorphonuclear elastase reached a peak at the end of the operation in group H and remained elevated up to 24 hours, whereas levels continued to rise in group C up to 4 hours. There were no significant differences in levels between groups at any time. There were no differences between the groups in blood loss or blood product usage.

CONCLUSIONS

Cardiopulmonary bypass induces a systemic inflammatory response with release of cytokines and activation of leukocytes. This correlates with the severe deterioration in pulmonary gas exchange from preoperative levels up to 6 hours postoperatively (p < 0.05). In the presence of systemic heparinization, Duroflo II heparin bondingtf the circuits has minor effects on the pattern of evolution of this inflammatory response.

Use of simple and complex in vitro models for multiparameter characterization of human blood-material/device interactions

Medical devices, intended for blood contacting applications, undergo extensive in vitro testing followed by animal and clinical feasibility studies. Besides the use of materials known to be intrinsically blood-compatible, the surface of such devices is often modified with a coating in order to improve the performance characteristics during blood exposure. In vitro evaluation of blood-device interactions accompanies the product development cycle from the early design phase using basic material geometries until final finished-product testing. Specific test strategies can vary significantly depending on the end application, the particular study objectives and variables of interest, and cost. To examine the degree to which findings derived from two different in vitro approaches complement one another, this report contrasts findings from a simple multipass loop model with findings from a simulated cardiopulmonary bypass (CPB) model. The loop model consists of tubular test materials, with and without surface modification, formed into valved Chandler loops. The CPB model has an oxygenator with and without surface modification connected to a reservoir and a blood pump. The surface modifications studied in this report are the Carmeda BioActive Surface and Duraflo II heparin coatings. Common blood parameters in the categories of coagulation, platelets, hematology, and immunology were monitored in each model. Ideal models employ the optimal level of complexity to study the design variables of interest and to meet practical cost considerations. In the case of medical device design studies, such models should also be predictive of performance. In the more complex and realistic simulated CPB model, experimental design and cost factors prevented easy/optimum manipulation of critical variables such as blood donor (use of paired samples) and heparin level. Testing in the simpler loop model, on the other hand, readily offered manipulation of these variables, and produced findings which overlapped with observations from the more complex CPB model. Thus, the models described here complimented one another. Moreover, conclusions from consistent findings, such as favorable responses associated with the heparin coatings, between the two models were considered to be more robust.

Heparin-coated cardiopulmonary bypass circuits: current status

Heparin-coated circuits have been subjected to vigorous testing, both experimentally and clinically, for the past decade. When the functions of heparin are preserved on the surface, the heparinized surface plays multiple roles in attenuating the systemic inflammatory response. These include the ability to attenuate contact activation, coagulation activation, complement activation and, directly or indirectly, platelet and leukocyte activation. The heparinized surface also renders the cardiopulmonary bypass (CPB) circuits hydrophilic and protein resistant and augments lipoprotein binding. The multifunctional nature of the heparinized surface contributes to the overall biocompatibility of the surface. Clinically, heparin-coated circuits become most effective in reducing systemic inflammatory response and in improving morbidity, mortality, and other patient outcome related parameters when material-independent blood activation is controlled or minimized through a global biocompatibility strategy. Techniques involved in the global biocompatibility strategy are readily available and are being effectively and safely practiced at several centers. With the global biocompatibility strategy, outstanding and reproducible results have been routinely achieved with conventional CPB techniques. Alternative revascularization procedures should equal or surpass conventional CPB, using best clinically proven strategies with respect to patient outcome and long-term graft patency.

Platelet activation and aggregation during normothermic cardiopulmonary bypass

OBJECTIVE

The usefulness of heparin-bonded circuits under normothermic cardiopulmonary bypass has not been elucidated. We studied platelet activation and aggregation differences between heparin-bonded and nonheparin-bonded circuits in patients undergoing surgery involving normothermic cardiopulmonary bypass.

METHODS

Eight patients underwent coronary artery bypass grafting with non heparin-bonded circuits (controls) and 7 the same with heparin-bonded circuits (heparin group). Heparin bonding was applied to the blood contact surface of our system, including the oxygenator and connecting tubes. Patient body temperature was kept between 36 and 37 degrees C. Beta-thromboglobulin and platelet factor 4 were measured before, during, and after cardiopulmonary bypass, and platelet aggregation was evaluated by laser-light scattering.

RESULTS

Changes in beta-thromboglobulin and platelet factor 4 during and after cardiopulmonary bypass were similar in both groups. Small particle formation was the primary aggregate induced during and after cardiopulmonary bypass in both groups, and serial changes in particle formation up to 24 hours after cardiopulmonary bypass were similar in both groups.

CONCLUSIONS

Our results indicate that in 2-3 hours of normothermic cardiopulmonary bypass, heparin-bonded circuits are similar to nonheparin-bonded ones in platelet compatibility.

Impact of heparin bonding on pediatric cardiopulmonary bypass: a prospective randomized study

BACKGROUND

Heparin-coated circuits reduce the inflammatory response to cardiopulmonary bypass in adult patients; however, little is known about its effects in the pediatric population. Two studies were performed to assess this technology's impact on inflammation and clinical outcomes.

METHODS

In a pilot study, complement and interleukins were measured in 19 patients who had either uncoated cardiopulmonary bypass circuits or heparin-bonded circuits. Subsequently, 23 additional patients were studied in a randomized fashion. Respiratory function and blood product utilization were recorded.

RESULTS

In the pilot study, heparin-bonded circuit patients had less complement 3a (p < 0.001) and interleukin-8 (p < 0.05) compared with uncoated cardiopulmonary bypass circuit patients. The randomized study revealed that the heparin-bonded circuit was associated with reduced complement 3a (p = 0.02). Multiple variable analysis revealed that the following postoperative variables were increased with bypass time (p = 0.01) and diminished with heparin-bonded circuits: interleukins (p = 0.01), peak airway pressures (p = 0.05), and prothrombin time (p = 0.03).

CONCLUSIONS

Heparin-bonded circuits significantly reduce cytokines and complement during cardiopulmonary bypass and lower interleukin levels postbypass; they were also associated with improved pulmonary and coagulation function. Heparin-bonded circuits ameliorate the systemic inflammatory response in pediatric patients from cardiopulmonary bypass.

Reduction of heparin dose is not beneficial to platelet function

BACKGROUND

To clarify the effects of the reduction of heparin dose on platelets, we conducted a prospective trial on patients undergoing cardiopulmonary bypass.

METHODS

Twenty-three patients undergoing coronary artery bypass grafting were studied. The systemic heparin dose was 300 IU/kg in the control group (n = 11) and 200 IU/kg in the low-dose group (n = 12). Heparin-coated cardiopulmonary bypass equipment was used for both the groups. Platelet counts, beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) concentrations were measured and the arterial filters in the circuits were observed by electron microscopy.

RESULTS

Platelet counts were higher in the low-dose group than in the control group (p < 0.01). No significant differences were found in the platelet release reaction (beta-TG and PF4). Electron microscopy demonstrated that cell adhesion on the arterial filters in the control group was significantly more marked than in the low-dose group (p < 0.01) and that most of the cells on the filters were neutrophils.

CONCLUSIONS

We conclude that the reduction of heparin dose with the use of heparin-coated equipment reduces platelet loss, but does not suppress the platelet release reaction. Furthermore, the reduction of heparin dose reduces adherence of leukocytes to the filter surface.

Coating-techniques to improve the hemocompatibility of artificial devices used for extracorporeal circulation

OBJECTIVE

Extracorporeal circulation procedures have been shown to induce complement and leukocyte activation, release of endotoxin and inflammatory mediators, including cytokines, nitric oxide, oxygen free radicals, and platelet activating factors. The contact between the blood and the various artificial surfaces of the extracorporeal system results in an unspecific post-perfusion syndrome. For diminishing these negative side effects several coating-techniques have been developed to create devices with improved hemocompatibility.

METHODS

This review deals with the current knowledge of heparin-coated and otherwise surface-modified perfusion systems. The pathway how heparin-coated surfaces work is discussed and techniques for surface-coatings, both clinically introduced as well as newly developed are presented.

RESULTS

Numerous clinical studies compared heparin-coated versus non-coated circuits. Heparin-bonded devices showed lessened humoral and cellular activation, in particular a reduced complement activation with a reduced inflammatory post-perfusion syndrome. Also platelet protection and more favorable post-operative lung function are of particular note. Recent clinical trials demonstrated shortened hospital stays, less drainage bleeding, and reduced cerebral complications using heparin-coated oxygenation systems. The diminished expression of the leukocyte adhesion molecules CD 11b/c in CBAS devices points to a decreased activation of neutrophils. In addition, one research group found a reduced production of oxygen radicals. Heparin-bonding minimizes oxygenator failure by a significant reduced pressure gradient across the oxygenator, probably caused by decreased fibrin and platelet deposition at the hollow fiber surfaces. A meta analysis examined the impact of heparin-bonded systems on clinical outcomes and resulting costs. Using heparin-bonded circuits led to total cost savings from US $1000 to 3000. Several authors demonstrated reduced blood loss and better clinical outcome by reduction of systemic heparinization and the employment of heparin-coated devices.

CONCLUSION

Above and beyond the long-term applications, routine heart operations have also markedly begun to utilize heparin-coated devices. This trend will assuredly continue in the coming years and is an important step toward higher hemocompatibility of blood-contacting surfaces in the ECC device. Heparin-coatings are merely the beginning of improved hemocompatibility for all materials that come into contact with human blood or tissues. Intelligent materials with almost completely physiological surfaces will be at the surgeon's disposal within the next few years.

Heparin-bonded circuits: clinical outcomes and costs

The aim of this study was to use meta-analysis to combine the results of numerous studies and examine the impact of heparin-bonded circuits on clinical outcomes and the resulting costs. Heparin-bonded circuits, both ionically and covalently bonded, are examined separately. The results of the study provide evidence that heparin-bonded circuits result in improved clinical outcomes when compared to the identical nonheparin-bonded circuits. These improved clinical outcomes result in subsequent lower costs per patient with their use. However, differences are apparent in the significance and magnitude of these outcomes between ionically and covalently bonded circuits. Covalently bonded circuits provide a greater magnitude and significance of improvement in clinical outcomes than ionically bonded circuits. Total cost savings can be expected to be three times greater with covalently bonded circuits ($3231 versus $1068). It was concluded that the choice regarding the use of a heparin-bonded circuits and the type of heparin-bonded circuit used has the potential to alter clinical outcomes and subsequent costs. Cost consideration cannot be ignored, but clinical benefits should be the main rationale for the choice of cardiopulmonary bypass circuit. This analysis provides evidence that clinical benefits and cost savings can both be derived from use of the same technology-covalently bonded circuits.

Inflammatory response to cardiopulmonary bypass: mechanisms involved and possible therapeutic strategies

BACKGROUND

Recent study of the inflammatory reactions occurring during and after cardiopulmonary bypass (CPB) has improved our understanding of the involvement of the inflammatory cascade in perioperative injury. However, the exact mechanisms of this complex response remain to be fully determined.

METHODS

Literature on the inflammatory response to CPB was reviewed to define current knowledge on the possible pathways and mediators involved, and to discuss recent developments of therapeutic interventions aimed at attenuating the inflammatory response to CPB.

RESULTS

CPB has been shown to induce complement activation, endotoxin release, leukocyte activation, the expression of adhesion molecules, and the release of many inflammatory mediators including oxygen-free radicals, arachidonic acid metabolites, cytokines, platelet-activating factor, nitric oxide, and endothelins. Therapies aimed at interfering with the inflammatory response include the administration of pharmacologic agents such as corticosteroids, aprotinin, and antioxidants, as well as modification of techniques and equipment by the use of heparin-coated CPB circuits, intraoperative leukocyte depletion, and ultrafiltration.

CONCLUSIONS

Improved understanding of the inflammatory reactions to CPB can lead to improved patient outcome by enabling the development of novel therapies aimed at limiting this response.

Biocompatibility in cardiopulmonary bypass

Recent advances in surgical techniques and perfusion technology allow cardiac operations to be performed routinely with low mortality rates. However, patients undergoing cardiac operations with cardiopulmonary bypass (CPB) are still associated with bleeding disorders, thrombotic complications, massive fluid shifts, and the activation of blood components that are collectively known as the whole body inflammatory response. In this review, the effect of cardiopulmonary bypass on various humoral and cellular components of blood is examined. Blood activation caused by interaction with artificial materials of extracorporeal circuit and by material-independent stimuli is discussed. Methods to control blood activation during and after cardiopulmonary bypass are described. These include surface modification of extracorporeal circuit, control of flow dynamics in the circuit, pharmacological intervention, and the use of extracorporeal devices to remove inflammatory mediators. Recent findings on the effects of heparin-coated circuits on inflammatory response and clinical outcome are reviewed. It appears that the causes of inflammatory response to cardiopulmonary bypass are multifactorial and that an integrated strategy is needed to control and eliminate the negative effects of CPB.

Low heparinization with heparin-bonded bypass circuits: is it a safe strategy?

BACKGROUND

The use of heparin-bonded cardiopulmonary bypass circuits with reduced doses of heparin sodium has been shown to give hemostatic benefits to the patient. However, fears persist that the use of less heparin may put the patient at risk for thrombotic events. This work tested the hypothesis that heparin-bonded circuits per se are effective in preserving cells and reducing thrombin generation when a reduced dose of heparin is used in vitro.

METHODS

Simulated extracorporeal circulation was carried out using the same unit of fresh heparinized (1.1 U/mL) human blood to simultaneously perfuse a heparin-bonded circuit and a nonbonded circuit. Samples were taken at 30, 60, 120, and 360 minutes and analyzed for markers of cell activation and thrombin generation.

RESULTS

The concentrations of platelet and white blood cell activation markers were found to be significantly lower in the heparin-bonded circuits compared with the nonbonded circuits. In addition, markers of thrombin generation were significantly lower in bonded circuits. Scanning electron microscopy revealed fewer adherent cells and less debris on the bonded surface compared with the nonbonded surface.

CONCLUSIONS

Cell activation and thrombin generation were significantly reduced as a result of the presence of immobilized heparin in a system of cardiopulmonary bypass with reduced plasma heparin. However, evidence of contact activation in the bonded circuits was found after 120 minutes, indicating that anticoagulation in the system was not adequate. This becomes more important clinically where the extrinsic pathway of coagulation is also involved.