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

Exploring the Impact of Chitosan Composites as Artificial Organs

Chitosan and its allies have in multiple ways expanded into the medical, food, chemical, and biological industries and is still expanding. With its humble beginnings from marine shell wastes, the deacetylated form of chitin has come a long way in clinical practices. The biomedical applications of chitosan are truly a feather on its cap, with rarer aspects being chitosan’s role in tissue regeneration and artificial organs. Tissue regeneration is a highly advanced and sensitive biomedical application, and the very fact that chitosan is premiering here is an authentication of its ability to deliver. In this review, the various biomedical applications of chitosan are touched on briefly. The synthesis methodologies that are specific for tissue engineering and biomedical applications have been listed. What has been achieved using chitosan and chitosan composites in artificial organ research as well as tissue regeneration has been surveyed and presented. The lack of enthusiasm, as demonstrated by the very few reports online with respect to chitosan composites and artificial organs, is highlighted, and the reasons for this lapse speculated. What more needs be done to expand chitosan and its allies for a better utilization and exploitation to best benefit the construction of artificial organs and building of tissue analogs has been discussed.

Bioinspired ultra-low fouling coatings on medical devices to prevent device-associated infections and thrombosis

Addressing thrombosis and biofouling of indwelling medical devices within healthcare institutions is an ongoing problem. In this work, two types of ultra-low fouling surfaces (i.e., superhydrophobic and lubricant-infused slippery surfaces) were fabricated to enhance the biocompatibility of commercial medical grade silicone rubber (SR) tubes that are widely used in clinical care. The superhydrophobic (SH) coatings on the tubing substrates were successfully created by dip-coating in superhydrophobic paints consisting of polydimethylsiloxane (PDMS), perfluorosilane-coated hydrophobic zinc oxide (ZnO) and copper (Cu) nanoparticles (NPs) in tetrahydrofuran (THF). The SH surfaces were converted to lubricant-infused slippery (LIS) surfaces through the infusion of silicone oil. The anti-biofouling properties of the coatings were investigated by adsorption of platelets, whole blood coagulation, and biofilm formation in vitro. The results revealed that the LIS tubes possess superior resistance to clot formation and platelet adhesion than uncoated and SH tubes. In addition, bacterial adhesion was investigated over 7 days in a drip-flow bioreactor, where the SH-ZnO-Cu tube and its slippery counterpart significantly reduced bacterial adhesion and biofilm formation of Escherichia coli relative to control tubes (>5 log10 and >3 log10 reduction, respectively). The coatings also demonstrated good compatibility with fibroblast cells. Therefore, the proposed coatings may find potential applications in high-efficiency on-demand prevention of biofilm and thrombosis formation on medical devices to improve their biocompatibility and reduce the risk of complications from medical devices.

Facile modification of electrospun fibrous structures with antifouling zwitterionic hydrogels

Electrospinning technology can easily produce different shaped fibrous structures, making them highly valuable to various biomedical applications. However, surface contamination of biomolecules, cells, or blood has emerged as a significant challenge to the success of electrospun devices, especially artificial blood vessels, catheters and wound dressings etc. Many efforts have been made to resist the surface non-specific biomolecules or cells adsorption, but most of them require complex pre-treatment processes, hard-to-remove metal catalysts or rigorous reaction conditions. In addition, the stability of antifouling coatings, especially in complex conditions, is still a major concern. In this work, inspired by the interpenetrating polymer network and reinforced concrete structure, an efficient and facile strategy for modifying hydrophobic electrospun meshes and tubes with antifouling zwitterionic hydrogels has been introduced. The resulting products could efficiently resist the adhesion of proteins, cells, or even fresh whole blood. Meanwhile, they could maintain the shapes and mechanical strength of the original electrospun structures. Furthermore, the hydrogel structures could retain stable in a physiological condition for at least 3 months. This paper provided a general antifouling and hydrophilicity surface modification strategy for various fibrous structures, and could be of great value for many biomedical applications where antifouling properties are critical.

Immobilized liquid layers: A new approach to anti-adhesion surfaces for medical applications

Surface fouling and undesired adhesion are nearly ubiquitous problems in the medical field, complicating everything from surgeries to routine daily care of patients. Recently, the concept of immobilized liquid (IL) interfaces has been gaining attention as a highly versatile new approach to antifouling, with a wide variety of promising applications in medicine. Here, we review the general concepts behind IL layers and discuss the fabrication strategies on medically relevant materials developed so far. We also summarize the most important findings to date on applications of potential interest to the medical community, including the use of these surfaces as anti-thrombogenic and anti-bacterial materials, anti-adhesive textiles, high-performance coatings for optics, and as unique platforms for diagnostics. Although the full potential and pitfalls of IL layers in medicine are just beginning to be explored, we believe that this approach to anti-adhesive surfaces will prove broadly useful for medical applications in the future.

A bioinspired omniphobic surface coating on medical devices prevents thrombosis and biofouling

Thrombosis and biofouling of extracorporeal circuits and indwelling medical devices cause significant morbidity and mortality worldwide. We apply a bioinspired, omniphobic coating to tubing and catheters and show that it completely repels blood and suppresses biofilm formation. The coating is a covalently tethered, flexible molecular layer of perfluorocarbon, which holds a thin liquid film of medical-grade perfluorocarbon on the surface. This coating prevents fibrin attachment, reduces platelet adhesion and activation, suppresses biofilm formation and is stable under blood flow in vitro. Surface-coated medical-grade tubing and catheters, assembled into arteriovenous shunts and implanted in pigs, remain patent for at least 8 h without anticoagulation. This surface-coating technology could reduce the use of anticoagulants in patients and help to prevent thrombotic occlusion and biofouling of medical devices.

Addressing the Inflammatory Response to Clinically Relevant Polymers by Manipulating the Host Response Using ITIM Domain-Containing Receptors

Tissue contacting surfaces of medical devices initiate a host inflammatory response, characterized by adsorption of blood proteins and inflammatory cells triggering the release of cytokines, reactive oxygen species (ROS) and reactive nitrogen species (RNS), in an attempt to clear or isolate the foreign object from the body. This normal host response contributes to device-associated pathophysiology and addressing device biocompatibility remains an unmet need. Although widespread attempts have been made to render the device surfaces unreactive, the establishment of a completely bioinert coating has been untenable and demonstrates the need to develop strategies based upon the molecular mechanisms that define the interaction between host cells and synthetic surfaces. In this review, we discuss a family of transmembrane receptors, known as immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptors, which show promise as potential targets to address aberrant biocompatibility. These receptors repress the immune response and ensure that the intensity of an immune response is appropriate for the stimuli. Particular emphasis will be placed on the known ITIM-containing receptor, Signal Regulatory Protein Alpha (SIRPhα), and its cognate ligand CD47. In addition, this review will discuss the potential of other ITIM-containing proteins as targets for addressing the aberrant biocompatibility of polymeric biomaterials.

Reduction of thrombogenicity of PVC-based sodium selective membrane electrodes using heparin-modified chitosan

Heparin-modified chitosan (H-chitosan) membrane was utilized to enhance biocompatibility of sodium selective membrane electrode based on the highly thrombogenic polyvinyl chloride (PVC). Sodium ion sensing film was prepared using PVC, sodium ionophore-X, potassium tetrakis(chlorophenyl)-borate, and o-nitrophenyloctylether. The PVC-based sensing film was sandwiched to chitosan or H-chitosan to prevent platelet adhesion on the surface of PVC. Potentiometric response characteristics of PVC-chitosan and PVC-H-chitosan membrane electrodes were found to be comparable to that of a control PVC based sodium-selective electrode. This indicates that chitosan and H-chitosan layers do not alter the response behaviour of the PVC-based sensing film. Biocompatibility of H-chitosan was confirmed by in vitro platelet adhesion study. The platelet adhesion investigations indicated that H-chitosan film is less thrombogenic compared to PVC, which could result in enhancement of biocompatibility of sodium selective membrane electrodes based on PVC, while maintaining the overall electrochemical performance of the PVC-based sensing film.

Chitosan and its derivatives for tissue engineering applications

Tissue engineering is an important therapeutic strategy for present and future medicine. Recently, functional biomaterial researches have been directed towards the development of improved scaffolds for regenerative medicine. Chitosan is a natural polymer from renewable resources, obtained from shell of shellfish, and the wastes of the seafood industry. It has novel properties such as biocompatibility, biodegradability, antibacterial, and wound-healing activity. Furthermore, recent studies suggested that chitosan and its derivatives are promising candidates as a supporting material for tissue engineering applications owing to their porous structure, gel forming properties, ease of chemical modification, high affinity to in vivo macromolecules, and so on. In this review, we focus on the various types of chitosan derivatives and their use in various tissue engineering applications namely, skin, bone, cartilage, liver, nerve and blood vessel.

In vitro hemocompatibility of albumin-heparin multilayer coatings on polyethersulfone prepared by the layer-by-layer technique

Polyethersulfone foils (PES)--a unique material for blood purification membranes--were coated with a multilayer assembly of heparin (unfractionated or high anticoagulant activity fraction heparin) and albumin (albumin-heparin coatings), or with a multilayer of albumin (albumin coating), using the layer-by-layer technique. The coatings combine advantages of albumin (reduction of nonspecific interactions) and heparin (specific interactions with blood coagulation proteins). The differences between the two heparins, while significant for their biological activity, had only a minor effect on the multilayer assembly with albumin monitored in situ by reflection infrared spectroscopy (FTIR MIRS). Uncoated as well as modified PES surfaces were evaluated using an in vitro assay with freshly drawn, slightly heparinized (1.5 IU heparin/mL) human whole blood. The blood was circulated with a roller pump over the sample surfaces in shear flow across rectangular slit channels ( app. 6 mL/min and 120 s(-1)) for 1.5 h at 37 degrees C. All coatings effectively reduced platelet adhesion and activation according to the PF4 release. The activation of coagulation evaluated as TAT generation was significantly lowered for the coating composed of albumin and high activity heparin. A further beneficial effect of the heparin containing coatings was reduced complement activation as determined by different complement fragments.

Blood compatibility of surface-engineered poly(ethylene terephthalate) via o-carboxymethylchitosan

Poly(ethylene terephthalate) (PET) films were treated by argon plasma following by graft copolymerization with acrylic acid (AAc). The obtained PET-surface grafted PAA (PET-g-PAA) was coupled with chitosan (CS) and o-carboxymethylchitosan (OCMCS) molecules, respectively. Their surface physicochemical properties were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle and streaming potential measurements. The PET-g-PAA surface containing carboxylic acid, CS immobilized PET surface containing amino and OCMCS immobilized PET surface containing both carboxylic acid and amino groups, make the PET surface exhibited a hydrophilic character. The blood compatibility was evaluated by platelet contacting experiments and protein adsorption experiments in vitro. The results demonstrate that the PET surface coupling OCMCS shows much less platelet adhesive and fibrinogen adsorption compared to the other surface modified PET films. The anticoagulation of PET-OCMCS is ascribed to the suitable balance of hydrophobicity/hydrophilicity, surface zeta potential and the low adsorption of protein.

[Inflammatory response and haematological disorders in cardiac surgery: toward a more physiological cardiopulmonary bypass]

The systemic inflammatory response in cardiac surgery is closely related to the haemostasis disturbances. It is responsible of a significant morbidity and mortality that was previously suspected to be caused by cardiopulmonary bypass alone. However, it is time now to clearly identify the factors that are material-dependent from that material-independent. From this point of view, off-pump surgery allowed for better comprehension of the multiple sources of the inflammatory response. Numerous pathways are activated, involving complement, platelets, neutrophiles and monocytes. The tissue pathway of the coagulation system, through tissue factor, is of major importance and has to be surgically considered in order to reduce the whole body inflammatory response postoperatively. The quality of the extracorporeal perfusion through its consequences on organ perfusion, particularly in the splanchnic area, also participates to this pathophysiological process. Beyond the progress of technology provided by the industry, particularly the minimally extracorporeal circulation derived from off-pump surgery evolution, the surgical approach is of major importance in the control of the systemic inflammatory response and must not be ignored yet.

A combined approach for improving cardiopulmonary bypass in coronary artery surgery: a pilot study

BACKGROUND

This is a pilot study carried out to assess the feasibility and the clinical impact of a combined approach of cardiopulmonary bypass (CPB) with reduced anti-coagulation.

METHODS

We used a retrospective, non-randomized analysis of 45 consecutive patients undergoing coronary artery bypass using standard CPB with full anticoagulation (activated clotting time, ACT, > 450 s) (Group 1; n = 23) or closed, heparin-coated CPB with low anticoagulation (ACT>250 s), precise heparin and protamine titration, controlled suction, and retrograde autologous prime (Group 2; n = 22).

RESULTS

Patients were similar except for a higher incidence of three-vessel disease in Group 2 (77.3% versus 47.8%; p < 0.03). Heparin was reduced by 41% in Group 2 and protamine by 56% (p < 0.0001). Total postoperative blood loss was similar between Groups 1 and 2 (429 +/- 149 versus 435+/-168 ml, respectively). However, the operative hematocrit decrease was lower in Group 2 (-1.6 +/- 7.5% versus -6.9 +/- 4.8%; p = 0.007), although hemodilution was similar, as reflected by the blood protein level. The need for postoperative inotropic support was less frequent in Group 2 (36.4% versus 65.2%; p = 0.05). Within the subgroup of patients weaned from CPB without requiring inotropic support (n = 35), the cardiac index dropped significantly in Group 1 (p = 0.003) 6 h after the start of CPB, whereas it remained stable in Group 2 (p = 0.92). Using multivariate analyses, Group 2 was found to be more protected than Group 1 against myocardial cellular injury (p = 0.046) and need for postoperative inotropic support (p = 0.014).

CONCLUSION

The pejorative postoperative outcome in coronary artery surgery was attenuated through a combined approach aimed at improving CPB.

Hemocompatibility of medical connectors with biopassive or bioactive surface coatings

Although medical connectors compose very small parts of the extracorporeal circulation (ECC) system they represent a critical localization where early thromboembolic processes can manifest. In the present study we modified an in vitro closed-loop model with fresh human whole blood for the preclinical evaluation of the hemocompatibility of three types of medical connectors: non-coated (control); with silicone-, and heparin-coating. Each single loop consists of five polycarbonate connectors joined together by five pieces of silicone tubes. Thrombin-antithrombin-III, beta-thromboglobulin (beta-TG), PMN-Elastase, terminal complement complex, CD 11b expression, and surface-absorbed fibrinogen were measured. After 1 and 2 h recirculation, platelet loss, release of beta-TG, and adsorption of fibrinogen were significantly higher (p<0.05) within the non-coated connectors compared to the silicone- and heparin-coated groups. Following this experiment, the connectors were filled again with fresh heparinized whole blood from the same donor to evaluate the influence of prior blood contact. Here, the activation of platelets and coagulation was dependent on the duration of the blood preincubation period. Probably, the coated surfaces possess a reduced, or selective adsorption of plasma proteins, which in turn leads to a faster creation of a blood-friendly secondary superficial membrane, and prevents a further denaturation and hence activation of the adsorbed proteins.

Blood-compatible biomaterials by surface coating with a novel antithrombin-heparin covalent complex

Covalent antithrombin-heparin complex (ATH) was covalently grafted to a polycarbonate urethane (Corethane) endoluminal graft (a kind gift of Corvita Corporation) after being activated using 0.3% m/m NaOCl in 0.15 M phosphate pH 6.0. ATH graft density (1.98 x 10(-7) mol/m2) was 6 times the maximum amount of unfractionated heparin (UFH) that could be bound to polycarbonate urethane surfaces. Surface-bound ATH could be stored in sterile 0.15 M NaCl at 4 degrees C for at least 2 months with good antithrombotic activity before being implanted into rabbits. Analysis of ATH-coated tubing showed that it contained significant direct thrombin inhibitory activity. In vivo testing in a rabbit model was compared to non-activated non-coated surfaces, activated-non-coated surfaces, hirudin-coated surfaces and antithrombin (AT)-coated surfaces. The weight of the clot generated in the ATH-coated graft tubing was significantly less than the weight of the clot generated within the hirudin-coated graft (p = 0.03 with a 1-tailed Student's t test). The anticoagulant nature of ATH grafts in vivo was shown to be due to bound ATH because boththe AT-coated surfaces and non-coated but activated surfaces showed similar thromboresistant efficacy to that of untreated material (ANOVA; p < 0.05). Apart from the direct antithrombin activity that contributed to much of the prolonged patency in vivo, surface-bound ATH likely catalyzed AT inhibition of thrombin, as evidenced by a significant number of 125I-AT binding sites (> or = 1.5 x 10(-8) mol/m2). Thus, ATH appears to be a good candidate for coating cardiovascular devices, such as endoluminal grafts, with high levels of substitution and significant long-term blood-compatibility.

Hemocompatibility of heparin-coated surfaces and the role of selective plasma protein adsorption

Although several studies have shown that heparin-coated surfaces reduce the activation of both the complement system and the coagulation system, there is still inadequate understanding of the factors initiating and controlling blood activation at these surfaces. We investigated the adsorption profile of 12 common plasma proteins (and the platelet receptor CD41) to a heparin coating (Carmeda BioActive surface (CBAS)) compared to uncoated controls (PVC) by using an in vitro whole blood Chandler-Loop model. Surface bound proteins were studied kinetically by a direct ELISA technique. Western blots were performed on the SDS eluates in order to detect adsorbed cleavage products and denatured proteins. Changes in plasma levels of neutrophil activation markers, platelet activation, coagulation activation, complement activation and the inflammatory response were measured by conventional ELISAs. This study showed significant differences in adsorption patterns among the heparin-coated and the uncoated surfaces, notably for fibronectin, fibrinogen, C3 and high molecular weight kininogen (HMWK). The kinetic studies confirmed the results obtained from Western blots and indicated specific adsorption profiles of plasma proteins. We assume that at least some of the improved blood compatibility of the heparin-coated surfaces may be ascribed to the selective uptake and cleavage of plasma proteins.

Mechanisms and attenuation of hemostatic activation during extracorporeal circulation

Patients undergoing cardiac surgery with cardiopulmonary bypass are at risk for excessive microvascular bleeding, which often leads to transfusion of allogeneic blood and blood components as well as reexploration in a smaller subset of patients. Excessive bleeding after cardiac surgery is generally related to a combination of several alterations in the hemostatic system pertaining to hemodilution, excessive activation of the hemostatic system, and potentially the use of newer, longer-acting antiplatelet or antithrombotic agents. Although several nonpharmacologic strategies have been proposed, this review summarizes the role of pharmacologic interventions as means to attenuate the alterations in the hemostatic system during CPB in an attempt to reduce excessive bleeding, transfusion, and reexploration. Specifically, agents that inhibit platelets, fibrinolysis, factor Xa and thrombin, as well as broad-spectrum agents, have been investigated with respect to their role in reducing consumption of clotting factors and better preservation of platelet function. Prophylactic administration of agents with antifibrinolytic, anticoagulant, and possibly antiinflammatory properties can decrease blood loss and transfusion. Although aprotinin seems to be the most effective blood conservation agent (which is most likely related to its broad-spectrum nature), agents with isolated antifibrinolytic properties may be as effective in low-risk patients. The ability to reduce blood product transfusions and to decrease operative times and reexploration rates favorably affects patient outcomes, availability of blood products, and overall health care costs.

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.

Heparin-coated extracorporeal circulation with full and low dose heparinization: comparison of thrombin related coagulatory effects

Thrombin related coagulatory effects of a heparin-coated cardiopulmonary bypass system combined with full and low dose systemic heparinization were investigated in a prospective, randomized study in coronary bypass surgery patients. One hundred nineteen patients were divided into 3 groups. Group A (n = 39) had a standard uncoated extracorporeal circulation (ECC) set, and systemic heparin was administered in an initial dose of 400 IU/kg body weight. During ECC activated clotting time (ACT) was maintained at > or =480 s. Group B (n = 42) had the same ECC set completely coated with low molecular weight heparin. Intravenous heparin was given in the same dose as in Group A, and ACT was kept at the same level. Group C (n = 38) had the same coated ECC set as Group B, but intravenous heparin was reduced to 150 IU/kg, and during ECC, ACT was set to be > or =240 s. The same ECC components were used in all 3 groups including roller pumps, coronary suction, and an open cardiotomy reservoir. Thrombin generation as indicated by F1/F2 was significantly elevated at an ECC duration >60 min if heparin-coated ECC combined with low dose systemic heparinization was employed. Complexed thrombin (TAT) was significantly elevated after administration of protamine. Release of D-dimers indicating fibrinolysis was not significantly different between groups. Signs of clinical thromboembolism, i.e., postoperative neurological deficit, occurred in 2 patients in Group A and 1 patient in Group C. We conclude that heparin-coated extracorporeal circulation combined with reduced systemic heparinization intraoperatively leads to significantly increased thrombin generation, but not to increased fibrinolysis.

Neurological and general outcome in low-risk coronary artery bypass patients using heparin coated circuits

OBJECTIVE

The clinical significance of heparin coating in cardiopulmonary bypass has previously been investigated. However, few studies have addressed the possible influence on brain function and memory disturbances.

METHODS

Three hundred low-risk patients exposed to coronary bypass surgery were randomised into three groups according to type of heparin coating: Carmeda Bioactive Surface, Baxter Duraflo II and a control group. Outcome was determined from a number of clinically oriented parameters, including a detailed registry of postoperative deviations from the normal postoperative course. Brain damage was assessed through S100 release and memory tests, including a questionnaire follow-up.

RESULTS

Clinical outcome was similar for all groups. Blood loss (Duraflo only), transfusion requirements and postoperative creatinine elevation were reduced in the heparin-coated groups. A lower incidence of atrial fibrillation was noted in the Duraflo group. Heparin coating did not uniformly attenuate the release of S100 or the degree of memory impairment.

CONCLUSIONS

Cardiopulmonary bypass (CPB) with heparin coating and a reduced dose of heparin seems to be safe. Clinical outcome and neurological injury seem not to be associated with type of heparin coating used for CPB. However, blood loss and transfusion requirements may be reduced.

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.

Heparin-coated circuits reduce myocardial injury in heart or heart-lung transplantation: a prospective, randomized study

BACKGROUND

The effects of heparin-coated (HC) circuits have been primarily investigated in routine cardiac operations with limited duration of cardiopulmonary bypass (CPB) and ischemia. Their benefits have not been conclusively proven but could be more significant when CPB and ischemic times are longer, such as during heart transplantation (HTx) or heart-lung transplantation (HLTx).

METHODS

In a 22-month period, 29 patients undergoing HTx and HLTx were randomly divided into two groups using HC (Duraflo II, n = 14, 10 HTx and 4 HLTx) or uncoated but identical circuits (NHC group, n = 15, 10 HTx and 5 HLTx). All patients received full systemic heparinization (3 mg/kg) during CPB. Plasma endotoxin, interleukin (IL)-6, IL-8, IL-10, IL-12, and cardiac troponin-I were measured before heparin administration, immediately after aortic cross-clamping, 5, 30, 60, 90, 120 minutes, and 12 and 24 hours after aortic declamping. The intensive care unit (ICU) staff and the laboratory technologists were blinded as to the use of HC circuits.

RESULTS

No statistically significant differences between groups were found with respect to all baseline values, duration of CPB and aortic cross-clamping, graft ischemic time, doses of heparin, postoperative blood loss and transfusion, peak lactate and creatine kinase-MB isoenzyme values, duration of mechanical ventilation, or length of ICU stay. One patient in each group died during the hospital stay. Patients in the HC group needed more protamine sulfate after CPB. Although endotoxin levels were similar in the two groups, significantly lower IL-6, IL-8, and IL-10 levels were observed 1 hour after aortic declamping in the HC group. The release of cardiac troponin-I was also significantly reduced in the HC group 12 and 24 hours after reperfusion.

CONCLUSIONS

The use of HC circuit limits both pro- and anti-inflammatory responses to CPB. It may also reduce myocardial injury after prolonged duration of CPB and ischemia.

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.

Aprotinin complements heparin bonding in an in vitro model of cardiopulmonary bypass

The relative contribution of full-dose aprotinin, used with heparin-bonded surfaces, to contact activation during cardiopulmonary bypass was examined. In vitro Carmeda-bonded cardiopulmonary bypass circuits were perfused with whole blood anticoagulated with heparin (3.3 U/ml). Aprotinin (300 kIU/ml) was added to the circuits of one set of experiments. Samples were taken prior to perfusion and at 30, 60, 120 and 360 min. The activated coagulation time was extended in the aprotinin experiments, significantly at 30 min (P=0.003) and 120 min (P=0.001). Thrombin-antithrombin complexes and prothrombin fragment F1+2 were both higher in the non-aprotinin experiments at 120 min (P=0.02 each) and 360 min (P=0.005 and 0.001, respectively). Plasma leucocyte elastase was raised in the non-aprotinin experiments in comparison to the aprotinin experiments at each timepoint (30 min, P=0.04; 60 min, P=0.006; 120 min, P=0.001; 360 min, P=0.0001), as was interleukin-8 at 120 min (P=0.05) and 360 min (P=0.0001). No differences were found for the platelet activation marker P-selectin. Platelet and white blood cell counts fell significantly in the non-aprotinin experiments compared with the aprotinin experiments at 360 min (P=0.05 and 0.03, respectively). It would appear that the use of aprotinin has additional haemostatic beneficial effects to those found with heparin-bonded circuits in terms of effects on contact activation and inflammation.

Heparin-coated equipment reduces the risk of oxygenator failure

BACKGROUND

The development of an abnormal pressure gradient (APG) across the oxygenator is the most common cause of oxygenator failure during cardiopulmonary bypass. This necessitated changing the oxygenator in 4 patients in this series. A retrospective analysis of conditions predisposing to APG was performed.

METHODS

One thousand nine hundred fifty-nine operations with cardiopulmonary bypass were performed in adults. A range of membrane oxygenators was used subject to availability; 769 oxygenators were heparin-coated and 1,190 were uncoated. The pressure gradient across the oxygenator was measured under standardized conditions. An APG was defined as a gradient of greater than twice the mean.

RESULTS

An APG occurred in 44 uncoated and 3 heparin-coated oxygenators (p < 0.001). The mean age was higher for the APG group (p < 0.001). Fibrin deposits in the arterial line filter were noted in 45 patients. Logistic regression revealed that only fibrin deposition in the arterial line filter and the use of uncoated oxygenators were significantly associated with APG.

CONCLUSIONS

We conclude that a heparin-coated oxygenator effectively prevents APG. This adds significantly to the safety of open heart operations.