Reduced granulocyte activation with a heparin-coated device in an in vitro model of cardiopulmonary bypass

Heparin surface treatment does not impair gas and heat transfer of an extracorporeal circuit

Surface treatment of a cardiopulmonary bypass circuit with heparin improves its haemocompatibility. However, potential side effects of this layer of heparin are impairment of O2 transfer and CO2 transfer in the oxygenator and heat transfer in the heat exchanger.

Therefore we studied these side effects during extracorporeal circulation with moderate hypothermia in 30 patients who underwent elective coronary artery bypass grafting surgery. All patients were heparinized systemically. In 15 patients (Duraflo II-group) we used an extracorporeal circuit (including a Bentley Bos-CM50 membrane oxygenator) which was treated with heparin. The results of this group were compared with those obtained from another group of 15 patients (control-group), who were operated upon with an identical extracorporeal circuit but without heparin surface treatment.

We found no significant differences between the two groups in O2 transfer, CO2 transfer or heat transfer during normothermia or hypothermia.

We concluded that neither O2 transfer and CO2 transfer of the oxygenator nor heat transfer of the heat exchanger were impaired by Duraflo II heparin surface treatment during clinical cardiopulmonary bypass with moderate hypothermia.

Off-pump cardiac surgery abolishes complement activation

Background. This prospective randomized study compared the inflammatory response in patients undergoing elective on-pump and off-pump coronary artery bypass grafting. Patients and methods. Forty-four patients undergoing elective coronary artery bypass grafting were recruited with 22 patients randomized to on-pump heart surgery and 22 patients to off-pump coronary bypass surgery. Plasma levels of C3bc, the terminal SC5b-9 complement complex, myeloperoxidase, β -thromboglobulin and prothrombin fragment F1 + 2 were measured before the operation, intraoperatively, at termination of the operation, and two hours post-operatively. Results. Complement was markedly activated in the on-pump group as indicated by a significant increase in C3bc and SC5b-9 (p < 0.001 for both), whereas no complement activation was seen in the off-pump group (p = 0.001 between the groups). In contrast, both groups showed significant activation of neutrophils, platelets and coagulation, as indicated by an early increase in myeloperoxidase and a post-operative increase in β-thromboglobulin and F1 + 2, respectively. Notably, there were no inter-group differences with regard to neutrophil and platelet activation, whereas coagulation activation was more pronounced in the off-pump group (p < 0.01). Conclusions. Off-pump surgery completely eliminated the heart-lung machine-induced complement activation. Neutrophils and platelets were equally activated in both groups, whereas coagulation was enhanced post-operatively in the off-pump group. Perfusion (2007) 22, 251—256.

Is there an alternative to systemic anticoagulation, as related to interventional biomedical devices?

To reduce the toxic effects, related clinical problems and complications such as bleeding disorders associated with systemic anticoagulation, it has been hypothesized that by coating the surfaces of medical devices, such as stents, bypass grafts, extracorporeal circuits, guide wires and catheters, there will be a significant reduction in the requirement for systemic anticoagulation or, ideally, it will no longer be necessary. However, current coating processes, even covalent ones, still result in leaching followed by reduced functionality. Alternative anticoagulants and related antiplatelet agents have been used for improvement in terms of reduced restenosis, intimal hyperphasia and device failure. This review focuses on existing heparinization processes, their application in clinical devices and the updated list of alternatives to heparinization in order to obtain a broad overview, it then highlights, in particular, the future possibilities of using heparin and related moieties to tissue engineer scaffolds.

Biocompatibility and pathways of initial complement pathway activation with Phisio- and PMEA-coated cardiopulmonary bypass circuits during open-heart surgery

A randomized open-heart surgery study comprising 30 patients was undertaken to compare the biocompatibility of Phisio-(phosphorylcholine) and PMEA-(poly-2-methoxyethyl acrylate) coated cardiopulmonary bypass (CPB) circuits and to assess the initial complement pathway activation during open-heart surgery. Blood samples were obtained at five time points, from the start of surgery to 24 hours postoperatively. The following analyses were performed: haemoglobin, lactate dehydrogenase, leukocyte and platelet counts, myeloperoxidase and neutrophil-activating peptide-2, thrombin-anti-thrombin complexes, syndecan-1 and the complement activation products C1rs-C1-inhibitor complexes, C4bc, C3bc, C3bBbP and the terminal complement complex (TCC). No significant inter-group difference was found in any parameters, except for the concentration of TCC which was moderately lower in the PMEA group at termination of CPB. Complement activation during open-heart surgery was mainly mediated through the alternative pathway. In conclusion, PMEA- and Phisio-coated circuits displayed similar biocompatibility with respect to inflammatory and haemostatic responses during and after open-heart surgery.

Comparable biocompatibility of Phisio- and Bioline-coated cardiopulmonary bypass circuits indicated by the inflammatory response

Background: The biocompatibility of cardiopulmonary bypass surfaces has been improved by heparin and polymer surface modifications. The present study compared the effect of two such coatings on the inflammatory reactions after open heart surgery.

Methods:Thirty patients undergoing elective heart surgery were randomly assigned to receive one of two types of coated circuits: Bioline (n=15) or phosphorylcholine (Phisio, n=15). The platelet and leukocyte counts, neutrophil activation (myeloperoxidase), complement activation (C3a and TCC), concentrations of lactate dehydrogenase, 27 cytokines (including interleukins, chemokines and growth factors), thrombin-antithrombin complexes, and the endothelial cell marker syndecan-1 were analyzed at five predetermined time points until 24 hrs post operatively.

Results: Most measurements were comparable in both groups. However, myeloperoxidase was significantly higher in the Bioline group (p < 0.001). Postoperative lactate dehydrogenase concentrations were significantly higher in the Phisio group (p<0.01) and the maximal concentration of thrombin-antithrombin complexes 2 hours postoperatively tended to be higher in the Phisio group (p=0.08), consistent with a longer aortic cross-clamp and cardiopulmonary bypass time. Conclusions: The two circuits exhibited a comparable degree of in vivo biocompatibility.

Blood interactions with plasticised poly (vinyl chloride): influence of surface modification

Surface modification of plasticised poly (vinyl chloride) (PVC), with di-(2-ethylhexyl) phthalate (DEHP) as plasticiser, for the improvement of blood compatibility in potential clinical use such as cardiopulmonary bypass was achieved by heparinisation. The influence of surface modification on blood compatibility was assessed in terms of the influence on fibrinogen and factor XII adsorption in vitro, and the generation of thrombin-antithrombin III complex (TAT) and the complement component C3a, in vitro and ex vivo. Electron spectroscopy for chemical analysis (ESCA) was used to characterise the heparinised surface in order to correlate the surface properties with the blood response. Results indicate that at the plasticised PVC surface there is a higher content of heparin than that of the PVC and the DEHP content is lower than that present at the surface of standard plasticised PVC. The blood compatibility assessment confirms the importance of surface modification for the improvement of blood compatibility.

Structural organization of the neutrophil NADPH oxidase: phosphorylation and translocation during priming and activation

The reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is part of the microbicidal arsenal used by human polymorphonuclear neutrophils (PMNs) to eradicate invading pathogens. The production of a superoxide anion (O2-) into the phagolysosome is the precursor for the generation of more potent products, such as hydrogen peroxide and hypochlorite. However, this production of O2- is dependent on translocation of the oxidase subunits, including gp91phox, p22phox, p47phox, p67phox, p40phox, and Rac2 from the cytosol or specific granules to the plasma membrane. In response to an external stimuli, PMNs change from a resting, nonadhesive state to a primed, adherent phenotype, which allows for margination from the vasculature into the tissue and chemotaxis to the site of infection upon activation. Depending on the stimuli, primed PMNs display altered structural organization of the NADPH oxidase, in that there is phosphorylation of the oxidase subunits and/or translocation from the cytosol to the plasma or granular membrane, but there is not the complete assembly required for O2- generation. Activation of PMNs is the complete assembly of the membrane-linked and cytosolic NADPH oxidase components on a PMN membrane, the plasma or granular membrane. This review will discuss the individual components associated with the NADPH oxidase complex and the function of each of these units in each physiologic stage of the PMN: rested, primed, and activated.

Comparison of a Duraflo II-coated cardiopulmonary bypass circuit and a trillium-coated oxygenator during open-heart surgery

BACKGROUND

Cardiopulmonary bypass (CPB) evokes a systemic inflammatory response. In attempting to improve the biocompatibility of the equipment, various methods to coat the inner surfaces of the CPB systems have been developed. The present study compares a Trillium Biopassive surface-coated Affinity oxygenator with a Duraflo II totally heparin-coated CPB system.

METHODS

Low-risk patients admitted for primary coronary artery bypass grafting or aortic valve replacement were randomized to operation using the Trillium- or the Duraflo II-coated setups. Heparin concentration, complement activation (C3bc activation products and terminal complement complex (TCC)), platelet activation (platelet numbers and beta-thromboglobulin (BTG)), leukocyte activation (leukocyte numbers and myeloperoxidase (MPO)), coagulation (thrombin/antithrombin complexes (TAT)) and fibrinolytic activity (plasmin/alpha2-antiplasmin complexes (PAP)) were measured during CPB and two hours postoperatively.

RESULTS

Platelet counts decreased during CPB, without significant intergroup differences. The median BTG concentration increased moderately in both groups and were slightly higher in the Trillium group during CPB (p < 0.05), but not postoperatively. Complement activation products (C3bc and TCC), leukocyte counts, MPO, TAT and PAP activity showed no differences between the two groups.

CONCLUSIONS

There were small differences in the inflammatory response between the two extracorporeal circulation devices compared in this study.

Endpoint-attached heparin blocks neutrophil sticking and spreading

Neutrophils adhere to polymer surfaces by partly unknown mechanisms. Heparin-coating of such surfaces is employed to improve biocompatibility of extracorporeal circulation. The aim of the study was to investigate mechanisms for interactions between neutrophils and uncoated versus heparin-coated surfaces. Isolated human neutrophils were incubated in tissue culture plates. Uncoated plates induced sticking and spreading of unstimulated neutrophils. Heparin-coating reduced sticking by approximately 75%, and adherent cells were less spread (p<0.001). Experiments in plates coated with modified heparins showed that sticking and spreading were not related to anticoagulatory ability or surface charge. Unstimulated neutrophil sticking was unchanged whether the media contained divalent cations or 1mM ethylenediaminetetraacetic acid (EDTA). Spreading on uncoated plates was greater in the presence of Ca(2+) and/or Mg(2+) than with EDTA. Spreading of unstimulated neutrophils on heparin-coated plates varied little with different media. Pre-incubation with anti-CD11b/CD18 antibodies did not significantly influence adhesion to heparin-coated plates. There were no differences in expression of the antiadhesive receptor CD43 (leukosialin) on adherent neutrophils on uncoated and heparin-coated plates, and pre-incubation with anti-CD43 antibody had little effect on neutrophil sticking. These data indicate an adhesive mechanism independent of selectins, integrins, and leukosialin, and inhibition of sticking and spreading by heparin-coating.

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.

Factor V(LEIDEN) and cardiopulmonary bypass: investigation of haemostatic parameters and the effect of aprotinin using an ex vivo model

It has been suggested that aprotinin results in significantly increased risk for perioperative thrombotic complications in patients with Factor V(LEIDEN) (F5L) due to its ability to competitively inhibit activated protein C (APC) function in vitro. No clinical studies have been performed to assess the effect of aprotinin on APC function of F5L in vivo. We developed an ex vivo model to mimic the effects of cardiopulmonary bypass with the exclusion of the patient in order to assess APC function. Blood from normal (n = 2) and F5L heterozygous donors (n = 2) was treated with aprotinin or placebo (saline). The blood was heparinized, added to the prime and circulated at 2 l/min through a modified cardiopulmonary bypass circuit. After 60 min of circulation, the heparin was neutralized with protamine sulfate. Blood samples, drawn at specific time points, were analysed for APC ratio. Results showed a decrease in APC ratio for both F5L and normal bloods with the addition of aprotinin (18% and 40%, respectively). APC ratios also decreased with the commencement of extracorporeal circulation for all bloods, resulting in an APC ratio of 1.35 in normal placebo-treated blood and 0.67 in F5L placebo-treated blood. The combined effect of aprotinin and extracorporeal circulation resulted in APC ratios of 0.90 for normal blood and 0.63 for F5L blood, corresponding to a severe dysfunction of APC intraoperatively (reference range 1.9-4.0). The data from this model predict an increased risk of perioperative thrombosis due to inhibition of APC function in cardiac surgical patients heterozygous for the F5L mutation. Aprotinin further compounds the severity of APC dysfunction, though the effect is more severe in normal blood. The ex vivo model employed was an effective tool for the investigation of the haemostatic effect of aprotinin. This model may be exploited for other applications such as the investigation of novel or emerging haemostatic agents prior to clinical trial.

Superior biocompatibility of heparin-bonded circuits in pediatric cardiopulmonary bypass

BACKGROUND

Heparin bonding of pediatric cardiopulmonary bypass circuits may decrease activation of blood compartments as inflammatory responses. We studied the biocompatibility of heparin-bonded circuits in infant cardiac surgery.

METHODS

Twenty-four infants undergoing elective cardiac surgery were randomly assigned to either a nonheparin-bonded control circuit (n = 12) or a fully heparin-bonded circuit (n = 12) including membrane oxygenator, reservoir, and all tubing. Blood samples were used to identify differences in complement activation and cytokine release between groups during and after cardiopulmonary bypass. The postbypass oxygenation index was also compared.

RESULTS

The C3 activation product in the heparin-bonded group was significantly lower during (p < 0.01) and just after (p < 0.05) cardiopulmonary bypass. No statistically significant difference in C4 activation products was observed. Lower interleukin-6 and tumor necrosis factor-alpha were found immediately after cardiopulmonary bypass (p < 0.05) and a higher mean postbypass oxygenation index was also seen (p < 0.05) in the heparin-bonded group.

CONCLUSION

We found that a heparin-bonded cardiopulmonary bypass circuit reduced inflammatory response and improved oxygenation in pediatric cardiac surgery. These results suggest that the superior biocompatibility of the bonded circuit may reduce pulmonary complications.

Biocompatibility of a silicone-coated polypropylene hollow fiber oxygenator in an in vitro model

BACKGROUND

A silicone-coated microporous hollow-fiber membrane oxygenator has been developed to prevent plasma leakage during long-term use. The objective of this study was to evaluate the biocompatibility of the oxygenator.

METHODS

A silicone-coated oxygenator was compared with an uncoated oxygenator in an in vitro model of cardiopulmonary bypass. Simulated circulation was maintained for 6 h at 37 degrees C.

RESULTS

Platelet counts decreased significantly (p < 0.05) and leukocyte counts tended to decline; however, the differences between groups were not significant. Concentrations of C3a increased significantly in both groups (p < 0.05), but levels were significantly less in the silicone-coated oxygenator (p = 0.008). In contrast, concentrations of C4a, beta-thromboglobulin, and granulocyte elastase increased significantly (p < 0.05), but the differences between groups were not significant.

CONCLUSIONS

Silicone coating over a microporous hollow-fiber membrane may improve biocompatibility by reducing C3a activation.

In vitro evaluation of new surface coatings for extracorporeal circulation

Cardiopulmonary bypass (CPB) exposes blood to large, foreign surfaces. This exposure may activate the cellular and humoral inflammatory systems, resulting in inflammatory reactions and organ dysfunction. Coating the inner surfaces of the bypass circuit may help alleviate these side-effects. The objective of this study was to determine the influence of two new surface treatments on blood cell and complement activation. Oxygenator and tubing sets coated with synthetic polymers (n = 7) or heparin (n = 7) were compared to uncoated sets (n = 7) in an in vitro model of CPB. The circuits were run at 4 l/min and recirculated for 120 min. The inflammatory response was assessed at regular intervals by platelet counts, and activation of complement, leucocytes and platelets. We found that the median platelet counts decreased from 127 to 122 x 10(9)/l (not significant, NS) in the synthetic polymer sets, from 96 to 88 x 10(9)/l (NS) in the heparin-coated sets, and from 93 to 54 x 10(9)/l (p < 0.01) in the uncoated sets after 2 h of recirculation. There were significant differences in platelet counts between the coated sets and the uncoated set at end of experiments (p < 0.05). Beta-thromboglobulin (BTG) concentrations increased in the synthetic polymer sets from 166 to 352 ng/ml (p < 0.01), in the heparin coated sets from 336 to 1168 ng/ml (p < 0.01), and in the uncoated sets from 301 to 3149 ng/ml (p < 0.01) after 2 h of recirculation. The differences in BTG at termination of the experiments were significant among all three sets (p < 0.05). Myeloperoxidase (MPO) concentrations in the synthetic polymer sets increased from 63 to 86 micrograms/l (p < 0.01), in the heparin-coated sets from 90 to 208 micrograms/l (p < 0.01), and in the uncoated sets from 122 to 513 micrograms/l (p < 0.01) after 2 h of recirculation. The differences in MPO at termination of the experiments were significant among all three groups (p < 0.01). There were no significant differences at termination of the experiments among the three sets regarding complement activation as measured by C3 activation products and the terminal complement complex. We conclude that in the current in vitro model of a CPB circuit, the synthetic polymer coating and the heparin coating caused significantly less platelet loss and granulocyte and platelet activation than the uncoated surface (p < 0.05). The synthetic polymer coating caused significantly less granulocyte and platelet activation than the heparin coating (p < 0.05). There was moderate complement activation within each group, but no significant differences among the three groups.

A new heparin-bonded dense membrane lung combined with minimal systemic heparinization prolonged extracorporeal lung assist in goats

Heparin was covalently bonded to a new hollow-fiber dense membrane artificial lung and extracorporeal circuit using a silane coupling agent and polyethyleneimine. This study investigated whether prolonged, venoarterial bypass extracorporeal lung assist (V-A bypass ECLA) could be sustained in a goat by the combination of the new membrane lung and minimal systemic heparinization. We maintained ECLA with the hollow-fiber lungs (surface area, 0.8 m2) and circuits by titrating the activated clotting time (ACT) to below 150 s with minimal systemic heparinization in 5 goats. The outcome was assessed from the function of the artificial lung via macro and microscopic examinations after the experiments and the incidence of systemic complications. The 5 goats were maintained on ECLA for 6 to 27 days. The bypass flow rate, blood gases at the return and drainage sites, platelet counts, and platelet aggregation activity were well maintained. Although the hemoglobin concentration, hematocrit, and plasma protein at the start of the ECLA were significantly lower than the pre-ECLA values due to hemodilution, the values remained stable during ECLA. A cerebral infarction occurred in 1 goat. However, in the other 4 goats, no complications such as bleeding, thrombosis, or plasma leakage from the artificial lung were observed. Although several thrombi were observed in the stagnant area of the artificial lung, these local thrombi did not cause the function of the artificial lung to deteriorate. We found that this new type of highly biocompatible, dense membrane artificial lung, when combined with minimal systemic heparinization, prolonged ECLA without the deterioration of the artificial lung function and was suitable for prolonged ECLA.

A second-generation blood substitute (perfluorodichlorooctane emulsion) does not activate complement during an ex vivo circulation model of bypass

OBJECTIVES

To examine whether a second-generation perfluorocarbon (PFC) blood substitute added to the cardiopulmonary bypass (CPB) prime influences complement production.

DESIGN

A prospective, randomized, single-blinded, ex vivo model.

SETTING

A university hospital, laboratory, and clinics.

PARTICIPANTS

Ten healthy adult consented volunteer blood donors (five men, five women).

INTERVENTIONS

Ex vivo closed-loop extracorporeal circuit including membrane oxygenator, tubing, and filter primed with crystalloid or crystalloid plus PFC was circulated for 1 hour with the addition of 500 mL of heparinized fresh human whole blood.

MEASUREMENTS AND MAIN RESULTS

Laboratory specimens were drawn from the circuit at 10-minute intervals for 1 hour and measured for complement (C3a, Bb fragment) concentrations, blood gases, fibrinogen concentration, platelet count, and hematocrit. In the PFC group, C3a and Bb fragments were equal to or less than those in the group that received crystalloid alone.

CONCLUSION

The second-generation PFC added to the prime of a CPB circuit does not independently increase complement production.

Synthesis of monomeric and polymeric conjugates carrying a thrombin inhibitor through an ester bond

Four kinds of monomers carrying a thrombin inhibitor, (2R,4R)-4-methyl-1-[N2-[(3-methyl-1,2,3,4-tetrahydro-8-quinolinyl)sulfon yl]-L-arginyl]-2-piperidinecarboxylic acid (argatroban), were synthesized. These monomers were copolymerized with acrylamide to yield water-soluble polymeric conjugates possessing the argatroban moiety in the side chain. Their antithrombogenic activities were determined from the inhibitory effect on thrombin action and the prolongation effect on blood clotting time. The monomeric conjugates of 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate (HEMA), and 4-hydroxybutyl acrylate (HBA) linked with argatroban through an ester bond were potent inhibitors of thrombin, prolonging the blood-clotting time, whereas a conjugate of amino methyl styrene (AMS) and argatroban through an amide bond was a less potent inhibitor than argatroban. None of the copolymers could prolong blood clotting when assessed just after preparation of their aqueous solutions, but the antithrombogenic activity of the aqueous solutions increased after incubation for 7 days at 37 degrees C for the polymeric conjugates through an ester bond. Free argatroban was detected in the aqueous solutions of polymeric conjugates after incubation, suggesting that argatroban was released by hydrolysis of the ester bond during incubation.

Cell activation and thrombin generation in heparin bonded cardiopulmonary bypass circuits using a novel in vitro model

OBJECTIVE

It is generally agreed that when the blood contact surfaces of a cardiopulmonary bypass circuit are treated with a layer of heparin molecules the activation of the humoral pathways is attenuated. However, there is still debate as to whether heparin-bonded circuits reduce thrombin generation. This study aims to examine the effects of immobilized heparin on cell activation and thrombin generation in a novel, well controlled model of cardiopulmonary bypass.

METHODS

The model used consisted of a heparin-bonded and a non-bonded cardiopulmonary bypass circuit perfused in tandem with the same unit of fresh heparinized (3.3 U/ml) human blood for a period of 6 h. Samples were taken for analysis from the bag just prior to perfusion and at 30, 60, 120 and 360 min of perfusion. Whole blood was used to analyse platelet and white blood cell count, haematocrit and activated coagulation time. Plasma samples were prepared for batch analysis of the cell activation markers p-selectin, elastase and interleukin-8, and the thrombin generation markers thrombin-antithrombin and prothrombin fragment F1 + 2. A sample of tubing was taken from each circuit at the end of the perfusion and prepared for visualization by scanning electron microscopy.

RESULTS

Platelet counts were significantly reduced in the non-bonded circuits compared with the heparin-bonded circuits at 30 (22 versus 200 x 10(9)/L P < 0.01), 60 (26 versus 193 x 10(9)/L P < 0.01) and 120 min (28 versus 193 x 10(9)/L P < 0.01) as were white blood cell counts at 30(1.5 versus 2.7 x 10(9)/L P < 0.01), 60 (0.9 versus 2.4 x 10(9)/L P < 0.01), 120 (0.9 versus 1.8 x 10(9)/L P < 0.01) and 360 min (0.4 versus 0.9 x 10(9)/L P < 0.05). The concentration of p-selectin was found to be significantly higher in the non-bonded circuits than in the heparin-bonded circuits at 30 (37 versus 29 ng/ml P < 0.01), 60 (37 versus 28 ng/ml P < 0.01). 120 (42 versus 27 ng/ml P < 0.01) and at 360 min (72 versus 46 ng/ml P < 0.01). Elastase was elevated in the non-bonded circuits at 30 (570 versus 145 micrograms/l P < 0.01), 60 (646 versus 278 micrograms/l P < 0.01) and 120 min (613 versus 403 micrograms/l P < 0.05) and interleukin-8 at 120 (705 versus 520 pg/ml P < 0.05) and 360 min (11326 versus 9910 pg/ml P < 0.05). A similar picture was found for the thrombin generation markers. Thrombin-antithrombin complexes were raised in the non-bonded circuits compared with heparin-bonded circuits at 60 (24 versus 13 micrograms/l P < 0.05) and 120 min (46 versus 17 micrograms/l P < 0.05) as was prothrombin fragment F1 + 2 at 30 (1.1 versus 0.7 nmol/l P < 0.01), 60 (1.3 versus 0.7 nmol/l P < 0.01), 120 (1.8 versus 0.9 nmol/l P < 0.01) and 360 min (15.0 versus 13.6 nmol/l P < 0.05). Scanning electron microscopy revealed a greater amount of adherent material on the non-bonded surface relative to the heparin-bonded surface.

CONCLUSIONS

In a cardiopulmonary bypass circuit perfused with human blood the activation of platelets and white blood cells has been seen to be significantly reduced in the presence of a heparin-bonded surface. Thrombin generation due to contact activation of the intrinsic coagulation pathway is also reduced.

Biocompatibility of heparin-coated circuits in pediatric cardiopulmonary bypass

In this study, we evaluated the biocompatibility of heparin-coated circuits in pediatric cardiopulmonary bypass (CPB). Eight patients were divided into 2 groups: the control group (Group C) and heparin-coated group (Group H). In Group H, CPB circuits, including the arterial pump, oxygenator, and cannulas were heparin-coated. Before, during, and after CPB, blood samples were obtained to assess the platelet counts (Plat), alpha 2-plasmin plasminogen inhibitor complex (PIC), thrombin-antithrombin III complex (TAT), C3 activation products (C3a), interleukin (IL)-6, IL-8, and polymorphonuclear neutrophil leukocyte (PMN) elastase. There was no significant difference in Plat, PIC, or TAT between groups. Group H showed significantly low levels of C3a (during and after CPB), PMN elastase (during CPB), and IL-6 (after CPB). These data demonstrated that in pediatric CPB, heparin-coated CPB circuits reduced the activation of complements and the production of PMN elastase and IL-6, suggesting the superior biocompatibility of the heparin-coated circuits.

Evaluation of an extracorporeal membrane oxygenation system using a nonporous membrane oxygenator and a new method for heparin coating

A new heparin binding method was applied to a miniature extracorporeal membrane oxygenation (ECMO) system with a nonporous membrane oxygenator (the priming volume, 45 mL; the membrane surface area, 0.4 m2; maximal flow rate, 2 L/min) that is resistant to plasma leakage. The authors evaluated the stability of the immobilized heparin in vitro and the feasibility of this system in animals. Samples of hollow fibers and tubing were rinsed at 40 degrees C for 4 days in normal saline, Ringer's lactate, and 1 mol/L NaCl solution. Heparin activities on hollow fibers after rinsing were 99 +/- 2.3% (mean +/- SD), 96 +/- 3.9%, and 93 +/- 2.0% of the control in each solution, while those of the tubing were 87 +/- 4.1%, 86 +/- 3.1%, and 76 +/- 8.6%, respectively. Veno-arterial ECMO using this heparin-coated system was performed on five beagles (8 to 12 kg) for 10 hours. Neither major thrombus formation nor plasma leakage was detected during the procedure in spite of a low flow rate (300 mL/min) and a reduced activated clotting time (mean, 128 seconds). Platelets decreased to 52% of the control (P < .01) at 1 hour, but no progressive decrease was seen thereafter. Antithrombin-III decreased (P < .01) and thrombin/antithrombin III complex increased (P < .05 at 4 hours and P < .01 at 6, 8, and 10 hours) during bypass, but the changes of fibrinogen and fibrinopeptide A were not significant. Fibrinogen/fibrin degeneration products, fibrinopeptide B beta 15-42, and plasma-free hemoglobin levels did not rise significantly. O2 transfer of the oxygenators at a flow rate of 300 mL/min were 12.3 +/- 0.4 mL/min at 30 minutes, 14.3 +/- 1.2 mL/min at 5 hours, and 14.7 +/- 1.7 mL/min at 10 hours (no statistical difference). Histological examination of the brains and the kidneys showed no evidence of thromboembolic sequela in any of the animals. These results suggest that this new system is a promising device for long-term ECMO in which the amount of systemic heparinization can be reduced with the minimal possibility of plasma leakage.

Immobilized heparin inhibits the increase in leukocyte surface expression of adhesion molecules

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 granulocytes and monocytes exposed to unmodified polyvinyl chloride tubes increased significantly compared with unmanipulated 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 CD45 correlated with the degree of complement activation in plasma (rho = 0.6, p = 0.003). The expression of CD14 (endotoxin receptor) and CD16 (Fc gamma 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 = -0.275, 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.

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.

Release of lipopolysaccharide toxicity-modulating proteins in patients undergoing cardiopulmonary bypass using noncoated and heparin-coated extracorporeal circuits. A clinical pilot study

STUDY OBJECTIVE

Cardiopulmonary bypass (CPB) induces a generalized inflammatory response, including activation of leukocytes, contributing to postoperative morbidity. The inflammatory pathways leading to this systemic inflammatory response syndrome are considered identical to those involved in septic shock. Therefore, we studied the release of bactericidal/permeability-increasing protein (BPI), lipopolysaccharide binding protein (LBP), and soluble CD14 (sCD14)-all proteins that modulate the effects of lipopolysaccharide (LPS)-in patients undergoing CPB. In addition, the effect of heparin coating of the extracorporeal bypass circuit on the release of these parameters was assessed.

DESIGN

Prospective, randomized clinical pilot study.

SETTING

Cardiothoracic Surgery Department in a university hospital.

PATIENTS

Fourteen patients undergoing elective coronary artery bypass grafting were included. Seven patients underwent CPB using a standard, noncoated extracorporeal circuit, and seven patients had CPB using a heparin-coated extracorporeal circuit (Duraflo II).

INTERVENTIONS

Blood samples were taken after induction of anesthesia, just before aortic crossclamping, and 0, 0.5, 1.5, 3, 6, 12, and 24 h after declamping.

MEASUREMENTS AND RESULTS

CPB with a noncoated extracorporeal circuit induced a sharp increase in neutrophil-derived BPI, manifest directly after release of the aortic crossclamp, which was significantly attenuated using a heparin-coated system. Also, CPB induced a gradual increase of the acute-phase reactant LBP, which was identical in the noncoated and heparin-coated groups. Systemic release of sCD14 after crossclamp release was significantly higher in the noncoated group compared with the heparin-coated group, but did not rise above baseline levels.

CONCLUSIONS

These data confirm that CPB-induced leukocyte activation is attenuated using a heparin-treated extracorporeal circuit and point to the possible role of LPS toxicity-modulating proteins in the systemic inflammatory response after bypass surgery.

Effects of heparin coating on the expression of CD11b, CD11c and CD62L by leucocytes in extracorporeal circulation in vitro

Leucocyte adhesion molecules are involved in the leucocyte-endothelial interaction and in the activation of coagulation and binding of complement and endotoxin. Thus, they are important in inflammation, systemic acute phase reaction, ischaemia reperfusion injury and resistance against infections. The expression of the adhesion molecules CD11b, CD11c and CD62L on leucocytes and changes in plasma products of neutrophil activation (myeloperoxidase, lactoferrin) and complement activation (C3bc, SC5b-9 (TCC)) were examined in an extracorporeal circulation (ECC) model and the effects of Carmeda bioactive surface (CBAS) heparin coating (n = 7) of the circuits were compared to uncoated control circuits (n = 5). In this model, new 'unactivated' cells mobilized from the bone marrow could not interfere with descriptive measures of cell activation as seen in in vivo studies. In the control group, CD11b and CD11c were upregulated on monocytes and granulocytes during ECC, whereas CD62L was downregulated. Heparin coating reduced the increase in CD11b and CD11c on granulocytes (p < 0.02 at 2 h), but the delayed increase in CD11c on monocytes and the delayed downregulation of CD62L on granulocytes and monocytes did not reach statistical significance. Further, heparin coating also reduced the initial decrease in the absolute cell counts of monocytes and granulocytes (p = 0.01 at 2 h), reflecting reduced adhesion to the oxygenator/tubing. The increases in plasma myeloperoxidase, lactoferrin, C3bc and TCC were lower in the heparin-coated group compared to the control group. The increases in plasma myeloperoxidase and lactoferrin correlated significantly to the increase in CD11b (r = 0.71, p = 0.02 and r = 0.64, p = 0.05, respectively) and CD11c (r = 0.72, p = 0.008 and r = 0.72, p = 0.008, respectively) on granulocytes, suggesting interacting regulatory pathways in the process of neutrophil adhesion, activation and degranulation. Thus, in this in vitro ECC model, heparin coating of oxygenator/tubing sets reduced leucocyte activation and leucocyte adhesion-related phenomena.

Duraflo II coating of cardiopulmonary bypass circuits reduces complement activation, but does not affect the release of granulocyte enzymes : a European multicentre study

OBJECTIVE

This study was carried out to: (a) compare complement and granulocyte activation during cardiac operations in patients operated with cardiopulmonary bypass coated with heparin by the Duraflo II method, with activation in patients operated with uncoated circuits; and (b) relate complement, and granulocyte activation to selected adverse effects.

METHODS

In a multicentre study among Rikshospitalet, Ullevaal Hospital in Norway and Uppsala University Hospital in Sweden, plasma concentrations of the complement activation products C4b/iC4b/C4c (C4bc), C3b/iC3b/C3c (C3bc), the terminal SC5b-9 complement complex (TCC), and the granulocyte proteins myeloperoxidase and lactoferrin were assessed in two groups of patients undergoing aortocoronary bypass. Seventy-six patients underwent surgery operated with circuits coated by the Duraflo II heparin coating and 75 uncoated circuits. The same amount of systemic heparin was administered to all patients.

RESULTS

In both groups a significant increase in C4bc was first seen by the end of operation, from 86.7 +/- 12.5 to 273.0 +/- 277.4 nM in controls and from 86.9 +/- 18.5 to 320.2 +/- 190.5 nM in the control group, confirming previous documentation that the classical pathway is not activated during CPB, but as a consequence of protamin administration. The formation of C4bc did not differ significantly between the two groups. In the uncoated group the C3bc concentration increased from 124.0 +/- 15.3 to a maximum of 1176.1 +/- 64.7 nM (P < 0.01) and in the coated group it increased from 129.8 +/- 16.1 to a maximum of 1019.4 +/- 54.9 nM (P < 0.01) during CPB. Summary values but not peak values differed significantly between the groups. In the uncoated group the TCC concentration increased from 0.52 +/- 0.03 to a maximum value of 8.09 +/- 0.57 AU/ml (P < 0.01) while in the coated group the TCC concentration increased from a baseline of 0.53 +/- 0.03 to a peak value of 5.2 +/- 0.24 AU/ml (P <0.01). The difference between the peak values was statistically significant (P = 0.00002). In both groups a significant increase in myeloperoxidase and lactoferrin release was observed by the end of operation. There was no difference in myeloperoxidase or lactoferrin release between the two groups. TCC levels were compared to the occurrence of perioperative infarction, development of lung or renal failure, postoperative bleeding, time on ventilator and days in hospital. Three patients developed perioperative infarction; the peak levels of TCC were significantly higher in these patients than in the 148 patients that did not develop infarction. The reduction in TCC formation in the heparin-coated group was not associated with differences in any of the other clinical parameters. Few adverse effects occurred in the study. The peak values of C3bc were higher in the patients needing inotropic support that in those who did not, the relevance of this finding remains uncertain.

CONCLUSION

It is concluded that the Duraflo II heparin coating reduces complement activation, particularly TCC formation, during CPB, but not the release of specific neutrophil granule enzymes. No certain correlation was established between complement and granulocyte activation and clinical outcome.

The influence of a heparin-coated oxygenator during cardiopulmonary bypass on postoperative lung oxygenation capacity in pediatric patients with congenital heart anomalies

BACKGROUND

Cardiopulmonary bypass (CPB) causes an inflammatory response and remarkably depresses the oxygenation capacity of the lung in pediatric patients with pulmonary hypertension. Although a heparin-coated circuit is more biocompatible than an uncoated circuit, the beneficial effect of a heparin-coated circuit on the postoperative lung function in the pediatric patients remains unknown.

METHODS

Sixty patients younger than 3-years-old undergoing heart operations for ventricular septal defect were divided into three groups: group I = children (n = 11) without pulmonary hypertension who underwent CPB with an uncoated oxygenator; group II = children (n = 32) with pulmonary hypertension who underwent CPB with an uncoated oxygenator; and group III = children (n = 17) with pulmonary hypertension who underwent CPB with a heparin-coated oxygenator. A respiratory index (RI) was used to assess the oxygenation capacity of the lung.

RESULTS

RI in group II was significantly higher than in group I and intubation time in group II was significantly longer than in group I. There was a positive correlation between preoperative pulmonary-systemic blood pressure ratio and RI at 3 hours post-CPB. Three and six hours post-CPB, RI in group III was significantly lower than in group II, but there was no significant difference in RI between both groups at 12 hours post-CPB.

CONCLUSIONS

Pulmonary hypertensive pediatric patients were vulnerable to postperfusion lung injury. Beneficial effects of a heparin-coated oxygenator in a CPB circuit was limited to the early hours post-CPB and the postoperative clinical course was not modified by the heparin-coating of a membrane oxygenator.

Cytokine generation in rabbits during extracorporeal lung assist with a mini hollow fiber lung

To examine host responses to extracorporeal lung assist (ECLA) in small animals, we developed a mini hollow fiber lung of nonmicroporous polyolefin and an extracorporeal bypass circuit with a priming volume of 25 ml. This circuit allowed ECLA of up to 72 h without blood transfusion in 20 rabbits. The ECLA procedure induced the appearance of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) receptor antagonist (IL-1Ra) in plasma, but not IL-1 beta. However, these changes were observed only at the initial stage of ECLA, and the levels returned to pre-ECLA levels within 24 h. Although leukocytes adhering to the hollow fibers were immunohisto-chemically positive for IL-1 beta and IL-Ra, the plasma levels of these cytokines in response to ECLA were not different from those observed in rabbits given anesthesia and subjected to minor surgery but without ECLA. Thus, ECLA itself is a minor factor in the production of these cytokines.

Neutrophil activation during cardiopulmonary bypass in paediatric and adult patients

It has been reported that the 'systemic inflammatory' response occurring during cardiopulmonary bypass (CPB) may be responsible for postoperative complications. This inflammatory response is triggered by the platelet coagulation system, complement activation, resulting in neutrophil activation and degranulation. The aim of this study was to quantify the specific markers of neutrophil activation in the adult and paediatric patient during CPB. We report that neutrophil myeloperoxidase (MPO) and human neutrophil elastase (HNE) are significantly increased in both the paediatric and adult patients. This study utilized enzymatic assays that quantified the enzymatic activity in the blood circulation rather than measurement of the enzyme protein complex. Increased concentrations of MPO were, in part, related to the blood prime with the paediatric patients and the HNE concentrations were related to time on CPB in both the paediatric and adult patient. This study demonstrated that there are significantly elevated neutrophil enzyme activities in the CPB patient and underscores the pivotal role of the neutrophil in the pathophysiology of CPB.

Surface-bound heparin fails to reduce thrombin formation during clinical cardiopulmonary bypass

The hypothesis that heparin-coated perfusion circuits reduce thrombin formation and activity; fibrinolysis; and platelet, complement, and neutrophil activation was tested in 20 consecutive, randomized adults who had cardiopulmonary bypass. Twenty identical perfusion systems were used; in 10, all blood-contacting surfaces were coated with partially degraded heparin (Carmeda process; Medtronic Cardiopulmonary, Anaheim, Calif.). All patients received a 300 U/kg dose of heparin. Activated clotting times were maintained longer than 400 seconds. Cardiopulmonary bypass lasted 36 to 244 minutes. Blood samples for platelet count, platelet response to adenosine diphosphate, plasma beta-thromboglobulin, inactivated complement 3b, neutrophil elastase, fibrinopeptide A, prothrombin fragment F1.2, thrombin-antithrombin complex, tissue plasminogen activator, plasminogen activator inhibitor-1, plasmin alpha 2-antiplasmin complex, and D-dimer were obtained at these times: after heparin was given, 5 and 30 minutes after cardiopulmonary bypass was started, within 5 minutes after bypass was stopped, and 15 minutes after protamine was given. After cardiopulmonary bypass, tubing segments were analyzed for surface-adsorbed anti-thrombin, fibrinogen, factor XII, and von Willebrand factor by radioimmunoassay. Heparin-coated circuits significantly (p < 0.001) reduced platelet adhesion and maintained platelet sensitivity to adenosine diphosphate (p = 0.015), but did not reduce release of beta-thromboglobulin. There were no significant differences between groups at any time for fibrinopeptide A, prothrombin fragment F1.2, or thrombin-antithrombin complex or in the markers for fibrinolysis: D-dimer, tissue plasminogen activator, plasminogen activator inhibitor-1, and alpha 2-antiplasmin complex. In both groups, concentrations of prothrombin fragment F1.2 and thrombin-antithrombin complex increased progressively and significantly during cardiopulmonary bypass and after protamine was given. Concentrations of D-dimer, alpha 2-antiplasmin complex, and plasminogen activator inhibitor-1 also increased significantly during bypass in both groups. Fibrinopeptide A levels did not increase during bypass but in both groups increased significantly after protamine was given. No significant differences were observed between groups for levels of inactivated complement 3b or neutrophil elastase. Radioimmunoassay showed a significant increase in surface-adsorbed antithrombin on coated circuits but no significant differences between groups for other proteins. We conclude that heparin-coated circuits used with standard doses of systemic heparin reduce platelet adhesion and improve platelet function but do not produce a meaningful anticoagulant effect during clinical cardiopulmonary bypass. The data do not support the practice of reducing systemic heparin doses during cardiac operations with heparin-coated extracorporeal perfusion circuitry.

Eosinophil granule proteins in cardiopulmonary bypass with and without heparin coating

Extracorporeal circulation with exposure of blood to foreign surfaces causes activation of different defense systems, eg, white cells. Several potent mediators are released into plasma, capable of causing harmful effects to different organs, contributing to postoperative morbidity after operations using cardiopulmonary bypass. The eosinophil granulocyte has not previously been investigated in this respect. We studied two of its activation products, eosinophil cationic protein and eosinophil protein X in coronary bypass patients. In 17 control patients, plasma levels of eosinophil cationic protein and eosinophil protein X increased considerably during cardiopulmonary bypass. In 19 patients with heparin-coated cardiopulmonary bypass equipment the levels were significantly reduced, indicating improved biocompatibility of the cardiopulmonary bypass circuit. The heparin-coated surface causes less activation of eosinophils; also released eosinophil cationic protein is bound to the heparinized surface.

Thrombin generation during cardiopulmonary bypass using heparin-coated or standard circuits

For quantitative comparison of thrombin generation during cardiopulmonary bypass (CPB) with heparin-coated vs conventional CPB circuits, thrombin-antithrombin III complex (TAT) and prothrombin fragment 1 + 2 (F1 + 2) were analyzed in 20 patients undergoing combined heart valve surgery and coronary artery bypass grafting (CABG), in ten cases with heparin-coated circuits (COMB-HC) and in ten with standard circuits (COMB-C). Extensive thrombin generation was found in both groups, with maximal TAT and F1 + 2 levels at the end of CPB. Of 15 operations with only CABG, seven were performed with heparin-coated circuits and heparin dose 40% of normal (CABG-HC), and eight with standard circuits and normal heparin doses (CABG-C). TAT was maximal at the end of CPB and F1 + 2 peaked 3 hours after protamine injection. At the end of CPB both levels were significantly higher in the CABG-HC than in the CABG-C group, though thrombin generation was less than in the COMB groups. The abundant thrombin generation during CPB thus was much more pronounced during complex operations. Use of heparin-coated circuits did not reduce thrombin generation, which was increased by 60% reduction of the systemic heparin dose. The clinical implications are still unknown, as no complications were observed.

Reduced complement and granulocyte activation with heparin-coated cardiopulmonary bypass

Plasma concentrations of the complement activation products C3b, iC3b, and C3c; the terminal C5b-9 complement complex; and the granulocyte proteins calprotectin, myeloperoxidase, and lactoferrin were assessed in two groups of patients undergoing aortocoronary bypass procedures. In 10 patients operated on, the bypass circuits were coated by the Carmeda Bio-Active Surface and systemic heparinization was reduced to 1.5 mg/kg; in another 10, the systems were uncoated and the dosage of systemic heparinization was 4 mg/kg. In both groups, significant complement activation was observed after the onset of cardiopulmonary bypass, but the maximum levels of C3b, iC3b, and C3c and the terminal C5b-9 complement complex were significantly lower in the heparin-coated group. In both groups, a significant increase in calprotectin, myeloperoxidase, and lactoferrin release was observed by the end of operation. The maximum myeloperoxidase levels were significantly lower in the heparin-coated group than those in the uncoated group (p = 0.03). There was a correlation of borderline significance between the formation of terminal C5b-9 complement complex and lactoferrin release, as well as between the formation of terminal C5b-9 complement complex and myeloperoxidase release (p = 0.05). The postoperative blood loss did not differ significantly between the two groups. We conclude that coating by end point-attached and functionally active heparin allows a significant reduction in the amount of systemic heparinization, and significantly reduces complement and granulocyte activation.

Heparin-coated cardiopulmonary bypass circuits

The indications for heparin-coated extracorporeal circuits cannot be defined or limited at present. Clinical investigation remains at an early stage of development. In situations where the risk of systemic anticoagulation is high, this technology would seem to hold great promise. Examples include extracorporeal lung assist and resuscitation from accidental hypothermia. Some have also suggested the use of heparin-coated circuits for percutaneous bypass in cardiopulmonary resuscitation. A significant advantage might also accrue in noncardiac surgical procedures requiring cardiopulmonary bypass, such as complex cerebral aneurysm or arteriovenous malformation resections, resections of the tracheal carina, or bilateral lung transplantations. Its role in routine cardiac surgical procedures remains uncertain, but the work of von Segesser et al suggests a need for continued investigation in that setting using reduced levels of systemic anticoagulation. That endeavor will be greatly assisted by the recent development of heparin-coated cardiotomy reservoirs. Although heparin-coated circuits have been safely used for extracorporeal lung assist with little or no systemic anticoagulation, prospective studies are clearly needed to determine if this approach is advantageous, and it would seem appropriate to develop heparin coating for silicone-based membrane oxygenators.

Biomaterials in cardiopulmonary bypass

The improved utilization of biomaterials in cardiopulmonary bypass is dependent on polymer science and technology, procedures for blood compatibility assessment, optimization of biomaterial/antithrombotic agent combinations and the interpretation of clinical data.

Inhibition of neutrophil adhesion during cardiopulmonary bypass

Blood contact with synthetic surfaces during cardiopulmonary bypass (CPB) causes a diffuse inflammatory reaction that includes neutrophil activation. The purpose of this study was to determine if inhibition of neutrophil adhesion with a new antiinflammatory agent NPC 15669 (N-(9H-(2,7-dimethylfluorenyl-9-methoxy)-carbonyl)-L-leucine) could reduce pulmonary injury in a porcine model of CPB. NPC 15669 blocks adherence of activated neutrophils by inhibiting upregulation of the Mac-1 (CD11b/CD18) adhesion molecule. Sixteen piglets underwent 2 hours of hypothermic CPB followed by 2 hours of observation; 8 received NPC 15669 (10 mg/kg intravenous bolus followed by 6 mg.kg-1.h-1 intravenous infusion) and 8 received equal volumes of vehicle. After 90 minutes of CPB, expression of neutrophil adhesion molecule subunit CD18 increased 118% in control piglets but only 36% in piglets treated with NPC 15669 (p < 0.01). Although neutropenia developed in all animals during CPB, lung tissue myeloperoxidase content was significantly lower in treated than in control animals 2 hours after CPB (94.9 +/- 10.4 versus 46.9 +/- 5.5 mumol.10 mg-1.min-1; p < 0.002). Free radical-mediated lipid peroxidation (quantitated by spectrophotometric assay of plasma conjugated dienes) was significantly reduced by treatment with NPC 15669 during and after CPB. Pulmonary function was better in NPC 15669-treated animals: 2 hours after CPB, pulmonary vascular resistance increased 477% in control piglets but only 140% in piglets receiving NPC 15669 (p < 0.03); arterial oxygen tension was significantly greater in piglets receiving NPC 15669 (428 +/- 33 mm Hg) than in controls (141 +/- 46; p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical cardiopulmonary bypass without systemic anticoagulation

Heparin-coated perfusion systems have been used to perform cardiopulmonary bypass with decreased systemic heparin dosages. We report the case of a 60-year-old man with end-stage liver disease and severe aortic stenosis who underwent an aortic valve replacement without systemic anticoagulation, employing a heparin-coated perfusion system. In patients with a contraindication to systemic anticoagulation, cardiopulmonary bypass with a heparin-coated system without systemic anticoagulation may be a viable alternative.

Femoral veno-arterial extracorporeal life support with minimal or no heparin

Recent technological advances in cardiopulmonary bypass circuits achieving surface bonding with heparin have permitted prolonged extracorporeal life support (ECLS) in experimental studies without the use of systemic anticoagulation. Excessive bleeding and the need for massive transfusions after extended ECLS with systemic heparinization have often led to the development of sepsis and multisystem organ failure. The Carmeda bioactive surface circuit, along with a Bio-Medicus centrifugal pump (Bio-Pump) and the femoral veno-arterial route, were used successfully in 3 patients requiring ECLS between April 1992 and December 1992. In 2 patients the need for ECLS was acute allograft dysfunction after orthotopic cardiac transplantation with no evidence of cellular rejection. Both patients were receiving multiple inotropes and intraaortic balloon counter-pulsation; their condition continued to deteriorate rapidly before the initiation of ECLS. The third patient failed to be weaned from cardiopulmonary bypass after myocardial revascularization for ischemic cardiomyopathy. Time on ECLS ranged from 57 to 128 hours. No systemic anticoagulation was used. One patient received no heparin, and the other 2 patients received intermittent heparin infusion to maintain an average activated clotting time of 195 and 214 seconds. Multisystem organ dysfunction present before initiation of ECLS was rapidly reversed, and all patients were weaned successfully without any immediate major complications. The ability to conduct prolonged ECLS without systemic anticoagulation and without repeat sternotomy opens new avenues for the use of this procedure in profound heart failure.

Complement activation and cytokine production as consequences of immunological bioincompatibility of extracorporeal circuits

The use of devices which result in exposure of blood to artificial surface has gained increasing importance in routine medical and surgical practice. In the field of biocompatibility, attention has long been directed at the mechanisms of thrombus formation of surfaces. In recent years however, a special interest has emerged for the study of the immunological consequences of blood-artificial surface interactions, thus broadening the concept of hemocompatibility. The contact of blood with artificial devices results in the activation of a number of humoral and cellular processes involved in natural and in specific immunological recognition of foreign surfaces by the host, and in the secondary occurrence of acute and chronic adverse reactions in patients undergoing extracorporeal circulation. The purpose of this review is to discuss the mechanisms involved in immunological bioincompatibility of extracorporeal circuits, with particular emphasis on the molecular basis of the activation of the complement system, the role of endotoxins, and the induction of cytokine production by activated monocytes.

Time for new concepts about measurement of complement activation by cardiopulmonary bypass?

Fifty-one patients admitted for routine coronary bypass operations were randomized to cardiopulmonary bypass with a membrane oxygenator (Capiox) or a bubbler (Polystan or William Harvey). Complement activation was measured using enzyme immunoassays for concentrations of C3 activation products and the terminal complement complex. From 5.8 to 8.1 arbitrary units (AU)/mL (medians), the plasma concentrations of C3 activation products increased by 119.9 AU/mL (Capiox), 124.6 AU/mL (Polystan), and 79.5 AU/mL (William Harvey) to a peak at closure of the sternum (not significant when related to baseline concentrations). The increase in C3 activation products and baseline C3 activation were linearly correlated (R2 = 0.30; p less than 0.0001). From 5.5 to 6.1 AU/mL, the plasma terminal complement complex concentrations increased by 45.2 AU/mL (Capiox), 15.4 AU/mL (Polystan), and 17.4 AU/mL (William Harvey) to a peak before termination of cardiopulmonary bypass. Maximal terminal (C5-C9) activation was significantly higher in the membrane oxygenator group (p less than 0.0001) and showed no relationship to C3 activation. Measurement of C3 activation only gives no information about C5-C9 activation. At present, terminal complement complex quantitation is probably the best index of C5-C9 activation during cardiopulmonary bypass.

Heparin-coated cardiopulmonary bypass circuits and 25% reduction of heparin dose in coronary artery surgery--a clinical study

Cardiopulmonary bypass with systemic heparinization causes trauma to blood cells and coagulation defects. Artificial surfaces could be coated by end-linkage binding of heparin (Carmeda Bioactive Surface, CBAS). Use of such surfaces during cardiopulmonary bypass in animals resulted in less postoperative blood loss and better preservation of blood cells. In this study heparin-coated circuits were employed during coronary artery grafting in 7 patients (Group HC). Concomitantly, the heparin dose was reduced by 25% and an activated clotting time (ACT) of 300 sec was accepted. Additional 7 patients were operated with standard circuits (Group C), requiring ACT above 400 sec with normal doses of heparin. There were no thromboembolic complications in Group HC. The postoperative bleeding was generally low and without significant intergroup differences. Coagulation parameters displayed significantly lower ACT and anti-Factor Xa during bypass in Group HC. A tendency towards less blood cell trauma was observed with heparin-coated circuits. The protamine dose could be reduced by 50%, which significantly reduced the protamine/heparin quotient. This study indicates that routine cardiopulmonary bypass could be performed safely with heparin-coated circuits and reduced intravenous doses of heparin and protamine. It is suggested that the use of heparin-coated circuits may lead to less blood cell trauma.