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

Postoperative morbidity after cardiopulmonary bypass most commonly manifests as bleeding diatheses or pulmonary dysfunction. The pathophysiology has been attributed to the activation of cellular and humoral components of blood after contact with an artificial surface. Development of a surface that would be nonthrombogenic and also would constitute a less potent inflammatory stimulus would therefore be beneficial. In the following experiments, we evaluated the heparin-bonded Carmeda Bioactive Surface (Medtronics Cardiopulmonary, Anaheim, Calif.) in an in vitro model of extracorporeal circulation at standard-dose heparin (5 U/ml), to examine the effects of the surface treatment on activation of blood elements, and at reduced-dose heparin (1 U/ml), to determine whether surface-bound heparin would serve as an effective anticoagulant. During the initial recirculation period, platelet counts in the Carmeda (n = 12) circuits were preserved at both doses of heparin and compared with control values (n = 12): At 5 U/ml, control 36% +/- 4% (mean +/- standard error of the mean) versus Carmeda 81% +/- 5%; at 1 U/ml, 43% +/- 3% versus 61% +/- 10%, expressed as a percent of baseline at 30 minutes, p < 0.05. Furthermore, plasma levels of platelet factor 4 and beta-thromboglobulin were significantly reduced in the Carmeda circuits throughout the experiment: At heparin 5 U/ml, 2500 +/- 340 ng/ml versus 604 +/- 191 ng/ml; at 1 U/ml, 2933 +/- 275 ng/ml versus 577 +/- 164 ng/ml of platelet factor 4 at 2 hours (p < 0.05). The pattern of beta-thromboglobulin release was similar, with effects more pronounced at the lower dose of heparin. Surface modification also reduced leukocyte depletion (p < 0.05) and release of elastase at both concentrations of heparin (5 U/ml, 0.72 +/- 0.29 ng/ml versus 0.33 +/- 0.23 ng/ml; 1 U/ml, 0.85 +/- 0.08 ng/ml versus 0.20 +/- 0.05 ng/ml, at 2 hours, p < 0.05). Moreover, as heparin concentration was reduced, Carmeda surface treatment significantly decreased generation of C3a des Arg (1 U/ml, 14,410 +/- 3558 ng/ml versus 3053 +/- 1039 ng/ml at 2 hours, p < 0.05). Although heparin bonding was originally intended to obviate the need for systemic heparinization, Carmeda treatment did not reduce fibrinopeptide A generation at the lower dose of heparin. In summary, Carmeda treatment failed to exhibit anticoagulant efficacy in this model; however, the data suggest that surface modification may have a role in ameliorating the typical inflammatory response initiated by blood contact with an artificial surface.

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.

Intracardiac thrombus: a risk of incomplete anticoagulation for cardiac operations.

Mitral valve replacement was performed urgently in a patient with hemorrhagic brain lesions. To decrease the risk of intracranial hemorrhage, cardiopulmonary bypass was performed using a heparin-coated perfusion system and a reduced dose of heparin. The detection of an acute intracardiac thrombus by transesophageal echocardiography during cardiopulmonary bypass exposed a potential hazard of techniques employing reduced systemic anticoagulation for cardiac operations.

Iloprost reduces procoagulant activity in the extracorporeal circuit.

Although activation of formed blood elements during cardiopulmonary bypass has been examined, its presumed procoagulant role has not been identified or quantified. We evaluated the effects of iloprost, an inhibitor of platelet and leukocyte function, on subclinical coagulation during simulated extracorporeal circulation. We determined that a heparin dose of 1 U/ml prevented clot formation in this model, but resulted in elevated plasma levels of fibrinopeptide A, the first cleavage product of fibrinogen. Human blood was recirculated with 1 U/ml heparin using a roller pump and pediatric reversed hollow fiber oxygenator (0.8 m2) for 2 hr at 37 degrees C. Iloprost (1 ng/ml, n = 5) reduced platelet adhesion, with platelet counts of 78 +/- 7% (mean +/- SEM) of baseline during 2 hr of simulated extracorporeal circulation, compared to 36 +/- 6% in control circuits (CONT: n = 6, P < 0.05). Plasma levels of platelet factor 4 and beta-thromboglobulin were also reduced by iloprost (486 +/- 116 ng/ml vs CONT, 2933 +/- 275 ng/ml, P < 0.05, and 938 +/- 274 ng/ml vs CONT, 5700 +/- 1109 ng/ml, P < 0.05, respectively). Circulating leukocyte counts were maintained in iloprost circuits (6.4 +/- 0.6 x 10(3)/mm3 vs CONT, 4.2 +/- 0.3 x 10(3)/mm3, P < 0.05), and neutrophil elastase levels rose to only 0.4 +/- 0.1 ng/ml in iloprost circuits, compared to 0.8 +/- 0.1 ng/ml in CONT (P < 0.05). Finally, iloprost treatment reduced fibrinopeptide A levels to 102 +/- 28 ng/ml (CONT, 793 +/- 337 ng/ml, P < 0.05) after 2 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of heparin bound surface modification (Carmeda Bioactive Surface) on human platelet alterations during simulated extracorporeal circulation.

To determine if treatment with covalently bound heparin (Carmeda Bioactive Surface (CBAS)) to the synthetic surface of the extracorporeal circuit (ECC) would alter the stereotypic pattern of adverse platelet alterations, 450 ml of heparinized blood (lU/ml) was recirculated at a flow rate of twice the circulating volume (L/min) for 2 hrs at 37 degrees C through either untreated (CONT,n=7) or treated (CBAS,n=7) circuits constructed of identical components including a pediatric (0.8m 2) reversed hollow fiber membrane oxygenator. In CONT circuits, platelet count maintained 88+1% (x+/-SEM) of its initial level in the circuit prime sample, dropped to 36+/-6% after 5 min, and returned to 56+/-2% following 2 hrs of ECC. In CBAS circuits, platelet count in the circuit prime sample demonstrated 90+/-4%, decreased to 68+/-10% after 5 min (p less than 0.05) and declined further to 45+/-5% after 2 hrs (NS). Although platelets from both groups retained reactivity to ADP after priming the circuit, only at 5 min of recirculation did CBAS circuits significantly preserve this responsiveness. In CONT circuits, baseline plasma levels of platelet factor 4 rose from 24+/-3 to 581+/-82 ng/ml in the primed circuit and continued to rise to 2933+/-276 ng/ml by 2 hrs of ECC. In contrast, CBAS circuits markedly reduced this release after 2 hrs (577+/-165 ng/ml). Furthermore by 2 hrs of ECC, plasma levels of thromboxane B 2 in the CBAS circuits were significantly reduced when compared to CONT circuits (3035+/-1529 vs 29916+/-16293 pg/ml, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of simulated extracorporeal circulation on human leukocyte elastase release, superoxide generation, and procoagulant activity.

Activated leukocytes are thought to contribute to respiratory dysfunction, alterations in microvascular permeability, disseminated intravascular coagulation, and thrombosis, all of which can complicate extracorporeal circulation. The purpose of this work was to determine the effects of extracorporeal circulation on leukocyte functions likely to mediate organ damage. White blood cell counts in the bubble circuits (n = 5) fell to 51% +/- 7% (mean +/- standard error of the mean; p less than 0.05) of initial levels within 2 hours of recirculation. In contrast, counts from both the spiral coil (n = 5) and hollow-fiber (n = 5) groups remained at 91% +/- 12% and 100%, respectively. Plasma levels of human neutrophil elastase rose from 0.28 +/- 0.06 micrograms/ml to 3.14 +/- 0.36 micrograms/ml (p less than 0.05) and 0.20 +/- 0.02 micrograms/ml to 1.61 +/- 0.35 micrograms/ml (p less than 0.05) in bubble and spiral coil circuits, respectively, but from only 0.20 +/- 0.03 micrograms/ml to 0.96 +/- 0.42 micrograms/ml in the hollow-fiber circuit despite 2 hours of recirculation. Consistently, in response to N-formyl-L-methionyl-L-leucyl-L-phenylalanine, a chemotactic peptide, cells from spiral coil and bubble circuits released and generated significantly less elastase and superoxide anion, respectively. In contrast, neutrophils from the hollow-fiber circuits demonstrated enhancement of N-formyl-L-methionyl-L-leucyl-L-phenylalanine-induced elastase release and superoxide generation. Finally, mixed leukocytes from all circuits expressed procoagulant activity reaching statistical significance in bubble circuits. In conclusion, extracorporeal circulation has pronounced effects on neutrophil elastase release, superoxide anion generation, and leukocyte procoagulant activity. Spiral coil and bubble oxygenators cause granule release and, subsequently, reduced sensitivity to soluble agonists. In contrast, hollow-fiber oxygenators "prime" cells, actually enhancing reactivity. Recirculation through all circuits induces leukocyte procoagulant activity that is likely to contribute to surface-induced thromboses and excessive bleeding.

Intraoperative management of patients with heparin-induced thrombocytopenia.

For 11 patients with confirmed heparin-induced thrombocytopenia, we used reversible platelet inhibition with iloprost, a stable prostacyclin analogue, to permit safe heparin administration for cardiac (n = 9) or vascular (n = 2) operations. In vitro, iloprost (0.01 mumol/L) prevented both heparin-induced platelet aggregation and 14C-serotonin release in all patients. Therefore, intraoperatively, a continuous infusion of iloprost was started before administration of heparin and was continued until 15 minutes after administration of protamine. For cardiac patients, after heparin administration, the whole blood platelet count did not change (171,000 +/- 29,000/microL versus 174,000 +/- 29,000/microL, mean +/- standard error of the mean); no spontaneous platelet aggregation was observed, and plasma levels of the alpha-granule constituents platelet factor 4 and beta-thromboglobulin increased from 38 +/- 14 and 140 +/- 18 ng/mL to 591 +/- 135 and 235 +/- 48 ng/mL, respectively. Fibrinopeptide A levels actually decreased from 287 +/- 150 to 27 +/- 6 ng/mL. Furthermore, adenosine diphosphate-induced platelet activation was preserved, postoperative bleeding times were unchanged, and no heparin-related deaths occurred. Similar results were obtained in both vascular patients. We conclude that temporary platelet inhibition with iloprost now permits safe heparin administration in all patients with heparin-induced thrombocytopenia who require a cardiac or vascular operation.

Temporary inhibition of platelet function with iloprost (ZK36374) preserves canine platelets during extracorporeal membrane oxygenation.

Contact between blood and artificial surfaces results in extensive quantitative and qualitative alterations in platelet function. We evaluated the efficacy of a brief infusion of iloprost (ZK36374), a stable analog of prostacyclin, in preventing these platelet changes during extracorporeal membrane oxygenation. Twelve nonsplenectomized male mongrel dogs (23 to 30 kg) were randomized to treatment (n = 6) and control (n = 6) groups. The treatment animals received an infusion of iloprost at a rate of 150 ng/kg/min with the infusion being terminated 30 minutes after the initiation of extracorporeal membrane oxygenation, despite the fact that all animals were maintained on extracorporeal membrane oxygenation for 3 hours. In the control group, platelet counts dropped to 54% +/- 8.9% (mean +/- standard error of the mean) of initial levels at 30 minutes of extracorporeal membrane oxygenation and gradually rose to 87.2% +/- 6.7% at 3 hours. In contrast, the platelet counts of the iloprost-treated dogs remained stable throughout extracorporeal membrane oxygenation at 98.3% +/- 4.2% of initial counts. Platelet reactivity toward adenosine diphosphate revealed a significant and permanent loss of platelet function in the control group (37.0% +/- 2.1% inhibition). In contrast, the iloprost group demonstrated significant inhibition of platelet reactivity (79.2% +/- 8.3%) during the iloprost infusion but a return to normal function (4.2% +/- 6.7% inhibition) after cessation of drug infusion which persisted throughout extracorporeal membrane oxygenation. Plasma levels of the platelet-specific protein thrombospondin rose progressively from 918 +/- 89 ng/ml to 1465 +/- 239 ng/ml (delta 548 +/- 179 ng/ml) at 30 minutes of extracorporeal membrane oxygenation, which indicates extensive release of platelet granule contents (p less than 0.05). In contrast, plasma thrombospondin levels in the iloprost group demonstrated no additional rise after cessation of the iloprost infusion. In conclusion, iloprost effectively preserves platelet number and function during extracorporeal circulation. The fact that its salutary effects outlast its presence in plasma suggests that prevention of initial platelet-synthetic surface interactions permits the appearance of reduced surface affinity for platelets and, thus, reduced synthetic surface thrombogenicity.