Biocompatibility of trillium biopassive surface–coated oxygenator versus uncoated oxygenator during cardiopulmonary bypass

ORIGINAL ARTICLES

Biocompatibility of Trillium Biopassive Surface–Coated Oxygenator Versus Uncoated Oxygenator During Cardiopulmonary Bypass Mark H. Ereth, MD, Gregory A. Nuttall, MD, Scott H. Clarke, MD, Joseph A. Dearani, MD, Bridget K. Fiechtner, BA, Cynthia R. Rishavy, Daniel A. Buda, CCP, Trudy A. Shaw, Thomas A. Orszulak, MD, and William C. Oliver, Jr, MD Objective: To determine if the Trillium Biopassive Surface (Medtronic Cardiopulmonary, Minneapolis, MN) coating added to the cardiopulmonary bypass oxygenator reduces inflammatory mediators, blood loss, and transfusion requirements. Design: Prospective, randomized, and blinded human trial. Setting: Tertiary care academic medical center. Participants: Thirty adult patients undergoing elective coronary artery bypass graft surgery. Interventions: Patients received visually identical coated or uncoated oxygenators. Measurements and Main Results: Hemoglobin, hematocrit, leukocyte count, platelet count, terminal complement complex, complement activation, myeloperoxidase, ␤-thromboglobulin, prothrombin fragment 1.2, plasmin-antiplasmin, heparin concentration, activated coagulation time, and fi-

brinogen concentration were measured. Blood loss and blood product usage were recorded. In both groups, there were significant inflammatory alterations with the initiation of cardiopulmonary bypass. In the postprotamine samples, the coated oxygenator group had small but significant increases in hemoglobin, hematocrit, and leukocyte count. There were no differences in inflammatory mediators, blood loss, or transfusion requirements between the coated and uncoated groups. Conclusion: This human trial of Trillium Biopassive Surface– coated oxygenators did not show clinical benefits or clinically important biochemical results. Copyright © 2001 by W.B. Saunders Company

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nary, Minneapolis, MN)– coated circuit represents a significant departure from previous heparin coating methods. The nature of the coating should lend itself to reduced protein adsorption that typically occurs immediately on initiation of CPB and is a principal step by which contact activation and the initiation of thrombosis and fibrinolysis occurs. The coating consists of 2 layers of different water-soluble synthetic polymers. The basal layer is a primer that adsorbs to CPB circuit surfaces. The second layer is bonded to the primer and is composed of sulfonate groups, polyethylene oxide (PEO) chains, and heparin. These groups are covalently incorporated into the coating and are likely nonleaching. The use of PEO chains capitalizes

XCESSIVE NONSURGICAL bleeding occurs in 5% to 20% of the 500,000 patients who undergo cardiopulmonary bypass (CPB) annually in the United States.1,2 This bleeding has been ascribed to inadequate hemostasis arising from thrombocytopenia, platelet dysfunction, deficiencies or inhibition of coagulation factors, and fibrinolysis.1-5 Possible causative factors include contact activation; plasminogen activation; and platelet reactions arising from exposure of blood to nonbiologic surfaces, shear forces, and hypothermia.6-9 These processes may directly affect hemostasis or through an illdefined systemic inflammatory response to CPB.10 Several approaches have been tried to reduce the inflammation associated with CPB, including hemodilution, moderate hypothermia, leukocyte filtration, and heparin or synthetic coating of the CPB surfaces.11 Heparin coating of an extracorporeal circuit for CPB is thought to improve the hemocompatibility of the circuit and to reduce the inflammatory response to CPB.12 Various modalities of heparin coating have been employed to reduce the inflammatory response and associated cascades initiated after blood contact with the extracorporeal circuit. To date, the success of these methods has been mixed. Some of the data suggest that a benefit of these heparin-coated circuits is the ability to reduce the actual dose of systemic heparin.13-16 The use of lower anticoagulation protocols (reduced heparin dosage) have shown impressive reductions in blood transfusion without increased thrombogenicity.15 Yet the clinical impact of heparin coating in the setting of CPB has not been uniformly embraced by the scientific and clinical communities. The Trillium Biopassive Surface (Medtronic Cardiopulmo-

KEY WORDS: cardiac surgery, transfusion, coatings, complement, platelet activation, biocompatibility

See Editorial by Alfred H. Stammers: Biocompatibility of Trillium Biopassive Surface-Coated Oxygenator During Cardiopulmonary Bypass (p 539)

From the Department of Anesthesiology, and the Division of Cardiovascular Surgery, Department of Surgery, Mayo Clinic and Mayo Foundation, Rochester, MN. Supported by Medtronic Cardiopulmonary and Mayo Foundation for Medical Education and Research. Address reprint requests to Mark H. Ereth, MD, Department of Anesthesiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905. Copyright © 2001 by W.B. Saunders Company 1053-0770/01/1505-0003$35.00/0 doi:10.1053/jcan.2001.26525

Journal of Cardiothoracic and Vascular Anesthesia, Vol 15, No 5 (October), 2001: pp 545-550

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on the idea of a hydrated dynamic surface to attempt to decrease protein adsorption and cell adhesion and reduce activation of the contact and cellular systems of blood. Factors thought to be responsible for decreased protein adsorption include PEO’s hydrophilicity, chain mobility, steric stabilization effects, and low interfacial free energy with water. Because of its strong hydrophilicity, the polymer is quickly hydrated, maximizing the interaction between itself and an aqueous environment. The rapid movement of hydrated PEO chains influences the surface characteristics and decreases the adsorption of proteins. A large number of sulfate and sulfonate groups have been incorporated into the Trillium Biopassive Surface coating, providing an anticoagulant effect.16 The localized negative charge of the sulfonate groups is believed to have an effect on the thromboresistance (similar to that of vascular endothelium) of materials by electrical repulsion of negatively charged blood components. In addition to sulfate and sulfonate groups, the Trillium Biopassive Surface coating includes covalently bound heparin, taking advantage of its natural anticoagulatory property. The combined effects of PEO chains (reducing protein absorption and cellular adhesion) and sulfate and sulfonate group additions (anticoagulant and thromboresistant properties) may synergistically reduce the humoral and cellular activation usually associated with CPB. It is possible that this unique coating would provide for a significant and clinically important limitation of the hematologic perturbations associated with CPB. The authors hypothesized that the addition of the Trillium Biopassive Surface coating to the CPB oxygenator would reduce inflammatory mediators, blood loss, and transfusion requirements. METHODS After receiving institutional review board approval and written informed consent, 30 adult patients scheduled for elective primary coronary artery bypass graft surgery were randomized, using a doubleblinded procedure, to a Trillium Biopassive Surface– coated Affinity oxygenator or a visually identical but uncoated Affinity oxygenator (Medtronic Cardiopulmonary, Minneapolis, MN). There was no alteration in the standard anesthetic or surgical management of these patients except that a total of 171 mL of blood was obtained for laboratory assay. After insertion of intravenous and radial arterial catheters and under standard monitoring conditions, anesthesia was induced with 5 to 20 ␮g/kg of fentanyl, 250 mg of thiopental, 2 to 4 mg of midazolam, and 0.05 to 0.15 mg/kg of pancuronium. Anesthesia was maintained with isoflurane, inspired concentration 0.25% to 1.0%; fentanyl, totaling 25 ␮g/kg; and supplemental pancuronium as required. During CPB, 1% isoflurane was added to the oxygenator gas. Patients did not receive any antifibrinolytic therapy and underwent full anticoagulation with heparin, 350 U/kg. Patients underwent mild hypothermic (34°C to 35.5°C) CPB at a flow of 2.0 to 2.4 L/min/m2. Target activated coagulation time (ACT) was ⬎450 seconds. Standard blood cardioplegia was administered in antegrade or retrograde fashion. Reversal of heparin anticoagulation was completed with protamine sulfate (1 mg/100 units of total heparin). The Hepcon/heparin concentration protamine titration assay (Medtronic Hemotec, Englewood, CO) was used to confirm adequate heparin antagonism after CPB. Blood samples were taken at the following intervals: before anticoagulation with heparin, before CPB, 10 and 30 minutes after initiation

of CPB, after aortic cross-clamp removal, 20 minutes after administration of protamine and adequate heparin reversal, and 3 hours after CPB. All samples were drawn and dispensed into glass tubes containing either ethylenediaminetetra-acetic acid (EDTA) or 3.8% citrate and immediately placed on ice for transport. Samples were centrifuged at 3500 rpm and 4°C for 15 minutes. Then the plasma was harvested on ice and stored at ⫺70°C for later assay. Variables recorded included age, sex, height, weight, body surface area, and duration of CPB and aortic cross-clamp. The following parameters were measured: hemoglobin, hematocrit, leukocyte count, platelet count, plasma terminal complement complex (SC5b-9), complement activation products (C3a), myeloperoxidase, ␤-thromboglobulin, prothrombin fragment 1.2 (F1.2), plasmin-antiplasmin, heparin concentration, kaolin-based ACT, platelet glass bead retention, and fibrinogen concentration. Chest tube drainage in the intensive care unit was recorded at 4, 12, and 24 hours. Perioperative allogeneic and autologous (cell salvage) blood product usage were recorded. Duration of endotracheal intubation, length of hospitalization, and perioperative morbidity were recorded. Criteria for the transfusion of red blood cells in this study included (1) hemoglobin ⬍8 g/dL in an otherwise healthy patient, (2) hemoglobin ⬍10 g/dL in a patient with ongoing myocardial ischemia, and (3) symptomatic anemia resulting in tachycardia and cardiac ischemia. The following specific methods were used during the study. Heparin Concentration and ACT Assays: The Hepcon instrument was prewarmed to 36.9°C, and the heparin dose response and kaolin-based ACT cartridges were allowed to equilibrate for 3 minutes. Blood (3 mL) was drawn into a 3-mL syringe, the air was evacuated, and a blunt-tip needle was placed on the syringe. The syringe was loaded into the device needle holder, any blood on the end of the syringe was blotted away, and the machine was activated. Glass Bead Retention Assay. Blood (7 mL) was drawn into a 20-mL heparinized syringe, the air was evacuated, and the syringe was carefully inverted 3 times to ensure agent mixing. A 1-mL portion was dispensed into a 4.5-mL EDTA tube labeled baseline and inverted 3 times. The syringe was placed onto the syringe pump and affixed to a 4-g column of glass beads (Sienco, Morrison, CO). The first 3 mL to pass through the glass bead column (at a rate of 6.75 mL/min) were discarded, and the fourth milliliter was collected into an EDTA tube, capped, and slowly inverted 3 times. The EDTA tubes were sent to the laboratory, where a platelet count was performed on the baseline and the fourth aliquot. Platelet function, as measured by platelet retention in the glass bead column, was determined by the percent of platelets retained within the column:17 Platelet count of baseline ⫺ platelet count of fourth aliquot Percent retention 共%兲 ⫽ Platelet count of baseline ⫻ 100

C3a Assay and SC5b-9 Assay. Complement system activity was measured using a C3a enzyme immunoassay and a SC5b-9 enzyme immunoassay (Quidel, San Diego, CA). Myeloperoxidase Assay. Neutrophil activation was measured using a myeloperoxidase sandwich enzyme-linked immunosorbent assay (ELISA) (Oxis International, Inc, Portland, OR). Plasmin-Antiplasmin Assay. Plasmin-antiplasmin concentration was measured using a sandwich ELISA (Behring Diagnostics, Inc, Westwood, MA). ␤-Thromboglobulin Assay. ␤-Thromboglobulin levels were determined in human plasma by using an enzyme immunoassay (Diagnostica Stago Products, Asnieres-sur-Seine, France). Prothrombin F1.2. Concentrations of prothrombin F1.2 were measured in human plasma by this ELISA (Organon Teknika Corpo-

TRILLIUM COATED VERSUS UNCOATED CPB OXYGENATOR

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Table 1. Demographic and Surgical Data Coated Oxygenator

Uncoated Oxygenator

Age (y) 64.7 ⫾ 10.2 65.2 ⫾ 12.4 n 14 16 Gender (%F/%M) 14%/86% 31%/69% Height (cm) 173 ⫾ 8 169 ⫾ 13 Weight (kg) 90 ⫾ 17 84 ⫾ 13 2.11 ⫾ 0.24 2.01 ⫾ 0.20 Body surface area (m2) Heparin dose (units) 42,100 ⫾ 11,600 35,000 ⫾ 10,000 Protamine dose (mg) 400 ⫾ 90 320 ⫾ 100 CPB duration (min) 71 ⫾ 33 77 ⫾ 43 Cross-clamp duration (min) 46 ⫾ 18 45 ⫾ 21

p Value

NS NS NS NS NS NS NS NS NS NS

NOTE. Values are mean ⫾ SD. Abbreviations: CPB, cardiopulmonary bypass; NS ⫽ no significant difference.

ration, Durham, NC). Before the plasma samples were stored at ⫺70°C, they were treated with a 100-␮L sample treatment reagent. For all of the above-listed immunoassays, plasma aliquots previously stored at ⫺70°C were thawed in a 37°C incubator, removed, and immediately assayed according to manufacturer methods. All data are reported as mean ⫾ SD. Blood loss and transfusion data are also reported as median, 25th percentile, and 75th percentile (interquartile ranges). Data were analyzed with repeated measures analysis of variance. This analysis was supplemented with 2-sample comparisons at each specific perioperative interval. A p value ⬍ 0.05 was considered statistically significant.

the duration of CPB or aortic cross-clamp between the 2 groups (Table 1). For each laboratory assay completed, data were analyzed to determine if the changes were due to CPB, to the oxygenator used, or both. The following assays changed significantly with initiation of CPB (pre-CPB to 10 minutes on CPB): hemoglobin, hematocrit, white blood cell count, platelet count, C3a, SC5b-9, myeloperoxidase, ␤-thromboglobulin, F1.2, plasmin-antiplasmin, heparin concentration, platelet glass bead retention, ACT, and fibrinogen (Figs 1-3). Overall, there were few differences between oxygenator groups. In the post-protamine samples, however, the coated oxygenator group had significantly higher hemoglobin, hematocrit, and white blood cell counts (Fig 2). The glass bead retention showed no differences between oxygenators except that the coated group showed an increase in platelet retention (preserved platelet function) after 10 minutes on CPB (Fig 2). The coated group had significantly reduced myeloperoxidase, plasmin-antiplasmin, and ␤-thromboglobulin after CPB. There was no difference in postoperative blood loss at 4 or 24 hours between the coated or uncoated groups. Increased blood loss was noted, however, in the coated oxygenator group for the 12-hour postoperative interval (Table 2). There was no difference in intraoperative or postoperative transfusion requirements between the coated and uncoated oxygenator groups (Table 3).

RESULTS

DISCUSSION

There were no differences in age, weight, gender distribution, body surface area, heparin and protamine usage, or

Use of the Trillium Biopassive Surface– coated oxygenator resulted in increased hemoglobin, hematocrit, and white blood

Fig 1. Inflammatory and hemostatic activation as measured by complement activation (C3a), terminal complement complex (C5b9), myeloperoxidase, ␤-thromboglobulin (␤-TG), plasmin antiplasmin (PAP), and prothrombin fragment 1.2 (PF1.2) before, during, and after cardiopulmonary bypass (CPB). All units are ␮M; *p < 0.05 coated versus uncoated by analysis of variance.

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Fig 2. Alterations in hemoglobin (HgB), hematocrit (Hct), platelet count, white blood cell count (WBC), platelet glass bead retention, and fibrinogen before, during, and after cardiopulmonary bypass (CPB); *p < 0.05 coated versus uncoated by analysis of variance.

cell counts after CPB. Increased platelet glass bead retention was shown on initiation of CPB in the Trillium Biopassive Surface– coated oxygenator group. Reduced inflammation (myeloperoxidase, plasmin-antiplasmin, and ␤-thromboglobulin) was also shown in the Trillium Biopassive Surface– coated oxygenator group during or after CPB. In all other parameters measured, including blood transfusion requirements, no differ-

ences between the groups were found except for a minor increase in 12-hour postoperative blood loss in the Trillium Biopassive Surface– coated oxygenator group. In this study, only the oxygenator was coated. Coating the entire CPB circuit instead of just the oxygenator may result in greater beneficial effects. Because most of the surface area of the CPB circuit is in the oxygenator, however, the oxygenator

Fig 3. Heparin concentration and activated coagulation time (ACT) before, during, and after cardiopulmonary bypass (CPB). No differences between coated and uncoated groups.

TRILLIUM COATED VERSUS UNCOATED CPB OXYGENATOR

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Table 2. Cumulative Mediastinal Blood Loss (mL) Coated Oxygenator Blood Loss

Mean ⫾ SD (median)

4h 12 h 24 h

350 ⫾ 200 (325) 750 ⫾ 405 (650) 1070 ⫾ 580 (860)

Uncoated Oxygenator

25%/75% (range)

Mean ⫾ SD (median)

25%/75% (range)

p Value

200/420 (70-870) 410/1040 (220-1570) 730/1540 (410-2320)

270 ⫾ 130 (240) 470 ⫾ 210 (420) 870 ⫾ 450 (785)

170/370 (90-490) 320/630 (180-870) 500/1160 (410-2130)

0.184 0.035 0.301

Biopassive Surface on heparin requirements is an area of active investigation.15 The results of this study are consistent with those of other studies completed on various methods of heparin coating of CPB circuits. Many studies have found differences in inflammatory, thrombotic, and hemostatic mediators, but only a few have shown significant clinical differences in patient outcome using coated oxygenators.13-15,20,21 Based on these data and others, it seems unlikely that there are any significant clinical benefits to using the Trillium Biopassive Surface– coated oxygenator under the conditions studied. It is possible that a patient benefit might be realized if the entire CPB circuit were coated and used in conjunction with air-segmented suction or in more complex operations that require longer CPB duration and have greater physiologic trespass. In its current applications, Trillium Biopassive Surface coating of the CPB oxygenator alone appears to provide limited benefit in the effort to reduce the incredibly complex pathophysiologic insult that results from blood contact with extracorporeal surfaces.

is the location where most of the protein adsorption and consequent activation of the complement and coagulation pathways occur. Other variables of the CPB circuit may affect the efficacy of coating methods. It has been shown that suction alone can cause activation of the coagulation and inflammation pathways that were measured in this study.18 It is not possible to determine from these data whether or not the oxygenator coating would prevent or decrease activation of inflammatory and coagulation pathways if suction or air-segmented suction were not used. This study was not a priori powered to determine statistical significance of blood loss data. As such, further study would be needed to determine if there is any difference in the postoperative blood loss between patients using Trillium Biopassive Surface– coated and uncoated oxygenators. This study was limited to only patients undergoing primary coronary artery bypass graft surgery. It did not study the effect of the Trillium Biopassive Surface– coated oxygenators on patients undergoing more complex procedures with longer CPB duration or patients undergoing emergency surgery, in whom heparin-coated circuits have shown some benefit.19 Of interest is the apparent nonsignificant trend in increased heparin requirements in patients undergoing CPB with the Trillium Biopassive Surface– coated oxygenator. The impact of hybrid heparin coatings such as Trillium

ACKNOWLEDGMENT The authors thank Ms Mary Lou Stewart and Ms Raynell J. Clark for their assistance with assay methodology; Mr Darrell R. Schroeder, MS, for his statistical analysis; and Ms Malinda Woodward for assistance with manuscript preparation.

Table 3. Perioperative Transfusion Requirements Coated Oxygenator

Uncoated Oxygenator

Percentile Mean

Intraoperative transfusion Intraoperative cell salvage (mL) Allogenic blood products Red blood cells (U) Fresh frozen plasma (U) Platelets (U) Hespan (mL) Albumin (mL) Transfusions within 24 h of surgery Allogenic blood products Red blood cells (U) Fresh frozen plasma (U) Platelets (U) Cryoprecipitate (U) Albumin (mL)

720

Median

25th

75th

750

460

900

0.5 0.9 0.9 36 18

0 0 0 0 0

0 0 0 0 0

0 0 0 0 0

0.7 1 2.1 0.7 925

0 0 0 0 1000

0 0 0 0 500

1 1 4.5 0 1238

Percentile Mean

570

25th

537.5

450

675

0.075

1 0 0 0 0

0.741 0.299 0.481 0.368 0.252

2.25 0 0 0 1110

0.233 0.320 0.632 0.293 0.575

0.6 0.3 0.4 94 140

0 0 0 0 0

0 0 0 0 0

1.5 0.4 1.5 0 785

0 0 0 0 625

0 0 0 0 250

75th

p Value

Median

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12. Boonstra PW, Akkerman C, Huyzen R, et al: Heparin coating of an extracorporeal circuit partly improves hemostasis after cardiopulmonary bypass. J Thorac Cardiovasc Surg 107:289-292, 1994 13. Oliver WC Jr, Nuttall GA, Rinder C, et al: Comparison of heparin coated extracorporeal circuit with a standard circuit in CABG surgery patients. Anesth Analg 84:127, 1997 14. Aldea GS, Doursounian M, O’Gara P, et al: Heparin-bonded circuits with a reduced anticoagulation protocol in primary CABG: A prospective, randomized study. Ann Thorac Surg 62:410-417, 1996 15. Aldea GS, O’Gara P, Shapira OM, et al: Effect of anticoagulation protocol on outcome in patients undergoing CABG with heparinbonded cardiopulmonary bypass circuits. Ann Thorac Surg 65:425433, 1998 16. van der Kamp KWHJ, van Oeveren W: Contact, coagulation and platelet interaction with heparin treated equipment during heart surgery. Int J Artif Organs 16:836-842, 1993 17. Salzman EW: Measurement of platelet adhesiveness: A simple in vitro technique demonstrating an abnormality in von Willebrand’s disease. J Lab Clin Med 62:724-735, 1963 18. Borowiec JW, Bozdayi M, Jaramillo A, et al: Influence of two blood conservation techniques (cardiotomy reservoir versus cell-saver) on biocompatibility of the heparin-coated cardiopulmonary bypass circuit during coronary revascularization surgery. J Card Surg 12:190197, 1997 19. Aldea GS, Lilly K, Gaudiani JM, et al: Heparin-bonded circuits improve clinical outcomes in emergency coronary artery bypass grafting. J Card Surg 12:389-397, 1997 20. te Velthuis H, Jansen PG, Hack CE, et al: Specific complement inhibition with heparin-coated extracorporeal circuits. Ann Thorac Surg 61:1153-1157, 1996 21. Weerwind PW, Maessen JG, van Tits LJ, et al: Influence of Duraflo II heparin-treated extracorporeal circuits on the systemic inflammatory response in patients having coronary bypass. J Thorac Cardiovasc Surg 110:1633-1641, 1995