Cardiopulmonary bypass with low systemic heparinization: an experimental study

Use of heparin-bonded surfaces in cardiopulmonary bypass

Heparin surface coating is a convenient means of improving the thrombo resistance of blood-exposed surfaces. At this time, heparin can be bonded to oxygenator/heat-exchanger structures, soft venous reservoirs, cardiotomy reservoirs, centrifugal pump heads, tubings, and cannulae. Following experimental evaluation, these devices have become available for clinical application. Cardiopulmonary bypass with low or no systemic heparinization can be realized in selected cases. Improved haemostasis in combination with modification of standard surgical techniques results in limited blood loss and reduced transfusion requirements and appears to be the main benefit of cardiopulmonary bypass with heparin-bonded surfaces. Experience using heparin- bonded equipment in various clinical situations is reviewed.

Heparin-coated cardiopulmonary bypass: a clinical case incorporating a standard cardiotomy

Heparin-less bypass systems are presently being used in the cardiothoracic surgery community. Their unique advantages include reduced utilization of heparin and its pharmacotoxic disadvantages, diminished utilization of protamine and its pharmacotoxicity, reduction in homologous blood utilization postbypass, moderation of the coagulation cascade, enhanced safety, and a remission in the thrombogenesis of the cardiopulmonary circuit. A clinical case is presented. Unique in this case was the incorporation of a standard cardiotomy. A change in performance characteristics for the oxygenator and postbypass coagulation profiles was also discovered.

Are standard human coagulation tests suitable in pigs and calves during extracorporeal circulation?

The thrombogenicity of membrane oxygenators as well as clotting parameters profiles, using standard human clotting tests, was analyzed in calves and pigs during 6 h perfusion. Three calves and 3 pigs were connected to extracorporeal circulation with standard heparinization. Blood samples were taken for coagulation variables throughout perfusion, and oxygenators were examined for clot deposits at the end of the experiment. Two out of 3 oxygenators of the calf group presented clot deposits while none in the pig group did. Baseline coagulation variables of pigs showed values similar to those of humans while neither extrinsic nor intrinsic pathways could be activated in calves with standard human coagulation tests. The calf model, in conclusion, was confirmed to be a difficult model for the testing of extracorporeal circulation device resistance to thrombus formation, which is, however, not reflected by standard human coagulation tests. The pig model is a better model in which both coagulation pathways could be activated with standard human coagulation tests.

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

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

Synthetic protein treated versus heparin coated cardiopulmonary bypass surfaces: similar clinical results and minor biochemical differences

OBJECTIVE

Complications associated with cardiopulmonary bypass (CPB) have gained more attention due to increased interest in coronary artery bypass grafting without CPB. The impact of heparin coating of CPB circuits has been discussed controversially. The present study examines if the treatment of the oxygenator surface with a synthetic protein may serve as an alternative to a completely heparin coated circuit.

METHODS

Fifty-eight patients undergoing coronary artery bypass grafting with CPB were randomly assigned to completely heparin coated circuits or synthetic protein treated oxygenators in a double blind protocol, focussing on the inflammatory reaction resulting in membrane damage, coagulation changes and markers of cerebral injury or dysfunction. Treatment groups did not differ as to preoperative demographics, and intraoperative clinical data. Patients with any neurologic disease or risk factors for cerebral dysfunction were not included in the study.

RESULTS

Postoperative clinical data did not differ between groups. Both surface treatments resulted in similar coagulation activation, hyperfibrinolysis and disseminated intravascular coagulation. Platelet count displayed a difference in favour of the heparin coated group (P = 0.029). Increased leukocyte activation reflected by rising myeloperoxidase concentrations on CPB was present in both synthetic protein and heparin coating groups. Interleukins 6 and 8 reacted similarly, but interleukin 8 increased significantly more (P = 0.0061) at the end of surgery in patients treated with protein treated oxygenators. The same pattern was observed for complement activation as determined by total complement complex (P = 0.006). Both surface changes resulted in moderately increased S-100B protein and neuron specific enolase, without difference between groups. Both markers did not reach concentrations associated with clinical manifestation of cerebral injury.

CONCLUSIONS

These results in routine patients with short bypass time, imply that protein treated oxygenators are associated with a limited increase of biochemical markers similar to heparin coating. However, significantly lower interleukin 8 release and complement activation can be achieved by heparin coating. The protein treatment is a standard feature of the oxygenator examined in both groups. It is not associated with additional cost and therefore appropriate for use in routine patients.

Clinical application of heparin-coated perfusion equipment with special emphasis on patients refusing homologous transfusions

Clinical application of heparin-coated cardiopulmonary bypass equipment during perfusion with low systemic heparinization is reported with special emphasis on patients refusing any transfusion of homologous blood or blood products. Using the described technique, coronary artery revascularization was successfully performed in three Jehovah's witnesses. During perfusion, the activated clotting time (ACT) was maintained above 180 seconds. Prebypass haematocrit was 38 +/- 3% and dropped to 22 +/- 1% after seven days. Hence, cardiopulmonary bypass with low systemic heparinization may further reduce bypass induced morbidity and improve the final outcome in selected patients.

Heparin-coated bypass circuits (Carmeda) suppress the release of tissue plasminogen activator during normothermic coronary artery bypass graft surgery

OBJECTIVES

To study fibrinolysis in a homogeneous first-time coronary artery bypass surgery (CABG) population in whom heparin-coated circuits were used.

DESIGN

A prospective, blinded, randomized, placebo-controlled study.

SETTING

A university hospital, tertiary care, intraoperative and postoperative intensive care unit.

PARTICIPANTS

Twenty-one adult elective primary CABG patients.

INTERVENTIONS

Randomized circuit-type centrifugal pump, membrane oxygenator, rigid cardiotomy reservoir, either placebo (n = 10) or heparin-coated (n = 11) (Carmeda; Medtronic Inc., Anaheim, CA).

MEASUREMENTS AND MAIN RESULTS

Blood samples were analyzed for tissue plasminogen activator (TPA) activity, TPA antigen, plasminogen activator inhibitor-1 (PAI-1) activity, prothrombin complex F1.2, and antithrombin III (AT-III) at the following times: before cardiopulmonary bypass (CPB), during CPB (30 and 60 minutes), post-CPB, and day 1 postsurgery. TPA activity and antigen increased fivefold in the placebo group during CPB, whereas it did not even double in the heparin-coated group. PAI-1, F1.2, and AT-III were not different between groups.

CONCLUSIONS

Heparin-coated CPB circuits reduced TPA release in this homogeneous CABG population with routine heparin/protamine management.

Safe use of heparin-coated bypass circuits incorporating a pump-oxygenator

Durable, covalently bonded, heparin-coated cardiopulmonary bypass (CPB) circuits with oxygenators have been developed. Proposed advantages of heparin-coated CPB circuits include improved biocompatibility and thromboresistance. The purpose of this study was to evaluate our experience with heparin-coated CPB circuits in 20 patients. Heparin was given to maintain an activated clotting time equal to or greater than 200 seconds, while flow rates were kept equal to or greater than 2 L/min. Indications for use of this circuit included recent stroke, posttraumatic injuries, recent gastrointestinal bleeding, protamine allergies, combined cardiac and noncardiac procedures, and ventricular assist. Mean heparin dosage was 0.50 +/- 0.18 mg/kg and protamine dosage was 57.14 +/- 39.36 mg. Postoperative blood loss and transfusion requirements were minimal. Postoperative complement levels of C3a and C5a were normal, suggesting excellent biocompatibility. There were no deaths or perioperative complications. Heparin-coated CPB circuits using a pump oxygenator can be used safely with low-dose heparin administration in select patients requiring CPB.

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.

Heparin-protamine management: a comparison study of three different heparin-protamine management protocols

In a prospective randomized open study, 180 patients underwent open-heart surgery using cardiopulmonary bypass (CPB) and were divided into three different heparin-protamine management protocols. Each group consisted of 60 patients. Patients were treated according to: (A) their dose-response curve using the Hemochron 800 system (International Technidyne Corporation): (B) their dose-response curve, but the heparin-protamine management was based on titrations using the Hepcon system 4 (Hemotec Inc.); or (C) the regular protocol in our hospital. The three groups were compared according to age, gender, weight, perfusion time and operation type. Fibrinogen levels and activated partial thrombin time (APTT) were measured before and after CPB1: during CPB, activated clotting time (ACT) was monitored. 2-4 At the onset of CPB an ACT value of at least 480 seconds was standard.4 Blood for ACT evaluation was drawn every 30 minutes during CPB. A significant difference in the heparin dose given to the different groups was noted, but there also was a significant difference in bodyweight. As calculated per kilogram bodyweight, group B's heparin dose was significantly lower than group A's and also significantly lower than group C's. Group C was given a significantly higher dose of protamine/kg than group A and group B, and Group B's dose was significantly higher than group A's. Hence, protamine/heparin ratios of 0.61 for group A, 0.74 for group B and 0.82 for group C resulted. There was no significant difference in blood loss for the three groups and there was also no significant difference in the use of bank blood for these three groups. APTT values, measured after protamine administration, were significantly higher in group A than in group C. This study suggests that a higher dose of protamine does not result in a decrease of blood loss postoperatively. Reduction in the amount of heparin and in the protamine/heparin ratio is possible by guiding the Hepcon or Hemochron measurements. This reduction, however, will not directly decrease postoperative blood loss. Accurate doses of heparin and protamine can be achieved with an individual patient-related protocol. Thus, an unnecessary excess of heparin and/or protamine can be eliminated.