Hemocompatibility of PMEA Coated Oxygenators Used for Extracorporeal Circulation Procedures

Comparison of complement consumption and platelet accumulation between membrane oxygenators coated with a polymer or heparin

INTRODUCTION

The membrane oxygenator in extracorporeal circulation circuits is coated with acrylate-copolymer (ACP) or immobilized heparin (IHP) to enhance hemocompatibility. To evaluate the relative features of both coatings, we compared blood components circulated in the circuits with ACP-and IHP-coated membranes in vitro using whole human blood.

METHODS

Whole human blood was heparinized and circulated in two experimental circuits with an ACP-coated reservoir, tubes, and an ACP- or IHP-coated membrane. Platelet (PLT) counts and the amount of total protein (TP), complement component 3 (C3), and complement component 4 (C4) were measured at 0, 8, 16, 24, and 32 h in each experiment (n = 5).

RESULTS

The PLT count at 0-h circulation was lower in the IHP-coated than in the ACP-coated circuits (p = 0.034); however, no significant difference was observed at other time points. Reduction in TP at 8-h and 16-h circulation and in C3 at 32-h circulation was lesser in the ACP-coated than in the IHP-coated circuits (p = 0.004, 0.034, and 0.027, respectively); reduction in TP and C3 at other time points and C4 at each time point was not significantly different. There were significant interactions between coating type and circulation duration in the PLT, TP, and C3 transitions (p = 0.008, 0.020, and 0.043, respectively).

CONCLUSIONS

Our findings suggest that ACP-coated membranes can prevent the initial drop in PLT count and C3 consumption over 32 h, whereas IHP-coated membranes could not prevent this drop in extracorporeal circulation. Therefore, ACP-coated membranes are suitable for short- and long-term extracorporeal life support.

Unravelling Surface Modification Strategies for Preventing Medical Device-Induced Thrombosis

The use of biomaterials in implanted medical devices remains hampered by platelet adhesion and blood coagulation. Thrombus formation is a prevalent cause of failure of these blood-contacting devices. Although systemic anticoagulant can be used to support materials and devices with poor blood compatibility, its negative effects such as an increased chance of bleeding, make materials with superior hemocompatibility extremely attractive, especially for long-term applications. This review examines blood-surface interactions, the pathogenesis of clotting on blood-contacting medical devices, popular surface modification techniques, mechanisms of action of anticoagulant coatings, and discusses future directions in biomaterial research for preventing thrombosis. In addition, this paper comprehensively reviews several novel methods that either entirely prevent interaction between material surfaces and blood components or regulate the reaction of the coagulation cascade, thrombocytes, and leukocytes.

Activity of anticoagulant proteins on the polymer-coated and heparin-coated membranes in an extracorporeal circulation circuit

INTRODUCTION

We performed in vitro experiments using whole human blood without anticoagulants to clarify the activity of anticoagulant proteins on membranes coated with acrylate-copolymer (ACP) with a hydrophilic blood-contacting layer compared to those coated by immobilizing heparin (IHP) in extracorporeal circulation.

METHODS

Whole human blood from healthy volunteers was recirculated in two types of experimental circuits with an ACP-coated reservoir and tubes and an ACP-coated or IHP-coated membrane. To compare the fluctuation of anticoagulant proteins, the circuit pressure at the inlet and outlet of the membrane was measured every 5 min; antithrombin antigen (ATQ), antithrombin activity, protein-C quantitation (PCQ), protein-C activity, protein-S free antigen (PSQ), and protein-S activity were measured at 0, 30, 60, 120, and 180 min in each experiment (n = 5).

RESULTS

The time taken to achieve high circuit pressure (> 300 mmHg) at the inlet of the membrane was significantly shorter in the ACP-coated membrane circuit (28 ± 2.7 min) than in the IHP-coated membrane circuit (54 ± 24 min); however, the ATQ, PCQ, and PSQ at 180 min of recirculation were significantly higher in the former than in the latter (all p < .05).

CONCLUSIONS

ACP-coated membranes can prevent the consumption of anticoagulant proteins but cannot delay circuit thrombogenicity compared to IHP-coated membranes. Considering patient care during the post-extracorporeal circulation period, the use of ACP coating, which can preserve anticoagulant protein, is better in extracorporeal circulation circuits.

Toward an artificial endothelium: Development of blood-compatible surfaces for extracorporeal life support

A new generation of extracorporeal artificial organ support technologies, collectively known as extracorporeal life support (ECLS) devices, is being developed for diverse applications to include acute support for trauma-induced organ failure, transitional support for bridge to organ transplant, and terminal support for chronic diseases. Across applications, one significant complication limits the use of these life-saving devices: thrombosis, bleeding, and inflammation caused by foreign surface-induced blood interactions. To address this challenge, transdisciplinary scientists and clinicians look to the vascular endothelium as inspiration for development of new biocompatible materials for ECLS. Here, we describe clinically approved and new investigational biomaterial solutions for thrombosis, such as immobilized heparin, nitric oxide-functionalized polymers, "slippery" nonadhesive coatings, and surface endothelialization. We describe how hemocompatible materials could abrogate the use of anticoagulant drugs during ECLS and by doing so radically change treatments in critical care. Additionally, we examine several special considerations for the design of biomaterials for ECLS, including: (1) preserving function of the artificial organ, (2) longevity of use, and (3) multifaceted approaches for the diversity of device functions and applications.

Combination of two antithrombogenic methodologies for preventing thrombus formation on a poly(ether ether ketone) substrate

To enhance the total antithrombogenicity of poly(ether ether ketone) (PEEK), we examined a combination of two methodologies for the suppression of activation in both the platelet and coagulation systems. A random copolymer (PMT) composed of a zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) unit and a cationic 2-methacryloyloxyethyl trimethylammonium chloride (TMAEMA) unit was grafted onto the PEEK surface by photoinduced self-initiated graft polymerization of the PEEK substrate (PMTx-g-PEEK). Then, negatively charged heparin was immobilized by ionic binding with TMAEMA units (Hep/PMTx-g-PEEK). The TMAEMA unit composition on grafted PMT altered the surface ζ-potentials of the PEEK substrates. Amounts of immobilized heparin depended on the ζ-potential. The concentration of heparin became constant on the sample surface where the TMAEMA unit composition was 30% or more, and was approximately 2.0 μg/cm2. The Hep/PMTx-g-PEEK with a TMAEMA unit composition of 50% showed not only decreased platelet adhesion, but also a 4-fold extension of the blood coagulation time of the poly(MPC)-g-PEEK substrate. The poly(MPC) layer could inhibit platelet adhesion and activation, resulting in surface antithrombogenic properties. Additionally, heparin released from the Hep/PMTx-g-PEEK prevented activation of the coagulation system in whole blood. Therefore, the combination of these antithrombogenic methodologies was promising for prolonging the blood coagulation period of the materials.

Biocompatibility of a polymer-coated membrane possessing a hydrophilic blood-contacting layer: Adsorption-related assessment

OBJECTIVE

Currently, the foreign surfaces of extracorporeal circulation devices are coated with an acrylate-based copolymer that creates a hydrophilic blood-contacting layer to enhance biocompatibility. Several reports of acrylate-based copolymer with respect to biocompatibility have been published; however, the adsorption of peptide compounds on acrylate-based copolymer-coated membranes still requires clarity. In this study, we aimed to understand the adsorption of several peptide compounds of various molecular weights, including albumin, lysozyme, and vancomycin, on acrylate-based copolymer-coated membranes using in vitro studies.

METHODS

Six experimental circuits consisting of acrylate-based copolymer-coated tubes and membranes, and six comprising acrylate-based copolymer-coated tubes and non-coated membranes were prepared for comparison. An experimental solution, composed of albumin, lysozyme, vancomycin, and saline, was continuously stirred in a reservoir, recirculated in each experimental circuit, and then filtered. Concentrations of albumin, lysozyme, and vancomycin were measured after 0, 15, 30, 45, 60, 90, and 120 min of recirculation. Similar experiments were performed in all the prepared circuits.

RESULTS

The ratio of measured values at each time point to those at 0 min was not significantly different between acrylate-based copolymer-coated and non-coated membranes for albumin and lysozyme, but differed significantly for vancomycin; the ratios were higher in acrylate-based copolymer-coated than in non-coated membranes.

CONCLUSION

This study suggests that albumin is not adsorbed on either acrylate-based copolymer-coated or non-coated membranes, that lysozyme is not adsorbed on either membrane or is adsorbed at a similar rate on both membranes, and that vancomycin is less adsorbed on acrylate-based copolymer-coated membranes. Thus, acrylate-based copolymer coating could inhibit the adsorption of various peptide compounds.

Compatibility of Nitric Oxide Release with Implantable Enzymatic Glucose Sensors Based on Osmium (III/II) Mediated Electrochemistry

The compatibility of nitric oxide (NO) release coatings with implantable enzymatic glucose sensors based on osmium (III/II) mediated electrochemical detection is examined for the first time. NO-releasing osmium-mediated glucose sensors are prepared using a S-nitrosothiol impregnated outer tubing and are tested in vitro in both phosphate buffer (pH 7.4) and whole porcine blood. It is demonstrated that after 3 days of continuous NO release at or above physiological levels, there are no negative effects on the osmium mediated electrochemical currents. Indeed, such sensors maintain their functionality, sensitivity, and accuracy for detecting glucose levels in blood. The results suggest that improved performance of both intravascular and, potentially, subcutaneous Os(III/II) mediated glucose sensors may be realized by taking advantage of NO's well-known anticlotting, anti-inflammatory, and antimicrobial properties.

Polymer-coated cardiopulmonary bypass circuit attenuates upregulation of both proteases/protease inhibitors and platelet degranulation in pigs

Introduction:

Interaction of blood with a cardiopulmonary bypass (CPB) circuit activates the coagulation-fibrinolysis, complement and kinin-kallikrein systems that are mainly supported by proteases and their inhibitors.

Methods:

Biocompatibility of a new polymer-coated (SEC-coated) CPB circuit was globally evaluated and compared with that of a non-coated CPB circuit by quantitative proteomics, using isobaric tags for relative and absolute quantification labeling tandem mass spectrometry. Plasma samples were taken three times (5 min after initiation of CPB, just before declamping and just before termination of CPB) in 12 pigs undergoing 120 min of CPB with the SEC-coated CPB circuit or a non-coated CPB circuit (n = 6, respectively).

Results:

Identified were 224 proteins having high protein confidence (>99%) and false discovery rate (FDR) <5%. Among these proteins, there were 25 significantly upregulated proteins in the non-coated CPB group compared to those in the SEC-coated CPB group. Dominant protein functions were platelet degranulation, serine-type (cysteine-type) endopeptidase inhibitor activity and serine-type endopeptidase activity in the 25 proteins. Bioinformatics analysis similarly revealed upregulation of proteins belonging to platelet degranulation and negative regulation of endopeptidase activity in the non-coated CPB group; these upregulations were effectively attenuated in the SEC-coated CPB group.

Conclusion:

The new polymer (SEC)-coated CPB circuit effectively attenuated upregulation of proteins compared to the non-coated CPB circuit. These proteins were associated with both proteases/protease inhibitors and platelet degranulation.

A prospective randomized trial comparing the clinical effectiveness and biocompatibility of heparin-coated circuits and PMEA-coated circuits in pediatric cardiopulmonary bypass

OBJECT

We compared the clinical effectiveness and biocompatibility of poly-2-methoxyethyl acrylate (PMEA)-coated and heparin-coated cardiopulmonary bypass (CPB) circuits in a prospective pediatric trial.

METHODS

Infants randomly received heparin-coated (n=7) or PMEA-coated (n=7) circuits in elective pediatric cardiac surgery with CPB for ventricular septum defects. Clinical and hematologic variables, respiratory indices and hemodynamic changes were analyzed perioperatively.

RESULTS

Demographic and clinical variables were similar in both groups. Leukocyte counts were significantly lower 5 minutes after CPB in the PMEA group than the heparin group. Hemodynamic data showed that PMEA caused hypotension within 5 minutes of CPB. The respiratory index was significantly higher immediately after CPB and 1 hour after transfer to the intensive care unit (ICU) in the PMEA group, as were levels of C-reactive protein 24 hours after transfer to the ICU.

CONCLUSION

Our study shows that PMEA-coated circuits, unlike heparin-coated circuits, cause transient leukopenia during pediatric CPB and, perhaps, systemic inflammatory respiratory syndrome after pediatric CPB.

Preclinical study of a novel hydrodynamically levitated centrifugal pump for long-term cardiopulmonary support : In vivo performance during percutaneous cardiopulmonary support

An extracorporeal centrifugal blood pump with a hydrodynamically levitated impeller was developed for use in a durable extracorporeal membrane oxygenation (ECMO) system. The present study examined the biocompatibility of the blood pump during long-term use by conducting a series of 30-day chronic animal experiments. The ECMO system was used to produce a percutaneous venoarterial bypass between the venae cavae and carotid artery in adult goats. No anticoagulation or antiplatelet therapy was administered during the experiments. Three out of four animals survived for the scheduled 30-day period, and the blood pumps and membrane oxygenators both exhibited sufficient hydrodynamic performance and good antithrombogenicity, while one animal died of massive bleeding from the outflow cannulation site. The animals' plasma free hemoglobin had returned to within the normal range by 1 week after the surgical intervention, and their hemodynamic and biochemistry parameters remained within their normal ranges throughout the experiment. The explanted centrifugal blood pumps did not display any trace of thrombus formation. Based on the biocompatibility demonstrated in this study, the examined centrifugal blood pump, which includes a hydrodynamically levitated impeller, is suitable for use in durable ECMO systems.

Extract of fetal membrane would inhibit thrombosis and hemolysis

The innermost layer of fetal membranes is amnion which has anti-adhesive, anti-inflammation and viscoelastic properties, as well as low immunogenicity. Amniotic membrane has been employed in variety of clinical fields as a natural biomaterial. Amniotic epithelial cells possess stem cell characteristics and capability to differentiate into endothelial cells. The basement membrane of amnion is an extracellular matrix enriched scaffold to support adhesion of endothelial cells. The matrix of amniotic membrane contains two kinds of glycosaminoglycans including perlecan (a heparan sulfate proteoglycan) and hyaluronic acid which both inhibit blood coagulation. Moreover, the other ingredients of amniotic membrane such as pigment-epithelium derived factor (PEDF), IL-10, MMP-9 inhibit platelet aggregation. Based on some biochemical and biomechanical evidences, we hypothesized in this paper that amniotic membrane could prevent thrombosis and hemolysis; therefore, has the capability to be applied in blood contacting devices and implants.

A novel minimal invasive mouse model of extracorporeal circulation

Extracorporeal circulation (ECC) is necessary for conventional cardiac surgery and life support, but it often triggers systemic inflammation that can significantly damage tissue. Studies of ECC have been limited to large animals because of the complexity of the surgical procedures involved, which has hampered detailed understanding of ECC-induced injury. Here we describe a minimally invasive mouse model of ECC that may allow more extensive mechanistic studies. The right carotid artery and external jugular vein of anesthetized adult male C57BL/6 mice were cannulated to allow blood flow through a 1/32-inch external tube. All animals (n = 20) survived 30 min ECC and subsequent 60 min observation. Blood analysis after ECC showed significant increases in levels of tumor necrosis factor α, interleukin-6, and neutrophil elastase in plasma, lung, and renal tissues, as well as increases in plasma creatinine and cystatin C and decreases in the oxygenation index. Histopathology showed that ECC induced the expected lung inflammation, which included alveolar congestion, hemorrhage, neutrophil infiltration, and alveolar wall thickening; in renal tissue, ECC induced intracytoplasmic vacuolization, acute tubular necrosis, and epithelial swelling. Our results suggest that this novel, minimally invasive mouse model can recapitulate many of the clinical features of ECC-induced systemic inflammatory response and organ injury.

The promise of microfluidic artificial lungs

Microfluidic or microchannel artificial lungs promise to enable a new class of truly portable, therapeutic artificial lungs through feature sizes and blood channel designs that closely mimic those found in their natural counterpart. These new artificial lungs could potentially: 1) have surface areas and priming volumes that are a fraction of current technologies thereby decreasing device size and reducing the foreign body response; 2) contain blood flow networks in which cells and platelets experience pressures, shear stresses, and branching angles that copy those in the human lung thereby improving biocompatibility; 3) operate efficiently with room air, eliminating the need for gas cylinders and complications associated with hyperoxemia; 4) exhibit biomimetic hydraulic resistances, enabling operation with natural pressures and eliminating the need for blood pumps; and, 5) provide increased gas exchange capacity enabling respiratory support for active patients. This manuscript reviews recent research efforts in microfluidic artificial lungs targeted at achieving the advantages above, investigates the ultimate performance and scaling limits of these devices using a proven mathematical model, and discusses the future challenges that must be overcome in order for microfluidic artificial lungs to be applied in the clinic. If all of these promising advantages are realized and the remaining challenges are met, microfluidic artificial lungs could revolutionize the field of pulmonary rehabilitation.

Development and hemocompatibility testing of nitric oxide releasing polymers using a rabbit model of thrombogenicity

Hemocompatibility is the goal for any biomaterial contained in extracorporeal life supporting medical devices. The hallmarks for hemocompatibility include nonthrombogenicity, platelet preservation, and maintained platelet function. Both in vitro and in vivo assays testing for compatibility of the blood/biomaterial interface have been used over the last several decades to ascertain if the biomaterial used in medical tubing and devices will require systemic anticoagulation for viability. Over the last 50 years systemic anticoagulation with heparin has been the gold standard in maintaining effective extracorporeal life supporting. However, the biomaterial that maintains effective ECLS without the use of any systemic anticoagulant has remained elusive. In this review, the in vivo 4-h rabbit thrombogenicity model genesis will be described with emphasis on biomaterials that may require no systemic anticoagulation for extracorporeal life supporting longevity. These novel biomaterials may improve extracorporeal circulation hemocompatibility by preserving near resting physiology of the major blood components, the platelets and monocytes. The rabbit extracorporeal circulation model provides a complete assessment of biomaterial interactions with the intrinsic coagulation players, the circulating platelet and monocytes. This total picture of blood/biomaterial interaction suggests that this rabbit thrombogenicity model could provide a standardization for biomaterial hemocompatibility testing.

Conduite et complications de l’oxygénation extracorporelle veinoveineuse

Cet article se propose de tracer, à la lumière de la littérature, les grandes lignes de la prise en charge des patients traités par oxygénation extracorporelle veinoveineuse pour une insuffisance respiratoire réfractaire aux traitements conventionnels. Nous diviserons la période d’assistance externe en trois phases successives : la phase d’initiation du traitement, une phase d’entretien et une phase de sevrage et d’arrêt de la thérapeutique. À chacune de ces périodes, nous nous attacherons à décrire les réglages et la surveillance du circuit extérieur ainsi que le traitement et la surveillance du patient lui-même. Nous nous attacherons également à décrire à chaque étape les complications le plus fréquemment rencontrées et les traitements proposés.

In vitro and in vivo study of sustained nitric oxide release coating using diazeniumdiolate-oped poly(vinyl chloride) matrix with poly(lactide-co-glycolide) additive

Nitric oxide (NO) is an endogenous vasodilator as well as natural inhibitor of platelet adhesion and activation that can be released from a NO donor species, such as diazeniumdiolated dibutylhexanediamine (DBHD/N2O2) within a polymer coating. In this study, various Food and Drug Administration approved poly(lactic-co-glycolic acid) (PLGA) species were evaluated as additives to promote a prolonged NO release from DBHD/N2O2 within a plasticized poly(vinyl chloride) (PVC) matrix. When using an ester-capped PLGA additive with a slow hydrolysis time, the resulting coatings continuously release between 7-18×10-10 mol cm-2 min-1 NO for 14 d at 37°C in PBS buffer. The corresponding pH changes within the polymer films were visualized using pH sensitive indicators and are shown to correlate with the extended NO release pattern. The optimal combined diazeniumdiolate/PLGA-doped NO release (NOrel) PVC coating was evaluated in vitro and its effect on the hemodynamics was also studied within a 4 h in vivo extracorporeal circulation (ECC) rabbit model of thrombogenicity. Four out of 7 control circuits clotted within 3 h, whereas all the NOrel coated circuits were patent after 4 h. Platelet counts on the NOrel ECC were preserved (79 ± 11% compared to 54 ± 6% controls). The NOrel coatings showed a significant decrease in the thrombus area as compared to the controls. Results suggest that by using ester-capped PLGAs as additives to a conventional plasticized PVC material containing a lipophilic diazeniumdiolates, the NO release can be prolonged for up to 2 weeks by controlling the pH within the organic phase of the coating.

Artificial Placenta - Lung Assist Devices for Term and Preterm Newborns with Respiratory Failure

Respiratory insufficiency is a major cause of neonatal mortality and long-term morbidity, especially in very low birth weight infants. Today, non-invasive and mechanical ventilation are commonly accepted procedures to provide respiratory support to newborns, but they can reach their limit of efficacy. To overcome this technological plateau and further reduce mortality rates, the technology of an “artificial placenta”, which is a pumpless lung assist device connected to the umbilical vessels, would serve to expand the therapeutic spectrum when mechanical ventilation becomes inadequate to treat neonates with severe respiratory insufficiency.

The first attempts to create such an artificial placenta took place more than 60 years ago. However, there has been a recent renaissance of this concept, including developments of its major components like the oxygenator, vascular access via umbilical vessels, flow control, as well as methods to achieve hemocompatibility in extracorporeal circuits. This paper gives a review of past and current development, animal experiments and human case studies of artificial placenta technology.

ECMO cannula review

This paper reviews the basic fluid dynamics underlying extracorporeal membrane oxygenation (ECMO) cannula design. General cannula features and their effect on flow are discussed and the specific requirements of different ECMO circuits are explained. The current commercially available cannula options for veno-arterial and veno-venous circuits are reviewed and the main characteristics presented.

The attenuation of platelet and monocyte activation in a rabbit model of extracorporeal circulation by a nitric oxide releasing polymer

Nitric oxide (NO) has been shown to reduce thrombogenicity by decreasing platelet and monocyte activation by the surface glycoprotein, P-selectin and the integrin, CD11b, respectively. In order to prevent platelet and monocyte activation with exposure to an extracorporeal circulation (ECC), a nitric oxide releasing (NORel) polymeric coating composed of plasticized polyvinyl chloride (PVC) blended with a lipophilic N-diazeniumdiolate was evaluated in a 4 h rabbit thrombogenicity model using flow cytometry. The NORel polymer significantly reduced ECC thrombus formation compared to polymer control after 4 h blood exposure (2.8 +/- 0.7 NORel vs 6.7 +/- 0.4 pixels/cm(2) control). Platelet count (3.4 +/- 0.3 NORel vs 2.3 +/- 0.3 x 10(8)/ml control) and function as measured by aggregometry (71 +/- 3 NORel vs 17 +/- 6% control) were preserved after 4 h exposure in NORel versus control ECC. Plasma fibrinogen levels significantly decreased in both NORel and control groups. Platelet P-selectin mean fluorescence intensity (MFI) as measured by flow cytometry was attenuated after 4 h on ECC to ex vivo collagen stimulation (27 +/- 1 NORel vs 40 +/- 2 MFI control). Monocyte CD11b expression was reduced after 4 h on ECC with NORel polymer (87 +/- 14 NORel vs 162 +/- 30 MFI control). These results suggest that the NORel polymer coatings attenuate the increase in both platelet P-selectin and monocytic CD11b integrin expression in blood exposure to ECCs. These NO-mediated platelet and monocytic changes were shown to improve thromboresistance of these NORel-polymer-coated ECCs for biomedical devices.

Effects of poly-2-methoxyethylacrylate (PMEA)-coating on CPB circuits

OBJECTIVES

In this study, the immuno- and neuroprotective effect of a novel cardiopulmonary bypass coating was investigated.

DESIGN

Thirty nine patients scheduled for elective coronary artery bypass grafting were randomly assigned to either PMEA-coated (n = 19) or non-coated CPB circuits (n = 20). Pericardial suction blood was separated and retransfused only if needed at the end of operation. Neurocognitive functions were examined preoperatively and 7-10 days postoperatively using a standard neuropsychological test battery. Assuming an inflammatory etiology, the most cogent inflammatory markers were perioperatively analyzed.

RESULTS

Postoperatively, patients of the PMEA-coated group performed better in Go/NoGo and Mini-Mental-test than patients of the non-coated group (p < 0.04). Other neurocognitive testing did not reveal significant differences between the groups. Although most inflammatory parameters showed a significant intraindividual increase during or shortly after CPB, there was no difference in inflammatory alteration between the groups.

CONCLUSIONS

PMEA-coating of cardiopulmonary bypass surfaces revealed some minor benefits in preservation of neurocognitive functions after surgery. The immediate inflammatory response remained mostly unaffected. Suction blood separation may additionally contribute to proper postoperative outcome.

Off-Pump Versus On-Pump Coronary Artery Surgery Identification of Fibrinolysis Using Rotation Thromboelastography; A Preliminary, Prospective, Randomized Study

The aim of this preliminary, prospective, randomized study was to compare rotation thromboelastography (roTEG) results and D-dimer levels in off-pump versus on-pump coronary surgery in order to identify the activation of fibrinolysis. Twenty patients scheduled for coronary bypass grafting were assessed (off-pump group A, n = 10; on-pump group B, n = 10). Blood samples for roTEG examination were taken preoperatively (t0), 15 minutes after sternotomy (t1), on the completion of peripheral bypass anastomoses (t2), and at the end of procedures (t3). The time points for D-dimer levels analyses were before operation, at the end of procedures, and 24 hours later. A certain degree of roTEG signs of fibrinolysis was noticed at time t2 in both groups and in group B these marks were quite widely, but not significantly expressed (P for intergroup differences for Lysis on Set Time at 60 and 150 minutes were P = 0.190 and P = 0.122, respectively), borderline differences were found for Maximum Clot Firmness (P = 0.082) with a lower mean value for group B (arithmetic means [95% confidence intervals]--57.7 [54.2; 61.2] mm). Completely expressed roTEG signs of hyperfibrinolysis were observed in 2 patients from group B. In group B also the highest geometric means of D-dimers (1326.0 [943.5; 1863.6] ng mL(-1)) and thus a dramatic intergroup difference (P < 0.001) were observed at the end of surgery; 24 hours later the significantly elevated D-dimer levels in both groups (A: 1070.0 [723.5; 1582.6] versus B: 1093.3 [732.0; 1632.9] ng mL(-1)) were equalized (P = 0.932). Our roTEG results display a slightly greater, but fairly subtle activation of fibrinolysis during the course of cardiopulmonary bypass, compared to off-pump cardiac surgery.

The systemic inflammatory response syndrome and cardiopulmonary bypass

Cardiac surgery using cardiopulmonary bypass (CPB) provokes a systemic inflammatory response. This is mainly triggered by contact activation of blood by artificial surfaces of the extracorporeal circuit. Although often remaining sub-clinical and resolving promptly at the end of CPB, in its most extreme form this inflammatory response may be associated with the development of the systemic inflammatory response syndrome (SIRS) that can often lead to major organ dysfunction (MODs) and death. Here, we review the pathophysiology behind the development of this "whole body" inflammatory response and some of the methods currently used to minimise it.