Macroscopic Clots Research Articles

The Effect of Dialysis Membranes on Coagulation Activation during Haemodialysis of Maintenance Haemodialysis Patients

Abstract Background Platelets, leukocytes, and the coagulation cascade are activated during hemodialysis. During hemodialysis, systemic anticoagulation is used to prevent clotting of the extracorporeal circuit which may lead either to complete clotting to the degree that prevent blood return to the patient or to a lesser extent can only affect the dialyzer membrane fibers which will decrease the effective surface area and that will decrease the session efficacy Aim of the Work The aim of the current study was to evaluate contact system activation and overall coagulation activation during in vivo hemodialysis in prevalent hemodialysis patients, using current generation dialyzer membranes. A crossover study design allowed assessment of differences among regular dialyzer membranes. Patients and Methods We performed a single-center sequential interventional clinical trial study. Twenty patients older than 18 years and treated with maintenance hemodialysis (>3 months) underwent 2 hemodialysis study sessions at Ain Shams University hospitals dialysis unit. Exclusion criteria were clopidogrel or anticoagulant therapy, active infection, presence of central venous catheter or arteriovenous graft and known vascular access dysfunction. Results The increase of TAT at 240 minutes after dialysis start in our study, irrespective of the dialyzer membrane used, suggests a late-onset threshold for thrombin generation, which is well before the treatment effect of the UFH is expected to have faded. The changes in TAT dynamics are in line with previously published results. Dialysis treatments were standardized except for dialyzer membrane. Hence, the differences between membranes are most likely due to differences in physicochemical characteristics. Whether these differences are clinically meaningful needs further study. Analysis costs and the exploratory set-up of the trial drove the small sample size and design of the study. A more comprehensive evaluation of the coagulation activation over a longer time period of hemodialysis treatment would be of interest. Conclusion Driven by the recent interest in the therapeutic options of specific contact system inhibitors, we aimed to evaluate contact system activation during in vivo he-modialysis. Chronic hemodialysis patients dialyzed through arteriovenous dialysis access show coagulation activation during hemodialysis, marked by increased TAT levels, despite using systemic anticoagulation to prevent macroscopic clotting of the extracorporeal circuit. The increase in thrombin generation markers was not associated with measurable contact system activation. Our results argue against effective contact system activation during hemodialysis and generate the hypothesis that novel specific contact system inhibitors alone might not suffice as anticoagulant treatment during hemodialysis.

Development of a parallel multiscale 3D model for thrombus growth under flow

Thrombus growth is a complex and multiscale process involving interactions spanning length scales from individual micron-sized platelets to macroscopic clots at the millimeter scale. Here, we describe a 3D multiscale framework to simulate thrombus growth under flow comprising four individually parallelized and coupled modules: a data-driven Neural Network (NN) that accounts for platelet calcium signaling, a Lattice Kinetic Monte Carlo (LKMC) simulation for tracking platelet positions, a Finite Volume Method (FVM) simulator for solving convection-diffusion-reaction equations describing agonist release and transport, and a Lattice Boltzmann (LB) flow solver for computing the blood flow field over the growing thrombus. Parallelization was achieved by developing in-house parallel routines for NN and LKMC, while the open-source libraries OpenFOAM and Palabos were used for FVM and LB, respectively. Importantly, the parallel LKMC solver utilizes particle-based parallel decomposition allowing efficient use of cores over highly heterogeneous regions of the domain. The parallelized model was validated against a reference serial version for accuracy, demonstrating comparable results for both microfluidic and stenotic arterial clotting conditions. Moreover, the parallelized framework was shown to scale essentially linearly on up to 64 cores. Overall, the parallelized multiscale framework described here is demonstrated to be a promising approach for studying single-platelet resolved thrombosis at length scales that are sufficiently large to directly simulate coronary blood vessels.

Resolving the missing link between single platelet force and clot contractile force

SummaryBlood clot contraction plays an important role in wound healing and hemostasis. Although clot contraction is known to be driven by platelets, how single platelet forces relate to the forces generated by macroscopic clots remains largely unknown. Using our microfabricated high-throughput platelet contraction cytometer, we find that single platelets have an average force of 34 nN ( healthy individuals). However, multiple bulk clot experiments predict a mean single platelet force lower than 0.5 nN. To resolve this discrepancy, we use a mesoscale computational model to probe the mechanism by which individual platelets induce forces in macroscopic clots. Our experimentally informed model shows that the number of platelets in the clot cross-section defines the net clot force. We provide a relationship between single platelet force and the clot force that is useful for better understanding of blood disorders associated with bleeding and thrombosis, and facilitates the development of platelet-based and platelet-mimetic biomaterials.

Blood Products, Crystalloids, and Rapid Infusion: An Experimental Study With Magnesium

Calcium and magnesium are concentration-dependent pro- and anticoagulant cofactors, and magnesium behaves similarly to calcium in the presence of citrate. The authors hypothesized that magnesium can cause clot formation (primary objective) when mixed with coagulation factor-containing blood products diluted with different crystalloids in a rapid- infuser reservoir. A secondary objective was the observation of any infuser alarms and stops in the event of clotting. An experimental in vitro study with blood products, crystalloids, magnesium, and calcium in a rapid infuser with a reservoir using a closed-loop system. Anesthesia research laboratory at an urban academic tertiary medical center PARTICIPANTS: Not applicable. Exposure of fresh frozen plasma (FFP) and packed red blood cells alone (control) or in combination with either normal saline (NS), lactated Ringer's solution (LR), or Plasma-Lyte A (PL) to increasing concentrations of magnesium sulphate (MgSO4) up to 1 g. After each incremental MgSO4 change, the authors applied a specific pump-flow sequence in a closed-loop system with a rapid-infuser reservoir, and if no clot was observed, the authors incrementally added calcium chloride (CaCl2) up to 1 g. Observation of macroscopic clot and time to event, as well as occurrence and type of any pump alarms or stops. LR experiments resulted in clot observation in the reservoir by a dedicated observer after MgSO4 275 ± 206 mg (95% confidence interval [CI], 9-541). Adding MgSO4 1 g in the NS, PL, or the control experiments did not result in clot observation. Only when CaCl2 166.7 ± 51.64 mg (95% CI, 112.0-22.01) was added to the combination of blood products alone or mixed with NS and PL, clotting occurred. The mean FFP volume was 281 ± 48.6 mL (range, 204-340 mL) and was not different between groups (p=0.44). Pump alarms and stops were inconsistent. The addition of magnesium to a combination of LR with coagulation factor- containing blood products consistently resulted in a visible blood clot in the rapid-infuser reservoir in the authors' experimental setup. In addition to MgSO4 1 g in the control, NS, and PL experiments, CaCl2 is needed before a clot can be observed.

Control of fibrinolytic drug injection via real-time ultrasonic monitoring of blood coagulation.

In the present study, we investigated the capabilities of a novel ultrasonic approach for real-time control of fibrinolysis under flow conditions. Ultrasonic monitoring was performed in a specially designed experimental in vitro system. Fibrinolytic agents were automatically injected at ultrasonically determined stages of the blood clotting. The following clots dissolution in the system was investigated by means of ultrasonic monitoring. It was shown, that clots resistance to fibrinolysis significantly increases during the first 5 minutes since the formation of primary micro-clots. The efficiency of clot lysis strongly depends on the concentration of the fibrinolytic agent as well as the delay of its injection moment. The ultrasonic method was able to detect the coagulation at early stages, when timely pharmacological intervention can still prevent the formation of macroscopic clots in the experimental system. This result serves as evidence that ultrasonic methods may provide new opportunities for real-time monitoring and the early pharmacological correction of thrombotic complications in clinical practice.

Platelet activation and clotting cascade activation by dialyzers designed for high volume online hemodiafiltration.

Hemodialysis patients are pro-thrombotic. Higher volume online postdilutional hemodiafiltration (OL-HDF), with increasing hematocrit increases the risk of clotting in the extracorporeal circuit (ECC). We wished to determine whether OL-HDF increased platelet activation and ECC clotting. Coagulation parameters, platelet, white cell, and endothelial activation markers were measured at the start and end of dialysis sessions in 10 patients and also pre- and post-dialyzer after 15 minutes using two different dialyzers designed for high volume OL-HDF; cellulose triacetate (TAGP) and polysulphone (PS), and polyvinylpyrrolidone (PVP). Patients were anticoagulated with a heparin bolus. At the start of OL-HDF, D dimers, thrombin antithrombin complexes (TATs), and soluble adhesions molecules (sICAM-1 and sVCAM-1) were increased. Post-treatment soluble P selectin (PS/PVP 26.7 ± 7.1 versus 36.6 ± 9.9; TAGP 28.7 ± 7.2 versus 43.5 ± 8.4 ng/ml, P < 0.001), and soluble CD40 ligand (PS/PVP 297 ± 228 versus 552 ± 272, TAGP 245 ± 187 versus 390 ± 205 ng/ml, P < 0.05) increased. Post-dialyzer concentrations increased versus pre-dialyzer for tissue factor (PS/PVP 117 ± 12 versus 136 ± 16, TAGP 100 ± 25 versus 128 ± 40 ng/ml, P < 0.05), factor VIIIc (PS/PVP 174 ± 54 versus 237 ± 83, TAGP 163 ± 60 versus 247 ± 102 IU/ml, P < 0.01), sVCAM-1 (PS/PVP 782 ± 64 versus 918 ± 140, TAGP 722 ± 121 versus 889 ± 168 ng/ml, P < 0.01), and D-dimers (PS/PVP 292 ± 132 versus 355 ± 167, TAGP 300 ± 129 versus 391 ± 171 ng/ml, P < 0.001). There was no macroscopic thrombus noted in the ECC, and no increase in microparticles, platelet factor-4, or TATs. Despite being pro-thrombotic, with activation of platelets, and lymphocytes during passage through ECC, no macroscopic clotting, or increased TATs were noted during OL-HDF, and no major differences between cellulosic and polysulphone dialyzers.

Effects of dielectrophoresis on thrombogenesis in human whole blood.

Thrombogenesis (blood clot formation) is a major barrier to the development of biomedical devices that interface with blood. Although state-of-the-art chemically and pharmacologically mediated clot mitigation strategies are effective, some limitations of such approaches include depletion of active agents, or adverse reactions in patients. Increased clotting protein adsorption and platelet adhesion, which occur when artificial surfaces are exposed to blood result in enhanced clot formation on artificial surfaces. It is hypothesized that repelling proteins and platelets using dielectrophoresis (DEP), a contact-free particle manipulation technique, will reduce clot formation in biomedical devices. In this paper, the effect of DEP on thrombogenesis in human blood is investigated. Undiluted whole blood from human donors is pumped through microchannels at a physiological shear rate (400s-1 ). Experiments are performed by applying 0V, 0.5Vrms , 2Vrms , and 3Vrms to electrodes in the channel. Clot formation is observed to decrease in experiments in which DEP electrodes are active (average of 6% coverage @ 0V reduced to 0.08% coverage @ 3Vrms ). Repulsion is more effective at higher voltages. DEP causes a quantifiable reduction in microscopic and macroscopic clot formation in PDMS microchannels.

Blood Products, Crystalloids, and Rapid Infusion: An Experimental Study.

Electromagnetic coil overheating, deformation, occlusion, and rupture during rapid infuser use have been previously reported. Although the etiology is unclear, prolonged machine use and reconstitution of citrated blood components with crystalloid solutions in the reservoir have been implicated. Lactated Ringer's (LR) solution is of particular concern as a diluent because of its calcium content. We sought to reproduce this failure mode using different infusion rates and different combinations of fluids for blood product reconstitution in the reservoir. We also introduced calcium chloride (CaCl2) to the mix to determine its role in macroscopic clot formation. In this in vitro study, we conducted 2 series of experiments using the Belmont FMS 2000 rapid infuser and a reservoir. In series I, we submitted a mix of 1 U fresh thawed plasma (FTP) and 1 U red blood cells (RBC) with 500 mL of LR solution, normal saline, Plasma-Lyte A, or albumin 5% to a specific pump flow sequence. If neither a pump failure mode or self-shutoff (primary outcome) nor macroscopic clot (secondary outcome) was observed during a pump flow sequence, the sequences were repeated after first adding an additional 500 mL of the initially used crystalloid or albumin and then CaCl2 beginning with 200 mg and up to 1 g to the reservoir. In series II, 7 different crystalloid-blood product combinations were tested by using a variety of pump flow sequences with the same end points. Descriptive statistics and analysis of variance were used, and data were reported as means ± SD. We did not observe a Belmont pump failure mode (coil deformation, occlusion, or rupture) as previously described. In series I, the addition of CaCl2 200 mg resulted in macroscopic clots in 9 of 10 experiments (95% confidence interval, 0.55-0.99). The time to clot formation was 9.1 ± 2.3 minutes (99% confidence interval, 6.74-11.46) and did not differ between solutions used for component reconstitution. In series II, adding variable amounts of CaCl2 to 4 different combinations of FTP/RBC with Plasma-Lyte A or LR solution led to clot formation. The use of only FTP in 2 experiments with either LR solution or normal saline resulted in formation of a fibrin clot. In 1 experiment of LR solution mixed with RBCs alone, no clot was observed even after addition of 1 g CaCl2. After the observation of clot in the reservoir, the fluid empty alarm occurred once in series I, the overheating alarm occurred once in series II, and the high-pressure alarms occurred 3 times in each series, all accompanied by self-shutoff. In this in vitro study, we were unable to reproduce the failure mode characterized by coil overheating, deformation, and rupture previously reported with use of the FMS 2000. Addition of CaCl2 in the range of 200 mg caused macroscopic coagulation in the reservoir when added to crystalloids or albumin mixed with different combinations of blood products containing FTP.

Significance of platelet and monocyte activation for therapeutic immunoglobulin-induced thromboembolism

Thromboembolic events (TEE) in patients receiving infusions of intravenous immunoglobulin (IVIG) products have recently been associated with contaminating factor XIa. We studied whether platelet and monocyte activation could also be involved. Twenty IVIG samples from five manufacturers were tested for the induction of visible whole blood clot formation. A selection of TEE-associated and not associated lots was further analyzed for effects on thromboelastometry, platelet activation and adhesion, as well as monocyte tissue factor surface expression. Pure factor XIa was included for comparison. Western blotting was applied to analyze anti-CD154-reactive proteins in IVIG. In whole blood, IVIG enhanced macroscopic clotting additively with factor XIa. In monocytes, all IVIG products induced the FcγRII-dependent tissue factor expression to a similar extent, which was not affected by addition of factor XIa. Testing platelet aggregation, IVIG strengthened the ADP and TRAP-6-elicited response. Furthermore, IVIG increased platelet-monocyte adhesion and annexin V binding to platelet microvesicles, and promoted platelet adhesion to IVIG-coated surfaces. The strongest effects were observed with TEE-associated lots. CD154-related proteins were detected in all IVIG products. CD154-related high molecular weight complexes were particularly found in the TEE-associated IVIG. In platelet aggregation, recombinant soluble CD154 enhanced aggregate formation and stability. Our data demonstrate that IVIG modulate platelet and monocyte activation and can thereby affect the hemostatic balance. These effects are either additive to or independent from factor XIa. CD154-related proteins are assumed to be involved in these interactions, the mechanism of which needs to be elucidated in further studies.

Impact of livestock hygiene education programs on mastitis in smallholder water buffalo ( Bubalus bubalis) in Chitwan, Nepal

A project implemented from 2003 to 2005 trained women in Chitwan District, Nepal, in hygienic dairy production using a process of social mobilization. The aim of this research was to assess if the prevalence of mastitis in water buffalo in the households of women who were trained was lower one year after training than in untrained households, if the training influenced knowledge and practices for the prevention or control of mastitis, and if these practices and knowledge were associated with a lower prevalence of mastitis. A total of 202 households from Eastern and Western Chitwan District were included in the study. Of these, 60 households had participated in the project and 142 had not. Milk samples were collected from 129 households (33 project households and 96 non-project households). Clinical mastitis was determined using visual inspection of udders and detection of macroscopic clots and flakes in milk. The California Mastitis Test was used to diagnose sub-clinical mastitis from milk samples, and the IDEXX SNAP test to identify the presence of tetracycline residues. The prevalence of mastitis in trained households (39.4%) was 43.78% of that in untrained households (60.4%), lower but not significantly so ( p = 0.08, 95% CI 0.17–1.12). Thirteen indicators of knowledge or practice for the control or prevention of mastitis were more likely to occur in trained households, four significantly so (not consuming milk from sick buffalo ( p = 0.001), using soap to wash hands before milking ( p = 0.001), discarding milk after antibiotic usage ( p = 0.01), and choosing appropriate flooring for their livestock ( p = 0.03)). Trained households that discarded milk from sick buffalo were 2.96 times more likely to have at least one animal with mastitis in the household ( p = 0.03, 95% CI 1.15–7.65). Trained households that knew to wash buffalos’ teats after milking were less likely (OR 0.25) to have mastitis in their herd ( p = 0.02, 95% CI 0.08–0.80). Of the 138 buffalos tested, only one tested positive for tetracycline residues.

Intraoperative blood salvage and retransfusion from citrate treated wounds is safe and feasible

Objectives. Allogenic blood transfusions are associated with increased morbidity and mortality in surgical patients. The study objective was to investigate the feasibility and safety of intraoperative autotransfusion of unwashed shed whole blood using a novel method. Design. Twenty pigs were randomised to autotransfusion or crystalloid volume replacement. In two separate surgical wounds, the surfaces and 400 ml of shed blood were treated in situ with citrate, delivered with an equipment transforming suction to positive pressure. Central haemodynamics were monitored with a pulmonary artery catheter. Effects on oxygen-carrying capacity, formed blood elements, haemolysis, inflammation, metabolism, and coagulation were evaluated with biochemical analyses. Results. No clinically relevant adverse effects on haemodynamics were encountered, apart from a decrease in cardiac output and mixed venous saturation similar to that in control animals. Haemoglobin level was better preserved in the autotransfused group (97 vs. 86 g/L, p=0.0007). There were no major differences in biochemical variables and no macroscopic clot formation precluding autotransfusion. Conclusions. The technique was safe and feasible for intraoperative blood salvage and auotransfusion. Haemodynamics and biochemical variables were similar to controls. The technique warrants further studies in humans, as it may contribute towards a reduction of allogenic blood transfusions.

Thrombolysis as a Therapeutic Modality in Cardiac Arrest

Introduction In recent years, thrombolysis has emerged as a potentially promising treatment for cardiac arrest. Patients with cardiac arrests from myocardial infarction or pulmonary embolism, as well as out-of-hospital cardiac arrests, were reported to have improvement in both survival and neurologic outcome after being treated with thrombolysis. This paper aims to review the available literature on the use of thrombolysis in cardiac arrest. Method Study of papers from PubMed literature search for all articles with terms related to thrombolysis and cardiac arrest in title or abstract. Results Thrombolytics are thought to act by lysing both macroscopic clots and microthrombi, particularly in the cerebral microcirculation, thus alleviating or reversing post-arrest cerebral no-reflow. Their use in cardiac arrest has been restrained by concerns over their safety after cardiopulmonary resuscitation, in particular bleeding-related complications, although these concerns seem to have been misplaced. Conclusions Thrombolysis for cardiac arrest is likely to be most efficacious in a pre-hospital environment, and future research should be directed to this setting.

Safety and Efficacy of Single Bolus Anticoagulation with Enoxaparin for Chronic Hemodialysis. Results of an Open-Label Post-Certification Study

Background: Low-molecular-weight heparin (LMWH) is supposed to be advantageous compared to unfractionated heparin for chronic hemodialysis (HD) with respect to lipid and bone metabolism, polymorphonuclear cell stimulation, induction of antibody-mediated thrombocytopenia, and aldosterone suppression. Due to longer biological half-life, LMWH offers the possibility of single bolus administration. Methods: To assess safety and efficacy of single bolus anticoagulation with enoxaparin for chronic HD, 781 stable HD patients from 79 German dialysis centers (mean age 62 years; 31% ESRD due to diabetes mellitus) were monitored by clinical and laboratory parameters for 32 weeks. Additionally, in a single dialysis center, 22 chronic HD patients were investigated by molecular markers of coagulation during chronic HD under conditions of single bolus or continuous anticoagulation regimens. Anti-Xa activity and the thrombin- antithrombin-III complex (TAT) were determined before the enoxaparin bolus, after 15 min, 2 h, and at the end of HD in venous and arterial blood lines. Results: Chronic HD was performed in 24,117 HD treatments with enoxaparin at a median dose of 70.1 IU/kg (5,000 IU median total dose) for single bolus anticoagulation. In 83.0% of HD treatments, enoxaparin was given as single bolus. In 98.3% of patients no adverse event was reported. No drug-related severe adverse event occurred. Significant clotting problems were observed in only 0.3% of HD treatments with single bolus anticoagulation. As assessed in 257 HD treatments, essentially identical anti-Xa levels were detected at the end of HD with single bolus (50 IU/kg) or continuous (mean total dose 43 IU/kg) anticoagulation regimens. Bolus anticoagulation resulted in higher TAT generation at the end of HD. However, this was not associated with increased macroscopic clot formation. Conclusion: Single bolus anticoagulation with enoxaparin was safe and effective for chronic HD. For a duration of 4 h HD, a median dose of 70 IU/kg can be recommended for regular use, which is in accordance with the manufacturer’s instructions for use of enoxaparin recommending a range of 50–100 IU/kg.

Inhibition of thrombin abrogates the instant blood-mediated inflammatory reaction triggered by isolated human islets: possible application of the thrombin inhibitor melagatran in clinical islet transplantation.

A thrombotic/inflammatory reaction is elicited when isolated islets of Langerhans come in contact with ABO-compatible blood. The detrimental effects of this instant blood-mediated inflammatory reaction (IBMIR) provide a reasonable explanation for the observation that an unexpectedly high number of islets, from several donors, are needed to produce normoglycemia in transplant patients with type 1 diabetes. In this study, the hypothesis that a specific thrombin inhibitor, Melagatran, could reduce IBMIR in an in vitro model in which human islets are exposed to ABO-compatible blood was tested. The administration of Melagatran abrogated IBMIR dose-dependently. Islets exposed to blood, in the absence or presence of 0.4 micromol/l Melagatran, exhibited a loss of integrity and were found to be trapped in macroscopic clots containing platelets and CD11b(+) leukocytes. At concentrations from 1 to 10 micromol/l, Melagatran inhibited both coagulation and complement activation. Also, platelet and leukocyte activation and consumption were decreased. Islet morphology was maintained with almost no platelets adhering to the surface, and infiltration by CD11b(+) leukocytes was considerably reduced. In conclusion, Melagatran significantly reduced IBMIR in this model system. This protective effect indicates that thrombin plays a pivotal role in IBMIR and suggests that thrombin inhibition can improve the outcome of clinical islet transplantation.

Cord blood collection before and after placental delivery: levels of nucleated cells, haematopoietic progenitor cells, leukocyte subpopulations and macroscopic clots.

The number of nucleated cells infused into the recipient of a cord blood (CB) transplant has emerged as the most important factor affecting the probability and speed of engraftment. At present, there is no international consensus on the procedure of CB collection in the maternity ward. In order to maximise the yield of viable cells in a CB unit, we aimed to investigate the efficiency of CB collection, with respect to the time of delivery of the placenta. We analysed stem and progenitor cells in terms of CD34+ cell content and colony-forming activities, lymphocyte subpopulations and the presence of macroscopic clots in 93 paired CB samples, collected before and after the delivery of the placenta. Our results demonstrated that the median concentrations of nucleated cells and total colony-forming unit (CFU) were significantly lower in CB collected after placenta delivery by 9.5% (P < 0.001) and 11.6% (P = 0.015), respectively, when compared to their counterparts collected before placental delivery. A reduction of granulocytes (P < 0.001), monocytes (P < 0.001) and CD19+ B lymphocytes (P = 0.031) was observed, with no significant change in the proportion of T cell subsets (CD4+, CD8+ cells) or activated T cells (CD25+, CD45RO+ cells) in samples collected after placenta delivery. The incidence of macroscopic clots was also higher in these samples (31% vs 1%, P < 0.001). The reduction of stem and progenitor cells correlated significantly with that of major cell populations, indicating a general cell loss, possibly due to clotting activities developed with time. Our study has documented strong evidence for recommending the collection of CB before the delivery of the placenta.

Titanium Is a Highly Thrombogenic Biomaterial: Possible Implications for Osteogenesis

Titanium has superior osteointegrating properties compared to other biomaterials. The mechanism for this is unknown. During the initial phase of bone implantation the biomaterial comes into direct contact with whole blood. In this study we use a newly developed in vitro chamber model to compare different commonly used biomaterials in contact with whole blood. These materials were selected with respect to their different osteointegrating properties in order to correlate these properties with the response to whole blood. In the presence of 3 IU/ml of heparin only titanium induced macroscopic clotting. This was reflected by the generation of thrombin-antithrombin which was much increased in blood in contact with titanium compared with steel and PVC. The coagulation activation caused by titanium was triggered by the intrinsic pathway because the generation of FXIIa-AT/C1 esterase inhibitor paralleled that of thrombin-antithrombin, and both thrombin-antithrombin complex and FXIIa-AT/C1 esterase inhibitor generation were abrogated by corn trypsin inhibitor, which is a specific inhibitor of FXIIa. The binding of platelets was increased on the titanium surface compared to the other biomaterial surfaces and the state of platelet activation was much more pronounced as reflected by the levels of beta-thromboglobulin and PDGF. This study indicates that titanium is unsuitable as a biomaterial in devices which are in direct contact with blood for a prolonged period. Furthermore, PDGF and other alpha-granule proteins e.g. TGF-beta, are known to be potent promotors of osteogenesis which suggests that the pronounced thrombogenic properties of titanium might contribute to the good osteointegrating properties.

Twenty-four-hour venoarterial extracorporeal membrane oxygenation without systemic heparinization in dogs

Venoarterial extracorporeal membrane oxygenation (ECMO) was performed in five dogs without systemic heparinization to assess the feasibility of heparin-free ECMO. The surfaces of the inverted hollow-fiber-type oxygenator and circuit of the ECMO system were coated with heparin by the endpoint-attached (covalent-bonded) technique. No heparin was administered to the animal except for a small dose to maintain patency of the arterial line (1 IU/h). ECMO was run for 24 h at a pump flow of 50 ml/kg · min and was successful throughout the experiment in four of the five dogs. Scanning electron microscopy did not detect any blood clots in the oxygenator or circuit except for inside and outside the cannulas that were not coated with heparin in the carotid artery and jugular vein. Activated clotting time (ACT), fibrinogen, and anti-thrombin III (AT-III) activity remained within the normal physiological range. Serum heparin concentrations were low throughout the experiment, indicating minimal heparin release. Platelet levels decreased and fibrinopeptide B β15-42 (FPB β15-42) increased significantly after 6 h ECMO. D-dimer levels did not change throughout the experiment. ECMO was discontinued in one case after successful a 23-h run because of macroscopic clot formation at the oxygenator blood inlet. ACT had suddenly increased to 160 s approximately 1 h prior to this clot formation. These results suggest that the amount of systemic heparinization required can be substantially reduced by a heparin-coated ECMO system. Total abolishment of heparin administration in pediatric venoarterial ECMO may be possible by refinement of this technique. Monitoring of AT-III and FPB β15-42 in addition to ACT may be useful for early diagnosis of latent but ongoing coagulopathies during ECMO.

Control and Treatment of Hemostasis in Cardiovascular Surgery.

The hemostasis protocol applied at the Cardiovascular Surgery Dept. of La Pitié Hospital has greatly reduced thromboembolic accidents and excessive bleeding, with consequent benefits for patients as well as cost reduction. Protocol also has been adopted for patients implanted with a circulatory assist device or a TAH. This paper presents our criteria on supervision and treatment of coagulation with such patients, who reflect all the acquired pathology in clinical hemostasis. From 04/86 to 07/94, 82 patients underwent TAH as a bridge to transplantation. Mean age: 38. Overall duration of mechanical support: 1930 days (mean: 23), of which 137 and 603 for 2 patients. Average duration of CPB: 150 min. Systematic approach to complex TAH-blood interaction and pre-operative multiple organ dysfunction used to control bleeding and/or thromboembolism after CPB. In addition to routine tests, specific regular testing was carried out at least once a day for platelet functions, for thrombin formation and its regulatory pathways, and for the fibrinolytic system. Patients were treated with small doses of Heparin, large doses of Dypyridamole, small doses of Aspirin, modulated doses of Aprotinin, Ticlopidine, Pentoxifylline, FFP, as well as Fibrinogen and AT III concentrates. Dosage was adapted to patient's clinical profile as well as to test interpretation criteria to provide personalized treatment. DIC, widely present in its different phases, was thus diagnosed and treated. All DIC bleeding was controlled, making it possible to detect other causes of post-operatory bleeding and use blood derivates rationally. There were no thromboembolic complications and no iatrogenic bleeding. TAH explanation shows no evidence of macroscopic clots in high risk sites, confirmed by microscopic analysis.

Retrieval of Placental Blood From the Umbilical Vein to Determine Volume, Sterility, and Presence of Clot Formation

From August 1988 to October 1989, 60 specimens of citrate-phosphate-dextrose-adenine anticoagulated blood were retrieved from the placental umbilical veins of newborns from three gestational age groups. The specimens were removed with a needle and syringe apparatus and placed directly into sterile transfusion packs. The specimens were evaluated for the volume obtained, sterility, and presence of macroscopic clots. A blood volume sufficient to provide at least one transfusion (10 mL/kg) for 87% of the premature infants studied was retrieved from the placenta. A greater blood volume per unit of birth weight was recovered from the placentas of the smaller newborns. A 12% positive culture frequency and a 7% frequency of detectable clots were identified. These rates of occurrence suggest the need for further studies to determine the origins of these complicating factors before the adoption of this technique in the clinical setting. These findings support the hypothesis that, with proper patient selection and with specimen culture and filtration, placental blood may be a viable option for the autologous transfusion of sick, premature infants.

Dose Finding Study of a Low Molecular Weight Heparin, Innohep, in Haemodialysis

A pilot investigation was performed with Innohep, a low molecular weight (LMWH) preparation (peak maximum molecular mass 3,000-6,000), to determine possible dose regimens for patients undergoing regular maintenance haemodialysis for chronic renal failure. Results from this study suggested that suppression of macroscopic clot formation and fibrinopeptide A (FPA), a marker of fibrin formation, could be achieved following bolus injections rather than bolus injections and an infusion. On the basis of these preliminary findings, a randomised crossover study was performed in eight patients undergoing regular maintenance haemodialysis for 5-7 h to determine the effective antithrombotic dose of this LMWH. Single i.v. bolus doses of 1,250 AFXa u, 2,500 AFXa u and 5,000 AFXa u (n = 7-8) were compared to an UFH regime of 5,000 iu + 1,500 iu/h. Excessive clot formation in the dialyser bubble trap, necessitating additional UFH to enable completion of a prolonged (up to 7 h) dialysis, was observed in all patients on the 1,250 AFXa u dose (mean duration of dialysis prior to UFH, 3 h) but in a single patient only receiving the other LMWH doses. A dose-related response in the AFXa activity, measured by chromogenic substrate (CS) assay was seen in the three LMWH groups, with levels declining significantly (p less than 0.05) from 1-7 h. This contrasted with the constant levels maintained during dialysis with UFH. FPA levels were significantly elevated after 2 h following the 1,250 AFXa u bolus and after 4 h following the 2,500 AFXa u bolus. There was no significant difference in FPA levels between the 5,000 AFXa u bolus and UFH.(ABSTRACT TRUNCATED AT 250 WORDS)