Hydroxyethyl starch enhances fibrinolysis in human plasma by diminishing α2-antiplasmin–plasmin interactions

Ethyl Hydroxyethyl Cellulose-A Biocompatible Polymer Carrier in Blood

The biocompatibility of carrier nanomaterials in blood is largely hampered by their activating or inhibiting role on the clotting system, which in many cases prevents safe intravascular application. Here, we characterized an aqueous colloidal ethyl hydroxyethyl cellulose (EHEC) solution and tested its effect on ex vivo clot formation, platelet aggregation, and activation by thromboelastometry, aggregometry, and flow cytometry. We compared the impact of EHEC solution on platelet aggregation with biocompatible materials used in transfusion medicine (the plasma expanders gelatin polysuccinate and hydroxyethyl starch). We demonstrate that the EHEC solution, in contrast to commercial products exhibiting Newtonian flow behavior, resembles the shear-thinning behavior of human blood. Similar to established nanomaterials that are considered biocompatible when added to blood, the EHEC exposure of resting platelets in platelet-rich plasma does not enhance tissue thromboplastin- or ellagic acid-induced blood clotting, or platelet aggregation or activation, as measured by integrin α_IIbβ₃ activation and P-selectin exposure. Furthermore, the addition of EHEC solution to adenosine diphosphate (ADP)-stimulated platelet-rich plasma does not affect the platelet aggregation induced by this agonist. Overall, our results suggest that EHEC may be suitable as a biocompatible carrier material in blood circulation and for applications in flow-dependent diagnostics.

Intravenous Fluid Administration and the Coagulation System

Intravenous fluid administration in veterinary patients can alter coagulation function by several mechanisms. Both crystalloid and colloid fluids cause hemodilution, reducing platelet count and plasma coagulation protein concentrations. Hemodilution is associated with a hypercoagulable effect at low dilutions and a hypocoagulable effect at higher dilutions. Composition of crystalloid fluids likely has a minor effect, primarily dependent on fluid ion composition. Hypertonic crystalloids may also cause hypocoagulability. Colloids, both synthetic and natural, can cause hypocoagulability by several mechanisms beyond the effects of hemodilution. These include impaired platelet function, decreased plasma coagulation factor activity, impaired fibrin formation and crosslinking, and accelerated fibrinolysis. The vast majority of the veterinary literature investigates the hypocoagulable effects of hydroxyethyl starch-containing fluids using in vitro, experimental, and clinical studies. However, results are inconsistent, likely due to the varying doses and physicochemical properties of the specific fluid products across studies. In addition, some evidence exists for hypocoagulable effects of gelatin and albumin solutions. There is also evidence that these colloids increase the risk of clinical bleeding in people. Limitations of the veterinary evidence for the hypocoagulable effects of colloid fluids include a predominance of in vitro studies and in vivo studies using healthy subjects, which exclude the interaction of the effects of illness. Therefore, clinical relevance of these effects, especially for low-molecular-weight hydroxyethyl starch, is unknown. Firm recommendations about the most appropriate fluid to use in clinical scenarios cannot be made, although it is prudent to limit the dose of synthetic colloid in at-risk patients. Clinicians should closely monitor relevant coagulation assays and for evidence of hemorrhage in at-risk patients receiving any type of fluid therapy, especially in large volumes.

Effects of Tranexamic Acid Based on its Population Pharmacokinetics in Pediatric Patients Undergoing Distraction Osteogenesis for Craniosynostosis: Rotational Thromboelastometry (ROTEMTM) Analysis

Background: Distraction osteogenesis for craniosynostosis is associated with significant hemorrhage. Additionally, patients usually require several transfusions. Tranexamic acid (TXA) is effective for reducing blood loss and the need for transfusions during surgeries. However, the significance of TXA infusion has not been thoroughly described yet. Methods: Forty-eight children undergoing distraction osteogenesis for craniosynostosis were administered intraoperative TXA infusion (loading dose of 10 mg/kg for 15 min, followed by continuous infusion at 5 mg/kg/h throughout surgery; n = 23) or normal saline (control, n = 25). Rotational thromboelastometry (ROTEM^TM) was conducted to monitor changes in coagulation perioperatively. Results: Blood loss during surgery was significantly lower in the TXA-treated group than it was in the control group (81 vs. 116 mL/kg, P = 0.003). Furthermore, significantly fewer transfusions of red blood cells and fresh frozen plasma were required in the TXA group. In the control group, clotting time during the postoperative period was longer than it was during the preoperative period. Similarly, clot strength was weaker during the postoperative period. D-dimer levels dramatically increased in the control group compared with the TXA group after surgery. The duration of mechanical ventilation and the number of postoperative respiratory-related complications were significantly greater in the control group than they were in the TXA group. Conclusions: TXA infusion based on population pharmacokinetic analysis is effective in reducing blood loss and the need for transfusions during the surgical treatment of craniosynostosis. It can also prevent the increase in D-dimer levels without affecting systemic hemostasis.

An Investigation Into the Effects of In Vitro Dilution With Different Colloid Resuscitation Fluids on Clot Microstructure Formation

BACKGROUND

Balancing the beneficial effects of resuscitation fluids against their detrimental effect on hemostasis is an important clinical issue. We aim to compare the in vitro effects of 3 different colloid resuscitation fluids (4.5% albumin, hydroxyethyl starch [Voluven 6%], and gelatin [Geloplasma]) on clot microstructure formation using a novel viscoelastic technique, the gel point. This novel hemorheologic technique measures the biophysical properties of the clot and provides an assessment of clot microstructure from its viscoelastic properties. Importantly, in contrast to many assays in routine clinical use, the measurement is performed using unadulterated whole blood in a near-patient setting and provides rapid assessment of coagulation. We hypothesized that different colloids will have a lesser or greater detrimental effect on clot microstructure formation when compared against each other.

METHODS

Healthy volunteers were recruited into the study (n = 104), and a 20-mL sample of whole blood was obtained. Each volunteer was assigned to 1 of the 3 fluids, and the sample was diluted to 1 of 5 different dilutions (baseline, 10%, 20%, 40%, and 60%). The blood was tested using the gel point technique, which measures clot mechanical strength and quantifies clot microstructure (df) at the incipient stages of fibrin formation.

RESULTS

df and clot mechanical strength decrease with progressive dilution for all 3 fluids. A significant reduction in df from baseline was recorded at dilutions of 20% for albumin (P < .0001), 40% for starch (P < .0001), and 60% for gelatin (P < .0001). We also observed significant differences, in terms of df, when comparing the different types of colloid (P < .0001). We found that albumin dilution produced the largest changes in clot microstructure, providing the lowest values of df (= 1.41 ± 0.061 at 60% dilution) compared with starch (1.52 ± 0.081) and gelatin (1.58 ± 0.063).

CONCLUSIONS

We show that dilution with all 3 fluids has a significant effect on coagulation at even relatively low dilution volumes (20% and 40%). Furthermore, we quantify, using a novel viscoelastic technique, how the physiochemical properties of the 3 colloids exert individual changes on clot microstructure.

FIBTEM provides prediction of massive bleeding in total hip replacement arthroplasty

This retrospective study evaluated the association between maximum clot firmness of FIBTEM (MCFFIB) and blood loss, and determined a cutoff value of MCFFIB that may predict massive bleeding in total hip replacement arthroplasty (THRA). Seventy-two adult patients undergoing THRA for avascular necrosis of the femoral head or degenerative arthritis of the hip were included. Patients' medical records were reviewed to collect pre and postoperative laboratory data, as well as the amount of intra and postoperative blood loss (IBL and PBL). Each pre and postoperative fibrinogen level had a significant correlation with the pre and postoperative MCFFIB, respectively (ρ = 0.289, P = 0.014 and ρ = 0.286, P = 0.015). IBL had significant correlations with pre and postoperative MCFFIB (ρ = -0.305, P = 0.010 and ρ = -0.297, P = 0.013, respectively), and PBL also showed significant correlations with the pre and postoperative MCFFIB (ρ = -0.471, P < 0.001 and ρ = -0.475, P < 0.001, respectively). A respective pre or postoperative MCFFI cutoff value of 16 mm or less or 10 mm or less showed the highest sensitivity and specificity for predicting IBL 1000 ml or above or PBL 400 ml or above. Postoperative transfusion was performed more frequently in patients showing postoperative MCFFIB 10 mm or less (31 vs. 3.3%, P = 0.005). MCFFIB correlated well with the amount of IBL or PBL. In addition, a particular value of pre or postoperative MCFFIB could offer the predictive standard for massive bleeding in THRA.

Comparison of the effects of a balanced crystalloid-based and a saline-based tetrastarch solution on canine whole blood coagulation and platelet function

OBJECTIVE

To evaluate the effects of a 6% hydroxyethyl starch (130/0.42) solution in either a buffered, electrolyte-balanced (HES-BAL), or a saline (HES-SAL) carrier solution on canine platelet function and whole blood coagulation.

DESIGN

Prospective, randomized study.

SETTING

University teaching hospital.

ANIMALS

Thirty-seven client-owned dogs undergoing general anesthesia for arthroscopy or imaging studies.

INTERVENTIONS

Dogs received a 15 mL/kg intravenous bolus of HES-SAL (n = 13), HES-BAL (n = 14), or a modified Ringer's solution (n = 10) over 30-40 minutes. Coagulation was analyzed using a Platelet Function Analyzer-100 (closure time [Ct_PFA ]), and whole blood thromboelastometry (ROTEM) with extrinsically (ex-tem and fib-tem) and intrinsically (in-tem) activated assays, which assessed clotting time (CT), clot formation time (CFT), maximal clot firmness (MCF), and lysis index (LI). Coagulation samples were assayed prior to fluid administration (T0), and 5 minutes (T1), and 3 hours (T2) following fluid bolus administration, respectively.

RESULTS

Both HES solutions resulted in impaired platelet function as indicated by a significant prolongation of Ct_PFA at T1 as compared to T0, but which resolved by T2. An IV bolus of Ringer's solution did not alter platelet function. In both HES groups, whole blood coagulation was significantly impaired at T1 as indicated by a significant increase in in-tem CFT, and a significant decrease in ex-tem, in-tem, and fib-tem MCF compared to T0. Furthermore, a significant increase in ex-tem CFT at T1 compared to T0 was found in the HES-SAL group. With the exception of in-tem MCF after HES-BAL, these effects were not present at T2. No significant differences were found in Ct_PFA or any ROTEM variable at any time point between HES-SAL and HES-BAL.

CONCLUSION

Administration of a single bolus of 15 mL/kg 6% HES 130/0.42 results in significant but short-lived impairment of canine platelet function and whole blood coagulation, regardless of carrier solution.

The effect of tranexamic acid on blood coagulation in total hip replacement arthroplasty: rotational thromboelastographic (ROTEM®) analysis

We evaluated changes in rotational thromboelastometry (ROTEM(®) ) parameters and clinical outcomes in patients undergoing total hip replacement arthroplasty, with concomitant infusions of tranexamic acid and of 6% hydroxyethyl starch 130/0.4. Fifty-five patients were randomly assigned to either the tranexamic acid (n = 29) or the control (n = 26) group. Hydroxyethyl starch was administered in the range of 10-15 ml.kg(-1) during the operation in both groups. In the control group, the clot formation time and maximum clot firmness of APTEM showed significant differences when compared with those of EXTEM at one hour postoperatively, suggestive of fibrinolysis. In the tranexamic acid group, there was no significant difference between each postoperative EXTEM and APTEM parameter. In the tranexamic acid and control group, postoperative blood loss was 308 ml (210-420 [106-745]) and 488 ml (375-620 [170-910], p = 0.002), respectively, and total blood loss was 1168 ml (922-1470 [663-2107]) and 1563 ml (1276-1708 [887-1494], p = 0.003). Haemoglobin concentration was higher in the tranexamic acid group on the second postoperative day (10.5 (9.4-12.1 [7.9-14.0]) vs. 9.6 (8.9-10.5[7.3-16.0]) g.dl(-1) , p = 0.027). In patients undergoing total hip replacement arthroplasty, postoperative fibrinolysis aggravated by hydroxyethyl starch was attenuated by co-administration of 10 mg.kg(-1) tranexamic acid, which may have led to less postoperative blood loss.

Hydroxyethyl starch: a review of pharmacokinetics, pharmacodynamics, current products, and potential clinical risks, benefits, and use

OBJECTIVE

To review and summarize the pharmacokinetics and pharmacodynamics of hydroxyethyl starch (HES), as well as reported risks and benefits of HES infusion, and to provide administration and monitoring recommendations for HES use in dogs and cats.

DATA SOURCES

Veterinary and human peer-reviewed medical literature, including scientific reviews, clinical and laboratory research articles, and authors' clinical experience.

SUMMARY

HES solutions are the most frequently used synthetic colloid plasma volume expanders in human and veterinary medicine. The majority of research in human medicine has focused on the adverse effects of HES infusion, with emphasis on acute kidney injury and coagulation derangements. The studies often differ in or fail to report factors, such as the type, amount, interval, and concentration of HES administered; the patient population studied; or concurrent fluids administered. Currently, there is no definitive clinical evidence that the reported adverse effects of HES use in human medicine occur in veterinary species. There is little information available on HES administration techniques or simultaneous administration of additional fluids in human and veterinary medicine. The rationale for HES use in small animals has been largely extrapolated from human medical studies and guidelines. A controlled approach to intravenous fluid resuscitation using crystalloid and HES volumes titrated to reach desired resuscitation end point parameters is outlined for small animal practitioners.

CONCLUSION

The extrapolation of data from human studies directly to small animals should be done with the knowledge that there may be species variations and different pharmacokinetics with different HES solutions. Veterinary reports indicate that bolus and continuous rate infusions of 6% hetastarch solutions at moderate doses are well tolerated in feline and canine subjects. Further research in domesticated species is necessary to better define and expand the knowledge regarding use of HES solutions in small animal medicine.

Influence of resuscitation fluids, fresh frozen plasma and antifibrinolytics on fibrinolysis in a thrombelastography-based, in-vitro, whole-blood model

Hyperfibrinolysis has been identified as a mechanism of trauma coagulopathy associated with poor outcome. The aim of the study was to create a trauma coagulopathy model (TCM) with a hyperfibrinolysis thrombelastography (TEG) pattern similar to injured patients and test the effects of different resuscitation fluids and antifibrinolytics on fibrinolysis. TCM was established from whole blood by either 15% dilution with isotonic saline, lactated Ringer's, Plasma-Lyte, 5% albumin, Voluven, Hextend, 6% dextran in isotonic saline or 30% dilution with lactated Ringer's plus Voluven and supplementation with tissue factor and tissue plasminogen activator (tPA). These combinations resulted in a TCM that could then be 'treated' with tranexamic acid (TXA) or 6-aminocaproic acid (ACA). Clot formation was evaluated by TEG. Whole-blood dilution by 15% with crystalloids and albumin in the presence of tissue factor plus tPA resulted in an abnormal TEG pattern and increased fibrinolysis, as did dilution with synthetic colloids. TXA 1 μg/ml or ACA 10 μg/ml were sufficient to suppress fibrinolysis when TCM was diluted 15% with lactated Ringer's, but 3 μg/ml of TXA or 30 μg/ml of ACA were needed for fibrinolysis inhibition induced by simultaneous euvolemic dilution with lactated Ringer's plus Voluven by 30%. A total of 15% dilution of whole blood in the presence of tissue factor plus tPA results in a hyperfibrinolysis TEG pattern similar to that observed in severely injured patients. Synthetic colloids worsen TEG variables with a further increase of fibrinolysis. Low concentrations of TXA or ACA reversed hyperfibrinolysis, but the efficient concentrations were dependent on the degree of fibrinolysis and whole-blood dilution.

Management of Dilutional Coagulopathy during Pediatric Major Surgery

Perioperative dilutional coagulopathy is a major coagulation disorder during adult and pediatric surgery. Although the main underlying mechanisms are comparable, data of the development and management of dilutional coagulopathy in children are scarce. Observational data showed that intraoperative coagulation disorders mainly based on complex disturbances of clot firmness including acquired fibrinogen as well as factor XIII deficiencies, while clotting time and platelet counts remained fairly stable. A fast and reliable monitoring of the entire coagulation process (e.g. thrombelastometry) might be of extreme value for detection and guidance of effective coagulation management. Although the transfusion of fresh frozen plasma was recommended in several guidelines, the use of coagulation factors might offer an alternative and potentially superior approach in managing perioperative coagulation disorders. Further studies are urgently needed to determine the efficacy of modern coagulation management.

Argatroban enhances fibrinolysis by differential inhibition of thrombin-mediated activation of thrombin activatable fibrinolysis inhibitor and factor XIII

Direct thrombin inhibitors enhance fibrinolysis more efficiently than heparin. Direct thrombin inhibitors and heparin enhance fibrinolysis by inhibition of activation of thrombin activatable fibrinolysis inhibitor (TAFI); however, the role played by other thrombin-activated proteins [e.g., factor XIII (FXIII)] in fibrinolysis remained to be elucidated. Our goal was thus to define the roles of TAFI and FXIII in direct thrombin inhibitor-mediated fibrinolysis enhancement. Plasma was exposed to argatroban or heparin, with coagulation initiated with kaolin/tissue factor and fibrinolysis initiated with tissue plasminogen activator. Additional experiments utilized TAFI and FXIII-deficient plasmas. Coagulation/fibrinolysis kinetics were monitored with thrombelastography. Argatroban (1.25, 2.5 microg/ml) significantly decreased clot lysis time and increased the maximum rate of lysis compared with unexposed plasma, whereas heparin exposure only diminished clot lysis time. When changes in maximum rate of lysis were related to changes in the maximum rate of thrombus generation, argatroban was associated with a greater increase in maximum rate of lysis per decrease in maximum rate of thrombus generation compared with heparin. Experiments with TAFI-deficient and FXIII-deficient plasma demonstrated a sparing of thrombin-mediated FXIII activation with concurrent inhibition of TAFI activation. The mechanism by which argatroban more efficiently enhanced fibrinolysis was via a differential inhibition of thrombin-mediated activation of TAFI and FXIII.

Beyond cell based models of coagulation: analyses of coagulation with clot "lifespan" resistance-time relationships

Cell based models of coagulation (CBM) have provided mechanistic insight into numerous hematological issues for nearly two decades. This review discusses another coagulation model system--the clot lifespan model (CLSM)--that has been designed to compliment the CBM-based approach to elucidating the mechanisms responsible for a variety of hemostatic disorders/phenomena. The CLSM is a thrombelastograph-based approach that utilizes a standardized clotting stimulus (e.g., celite, tissue factor) and a fibrinolytic stimulus (e.g., tissue type plasminogen activator) to assess clot growth and disintegration via changes in clot resistance. The CLSM utilizes parametric, elastic modulus-based parameters to document these phenomena. The CLSM has recently been employed to discern the effects of protamine and hydroxyethyl starch on key fibrinolytic-antifibrinolytic protein interactions, as well as demonstrating differences in fibrinolytic kinetics dependent on whether contact pathway proteins or tissue factor is used to initiate coagulation. The CLSM is presently being utilized to investigate the effects of ventricular assist device placement on fibrinolysis, and it is anticipated that this model system will be employed in both basic science and clinical investigations in the future.