Evaluation of coagulation during cardiopulmonary bypass with a heparinase-modified thromboelastographic assay

Thromboelastography in the Perioperative Period: A Literature Review

Assessing coagulation status is essential for prompt intervention to reduce morbidity and mortality related to bleeding and thrombotic complications during the perioperative period. Traditional coagulation tests such as platelet count, activated partial thromboplastin time (aPTT), prothrombin time (PT), international normalized ratio (INR), and activated clotting time (ACT) provide only static evaluation. These tests are not designed for assessment of dynamically changing coagulation conditions during the perioperative time. However, viscoelastic coagulation testing such as thromboelastography (TEG) produces a rapid numerical and graphical representation that helps to detect and direct targeted hemostatic therapy. Searching the literature through PubMed, Medline, Ovid, CINAHL, and ClinicalTrials.gov we retrieved 210 studies, which represent the use of TEG in the perioperative period. The included studies were categorized under various settings such as trauma, obstetrics, orthopedics, intensive care unit (ICU), cardiovascular, transplant, and miscellaneous scenarios. TEG showed promising results in trauma surgeries in predicting mortality, hypercoagulability, and bleeding even when it was compared to conventional methods. TEG was also useful in monitoring anticoagulant therapy in orthopedic and obstetric surgeries; however, its role in predicting thrombotic events, hypercoagulability, or complications was questionable. In ICU patients, it showed promising results, especially in the prediction or improvement of sepsis, coagulopathy, thrombotic events, ICU duration, hospital stay, and ventilator duration. TEG parameters effectively predicted hypercoagulation in transplant surgeries. Regarding cardiovascular surgeries, they were effective in the prediction of the need for blood products, coagulopathy, thrombotic events, and monitoring anticoagulation therapy. More randomized clinical trials comparing TEG parameters with standardized tools are needed to produce robust results to standardize its use in different perioperative settings.

Use of viscoelastic tests in the principle bleeding scenarios in Spanish hospitals

Viscoelastic tests are designed to study the dynamics of clot formation, identify coagulopathies in real time, arrive at a diagnosis, and guide patient-specific administration of haemostatics. They are mainly used to treat clinically significant bleeding in any setting, and are also used in other situations involving clinically relevant alterations in haemostasis, such as coagulopathy in critically ill patients. These tests are administered following evidence-based algorithms that vary depending on the clinical context. This review summarises the results of a survey conducted in several hospitals to determine the prevalence and standardisation of viscoelastic tests in cardiac surgery, liver transplantation, and multiple trauma patients in Spain. The results reveal divergent opinions on key aspects, ranging from the diagnostic capacity of these tests to the interpretation of the basic parameters. On the basis of these findings, we propose a number of potential areas in which further research will improve the performance of these tests.

Viscoelastic Testing in the Management of Adult Patients on Mechanical Circulatory Support Devices with Focus on Extracorporeal Membrane Oxygenation

Thromboembolic and hemorrhagic complications continue to remain frequent complications that significantly impact the morbidity and mortality of patients implanted with mechanical circulatory support devices (MCSDs). The severe acute respiratory syndrome caused by coronavirus 2 (SARS-CoV-2) has resulted in a number of COVID-19 patients being supported by MCSDs, specifically extracorporeal membrane oxygenation (ECMO), which in turn has created a crucial need for rapid assessment of hemostatic status in these patients to avoid bleeding and thrombotic complications. Currently, conventional plasma-based coagulation assays such as prothrombin time and activated partial thromboplastin time (aPTT) are used to assess hemostasis, and the activated clotting time (ACT) and aPTT are the most common tests used to monitor heparin anticoagulation in patients on ECMO. Unfractionated heparin remains the mainstay anticoagulation therapy for patients on ECMO. Extracorporeal Life Support Organization (ELSO) offers little guidance on the subject but does state that each institution should create its internal anticoagulation protocols. Viscoelastic assays (VEAs) are increasingly recognized by ELSO and ECMO community for their potential to assess hemostatic derangements in patients implanted with MCSDs as well as guidance for appropriate hemostatic therapy. This review focuses on the evidence for the use of viscoelastic assays to assess overall hemostasis and to guide the treatment of adult patients connected to an ECMO circuit. Limitations of the use of conventional assays, ACT, and VEA are also discussed.

Prognostic value of repeated thromboelastography measurement for favorable neurologic outcome during targeted temperature management in out-of-hospital cardiac arrest survivors

BACKGROUND

Cardiac arrest can activate blood coagulation, which clinically manifests as obstruction of the microcirculation and multiple organ dysfunction. Thromboelastography (TEG) provides a rapid and comprehensive assessment of hemostatic processes, but there are limited data on the use of sequential TEG values during targeted temperature management (TTM) in out-of-hospital cardiac arrest (OHCA) survivors. The aim of this study was to investigate the prognostic value of coagulopathy assessed by repeated TEG to predict neurologically intact survival.

METHODS

A prospective cohort of consecutive non-trauma OHCA patients who were successfully resuscitated and treated with TTM. Patients with a target temperature of 36 ℃, no TEG data, and who declined appropriate treatment were excluded. TEG was measured at three time points of TTM (initial phase, target phase, and rewarming phase). The primary outcome was 28 day favorable neurologic function, defined as a Cerebral Performance Category of 1 or 2.

RESULTS

A total of 125 patients (mean age, 61 years; 63.2% male) were analyzed. A favorable neurologic outcome at 28 days was seen in 40 patients (32.0%). TEG values of R and LY30 in the initial phase were significantly lower in the favorable neurologic outcome group than in the unfavorable group (5.8 vs. 8.1 and 0.1 vs. 0.7, respectively; p < 0.01). TEG values of R < 5 or LY30 < 7.5 in the initial phase were more frequently seen in the favorable outcomes group than in the unfavorable group (37.5% vs. 12.9%, p = 0.002 and 95.0% vs. 72.9%, p = 0.004, respectively). However, no significant differences were seen between the two groups in other TEG values (R, K, alpha, and MA) in the target and rewarming phases (p > 0.05 for all). Univariate analysis showed higher D-dimer levels, prothrombin time, and activated partial thromboplastin time in the unfavorable outcome group. In the multivariable analysis, TEG values of combination of R < 5 and LY30 < 7.5 in the initial phase were the only coagulation profiles seen to be independently associated with favorable neurologic outcome (OR, 4.508, 95% CI, 1.254-16.210).

CONCLUSION

TEG results are available within minutes, and shorted R values or the absence of prolonged LY30 values in the initial phase are an early predictor of neurologically intact survival in successfully resuscitated OHCA patients.

The Effect of Excess Protamine on Thrombelastography in Vitro

The aim of the current study was to assess the direct effect of protamine on conventional thrombelastography in vitro. Protamine was added to blood samples collected from 25 adult cardiac surgical patients prior to the induction of anaesthesia and after separation from cardiopulmonary bypass. The final protamine concentrations were 0 (control), 0.05 mg/ml, 0.1 mg/ml and 0.2 mg/ml (i.e. sufficient to reverse heparin 0, 5, 10 and 20 IU/ml respectively, assuming a 1:1 reversal ratio). In the pre-induction samples, protamine was associated with increases in r time and reductions in maximum amplitude (P<0.01). After bypass, the control samples demonstrated a heparin effect as expected, which was corrected by the addition of protamine 0.05 mg/ml. However, the higher concentrations of protamine were again associated with increases in r time and reductions in maximum amplitude (P<0.01). The results indicate that protamine has a direct anticoagulant effect on conventional thrombelastography in vitro. This effect occurs whether protamine is present alone, or whether protamine is present in excess after neutralization of heparin. Unless this effect is taken into account, excess protamine may confound the interpretation of conventional thrombelastography in cardiac surgical patients.

Systemic Anticoagulant Effect of Low-Dose Subcutaneous Unfractionated Heparin as Determined Using Thrombelastography

In an observational study using heparinase-modified thrombelastography, we investigated the percentage of elective cardiothoracic surgical patients receiving low-dose unfractionated heparin (5000 IU 12 hourly subcutaneously) who had a demonstrable systemic heparin effect.

Blood samples were obtained at induction from 40 adult elective cardiothoracic surgical patients who had received 5000 IU unfractionated heparin subcutaneously within six hours. Simultaneous kaolin and heparinase-modified thrombelastographies were run on all samples. Fourteen patients (35%; 95% CI: 20 to 50%) had a demonstrable heparin effect(defined as a kaolin thrombelastography R time >25% longer than the heparinase-modified control). Their mean±SD kaolin thrombelastography R time was 13.6±5.9 minutes (normal range 4 to 8 minutes) vs. 7.1±2.0 minutes for the heparinase-modified controls. In 10 patients the thrombelastography R times were >50% longer and in four patients >100% longer, than their respective heparinase-modified controls. In a post hoc analysis, there was little correlation between the extent of the prolongation and patient age (r=0.02), weight (r=-0.31), preoperative creatinine (r=-0.17), or time since administration of heparin (r=0.14).

These results indicate that about one third of patients who have received low-dose unfractionated heparin subcutaneously within six hours have a demonstrable heparin effect. The potential for this effect should be considered if central neural blockade is planned.

Evidence Based Coagulation Monitors: Heparin Monitoring, Thromboelastography, and Platelet Function

The hemostatic management of patients undergoing cardiac surgery is a unique challenge. Since its inception, cardiopulmonary bypass (CPB) has required meticulous attention to maintaining adequate anticoagulation. New anticoagulants and alternative monitoring techniques present an opportunity to investigate potential advances in the area of anticoagulation for CPB. Hemostasis after CPB is still a vexing problem, and the addition of antiplatelet medication to the platelet defect already incurred during CPB has led to hemorrhagic complications in cardiac surgery. The two opposing processes of anticoagulation and hemostasis must be managed carefully and modified with respect to the patient's hematologic status and desired hemostatic outcome. Cardiac surgical patients consume a much larger fraction of perioperative blood transfusions than the percentage of the surgical population they represent. Thus, during CPB, careful attention must be paid to optimal anticoagulation, platelet quiescence, biocompatible circuitry and interventions, and to monitoring hemostasis. The multifactorial etiology of the CPB-induced hemostatic defect requires a multimodal approach to blood conservation and hemostasis monitoring, including heparin maintenance and sophisticated point-of-care hemostasis monitoring. Each technology has its own attributes and each may be suitable for different populations based upon the expected defects being measured. This article reviews the evidence supporting the use of point-of-care monitors in coagulation and hemostasis management in cardiac surgical patients.

Platelet Function and Cardiopulmonary Bypass

Cardiopulmonary bypass (CPB) is a nonphysiologic state that has many detrimental effects on a patient's hemostatic integrity. Exposure to the extracorporeal circuit and subsequent activation of the coagulation and fibrinolytic systems are factors that contribute to morbidity and mortality in cardiac surgical patients. These effects can be prevented in part or appropriately treated if practitioners understand the basic mecha nisms. This article reviews the effects of CPB on platelet function, the relationship of platelet function to post operative bleeding, the monitors available to measure platelet function, and the impact of antiplatelet therapy on bleeding in cardiac surgery.

Endogenous Fibrinolysis: An Important Mediator of Thrombus Formation and Cardiovascular Risk

Most acute cardiovascular events are attributable to arterial thrombosis. Plaque rupture or erosion stimulates platelet activation, aggregation, and thrombosis, whilst simultaneously activating enzymatic processes that mediate endogenous fibrinolysis to physiologically maintain vessel patency. Interplay between these pathways determines clinical outcome. If proaggregatory factors predominate, the thrombus may propagate, leading to vessel occlusion. However, if balanced by a healthy fibrinolytic system, thrombosis may not occur or cause lasting occlusion. Despite abundant evidence for the fibrinolytic system regulating thrombosis, it has been overlooked compared with platelet reactivity, partly due to a lack of techniques to measure it. We evaluate evidence for endogenous fibrinolysis in arterial thrombosis and review techniques to assess it, including biomarkers and global assays, such as thromboelastography and the Global Thrombosis Test. Global assays, simultaneously assessing proaggregatory and fibrinolytic pathways, could play a role in risk stratification and in identifying impaired fibrinolysis as a potential target for pharmacological modulation.

Validation of rotational thromboelastometry during cardiopulmonary bypass: A prospective, observational in-vivo study

BACKGROUND

Rotational thromboelastometry (ROTEM) is a whole blood point-of-test used to assess the patient's coagulation status. Three of the available ROTEM tests are EXTEM, INTEM and HEPTEM. In the latter, heparinase added to the INTEM reagent inactivates heparin to reveal residual heparin effect. Performing ROTEM analysis during cardiopulmonary bypass (CPB) might allow the anaesthesiologist to anticipate the need for blood products.

OBJECTIVE

The goal of this study was to validate ROTEM analysis in the presence of very high heparin concentrations during CPB.

DESIGN

Prospective, observational trial.

SETTING

Single University Hospital.

PARTICIPANTS

Twenty patients undergoing coronary artery bypass grafting.

MAIN OUTCOME MEASURE

ROTEM analysis was performed before heparin administration (T0), 10 min after heparin (T1), at the end of CPB (T2) and 10 min after protamine (T3). The following tests were performed: EXTEM, INTEM, and HEPTEM. Heparin concentrations were measured at T1 and at the end of bypass (T2).

RESULTS

At T1, EXTEM differed from baseline for coagulation time: +26.7 s (18.4 to 34.9, P < 0.0001), α: -3° (1.0 to 5.4, P = 0.006) and A10: -4.4 mm (2.3 to 6.5, P = 0.0004). INTEM at T0 was different from HEPTEM at T1 for coagulation time: + 47 s (34.3 to 59.6, P > 0.0001), A10: -2.3 mm (0.5 to 4.0, P = 0.01) and α -2° (1.0 to 3.0; P = 0.0007). At T2, all parameters in EXTEM and HEPTEM related to fibrin-platelet interaction deteriorated significantly compared to T1. At T3, EXTEM and INTEM were comparable to EXTEM and HEPTEM at T2.

CONCLUSION

HEPTEM and EXTEM measurements are valid in the presence of very high heparin concentrations and can be performed before protamine administration in patients undergoing cardiac surgery with CPB.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01455454.

Thrombin based gelatin matrix and fibrin sealant mediated clot formation in the presence of clopidogrel

BACKGROUND

Platelet inhibitors are commonly used to reduce the risk of atherothrombotic events. The aim of this study was to determine the impact of platelet inhibitors, specifically clopidogrel and aspirin, on clot kinetics, strength, and/or structure during the use of thrombin based gelatin matrices and fibrin sealants.

METHODS

Blood was collected and heparinized from donors on clopidogrel (and aspirin) and age matched control donors. Blood component analysis, whole blood platelet aggregometry, and activated clotting time (ACT) were used to monitor compliance to therapy and identify any differences between donor groups. Clot kinetics and strength were analyzed using thrombelastography (TEG). Field Emission Scanning Electron Microscopy (FESEM) was used to analyze clot structure.

RESULTS

Blood component profiles were similar for both donor groups. Aggregometry indicated that aggregation response to adenosine diphosphate (ADP) for clopidogrel donors was 12% of that for the controls (p = 0.0021), an expected result of clopidogrel induced platelet inhibition. However, blood from both donor groups had an elevated thrombin induced aggregation response. Heparinization of donor blood resulted in similarly elevated ACTs for both donor groups. TEG results indicated similar clot kinetics and strength between clopidogrel and control donor groups for blood alone and when clotting was induced using thrombin based gelatin matrices and fibrin sealants. FESEM images supported TEG findings in that similar morphologies were observed in ex vivo formed clots from both donor groups when thrombin based gelatin matrices and fibrin sealants were used.

CONCLUSION

These results suggest that platelet inhibitors do not negatively impact clot kinetics, strength, and structure when clotting is initiated with thrombin based gelatin matrices and fibrin sealants.

Monitoring incomplete heparin reversal and heparin rebound after cardiac surgery

OBJECTIVES

To assess the incidence of incomplete heparin reversal and heparin rebound after cardiac surgery with cardiopulmonary bypass (CPB) and the ability of the activated coagulation time (ACT) and thromboelastography (TEG) to detect these phenomena.

DESIGN

Prospective single-center study.

SETTING

University hospital.

PARTICIPANTS

Forty-one patients undergoing elective cardiac surgery with CPB and with normal preoperative TEG parameters.

INTERVENTIONS

ACT, TEG, and plasma heparin levels were measured in all patients at 5 different times between 20 minutes and 3 hours after protamine administration. The variability of TEG reaction time (R) with and without heparinase (delta-R [DR]) was used to detect the presence of residual heparin.

MEASUREMENTS AND MAIN RESULTS

Plasma heparin expressed as anti-FXa activity was detected in 180 (88%) samples. At univariate analysis, ACT, R-kaolin (R-k), and DR significantly correlated with plasma heparin concentration (respectively, p = 0.007, p = 0.006, and p = 0.002). At multivariate analysis, R-k and DR remained associated with plasma heparin concentration (respectively, p = 0.014 and p = 0.004). Greater quartiles of heparin were associated with higher values of R-k and DR. Combined procedures had significantly lower DR than isolated procedures (p = 0.017), and CPB time and heparinization time positively correlated with R-k (respectively, p = 0.044 and p = 0.022). No association was observed between heparin concentration, ACT, and TEG parameters with postoperative bleeding and need for blood and blood components transfusions.

CONCLUSIONS

Heparin rebound and incomplete heparin reversal are very common phenomena after cardiac surgery with CPB; ACT is not able to detect residual heparin activity, whereas TEG analysis with and without heparinase allows the diagnosis of heparin rebound.

Coagulopathy and hemostatic monitoring in cardiac surgery: an update

OBJECTIVES

Cardiac surgery with cardiopulmonary bypass (CPB) causes severe derangements in the hemostatic system, which in turn puts the patient at risks of microvascular bleeding. Excessive transfusion and surgical re-exploration after cardiac surgery are potentially associated with a number of adverse outcomes including increased mortality.

DESIGN

This review describes coagulopathies occurring in cardiac surgery and the monitoring of these. Viscoelastic hemostatic assays (VHA) have routinely been used in cardiac surgery for more than 25 years and at least 16 studies (involving more than 3250 patients, including three randomized controlled trials) have compared VHA to routine coagulation tests (RCoT) with regards to their ability to predict bleeding and re-do surgery and also with regards to transfusion requirements secondary to hemostatic therapy based on VHA vs. RCoT.

RESULTS

All 16 studies demonstrated superiority with VHA as compared to RCoT both in predicting bleeding and need for re-do surgery and in reducing the total amount of blood transfusions by employing goal-directed administration of blood products based on VHA as compared RCoT based therapy or at the clinicians discretion.

CONCLUSIONS

The different types of coagulopathies observed in patients undergoing cardiac surgery requires adequate and timely hemostatic therapy and real-time monitoring with WHA such as TEG/ROTEM and whole blood platelet aggregometry.

Point-of-care testing in haemostasis

Point-of-care testing (POCT) in haematology has seen a significant increase in both the spectrum of tests available and the number of tests performed annually. POCT is frequently undertaken with the belief that this will reduce the turnaround time for results and so improve patient care. The most obvious example of POCT in haemostasis is the out-of-hospital monitoring of the International Normalized Ratio in patients receiving a vitamin K antagonist, such as warfarin. Other areas include the use of the Activated Clotting Time to monitor anticoagulation for patients on cardio-pulmonary bypass, platelet function testing to identify patients with apparent aspirin or clopidogrel resistance and thrombelastography to guide blood product replacement during cardiac and hepatic surgery. In contrast to laboratory testing, POCT is frequently undertaken by untrained or semi-trained individuals and in many cases is not subject to the same strict quality control programmes that exist in the central laboratory. Although external quality assessment programmes do exist for some POCT assays these are still relatively few. The use of POCT in haematology, particularly in the field of haemostasis, is likely to expand and it is important that systems are in place to ensure that the generated results are accurate and precise.

Point-of-care coagulation testing and transfusion algorithms

Patients with cardiovascular disease have an array of haemostasis disorders that predispose to the development of thrombotic and embolic disease states. These patients are often maintained on anti-thrombotic medication to prevent adverse cardiovascular events. Patients undergoing cardiac surgery also have haemostatic disorders that include their intrinsic disease state, adjunctive medication, and the coagulation disturbances induced by cardiopulmonary bypass. The following review introduces the monitors that are available for monitoring perioperative coagulation, with an emphasis on cardiovascular surgery. Heparin monitors, platelet function monitors for use in transfusion algorithms, and monitoring anti-platelet drugs will be discussed.

The effect of acute autologous blood transfusion on coagulation dysfunction after cardiopulmonary bypass

OBJECTIVE

To evaluate the influence of acute autologous blood transfusion on postcardiopulmonary bypass coagulation disturbances evaluated by thromboelastography (TEG) as a point-of-care test.

METHODS

This prospective randomized controlled study included consecutive patients who underwent elective cardiac surgery with cardiopulmonary bypass. The patients in group A underwent acute autologous blood transfusion with acute normovolemic haemodilution and those in group H received homologous blood, if needed, and served as controls.

RESULTS

A total of 62 patients, from 68 enrolled, completed the study: 27 in group A and 35 in group H. Both groups had similar prolongation of prothrombin time and partial thromboplastin time, decreased platelets count and changes in postoperative thromboelastographic variables. There were no differences between them for postoperative bleeding, blood transfusions or haemoglobin values. There was significant prolongation of the R value of TEG (without heparinase) in both groups at 4 h after surgery compared with the immediate postoperative values: from 11.3 +/- 4.2 to 12.3 +/- 5.5 mm, P < 0.05 for group A and from 9.9 +/- 3.7 to 12.5 +/- 5.4 mm, P < 0.01 for group H. The R values of TEG with and without heparinase differed significantly (P < 0.05) at 4 h postoperatively.

CONCLUSION

Autologous blood transfusion of 15% estimated blood volume did not affect postcardiopulmonary bypass coagulopathy, nor did it decrease blood loss or homologous blood and its products transfusion in the early postoperative period. TEG is a valuable measure for detecting coagulation dysfunction with a potential role in the postoperative management of cardiac patients.

Global hemostasis testing thromboelastography: old technology, new applications

Thromboelastography (TEG) as a method of assessing global hemostatic and fibrinolytic function has existed for more than 60 years. Improvements in TEG technology have led to increased reliability and thus increased usage. The TEG has been used primarily in the settings of liver transplant and cardiac surgery, with proven utility for monitoring hemostatic and fibrinolytic derangements. In recent years, indications for TEG testing have expanded to include managing extracorporeal membrane oxygenation (ECMO) therapy, assessing bleeding of unclear etiology, and assessing hypercoagulable states. In addition, TEG platelet mapping has been utilized to monitor antiplatelet therapy. Correlation between TEG platelet mapping and other platelet function tests such as the PFA-100 or platelet aggregation studies, however, has not been evaluated fully for clinical outcomes, and results may not be comparable. In general, the advantages of the TEG include evaluation of global hemostatic function using whole blood, a quick turn-around-time, the possibility of both point-of-care-testing and performance in central laboratories, the ability to detect hyperfibrinolysis, monitoring therapy with recombinant activated factor VII, and detection of low factor XIII activity. Potential applications include polycythemia and dysfibrinogenemia. Disadvantages of TEG include a relatively high coefficient of variation, poorly standardized methodologies, and limitations on specimen stability of native whole blood samples. In the pediatric setting, an additional advantage of the TEG is a relatively small sample volume, but a disadvantage is the difference in normal ranges between infants, especially newborns, and adults. In summary, TEG is an old concept with new applications that may provide a unique perspective on global hemostasis in various clinical settings.

Anticoagulation and coagulation management for ECMO

Advances in extracorporeal membrane oxygenation (ECMO) management have helped to reduce complications compared with its inception but they remain high. The principal causes of mortality and morbidity are bleeding and thrombosis. The nonbiologic surface of an extracorporeal circuit provokes a massive inflammatory response leading to consumption and activation of procoagulant and anticoagulant components. The vast differences in neonatal and adult anticoagulation and transfusion requirements demands tremendous clinical knowledge to provide the best care. Increased use of thrombelastogram will complement other methods currently being used to improved care. Methods to recognize the level of thrombin formation at the bedside could help reduce neurologic complications. ECMO requires a multidisciplinary team approach to achieve the best outcomes.

Thrombelastography and tromboelastometry in assessing coagulopathy in trauma

Death due to trauma is the leading cause of lost life years worldwide, with haemorrhage being responsible for 30-40% of trauma mortality and accounting for almost 50% of the deaths the initial 24 h. On admission, 25-35% of trauma patients present with coagulopathy, which is associated with a several-fold increase in morbidity and mortality. The recent introduction of haemostatic control resuscitation along with emerging understanding of acute post-traumatic coagulability, are important means to improve therapy and outcome in exsanguinating trauma patients. This change in therapy has emphasized the urgent need for adequate haemostatic assays to monitor traumatic coagulopathy and guide therapy. Based on the cell-based model of haemostasis, there is emerging consensus that plasma-based routine coagulation tests (RCoT), like prothrombin time (PT) and activated partial thromboplastin time (APTT), are inappropriate for monitoring coagulopathy and guide therapy in trauma. The necessity to analyze whole blood to accurately identify relevant coagulopathies, has led to a revival of the interest in viscoelastic haemostatic assays (VHA) such as Thromboelastography (TEG^®) and Rotation Thromboelastometry (ROTEM^®). Clinical studies including about 5000 surgical and/or trauma patients have reported on the benefit of using the VHA as compared to plasma-based assays, to identify coagulopathy and guide therapy.

This article reviews the basic principles of VHA, the correlation between the VHA whole blood clot formation in accordance with the cell-based model of haemostasis, the current use of VHA-guided therapy in trauma and massive transfusion (haemostatic control resuscitation), limitations of VHA and future perspectives of this assay in trauma.

Point-of-care assessment of antiplatelet agents in the perioperative period: a review

The aim of this paper was to review the strengths and limitations of current 'point-of-care' techniques for the detection of antiplatelet drug effects. The review was based on a Medline search for articles with key words related to "platelet function tests", "point-of-care", and "anaesthesia", published in English between January 1996 and September 2008. It was found that global assessments of 'haemostasis', such as the standard thrombelastograph, Sonoclot, Clot Signature Analyser and Hemodyne, are not specific for platelet function and are essentially insensitive to cyclooxygenase inhibitors (aspirin, non-steroidal anti-inflammatory drugs) and P2Y12 antagonists (ticlopidine, clopidogrel). Global assessments of 'platelet function', such as the PFA-100 and PlateletWorks, are more specific for platelet function, but also have limited sensitivity for cyclooxygenase inhibitors and P2Y12 antagonists. The newer devices developed specifically for the assessment of antiplatelet drugs, such as Platelet Mapping, the Impact Cone and Platelet Analyser and the VerifyNow, are more promising, but are not as sensitive as laboratory platelet aggregometry. All three categories of devices detect G(p)II(b)/III(a) antagonists (abciximab, tirofiban, eptifibatide) activity, but not all provide quantitative assessments for monitoring therapy. The limitations appeared to be related to the complexity of platelet function, the multiple pathways of platelet activation, the wide interpatient variability in platelet responses and the interdependence between platelets and other aspects of coagulation. The strengths and limitations of point-of-care devices should be appreciated before they are used to assist clinical decision-making in the perioperative period.

Heparin-like effect in liver disease and liver transplantation

Liver cirrhosis is characterized by impairment of primary and secondary hemostasis but it is not clear how this impairment is related to the bleeding problems seen in cirrhosis. This delicate hemostatic balance can be perturbed by numerous conditions, such as variceal bleeding, renal failure, or infection/sepsis, which may lead to worsening of coagulation status to date. The role of endogenous heparinoids (glycosaminoglycans) in the coagulopathy of patients who have cirrhosis has been demonstrated by thromboelastography with the addition of heparinase I in patients who have recent variceal bleeding and infection. The heparin-like effect has also been demonstrated to be part of the coagulopathy seen after reperfusion in patients who have cirrhosis and are undergoing liver transplant. Therapeutic implications of these findings are not clear at the moment and the use of drugs able to cleave heparinoids should be explored.

The effects of glycosaminoglycans on coagulation: a thromboelastographic study

Endogenous heparinoids impair coagulation, evidenced by thrombelastography in cirrhotic patients with bacterial infection, but it is not clear which glycosaminoglycans can be detected by native and heparinase-modified thrombelastography. To assess the effects of different glycosaminoglycans on thrombelastography parameters and the reversibility of these effects by heparinase-I-modified thrombelastography. Twenty volunteers were enrolled. Solutions of heparan sulphate, dermatan sulphate, and chondroitin-4-sulphate were prepared at 'equivalent' concentrations, based on the composition and anticoagulant activity of danaparoid. Serial dilutions of each glycosaminoglycan were prepared to achieve 1.0, 0.5, 0.1, and 0.05 U/ml. Native and heparinase-modified thrombelastography, anti-activated factor X activity and heparin cofactor II activity were evaluated at each concentration. A statistically significant heparin-like effect was seen with 1 and 0.5 U/ml heparan sulphate, and 1 and 0.5 U/ml dermatan sulphate, which was completely reversed by heparinase-modified thrombelastography. Anti-activated factor X activity was significantly increased in samples containing heparan and dermatan sulphates. The heparin cofactor II activity decreased with 1.0 and 0.5 U/ml dermatan sulphate and chondroitin-4-sulphate, but not with heparan sulphate. Heparan and dermatan sulphates affect haemostasis when added to whole blood in vitro, detectable by native thrombelastography and completely reversed by heparinase-I-modified thrombelastography. They may therefore be responsible for the heparin-like effect seen by thrombelastography in patients with cirrhosis and bacterial infection.

Coagulation Monitoring

Monitoring hemostasis is now possible by different modalities, of which the point of care devices seem most helpful to the clinician in the operating room. Most of these monitors are being used in the cardiac population, and their significance in other fields remains to be assessed.

Activated thrombelastogram in neonates and infants with complex congenital heart disease in comparison with healthy children

BACKGROUND

The goal of the study was to determine activated thrombelastographic (TEG(R)) parameters with the rotational TEG(R) (ROTEG or ROTEM) device (Pentapharm GmbH, Munich, Germany) in neonates and infants <1 yr with complex congenital heart disease (CCHD) and to compare them with those of healthy children.

METHODS

A total of 59 children were included: Group I (Gr I) 24 children, ASA I, scheduled for minor surgery; and Group II (Gr II) 35 children with CCHD, ASA III-IV, scheduled for cardiac surgery. Each group was subdivided into four age groups. Blood samples were obtained before the surgical procedure.

RESULTS

Statistically significant differences (two-way anova analysis) between Gr I and Gr II [mean (SD); P-value] were found in INTEG-CT [Gr I 175(19), Gr II 271(162); P=0.049], EXTEG-MCF [Gr I 63(8), Gr II 56(8); P=0.013], EXTEG-MCE [Gr I 186(65), Gr II 137(41); P=0.003], FIBTEG-MCF [Gr I 24(7), Gr II 19(5); P=0.012], FIBTEG-MCE [Gr I 32(13), Gr II 24(8); P=0.012] and EXTEG-MCE-FIBTEG-MCE [Gr I 155(55), Gr II 113(37); P=0.003]. Clotting time via contact activation was prolonged in Gr II and varied widely, mainly in the age group 0-1 month and to a lesser extent in 1-3 months, and maximum clot firmness was reduced in the same age groups. In comparison with Gr II, the healthy children showed relatively homogenous TEG values with a tendency to hypercoagulability; the maximum was found in age group 1-3 months, decreasing towards adult values in the course of the first year of life.

CONCLUSIONS

These preliminary TEG results indicate that the coagulation-fibrinolytic system in CCHD patients <1 yr is functionally intact and balanced but at a lower level than in healthy children. This could be interpreted as a reduction in the haemostatic potential with less reserve.

Platelet dysfunction during cardiopulmonary bypass assessed by a novel whole-blood aggregometer

OBJECTIVE

The purpose of this study was to assess perioperative platelet function with 2 types of monitors (a whole-blood aggregometer [WBA analyzer; Mebanix, Tokyo, Japan]) and the Sonoclot monitor [Sienco, Wheat Ridge, CO]) in patients undergoing hypothermic cardiopulmonary bypass (CPB).

DESIGN

Prospective, observational study.

SETTING

Single-center study at a university hospital.

PARTICIPANTS

Twenty-six patients who underwent coronary artery bypass grafting or valve replacement under hypothermic CPB without platelet transfusion or fresh frozen plasma administration.

INTERVENTIONS

Blood sampling was performed at the following time periods: after anesthetic induction, after CPB, and on the first postoperative day. These samples were assessed with the WBA analyzer and the Sonoclot.

MEASUREMENTS AND MAIN RESULTS

Significant attenuation of adenosine diphosphate-induced platelet aggregation was detected shortly after CPB by 2 WBA analyzer-derived parameters: a decrease in the filtration pressure rate and an increase in the platelet aggregatory threshold index. Platelet aggregation returned to the preoperative level on the next day. There was no correlation between the amount of postoperative mediastinal drainage and defects in platelet aggregation. On the other hand, time to peak obtained by the Sonoclot did not show any significant changes.

CONCLUSIONS

Whole-blood aggregation measured with the WBA analyzer detected transient platelet dysfunction shortly after CPB, whereas the Sonoclot was less sensitive to this change.

The effects of unfractionated heparin, low molecular weight heparin and danaparoid on the thromboelastogram (TEG): an in-vitro comparison of standard and heparinase-modified TEGs with conventional coagulation assays

To investigate the effects of unfractionated heparin (UFH), low molecular weight heparin (LMWH) and danaparoid (DPD) added to whole blood in vitro on standard and heparinase-modified thromboelastogram (TEG) parameters compared with conventional assays of coagulation. The effects of UFH, LMWH and DPD on standard TEG parameters were compared with the prothrombin time, activated partial thromboplastin time, thrombin time and anti-activated factor X (anti-FXa) activity, at concentrations of these anticoagulants ranging from 0.025 to 1 U/ml. In the second part of the study, the effects of very low concentrations (0.005-0.05 U/ml) of UFH, LMWH and DPD on the difference between standard and heparinase-modified TEG parameters were compared with the prothrombin time, activated partial thromboplastin time, thrombin time and anti-FXa activity. Standard TEG parameters were outside the reference range at lower concentrations of UFH, LMWH and DPD than most conventional coagulation assays were able to detect. Only anti-FXa activity was more sensitive to the presence of these anticoagulants than the standard TEG alone. The lowest concentration of UFH, LMWH and DPD used in this study (0.005 U/ml) caused significant differences between the standard and heparinase-modified alpha-angles of the TEG. In addition, the difference between standard and heparinase-modified TEG parameters distinguished between low concentrations (0.005-0.05 U/ml) of UFH with greater sensitivity than anti-FXa activity, but were less sensitive to LMWH and DPD. The standard TEG is more sensitive to UFH, LMWH and DPD than most conventional coagulation tests, with the exception of anti-FXa activity. Calculation of the difference between standard and heparinase-modified TEG parameters greatly increases the sensitivity of the assay for the effects of these anticoagulants, and is more sensitive to very low quantities of UFH than anti-FXa activity.

The kaolin-activated Thrombelastograph predicts bleeding after cardiac surgery

OBJECTIVE

The objective of this study was to determine the relationship of the kaolin-activated Thrombelastograph (TEG) with postoperative bleeding and laboratory tests of coagulation in the setting of cardiac surgery with the routine use of -aminocaproic acid.

DESIGN

Prospective observational study.

SETTING

An adult heart center at a tertiary referral, university hospital.

PARTICIPANTS

Thirty adult cardiac surgical patients.

INTERVENTIONS

The kaolin-activated TEG, platelet counts, prothrombin times, activated partial thromboplastin times, and fibrinogen levels were measured before induction of anesthesia, during cardiopulmonary bypass, and on arrival in the intensive care unit. Mediastinal and thoracostomy drainage were measured every hour for 4 hours after arrival in the intensive care unit.

MEASUREMENTS AND MAIN RESULTS

Correlation and multivariate linear regression modeling were used to describe relationships among coagulation tests, TEG parameters, and early postoperative bleeding. The TEG maximum amplitude (MA) parameter correlated well with postoperative bleeding (r = -0.6, p = 0.0018), more so than platelet count (r = -0.45, p = 0.02), fibrinogen level (r = -0.40, p = 0.06), or prothrombin time (r = 0.43, p = 0.02). The receiver operating characteristic curve c-index describing MA as a predictor for postoperative bleeding is 0.78. Abnormalities in all the laboratory test results were associated with an abnormal MA.

CONCLUSIONS

In conclusion, the kaolin-activated TEG is associated with early coagulopathic bleeding. It may reflect the severity of a global coagulopathy affecting both platelets and coagulation factors and be a guide to incremental prohemostatic therapy in this setting.

The ‘heparin lock’

BACKGROUND AND OBJECTIVE

The reasons for coagulopathy may be multiple and the identification of the underlying cause is often difficult. Recently, we identified two patients showing characteristics of heparin overdose during surgery. We hypothesised that filling a Shaldon dialysis catheter with heparin prior to closure, so-called heparin lock, might have triggered this coagulation disorder. Therefore, the aim of this in vitro study was to show whether this procedure can lead to an iatrogenic administration of heparin.

METHODS

A Shaldon catheter (GamCath; Joka Kathetertechnik, Hechingen, Germany) was hung up in a container filled with NaCl solution 0.9% 5 mL and a heparin lock was simulated. Instead of using heparin solution we injected 1 mL of a KCl solution (1 mol L(-1)) into the Shaldon catheter, because the measurement of the potassium concentration is faster and more reliable than that of heparin. Ten measurements were taken after fast (0.5 s) and slow (3 s) injection speeds.

RESULTS

Although the catheter volume is specified as 1.07 mL, an amount up to 0.51 mL KCl solution on average was detectable in the solution after locking the catheter with 1 mL KCl solution.

CONCLUSIONS

Following a heparin lock a considerable amount of the injected solution is accidentally administered to the patient. Only 49.1% of the injected volume may remain in the Shaldon catheter. This could lead to an increased risk of coagulopathy.

Multi-centre investigation on reference ranges for ROTEM thromboelastometry

Reagent-supported thromboelastometry (TEM) with the ROTEM Whole Blood Haemostasis Analyser is an enhancement of thromboelastography, a method that is increasingly used for the point of care monitoring of acute perioperative bleeding disorders. We investigated the reference ranges of two activated tests (INTEM and EXTEM) and a test analysing specifically the fibrin component of coagulation (FIBTEM) in a multi-centre approach. The reference ranges obtained for the clotting time (CT), clot formation time (CFT), alpha angle (ALP), maximum clot firmness (MCF) and clot lysis parameters were comparable from centre to centre. INTEM: CT equals; 137-246 s, CFT equals; 40-100 s, MCF equals; 52-72 mm. EXTEM: CT equals; 42-74 s, CFT equals; 46-148 s, MCF equals; 49-71 mm. FIBTEM: MCF equals; 9-25 mm. ROTEM whole blood coagulation correlated weakly with a trend towards enhanced coagulation in females compared with males and in advanced age. The repeatability (within-run imprecision) of the results was dependent on the test with the following coefficients of variation: 1-5% (clot firmness, alpha angle), 3-12% (CT, CFT), 6-13% (FIBTEM clot firmness). Citrated blood samples were stable for ROTEM analysis stored within 6 h from drawing. In summary, the data showed that ROTEM thromboelastometry yields consistent values between centres and that providing general orientating reference ranges seems to be possible.

Effects of protamine and heparin can be detected and easily differentiated by modified thrombelastography (Rotem ® ): an in vitro study

BACKGROUND

Precise coagulation monitoring might help prevent heparin-protamine mismatch and thus decrease postoperative blood loss. We therefore measured coagulation time (CT) by modified thrombelastography (Rotem) as a possible differential monitor of the effects of heparin and protamine.

METHODS

Undiluted and diluted blood samples from 26 healthy volunteers were spiked with increasing concentrations of heparin (0.1, 0.2, 0.4, 0.8 and 1 U ml(-1)). In addition, undiluted blood was spiked with protamine hydrochloride (0.1, 0.2, 0.4, 0.8 and 1.6 U ml(-1)), and we tested the effect of protamine on the reversal of heparin 0.4 U ml(-1). Heparin-containing samples were analysed using the heparin-sensitive INTEM test and the heparinase-containing HEPTEM test; protamine series were also analysed with the EXTEM test (tissue factor activation).

RESULTS

CT by the INTEM test [CT-INTEM; median (min/max)] increased significantly and dose-dependently with increasing concentrations of heparin [control, 175 s (146/226); heparin, 1.0 U ml(-1) 1320 s (559/2100); P<0.001] and protamine [control, 172 s (150/255); protamine, 1.6 U ml(-1) 527 s (300/1345); P<0.0001]. Up to heparin concentrations of 0.4 U ml(-1), results were similar in undiluted and diluted blood samples. As expected, CT-HEPTEM remained within the normal range for all tested heparin concentrations (median 180-183 s), but increased similarly to CT-INTEM for increasing protamine concentrations.

CONCLUSION

CT measurement using the Rotem technique appears to be a valuable tool for heparin-protamine management. For detection of heparin alone, protamine alone and the two combined, the ratio of CT-INTEM:CT-HEPTEM can be used to distinguish the effects of heparin excess (CT-INTEM:CT-HEPTEM>1) from those of protamine excess (CT-INTEM:CT-HEPTEM=1).

Evaluation of the profile of thrombin generation during the process of whole blood clotting as assessed by thrombelastography

The objective of this study was to evaluate the possibility of linking the tracing of whole blood clotting in a thrombelastograph (TEG) hemostasis system with the generation of thrombin assessed by thrombin/antithrombin complex (TAT). Citrated whole blood containing corn trypsin inhibitor from volunteers was clotted in the presence of CaCl2 and tissue factor. Clotting was monitored with the eight channels of a TEG system. At different time points, the whole blood TEG reaction cups were kept in a cold quenching solution, centrifuged, and the supernatants were kept at -80 degrees C until assayed for TAT by ELISA. The total thrombus generation (TTG) was calculated from the first derivative of the TEG waveform and was compared with thrombin generation measured by TAT. The two vector values--the TAT thrombin generation data and the corresponding TEG TTG--were analyzed using Pearson correlation coefficients (r) and linear, non-linear and natural log (ln) transformation of TAT values for least-squares goodness-of-fit curves. The best least-squares fit is an exponential curve. Linearizing using the ln of the TAT thrombin generation variable produces the same r (0.94) as of the exponential curve. The prediction equation is y = 8.0465 + 0.0005x (P < or = 0.0001), where y is the TAT thrombin generation variable in the ln transformation and x is the TEG TTG variable. The high magnitude of r and the high significance of the prediction equation demonstrate the high efficacy of the prediction of TAT thrombin generation by the use of TEG TTG.

Comparison of structured use of routine laboratory tests or near-patient assessment with clinical judgement in the management of bleeding after cardiac surgery

BACKGROUND

Using algorithms based on point of care coagulation tests can decrease blood loss and blood component transfusion after cardiac surgery. We wished to test the hypothesis that a management algorithm based on near-patient tests would reduce blood loss and blood component use after routine coronary artery surgery with cardiopulmonary bypass when compared with an algorithm based on routine laboratory assays or with clinical judgement.

METHODS

Patients (n=102) undergoing elective coronary artery surgery with cardiac bypass were randomized into two groups. In the point of care group, the management algorithm was based on information provided by three devices, the Hepcon, thromboelastography and the PFA-100 platelet function analyser. Management in the laboratory test group depended on rapidly available laboratory clotting tests and transfusion of haemostatic blood components only if specific criteria were met. Blood loss and transfusion was compared between these two groups and with a retrospective case-control group (n=108), in which management of bleeding had been according to the clinician's discretion.

RESULTS

All three groups had similar median blood losses. The transfusion of packed red blood cells (PRBCs) and blood components was greater in the clinician discretion group (P<0.05) but there was no difference in the transfusion of PRBCs and blood components between the two algorithm-guided groups.

CONCLUSION

Following algorithms based on point of care tests or on structured clinical practice with standard laboratory tests does not decrease blood loss, but reduces the transfusion of PRBCs and blood components after routine cardiac surgery, when compared with clinician discretion. Cardiac surgery services should use transfusion guidelines based on laboratory-guided algorithms, and the possible benefits of point of care testing should be tested against this standard.

Tissue Factor-Activated Thromboelastograms in Children Undergoing Cardiac Surgery: Baseline Values and Comparisons

Activation of clotting with tissue factor (TF) allows rapid evaluation of thromboelastograms but alters the values of thromboelastogram variables. We have performed TF-activated thromboelastograms in 250 children <2 yr old undergoing cardiac surgery to establish baseline values. Five groups were distinguished to evaluate the effects of quantitative deficiencies in coagulation factor levels during infancy: <30 days, 1-3 mo, 3-6 mo, 6-12 mo, and 12-24 mo. Activation of clotting (R and K values) was similar among groups. Infants 1-3 mo of age demonstrated increased clot strength compared with the other groups, a finding similar to previous evaluation of native thromboelastograms. The alpha and maximum amplitude values were numerically almost identical in each age group, a unique finding in activated thromboelastograms. Fibrinolysis was similar among groups. We believe that knowledge of baseline TF-activated thromboelastogram variables in young children will be useful in interpreting these thromboelastograms in clinical scenarios, in using these thromboelastograms as part of coagulopathy treatment algorithms, and during the application of more specific thromboelastogram modifiers. Additionally, the similarity of alpha and maximum amplitude values in each age group will allow even faster interpretation of thromboelastogram data.

IMPLICATIONS

Baseline values for tissue factor-activated thromboelastograms in young children undergoing cardiac surgery have been established and will permit accurate use and interpretation of this thromboelastogram modification in evaluating and managing coagulopathies.

Monitoring anticoagulation and hemostasis in cardiac surgery

The need to monitor anticoagulation and hemostasis during and after cardiac surgery has led to recognition of the importance of evaluation and use of hemostasis monitors in this setting. Consequently, rapid and accurate identification of abnormal hemostasis has been the major impetus for the development of point-of-care tests and their use in transfusion algorithms for cardiac surgical and other critically ill patients.

[Epidural analgesia in a pregnant woman with essential thrombocythaemia]

Epidural analgesia is often considered as risk of epidural haematoma in patient with essential thrombocythaemia because of the platelet disorder. In this observation, uncomplicated epidural analgesia was performed in a pregnant woman with asymptomatic essential thrombocythaemia, because the absence of bleeding symptoms was associated with normal thrombo-elastography and time of occlusion by PFA-100 suggesting normal platelet function. PFA-100 is a biological test evaluating platelet function in whole blood, which is easy and quick to perform. This case study suggests that this test might be useful in evaluating platelet function in obstetrics but must be validated before recommending its extensive use.

Agreements between the prothrombin times of blood treated In Vitro with heparinase during cardiopulmonary bypass (CPB) and blood sampled after CPB and systemic protamine

The prothrombin time (PT) is useful for identifying coagulation factor deficits after cardiopulmonary bypass (CPB). However, long processing times and the need for fresh frozen plasma (FFP) to be thawed cause delays in factor replacement. We hypothesized that, by treating with heparinase, blood sampled toward the end of CPB can provide PT results that help to determine the requirement for FFP after CPB. Laboratory delays can be eliminated with point-of-care monitors. We studied 158 adults undergoing nonemergent cardiac surgery. Blood taken before separation from CPB was mixed with heparinase, and PT was measured in the laboratory with a HemoTec timer. Agreements between these results and laboratory measurements of blood taken after systemic protamine were compared by using Bland and Altman plots with the threshold of +/-1.0 s. We found that the laboratory PT measurements during CPB versus after CPB were compara-ble, but the limits of agreement exceeded these thresholds. Similarly, there was unsatisfactory agreement between the HemoTec and laboratory PT results measured before, during, and after CPB. For each PT measured during CPB, the corresponding confidence interval for the postprotamine PT was calculated. During CPB, a laboratory PT of < or =16 s or > or =18 s suggests a > or =83% or > or =93% probability of not requiring or potentially requiring, respectively, FFP after CPB. We conclude that the majority of PT measurements obtained from blood taken before weaning from CPB and treated in vitro with heparinase was associated with a high probability of whether or not FFP would be needed after CPB.

IMPLICATIONS

Coagulation dysfunction after cardiopulmonary bypass may contribute to bleeding. Obtaining coagulation tests and fresh frozen plasma requires time and delays treatment in patients who need fresh frozen plasma. We have devised a technique to provide early estimation of postbypass coagulation status.