Assessment of thrombin generation measured before and after cardiopulmonary bypass surgery and its association with postoperative bleeding

Effect of cardiopulmonary bypass on coagulation factors II, VII and X in a primate model: an exploratory pilot study

OBJECTIVES

The use of cardiopulmonary bypass (CPB) in cardiac surgery is a major risk factor for postoperative bleeding. We hypothesized that consumptive coagulopathy and haemodilution influence the coagulation factors; therefore, we aimed to estimate the activity profiles of coagulation factors II, VII and X during CPB circulation.

METHODS

A 120-min bypass was surgically established in cynomolgus monkeys (n = 7). Activities of coagulation factors II, VII and X were measured at 6 time points during the experiment (baseline, 0, 30, 60, 120 min of bypass and 60 min after bypass). To assess the influence of consumptive coagulopathy, the values were adjusted for haemodilution using the haematocrit values. Data were expressed as mean (standard deviation).

RESULTS

Activities of coagulation factors decreased during the experiment. In particular, the activities for II, VII and X were decreased the most by 44.2% (5.0), 61.4% (4.3) and 49.0% (3.7) at 30 min following CPB initiation (P < 0.001, P < 0.001 and P < 0.001, respectively). Following adjustments for haemodilution, change magnitudes lessened but remained significant for factor VII. The adjusted concentration of factor VII was observed to decrease from the baseline to the initiation of bypass circulation.

CONCLUSIONS

In conclusion, coagulation factor II, VII and X concentrations decreased during CPB. Following adjustment for haemodilution, a decrease in concentration was observed with factor VII.

Thrombin generation, bleeding and hemostasis in humans: Protocol for a scoping review of the literature

INTRODUCTION

Hemostasis and bleeding are difficult to measure. Thrombin generation assays (TGAs) can measure both procoagulant and anticoagulant contributions to coagulation. TGAs might prove useful for the study of bleeding disorders. There has been much progress in TGA methodology over the past two decades, but its clinical significance is uncertain. We will undertake a scoping review of the literature to synthesize available information on the application of TGAs towards the study of bleeding and hemostasis, TGA methodologies being used and to summarize available literature on associations between TGA parameters, bleeding and hemostatic outcomes.

METHODS AND ANALYSIS

MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials (CENTRAL) will be searched in collaboration with an information specialist. Title/abstract and full-text screening will be carried out independently and in duplicate; eligible study types will include randomized controlled trials, non-randomized studies, systematic reviews, and case series reporting TGA results and bleeding/hemostatic outcomes among humans. Mapping the information identified will be carried out with results presented using qualitative data analytical techniques.

ETHICS AND DISSEMINATION

This scoping review will use published, publicly available information. Research ethics approval will not be required. We will disseminate our findings using conference presentations, peer-reviewed publications, social media, and engagement with knowledge users. This review will outline knowledge gaps concerning TGAs, better delineate its applicability as a clinically relevant assay for bleeding. and seek to identify ongoing barriers to its widespread adoption in clinical research, and eventually, in the clinical setting.

TRAIL REGULATIONS

Registration ID with Open Science Framework: osf.io/zp4ge.

Perturbations in kinetics of the thrombin generation assay identify women at risk of preeclampsia in the first trimester and provide the rationale for a preventive approach

BACKGROUND

Activation of the coagulation system and increased thrombin generation have been implicated in the pathophysiology of preeclampsia, and this rationale supports the administration of low-molecular-weight heparin to prevent this syndrome in patients at risk. Yet, randomized trials of this prophylactic measure have yielded contradictory results. A possible explanation is that only a subset of patients with preeclampsia have excessive thrombin generation and would benefit from the administration of low-molecular-weight heparin. Therefore, the key questions are whether and when patients who subsequently develop preeclampsia present evidence of abnormal thrombin generation.

OBJECTIVE

This study aimed to determine (1) the kinetics of thrombin generation throughout gestation in women with a normal pregnancy and in those with early and late preeclampsia, and (2) the diagnostic performance of in vivo thrombin generation parameters to predict the development of preeclampsia.

STUDY DESIGN

This retrospective, nested case-control study was based on a prospective longitudinal cohort of singleton gestations. Cases comprised women who developed preeclampsia (n=49), and controls consisted of patients with a normal pregnancy (n=45). Preeclampsia was classified into early-onset (n=24) and late-onset (n=25). Longitudinal changes in the parameters of the thrombin generation assay (lag time, time to peak thrombin concentration, peak thrombin concentration, endogenous thrombin generation, and velocity index) throughout gestation were compared between the study groups, and normal pregnancy percentiles were derived from the control group. We tested whether a single parameter or a combination of parameters, derived from the kinetics of thrombin generation, could identify patients who subsequently developed preeclampsia. Time-related parameters <10th percentile were considered short, and concentration-related parameters >90th percentile were considered high.

RESULTS

(1) Patients who developed preeclampsia (early- and late-onset) had abnormal thrombin generation kinetics as early as 8 to 16 weeks of pregnancy; (2) patients with a combination of a short lag time and high peak thrombin concentration at 8 to 16 weeks of pregnancy had an odds ratio of 43.87 for the subsequent development of preeclampsia (area under the curve, 0.79; sensitivity, 56.8%; specificity, 92.7%; positive likelihood ratio, 7.76); (3) at 16 to 22 weeks of gestation, patients with a combination of a short lag time and a high velocity index had an odds ratio of 16 for the subsequent development of preeclampsia (area under the curve, 0.78; sensitivity, 62.2%; specificity, 92.5%; positive likelihood ratio, 8.29).

CONCLUSION

During early pregnancy, the thrombin generation assay can identify the subset of patients at a greater risk for the development of preeclampsia owing to accelerated and enhanced production of thrombin. This observation provides a rationale for testing the efficacy of low-molecular-weight heparin in this subset of patients. We propose that future research on the efficacy of low-molecular-weight heparin and other interventions targeting the coagulation system to prevent preeclampsia should be focused on patients with abnormal kinetics of thrombin generation.

Platelet Function is Preserved After Moderate Cardiopulmonary Bypass Times But Transiently Impaired After Protamine

OBJECTIVES

Previous studies have described impaired platelet function after cardiopulmonary bypass (CPB). Whether this is still valid in contemporary cardiac surgery is unclear. This study aimed to quantify changes in function and number of platelets during CPB in a present-day cardiac surgery cohort.

DESIGN

Prospective, controlled clinical study.

SETTING

A single-center university hospital.

PARTICIPANTS

Thirty-nine patients scheduled for coronary artery bypass graft surgery with CPB.

INTERVENTIONS

Platelet function and numbers were measured at 6 timepoints in 39 patients during and after coronary artery bypass graft surgery; at baseline before anesthesia, at the end of CPB, after protamine administration, at intensive care unit (ICU) arrival, 3 hours after ICU arrival, and on the morning after surgery.

MEASUREMENTS AND MAIN RESULTS

Platelet function was assessed with impedance aggregometry and flow cytometry. Platelet numbers are expressed as actual concentration and as numbers corrected for dilution using hemoglobin as a reference marker. There was no consistent impairment of platelet function during CPB with either impedance aggregometry or flow cytometry. After protamine administration, a decrease in platelet function was seen with impedance aggregometry and for some markers of activation with flow cytometry. Platelet function was restored 3 hours after arrival in the ICU. During CPB (85.0 ± 21 min), the number of circulating platelets corrected for dilution increased from 1.73 ± 0.42 × 10⁹/g to 1.91 ± 0.51 × 10⁹/g (p < 0.001).

CONCLUSIONS

During cardiac surgery with moderate CPB times, platelet function was not impaired, and no consumption of circulating platelets could be detected. Administration of protamine transiently affected platelet function.

Perioperative Gelatin Use Is Associated With Increased Complication Rates and Does Not Prevent Postoperative Fluid Overload in Patients Undergoing Elective Cardiac Surgery

OBJECTIVES

The benefit of using gelatin solution in cardiac surgery is still controversial. Previous data suggested adverse interactions of gelatin infusion with acute kidney injury (AKI) or coagulopathy. The purpose of this study was to evaluate the association between perioperative gelatin use and fluid overload (FO), hemodynamic stability, and outcomes compared to crystalloid-based fluid management.

DESIGN

A retrospective study design.

SETTING

At a single-center tertiary university setting.

PARTICIPANTS

Propensity score-matched cohort study of 191 pairs of patients scheduled for cardiac surgery.

INTERVENTIONS

Patients received either gelatin + crystalloid or pure crystalloid-based perioperative fluid management. The primary outcomes were the frequency of FO and hemodynamic stability defined by the vasoactive-inotropic score. Postoperative complications and 3-year survival were analyzed also.

MEASUREMENTS AND MAIN RESULTS

Patients who received gelatin experienced more frequent postoperative FO than controls (11.0% v 3.1%, p = 0.006) despite comparable hemodynamic stability in both groups. Gelatin administration was linked with a higher rate of postoperative complications, including blood loss, AKI, and new-onset postoperative atrial fibrillation. Use of gelatin infusion resulted in an adjusted odds ratio of 1.982 (95% CI 1.051-3.736, p = 0.035) for developing early postoperative AKI. This study confirmed a dose-dependent relationship between gelatin infusion and AKI. Thirty-day mortality and 3-year survival were similar in the groups.

CONCLUSIONS

Gelatin administration versus crystalloid fluid management showed a significant association with a higher rate of FO and an increased risk for early postoperative AKI in a dose-dependent manner.

Assessing the individual roles of FII, FV, and FX activity in the thrombin generation process

Thrombin generation (TG) is known as a physiological approach to assess the hemostatic function. Although it correlates well with thrombosis and bleeding, in the current setup it is not sensitive to the effects of fluctuations in single coagulation factors. We optimized the calibrated automated thrombinography (CAT) method to quantify FII, FV and FX activity within the coagulation system. The CAT assay was fine-tuned for the assessment of FII, FV and FX by diluting the samples in FII-, FV-, or FX-deficient plasma, respectively, and measuring TG. Plasma FII levels correlated linearly with the ETP up to a plasma concentration of 100% FII. FV and FX levels correlated linearly with the peak height up to a plasma level of 2.5% FV and 10% FX, respectively. Sensitized CAT protocols were designed by adding a fixed volume of a pre-diluted patient sample to FII, FV, and FX deficient plasma in TG experiments. This approach makes the TG measurement dependent on the activity of the respective coagulation factor. The ETP or peak height were quantified as readouts for the coagulation factor activity. The intra- and inter-assay variation coefficients varied from 5.0 to 8.6%, and from 3.5 to 5.9%, respectively. Reference values were determined in 120 healthy subjects and the assays were clinically validated in 60 patients undergoing coronary artery bypass grafting (CABG). The sensitized CAT assays revealed that the contribution of FII, FV, and FX to the TG process was reduced after CABG surgery, leading to reduced prothrombin conversion and subsequently, lower TG.

Titrated versus conventional anticoagulation management for thrombin generation in cardiac surgery: a randomized controlled trial

PURPOSE

Optimal heparin titration during cardiopulmonary bypass (CPB) may reduce coagulation system activation and preserve hemostatic function post-CPB. Our objective was to assess if the Heparin Management System (HMS) Plus improves heparin titration, thereby leading to higher thrombin generation post-CPB compared with activated clotting time (ACT)-guided management.

METHODS

We conducted a randomized controlled trial of 100 patients undergoing cardiac surgery with CPB at a single center. A total of 50 patients were randomized to conventional ACT-guided management, and 50 to the HMS Plus system. The primary outcome was change in thrombin generation post-CPB compared with baseline, as assessed by calibrated automated thrombography. Secondary outcomes included intraoperative blood loss, chest drain output up to 72 hr, and transfusions. In an exploratory analysis, we compared the quintile of patients with the highest average heparin concentration on CPB (≥ 4.0 mg⋅kg-1) with the rest of the cohort.

RESULTS

A total of 100 patients were included in an intent-to-treat analysis. We observed no difference in post-CPB thrombin generation or secondary outcomes. However, patients in the HMS Plus group had higher average heparin concentrations while on CPB than patients in the conventional management group did (mean difference, -0.21; 95% confidence interval, -0.42 to -0.01). The quintile of patients with the highest average heparin concentration (4.0 mg⋅kg-1) had higher thrombin generation post-CPB than the rest of the cohort did.

CONCLUSIONS

The HMS Plus system did not show significant benefits in thrombin generation, bleeding outcomes, or transfusion in patients undergoing cardiac surgery with CPB. Higher average heparin concentrations on CPB were associated with higher post-CPB thrombin generation.

STUDY REGISTRATION

www.

CLINICALTRIALS

gov (NCT03347201); first submitted 12 October 2017.

miR-3064-5p and miR-4745-5p affect heparin sensitivity in patients undergoing cardiac surgery by regulating AT-III and factor X mRNA levels

Subject: Perioperative regulation of coagulation function through heparin in patients undergoing cardiac surgery with cardiopulmonary bypass is an important part of performing cardiac surgery, and postoperative bleeding due to abnormal coagulation function caused by differences in heparin sensitivity in different individuals is an independent risk factor for postoperative complications and death.

Method: Using an online database, 10 miRNAs interacting with AT-III and FX genes were predicted. Patients were divided into three groups according to the difference in activated clotting time (ACT) after the first dose of heparin (2.5 mg kg−1): group A: hyposensitive group (ACT &lt; 480 s); group B: sensitive group (480 s ≤ ACT ≤ 760 s); and group C: hypersensitive group (ACT &gt; 760 s). Perioperative and 24 h postoperative blood loss and other clinical data of patients in the three groups were recorded. Blood samples were collected before surgery, and RT-PCR was used to detect the levels of AT-III and FX gene mRNA and the levels of predicted 10 miRNAs.

Result: Heparin sensitivity was positively correlated with AT-III mRNA levels and negatively correlated with FX gene mRNA levels in the three groups, and the blood loss in group B was significantly lower than that in groups A and C, which was statistically significant (p &lt; 0.05). miR-3064-5p and miR-4745-5p expression levels were significantly different among group A, group B, and group C (p &lt; 0.05) and were closely correlated with AT-III and FX gene mRNA expression levels, respectively.

Conclusion: Differences in heparin sensitivity in patients undergoing cardiac surgery were associated with the mRNA expression of AT-III and FX genes, and the expression levels of miR-3064-5p and miR-4745-5p were found to be closely related to the AT-III and FX gene mRNA, respectively, indicating that miR-3064-5p and miR-4745-5p affect the differences in heparin sensitivity among different individuals by regulating the mRNA expression levels of AT-III and FX genes.

Clinical Trial Registration:http://www.chictr.org.cn/abouten.aspx, identifier registration number: ChiCTR-2100047348

The mediating role of coagulation function on the association of prenatal exposure to aflatoxin B1 and postpartum hemorrhage in Guangxi, China

Pregnant women are vulnerable to certain environmental agents, one of which is aflatoxin. As one of the most popular aflatoxins, Aflatoxin B1 (AFB1) has recently garnered increased attention concerning its potential association between exposure and adverse pregnancy outcomes. The aims of the study were to examine the associations between prenatal exposure to AFB1 and postpartum hemorrhage (PPH), and whether coagulation function has a mediating effect on their relationship. A total of 379 mother-infant pairs were included in the present study. Prenatal serum AFB1 albumin (AFB1-Alb) adduct levels in peripheral venous blood were detected by using an ELISA kit. Multiple linear and logistics regression models were applied to analyze the relationship between AFB1-Alb levels and PPH. We found mothers with high levels of AFB1-Alb adduct levels had significantly increased postpartum blood loss (partial regression coefficient (β) = 50.71, 95% confidence interval (CI) 3.48, 97.95). Mothers with high levels of AFB1-Alb adduct levels also had significantly increased risk of PPH (odds ratio (OR) = 4.81, 95% CI 1.01, 22.98). Moreover, concentrations of AFB1-Alb were positively associated with activated partial thromboplastin time (APTT) while negatively associated with fibrinogen (FIB). One-unit increase in APTT was correlated with a 6.62-ml (95% CI 3.04, 10.20) increase in postpartum blood loss. Mediation analysis suggested that the maternal blood APTT levels had a positive mediating effect in the association between AFB1-Alb adduct levels and postpartum blood loss (β = 0.32, 95% CI 0.04, 0.68). These results indicated that prenatal exposure to AFB1 was associated with increased postpartum blood loss, possibly by interfering with maternal APTT levels.

Thrombin Generation in Cardiac Versus Noncardiac Surgical Cohorts

BACKGROUND

Bleeding can be a significant problem after cardiac surgery. As a result, venous thromboembolism (VTE) or anticoagulation or both following mechanical valve implantation are often delayed in these patients. The calibrated automated thrombin (CAT) generation assay has become the gold standard to evaluate thrombin generation, a critical step in clot formation independent of other hemostatic processes (eg, platelet activation, fibrin cross-linking, and fibrinolysis), and is increasingly used to examine thrombotic and hemorrhagic outcomes. No study has currently used this assay to compare the thrombin generation profiles of cardiac surgical patients to noncardiac surgical patients. We hypothesize that noncardiac patients may be less prone to postoperative changes in thrombin generation.

METHODS

A prospective, observational, cohort study was undertaken using blood samples from 50 cardiac and 50 noncardiac surgical patients preoperatively, immediately postoperatively, and on postoperative days 1 to 4. Platelet-poor plasma samples were obtained from patients preoperatively, on arrival to the postanesthesia care unit (PACU) or intensive care unit (ICU), and daily on postoperative days 1 to 4 if patients remained inpatient. Samples were evaluated for CAT measurements. Patient and surgical procedure characteristics were obtained from the electronic medical record.

RESULTS

The primary outcome variable, median endogenous thrombin potential (ETP), measured in nanomolar × minutes (nM × min), was decreased 100% in cardiac surgical versus 2% in noncardiac patients (P < .001). All parameters of thrombin generation were similarly depressed. Cardiac (versus noncardiac) surgical type was associated with -76.5% difference of percent change in ETP on multivariable regression analysis (95% confidence interval [CI], -87.4 to -65.5; P value <.001).

CONCLUSIONS

Cardiac surgical patients exhibit a profound decrease in thrombin generation postoperatively compared with noncardiac surgical patients evaluated by this study. Hemodilution and coagulation factor depletion likely contribute to this decreased thrombin generation after cardiac surgery.

Assessment of Rotational Thromboelastometry and Thrombin Generation Assay to Identify Risk of High Blood Loss and Re-Operation After Cardiac Surgery

Introduction: We aimed to investigate parameters for prediction of post-operative blood loss and re-operation in patients who underwent cardiopulmonary bypass. Methods: Thrombin generation assay, activated partial thromboplastin time, activated clotting time and rotational thromboelastometry (ROTEM) tests were performed at 4 time points in 65 patients: before skin incision (T1), after heparin injection (T2), after protamine reversal (T3) and before skin closure (T4). Results: Pre-operative endogenous thrombin potential (ETP) and peak thrombin levels were significantly lower in patients with high post-operative blood loss (≥ 800 mL) within 24 h than in those with low blood loss (< 800 mL). Clotting time (CT), maximal clotting firmness, clotting firmness time and alpha angle values of ROTEM measured at T2, T3 or T4 were significant predictors for high post-operative blood loss. An increase in CT-EXTEM over 4 time points was significant in patients who had a re-operation within 48 h compared to their counterparts. Conclusions: This study indicates that pre-operative ETP could predict high post-operative blood loss and that intra-operative ROTEM also helps to stratify risks of high post-operative blood loss and re-operation.

The association of thrombin generation with bleeding outcomes in cardiac surgery: a prospective observational study

BACKGROUND

Cardiac surgery with cardiopulmonary bypass (CPB) is associated with coagulopathic bleeding. Impaired thrombin generation may be an important cause of coagulopathic bleeding but is poorly measured by existing hemostatic assays. We examined thrombin generation during cardiac surgery, using calibrated automated thrombography, and its association with bleeding outcomes.

METHODS

We conducted a prospective observational study in 100 patients undergoing cardiac surgery with CPB. Calibrated automated thrombography parameters were expressed as a ratio of post-CPB values divided by pre-CPB values. The association of thrombin generation parameters for bleeding outcomes was compared with conventional tests of hemostasis, and the outcomes of patients with the most severe post-CPB impairment in thrombin generation (≥ 80% drop from baseline) were compared with the rest of the cohort.

RESULTS

All 100 patients were included in the final analysis, with a mean age of 63 (12) yr, 31 (31%) female, and 94 (94%) undergoing bypass and/or valve surgery. Post-CPB, peak thrombin decreased by a median of 73% (interquartile range [IQR], 49-91%) (P < 0.001) and total thrombin generation, expressed as the endogenous thrombin potential (ETP), decreased 56% [IQR, 30-83%] (P < 0.001). In patients with ≥ 80% decrease in ETP, 21% required re-exploration for bleeding compared with 7% in the rest of the cohort (P = 0.04), and 48% required medical or surgical treatment for hemostasis compared with 27% in the rest of the cohort (P = 0.04).

CONCLUSIONS

Thrombin generation is significantly impaired by CPB and associated with higher bleeding severity. Clinical studies aimed at the identification and treatment of patients with impaired thrombin generation are warranted.

Clinical use of thrombin generation assays

Determining patient's coagulation profile, i.e. detecting a bleeding tendency or the opposite, a thrombotic risk, is crucial for clinicians in many situations. Routine coagulation assays and even more specialized tests may not allow a relevant characterization of the hemostatic balance. In contrast, thrombin generation assay (TGA) is a global assay allowing the dynamic continuous and simultaneous recording of the combined effects of both thrombin generation and thrombin inactivation. TGA thus reflects the result of procoagulant and anticoagulant activities in blood and plasma. Because of this unique feature, TGA has been widely used in a wide array of settings from both research, clinical and pharmaceutical perspectives. This includes diagnosis, prognosis, prophylaxis, and treatment of inherited and acquired bleeding and thrombotic disorders. In addition, TGA has been shown to provide relevant information for the diagnosis of coagulopathies induced by infectious diseases, comprising also disturbance of the coagulation system in COVID-19, or for the assessment of early recurrence in breast cancer. This review article aims to document most clinical applications of TGA.

The association of prothrombin complex concentrates with postoperative outcomes in cardiac surgery: an observational substudy of the FIBRES randomized controlled trial

Purpose

The mainstay of therapy for coagulation factor deficiency in cardiac surgical patients is frozen plasma (FP); however, prothrombin complex concentrates (PCCs) may offer logistical and safety advantages. As there is limited comparative evidence, we conducted this study to explore the association of comparable PCC or FP doses with transfusion and outcomes.

Methods

This was a post hoc analysis of a multicentre randomized trial comparing fibrinogen concentrate with cryoprecipitate (FIBRES trial) in bleeding cardiac surgical patients. This analysis included 415 patients who received only PCC (n = 72; 17%) or only FP (n = 343; 83%) for factor replacement. The main outcomes of interest were red blood cell (RBC) and platelet transfusion within 24 hr of cardiopulmonary bypass. Secondary outcomes included postoperative adverse events. Associations were examined by hierarchical generalized estimating equation models adjusted for demographic and surgical characteristics.

Results

The median [interquartile range (IQR)] PCC dose was 1,000 [1,000–2,000] units, while the median [IQR] FP dose was 4 [2–6] units. Each unit of FP was independently associated with increased adjusted odds of RBC (1.60; 95% confidence interval [CI], 1.36 to 1.87; P < 0.01) and platelet transfusion (1.40; 95% CI, 1.15 to 1.69; P < 0.01) while each 500 units of PCC was independently associated with reduced adjusted odds of RBC (0.67; 95% CI, 0.50 to 0.90; P < 0.01) and platelet transfusion (0.80; 95% CI, 0.70 to 0.92; P < 0.01). Adverse event rates were comparable.

Conclusions

In cardiac surgical patients with post-cardiopulmonary bypass bleeding, PCC use was associated with lower RBC and platelet transfusion than FP use was. Prospective, randomized clinical trials comparing FP with PCC in this setting are warranted.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12630-021-02100-4.

Thrombin: A Pivotal Player in Hemostasis and Beyond

The serine protease thrombin, a naturally derived enzyme, plays a key role in hemostasis by converting fibrinogen to fibrin and activating coagulation factor XIII whereby the fibrin clot is stabilized. Furthermore, thrombin activates platelets through protease-activated receptors on the platelet surface. Conversely, thrombin also exerts anticoagulant effects, enhancing the protein C activity while complexed with thrombomodulin. During recent years, it has become evident that thrombin has significant effects beyond hemostasis, as it contributes also to modulation of the endothelium, promotes inflammation and angiogenesis, and plays a role in tumor progression. Yet, due to the very short half-life and almost immediate inhibition in fluid phase by antithrombin, thrombin itself remains elusive, and only indirect measurement of thrombin generation is possible. This review provides a description of structure and mechanisms of action of thrombin both in physiological and pathological processes. Furthermore, it summarizes laboratory tests that measure in vivo or ex vivo thrombin generation, and presents knowledge on the value of these biomarkers in bleeding disorders, cardiopulmonary bypass surgery, and thromboembolic risk assessment in different patient populations. Finally, this review outlines further perspectives on using thrombin generation biomarkers for research purposes and in clinical practice.

Perioperative Factor Concentrate Use is Associated With More Beneficial Outcomes and Reduced Complication Rates Compared With a Pure Blood Product-Based Strategy in Patients Undergoing Elective Cardiac Surgery: A Propensity Score-Matched Cohort Study

OBJECTIVE

The goal of this study was to compare factor concentrate (FC)-based and blood product-based hemostasis management of coagulopathy in cardiac surgical patients in terms of postoperative bleeding, required blood products, and outcome.

DESIGN

Retrospective, propensity score-matched analysis.

SETTING

Single, tertiary, academic medical center.

PARTICIPANTS

One hundred eighteen matched pairs of 433 consecutive patients scheduled for cardiac surgery in two isolated periods with distinct strategies of hemostasis management.

INTERVENTIONS

Patients received either blood product-based (period I) or FC-based (period II) hemostasis management to treat perioperative coagulopathy.

MEASUREMENTS AND MAIN RESULTS

Patients treated with FC management experienced less postoperative blood loss (907 v 1,153 mL, p = 0.014) and required less red blood cell and fresh frozen plasma transfusion (2.3 v 3.7 units p < 0.0001, and 2.0 v 3.4 units p < 0.0001, respectively) compared with subjects in the blood product-based management group. The frequency of Stage 3 acute kidney injury and 30-day mortality rate were significantly higher in the blood product-based group than in the FC management group (6.8% v 0.8%, p = 0.016, and 7.2% v 0.8%, p = 0.022, respectively). FC management-related thromboembolic events were not registered. The FC strategy was associated with a 2.19-fold decrease in the odds of massive postoperative bleeding (p < 0.0001), a 2.56-fold decrease in the odds of polytransfusion (p < 0.0001), and a 13.16-fold decrease in the odds of early postoperative death (p = 0.003).

CONCLUSIONS

FC-based versus blood product-based management is associated with reduced blood product needs and fewer complications, and was not linked to a higher frequency of thromboembolic events or a decrease in long-term survival in cardiac surgical patients developing perioperative coagulopathy and bleeding.

Managing the coagulopathy associated with cardiopulmonary bypass

Cardiopulmonary bypass (CPB) has allowed for significant surgical advancements, but accompanying risks can be significant and must be expertly managed. One of the foremost risks is coagulopathic bleeding. Increasing levels of bleeding in cardiac surgical patients at the time of separation from CPB are associated with poor outcomes and mortality. CPB-associated coagulopathy is typically multifactorial and rarely due to inadequate reversal of systemic heparin alone. The components of the bypass circuit induce systemic inflammation and multiple disturbances of the coagulation and fibrinolytic systems. Anticipating coagulopathy is the first step in managing it, and specific patient and procedural risk factors have been identified as predictors of excessive bleeding. Medication management pre-procedure is critical, as patients undergoing cardiac surgery are commonly on anticoagulants or antiplatelet agents. Important adjuncts to avoid transfusion include antifibrinolytics, and perfusion practices such as red cell salvage, sequestration, and retrograde autologous priming of the bypass circuit have varying degrees of evidence supporting their use. Understanding the patient's coagulation status helps target product replacement and avoid larger volume transfusion. There is increasing recognition of the role of point-of-care viscoelastic and functional platelet testing. Common pitfalls in the management of post-CPB coagulopathy include overdosing protamine for heparin reversal, imperfect laboratory measures of thrombin generation that result in normal or near-normal laboratory results in the presence of continued bleeding, and delayed recognition of surgical bleeding. While challenging, the effective management of CPB-associated coagulopathy can significantly improve patient outcomes.

Rapid thrombelastography predicts perioperative massive blood transfusion in patients undergoing coronary artery bypass grafting: A retrospective study

Massive blood transfusion (MBT) is a relatively common complication of cardiac surgery, which is independently associated with severe postoperative adverse events. However, the value of using rapid thrombotomography (r-TEG) to predict MBT in perioperative period of cardiac surgery has not been explored. This study aimed to identify the effect of r-TEG in predicting MBT for patients undergoing coronary artery bypass grafting (CABG).This retrospective study included consecutive patients first time undergoing CABG at the Zhongnan Hospital of Wuhan University between March 2015 and November 2017. All the patients had done r-TEG tests before surgery. The MBT was defined as receiving at least 4 units of red blood cells intra-operatively and 5 units postoperatively (1 unit red blood cells from 200 mL whole blood).Lower preoperative hemoglobin level (P = .001) and longer cardiopulmonary bypass time (P = .001) were the independent risk factors for MBT during surgery, and no components of the r-TEG predicted MBT during surgery. Meanwhile, longer activated clotting time (P < .001), less autologous blood transfusion (P = .001), and older age (P = .008) were the independent risk factors for MBT within 24 hours of surgery.Preoperative r-TEG activated clotting time can predict the increase of postoperative MBT in patients undergoing CABG. We recommend the careful monitoring of coagulation system with r-TEG, which allows rapid diagnosis of coagulation abnormalities even before the start of surgery.

Impact of minimally invasive extracorporeal circulation on coagulation-a randomized trial

OBJECTIVES

Minimally invasive extracorporeal circulation (MiECC) is suggested to have favourable impact on blood loss compared to conventional extracorporeal circulation. We aimed to compare the impact of both systems on coagulation.

METHODS

Randomized trial comparing endogenous thrombin-generating potential early after elective coronary surgery employing either MiECC group (n = 30) or conventional extracorporeal circulation group (n = 30). Secondary outcomes were in vivo thrombin generation, bleeding end points and haemodilution, as well as morbidity and mortality up to 30-day follow-up.

RESULTS

Compared to the conventional extracorporeal circulation group, the MiECC group showed (i) a trend towards a higher early postoperative endogenous thrombin-generating potential (P = 0.06), (ii) lower intraoperative levels of thrombin-antithrombin complex and prothrombin fragment 1 + 2 (P < 0.001), (iii) less haemodilution early postoperatively as measured by haematocrit and weight gain, but without correlation to coagulation factors or bleeding end points. Moreover, half as many patients required postoperative blood transfusion in the MiECC group (17% vs 37%, P = 0.14), although postoperative blood loss did not differ between groups (P = 0.84). Thrombin-antithrombin complex levels (rs = 0.36, P = 0.005) and prothrombin fragment 1 + 2 (rs = 0.45, P < 0.001), but not early postoperative endogenous thrombin-generating potential (rs = 0.05, P = 0.72), showed significant correlation to increased transfusion requirements. The MiECC group demonstrated significantly lower levels of creatine kinase-MB, lactate dehydrogenase and free haemoglobin indicating superior myocardial protection, less tissue damage and less haemolysis, respectively. Perioperative morbidity and 30-day mortality did not differ between groups.

CONCLUSIONS

Conventional but not MiECC is associated with significant intraoperative thrombin generation despite full heparinization. No correlation between coagulation factors or bleeding end points with the degree of haemodilution could be ascertained.

CLINICALTRIALS.GOV IDENTIFIER

NCT03216720.

Thrombin generation and bleeding in cardiac surgery: a clinical narrative review

This narrative review discusses the role of thrombin generation in coagulation and bleeding in cardiac surgery, the laboratory methods for clinical detection of impaired thrombin generation, and the available hemostatic interventions that can be used to improve thrombin generation. Coagulopathy after cardiopulmonary bypass (CPB) is associated with excessive blood loss and adverse patient outcomes. Thrombin plays a crucial role in primary hemostasis, and impaired thrombin generation can be an important cause of post-CPB coagulopathy. Existing coagulation assays have significant limitations in assessing thrombin generation, but whole-blood assays designed to measure thrombin generation at the bed-side are under development. Until then, clinicians may need to institute therapy empirically for non-surgical bleeding in the setting of normal coagulation measures. Available therapies for impaired thrombin generation include administration of plasma, prothrombin complex concentrate, and bypassing agents (recombinant activated factor VII and factor eight inhibitor bypassing activity). In vitro experiments have explored the relative potency of these therapies, but clinical studies are lacking. The potential incorporation of thrombin generation assays into clinical practice and treatment algorithms for impaired thrombin generation must await further clinical development.

Heparin sensitivity and postoperative blood loss in patients undergoing cardiac surgery with cardiopulmonary bypass

BACKGROUND

Heparin-associated coagulation disorder is an important factor related to postoperative bleeding in patients undergoing cardiac surgery with cardiopulmonary bypass. Currently, the relationship between heparin sensitivity and postoperative bleeding is unknown.

OBJECTIVE

To investigate the relationship between individual heparin sensitivity and postoperative blood loss in patients undergoing cardiac surgery.

DESIGN

Prospective controlled study.

SETTING

Tertiary teaching hospital, Urumqi, Xinjiang, PR China. The study was conducted from January 2016 to August 2018.

PATIENTS

A total of 195 adult patients undergoing cardiac valve replacement surgery were included.

INTERVENTION

After initial heparin dosing (2.5 mg kg), patients were divided into three groups according to the whole blood activated clotting time (ACT): group A, insensitive group (ACT < 480 s); group B, sensitive group (480 s < ACT < 750 s); group C, hypersensitive group (ACT > 750 s).

MAIN OUTCOME MEASURES

First, intra-operative and 24-h postoperative blood loss. Second, antithrombin (AT) and factor X mRNA levels. Third, the plasma levels of AT-III and factor X. Fourth, heparin sensitivity index.

RESULTS

Blood loss was approximately 20 to 25% lower in group B than in groups A and C, which was statistically significant (P < 0.01). The AT-III mRNA levels increased from groups A to C and was positively associated with heparin sensitivity; the factor X mRNA levels changed in the opposite direction; a significant difference was observed between groups A and C (P < 0.05). The factor X plasma level showed the same trend as its mRNA. The AT-III plasma level was significantly lower in group B than in groups A and C (P < 0.05).

CONCLUSION

Postoperative blood loss is related to heparin sensitivity in patients undergoing cardiac surgery, and the moderately sensitive patients have the least postoperative bleeding. Individual variation in heparin sensitivity is related to the mRNA and plasma levels of AT-III and factor X.

TRIAL REGISTRATION

Registration number ChiCTR-RPC-17012259.

The velocity curve of the clotting waveform of rotational thromboelastometry predicts bleeding after cardiac surgery but conventional rotational thromboelastometric parameters do not

BACKGROUND

Early detection of a risk of postoperative bleeding is essential in cardiac surgery patients. The aim of the present study was to evaluate the utility of the first derivative curve (the V-curve) of the clotting waveform of rotational thromboelastometry (ROTEM) in terms of predicting bleeding after cardiac surgery.

METHODS

We retrospectively analysed 534 cardiac surgery patients. We used the chest tube output during the stay in the intensive care unit to divide patients into a higher blood loss group (HBL group; the fourth quartile) and a lower blood loss group (LBL group; the lower quartiles). We performed multivariable logistic regression using the V-curve parameters and potential confounders including conventional ROTEM parameters.

RESULTS

In the multivariable model, the adjusted odds ratios for HBL of patients with a lower maximum clotting velocity (MaxVel ≤9 mm*100 s-1) as revealed by extrinsically activated ROTEM (EXTEM), and the area under the velocity curve (AUC ≤988 mm*100) of the fibrin-based extrinsically activated ROTEM (FIBTEM), both measured at skin closure in the end of surgery, were 1.78 (95% CI 1.03 to 3.07) and 2.14 (95% CI 1.20 to 3.82), respectively. However, conventional ROTEM parameters were not included in the final model. Additionally, lower EXTEM MaxVel and FIBTEM AUC values were associated with the need for a higher transfusion volume, longer postoperative intensive care unit and hospital stays, and more frequent re-exploration to control bleeding.

CONCLUSIONS

The ROTEM V-curve parameters can predict postoperative bleeding and clinical outcomes after cardiac surgery.

A comparison of haemostatic biomarkers during low-risk patients undergoing cardiopulmonary bypass using either conventional centrifugal cell salvage or the HemoSep device

BACKGROUND

Cardiac surgery using cardiopulmonary bypass (CPB) is associated with a coagulopathy due to haemodilution, thrombocytopenia and platelet dysfunction and the activation of coagulation and fibrinolysis, despite the use of large doses of unfractionated heparin. Conventional red cell salvage may exacerbate post-operative bleeding as plasma containing haemostatic factors is discarded. We hypothesized that a novel cell salvage device (HemoSep) may attenuate haemostatic changes associated with red cell salvage. We studied haemostatic markers following autologous transfusion from conventional cell salvage or the HemoSep device.

METHODS

This randomised, controlled trial compared haemostatic markers in patients undergoing coronary artery bypass grafting or aortic valve replacement who received autologous blood returned from cell salvage (control) or HemoSep (study). Blood samples were taken pre-operatively, end of CPB, post-transfusion of salvaged blood and 3 hours post-operatively and analysed for full blood count (FBC), prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, D-dimer and endogenous thrombin potential (ETP).

RESULTS

Fifty-four patients were recruited (n=28 control, n=26 study). Processed blood volume for transfusion was significantly (p<0.001) higher in the HemoSep group. In the HemoSep group, the PT was shorter (18.7±0.3 vs 19.9±0.3 sec; p<0.05) post-operatively and the aPTT was longer (48.6±3.8 vs 37.3±1.0 sec; p<0.01) following autologous transfusion. In the control group, D-dimer and ETP levels were higher (1903±424 vs.1088±151; p<0.05 and 739±46 vs. 394±60; p<0.001, respectively) following autologous transfusion.

CONCLUSIONS

Although centrifuged cell salvage is known to adequately haemoconcentrate and remove unwanted substrates and bacteriological contamination, the process can exacerbate coagulopathy. The HemoSep device demonstrated some increase in haemostatic markers when used in low-risk cardiac surgery patients.

Calibrated Automated Thrombinography (CAT), a Tool to Identify Patients at Risk of Bleeding during Anticoagulant Therapy: A Systematic Review

Background  Bleeding is a feared adverse event during anticoagulant treatment. In patients on vitamin K antagonists, most bleedings occur with the international normalized ratio (INR) in the therapeutic range. Currently, identification of high-risk patients via laboratory methods is not reliable. In this systematic review, we assessed the ability of calibrated automated thrombin generation (CAT-TG) to predict bleeding in patients on anticoagulant treatment. Methods  A systematic search was executed in three databases: Medline, Embase, and Cochrane. Results  Seven studies were included; two were of good methodological quality. One study showed that patients on warfarin with INRs in range (2-3) admitted for hemorrhage ( n  = 28), had lower CAT-TG levels (endogenous thrombin potential [ETP]: 333 ± 89 nM/min) than patients on warfarin admitted for other reasons (ETP: 436 ± 207 nM/min; p  < 0.001). Another study found no difference in ETP or peak levels between bleeding and nonbleeding patients in PPP or PRP. When measured in whole blood, both levels were significantly lower in patients with bleeding compared with nonbleeding patients (median [interquartile range, IQR] ETP: 182.5 [157.2-2,847 nM/min] vs. median [IQR] ETP: 256.2 [194.9-344.2 nM/min]; p  < 0.001) and median [IQR] peak: 23.9 [19.6-41.8 nM] vs. median [IQR] peak: 39.1 [24.9-53.2 nM]; p  < 0.05). From the remaining studies, four suggested that CAT-TG is more sensitive in detecting hemostatic abnormalities than INR and one article found ETP and INR to be equally useful. However, insufficient data were provided to validate these conclusions. Conclusion  Studies investigating the direct association between decreased CAT-TG values and hemorrhagic events are rare. Therefore, the clinical consequences of low CAT-TG values remain to be further investigated.

Higher Preoperative Plasma Thrombin Potential in Patients Undergoing Surgery for Aortic Stenosis Compared to Surgery for Stable Coronary Artery Disease

Aortic stenosis (AS) and coronary artery disease (CAD) influence the coagulation system, potentially affecting hemostasis during cardiac surgery. Our aim was to evaluate 2 preoperative global hemostasis assays, plasma thrombin potential and thromboelastometry, in patients with severe aortic valve stenosis compared to patients with CAD. A secondary aim was to test whether the assays were associated with postoperative bleeding. Calibrated automated thrombogram (CAT) in platelet-poor plasma and rotational thromboelastometry (ROTEM) in whole blood were analyzed in patients scheduled for elective surgery due to severe AS (n = 103) and stable CAD (n = 68). Patients with AS displayed higher plasma thrombin potential, both thrombin peak with median 252 nmol/L (interquartile range 187-319) and endogenous thrombin potential (ETP) with median 1552 nmol/L/min (interquartile range 1340-1838), when compared to patients with CAD where thrombin peak was median 174 nmol/L (interquartile range 147-229) and ETP median 1247 nmol/L/min (interquartile range 1034-1448; both P < .001). Differences persisted after adjustment for age, gender, comorbidity, and antithrombotic treatment. Differences observed in thromboelastometry between the groups did not persist after adjustment for baseline characteristics. Bleeding amount showed no relationship with plasma thrombin potential but weakly to thromboelastometry (R² = .064, P = .001). Patients with AS exhibited preoperatively increased plasma thrombin potential compared to patients with CAD. Plasma thrombin potential was not predictive for postoperative bleeding in patients scheduled for elective surgery.

Enzymatically oxidized phospholipids restore thrombin generation in coagulation factor deficiencies

Hemostatic defects are treated using coagulation factors; however, clot formation also requires a procoagulant phospholipid (PL) surface. Here, we show that innate immune cell–derived enzymatically oxidized phospholipids (eoxPL) termed hydroxyeicosatetraenoic acid–phospholipids (HETE-PLs) restore hemostasis in human and murine conditions of pathological bleeding. HETE-PLs abolished blood loss in murine hemophilia A and enhanced coagulation in factor VIII- (FVIII-), FIX-, and FX-deficient human plasma . HETE-PLs were decreased in platelets from patients after cardiopulmonary bypass (CPB). To explore molecular mechanisms, the ability of eoxPL to stimulate individual isolated coagulation factor/cofactor complexes was tested in vitro. Extrinsic tenase (FVIIa/tissue factor [TF]), intrinsic tenase (FVIIIa/FIXa), and prothrombinase (FVa/FXa) all were enhanced by both HETE-PEs and HETE-PCs, suggesting a common mechanism involving the fatty acid moiety. In plasma, 9-, 15-, and 12-HETE-PLs were more effective than 5-, 11-, or 8-HETE-PLs, indicating positional isomer specificity. Coagulation was enhanced at lower lipid/factor ratios, consistent with a more concentrated area for protein binding. Surface plasmon resonance confirmed binding of FII and FX to HETE-PEs. HETE-PEs increased membrane curvature and thickness, but not surface charge or homogeneity, possibly suggesting increased accessibility to cations/factors. In summary, innate immune-derived eoxPL enhance calcium-dependent coagulation factor function, and their potential utility in bleeding disorders is proposed.

Innate immune-derived enzymatically oxidized phospholipids enhance calcium-dependent coagulation factor function.

Retrospective Review of a Prothrombin Complex Concentrate (Beriplex P/N) for the Management of Perioperative Bleeding Unrelated to Oral Anticoagulation

A multicenter, retrospective, observational study of 4-factor prothrombin complex concentrate (PCC) and/or fresh frozen plasma (FFP) use within routine clinical care unrelated to vitamin K antagonists was conducted. The PCC was administered preprocedure for correction of coagulopathy (prophylactic cohort) and treatment of bleeding postsurgery (treatment cohort). Of the 445 patients included, 40 were in the prophylactic cohort (PCC alone [n = 16], PCC and FFP [n = 5], FFP alone [n = 19]) and 405 were in the treatment cohort (PCC alone [n = 228], PCC and FFP [n = 123], FFP alone [n = 54]). Cardiovascular surgery was the most common setting. PCC doses ranged between 500 and 5000 IU. Effectiveness (assessed retrospectively) was reported as effective in 93.0% in the PCC-only group (95% confidence interval, 89.1% to 95.9%), 78.9% (70.8% to 85.6%) with PCC and FFP, and 86.3% (76.2% to 93.2%) with FFP alone. In the treatment cohort, international normalized ratio was significantly reduced in all 3 groups. In patients who received PCC, the rate of thromboembolic events (1.9%) was below rates in the literature for similar procedures. PCCs offer a potential alternative to FFP in the management of perioperative bleeding unrelated to oral anticoagulant therapy.

Prothrombin Complex Concentrates in Pediatric Cardiac Surgery: The Current State and the Future

BACKGROUND

After decades of practice of pediatric cardiac surgery, postoperative bleeding due to the immaturity of hemostasis, hemodilution, and hypothermia remains a concern. Recently, a new approach for adult coagulopathy after bypass has emerged. Prothrombin complex concentrates (PCCs), designed to treat bleeding in hemophilia patients, are safely and efficiently used off label for hemorrhage after bypass. However, optimal dosing, indications and contraindications, and laboratory tests to assess the efficacy of PCC use in children have not yet been established. This literature review outlines the challenges of bypass-related coagulopathy, the pharmacology, and the experience in use of PCCs, with a focus on their potential in pediatric cardiac surgery.

METHODS

After a thorough literature search of MEDLINE, Scopus, and Ovid databases using the term "prothrombin complex concentrate AND pediatric," 23 relevant articles were selected.

RESULTS

The data supporting successful use of PCCs in acquired coagulopathy after cardiac surgery in adults have been increasing. Although small volume, low immunogenicity, efficiency, and speed in correcting coagulopathy are attractive qualities of PCCs for pediatric practice, current evidence is only anecdotal. The main concerns are unknown dosing regimens, the inability to closely monitor the effects of PCCs in real time, and a possibility of thrombotic complications, which can be particularly devastating in young congenital cardiac patients whose lives frequently depend upon the patency of artificial shunts.

CONCLUSIONS

Extensive, high-quality research is warranted to fill in the gaps of knowledge regarding using PCCs in pediatric cardiac practice.

Thromboelastometry and Thrombelastography Analysis under Normal Physiological Conditions - Systematic Review

BACKGROUND

Studies investigating thromboelastometry or thrombelastography analyses in a physiological context are scattered and not easy to access.

OBJECTIVE

To systematically retrieve and describe published reports studying healthy subjects and targeting at the correlation of ROTEM® and TEG® measurements with conventional parameters of hemostasis.

METHODS

Systematic Review: Papers were searched in Medline, Scopus and the Science Citation Index database. Reference lists of included studies and of reviews were screened. To be included papers had to report ROTEM or TEG data on healthy subjects. Two reviewers screened papers for inclusion, read full texts of potentially relevant papers, and extracted data of included papers.

RESULTS

Searches identified 1,721 records of which 1,713 were either excluded immediately or after reading the full text. The remaining 8 studies enrolled 632 subjects. The association of conventional parameters of hemostasis with ROTEM and with TEG was investigated in one and two studies, respectively. Overall correlation was limited and ranged from 0.0 to 0.40 (total thrombus generation vs. fibrinogen; clotting time INTEM vs. activated partial thromboplastin time).

CONCLUSIONS

Studies assessing the relationship between thromboelastometry or thromboelastography analyses and conventional parameters of hemostasis in healthy subjects remains scarce, and correlations are limited. Further research is needed to understand the physiology of thromboelastometry and thromboelastography parameters.

Prothrombin Complex Concentrates for Bleeding in the Perioperative Setting

Prothrombin complex concentrates (PCCs) contain vitamin K-dependent clotting factors (II, VII, IX, and X) and are marketed as 3 or 4 factor-PCC formulations depending on the concentrations of factor VII. PCCs rapidly restore deficient coagulation factor concentrations to achieve hemostasis, but like with all procoagulants, the effect is balanced against thromboembolic risk. The latter is dependent on both the dose of PCCs and the individual patient prothrombotic predisposition. PCCs are approved by the US Food and Drug Administration for the reversal of vitamin K antagonists in the setting of coagulopathy or bleeding and, therefore, can be administered when urgent surgery is required in patients taking warfarin. However, there is growing experience with the off-label use of PCCs to treat patients with surgical coagulopathic bleeding. Despite their increasing use, there are limited prospective data related to the safety, efficacy, and dosing of PCCs for this indication. PCC administration in the perioperative setting may be tailored to the individual patient based on the laboratory and clinical variables, including point-of-care coagulation testing, to balance hemostatic benefits while minimizing the prothrombotic risk. Importantly, in patients with perioperative bleeding, other considerations should include treating additional sources of coagulopathy such as hypofibrinogenemia, thrombocytopenia, and platelet disorders or surgical sources of bleeding. Thromboembolic risk from excessive PCC dosing may be present well into the postoperative period after hemostasis is achieved owing to the relatively long half-life of prothrombin (factor II, 60-72 hours). The integration of PCCs into comprehensive perioperative coagulation treatment algorithms for refractory bleeding is increasingly reported, but further studies are needed to better evaluate the safe and effective administration of these factor concentrates.

Simultaneous measurement of thrombin generation and fibrin formation in whole blood under flow conditions

Assays based on the formation of thrombin and fibrin are frequently used, and results are considered exchangeable in research/clinical settings. However, thrombin generation and fibrin formation do not always go hand in hand and flow profoundly influences thrombus formation. We describe the technical/clinical evaluation of an assay to simultaneously measure thrombin generation and fibrin formation under conditions of flow. Introduction of a fluorometer into a 'cone and base principle'-based rheometer allowed the measurement of thrombin generation (using a thrombin-sensitive substrate) and fibrin formation (changes in viscosity), while applying a linear shear flow. Increasing shear rates inversely related with thrombin generation and fibrin formation. Increasing fibrinogen concentrations in defibrinated plasma resulted in increased thrombin generation and fibrin formation. In pre-operative samples of 70 patients undergoing cardiothoracic surgery, fibrin formation and thrombin generation parameters correlated with fibrinogen content, rotational thromboelastometry (ROTEM) and whole blood Calibrated Automated Thrombinography (CAT) parameters, respectively. Upon dividing patients into two groups based on the median clot strength, a significant difference in perioperative/total blood loss was established. In conclusion, we clinically evaluated a method capable of simultaneously measuring thrombin generation and fibrin formation in plasma/whole blood under continuous flow, rendering our method one step closer to physiology. Importantly, our test proved to be indicative for the amount of blood loss during/after cardiothoracic surgery.

Perioperatively acquired disorders of coagulation

Purpose of review

To provide an overview of acquired coagulopathies that can occur in various perioperative clinical settings. Also described are coagulation disturbances linked to antithrombotic medications and currently available strategies to reverse their antithrombotic effects in situations of severe hemorrhage.

Recent findings

Recent studies highlight the link between low fibrinogen and decreased fibrin polymerization in the development of acquired coagulopathy. Particularly, fibrin(ogen) deficits are observable after cardiopulmonary bypass in cardiac surgery, on arrival at the emergency room in trauma patients, and with ongoing bleeding after child birth. Regarding antithrombotic therapy, although new oral anticoagulants offer the possibility of efficacy and relative safety compared with vitamin K antagonists, reversal of their anticoagulant effect with nonspecific agents, including prothrombin complex concentrate, has provided conflicting results. Specific antidotes, currently being developed, are not yet licensed for clinical use, but initial results are promising.

Summary

Targeted hemostatic therapy aims to correct coagulopathies in specific clinical settings, and reduce the need for allogeneic transfusions, thus preventing massive transfusion and its deleterious outcomes. Although there are specific guidelines for reversing anticoagulation in patients treated with antiplatelet agents or warfarin, there is currently little evidence to advocate comprehensive recommendations to treat drug-induced coagulopathy associated with new oral anticoagulants.

Heparin and Protamine Titration Does Not Improve Haemostasis after Cardiac Surgery: A Prospective Randomized Study

Background

Bleeding complications are common in cardiac surgery. Perioperative handling of heparin and protamine may influence the haemostasis. We hypothesized that heparin and protamine dosing based on individual titration curves would improve haemostasis in comparison to standard dosing.

Subjects and Methods

Sixty patients scheduled for first time elective coronary artery bypass grafting or valve surgery were included in a prospective randomized study. The patients were randomized to heparin and protamine dosing with Hepcon HMS Plus device or to standard weight and activated clotting time (ACT) based dosing. Blood samples were collected before and 10 minutes, 2 hours and 4 hours after cardiopulmonary bypass. Primary endpoint was endogenous thrombin potential in plasma 2 hours after surgery as assessed by calibrated automated thrombography. Secondary endpoints included total heparin and protamine doses, whole blood clot formation (thromboelastometry) and post-operative bleeding volume and transfusions. Heparin effect was assessed by measuring anti-Xa activity.

Results

Endogenous thrombin potential and clot formation deteriorated in both groups after surgery without statistically significant intergroup difference. There were no significant differences between the groups in total heparin and protamine doses, heparin effect, or postoperative bleeding and transfusions at any time point. Significant inverse correlations between anti-Xa activity and endogenous thrombin potential were observed 10 min (r = -0.43, p = 0.001), 2 hours (r = -0.66, p<0.001) and 4 hours after surgery (r = -0.58, p<0.001).

Conclusion

In conclusion, the results suggest that perioperative heparin and protamine dosing based on individual titration curves does not improve haemostasis after cardiac surgery. Postoperative thrombin generation capacity correlates to residual heparin effect.

Trial Registration

www.isrctn.comISRCTN14201041.

Validation of viscoelastic coagulation tests during cardiopulmonary bypass

BACKGROUND

Viscoelastic point-of-care tests such as thromboelastography (TEG) and rotational thromboelastometry (ROTEM) are increasingly used to guide hemostatic therapy after cardiac surgery. The aim of this study was to assess their clinical utility during cardiopulmonary bypass to predict postbypass coagulation status and to guide therapy.

METHODS

In this prospective study, TEG and ROTEM tests were performed in 52 adult patients undergoing elective cardiac surgery at two time points: near the end of cardiopulmonary bypass and after heparin reversal with protamine. The 95% confidence intervals of the mean difference were compared with a prespecified clinically relevant limit of ± 20% of the value after protamine.

RESULTS

Both viscoelastic fibrinogen assays were well within the prespecified clinically relevant limit (≥ 79% of patients). The laboratory Clauss fibrinogen was much lower during cardiopulmonary bypass than after protamine (mean difference 1.2 g L(-1) , 95% CI 1.03-1.4, which was outside a clinically acceptable difference. For intrinsically activated tests, clotting times (CT) were different and outside the prespecified limit on TEG (mean difference -1.2 min, 95% CI -1.8 to -0.6) but not on ROTEM (mean difference 2.3 sec, 95% CI -8.6 to 13.2), while clot strength was well within the clinical limit on both devices (≥ 94% of patients). For extrinsically activated tests, clot strength on both TEG and ROTEM was within the pre-specified limit in 98% of patients.

CONCLUSIONS

Results from TEG and ROTEM tests performed toward the end of cardiopulmonary bypass are similar to results after reversal of heparin. Amplitudes indicating clot strength were the most stable parameters across all tests, whereas CT showed more variability. In contrast, laboratory testing of fibrinogen using the Clauss assay was essentially invalid during cardiopulmonary bypass.

Evaluation of dynamic parameters of thrombus formation measured on whole blood using rotational thromboelastometry in children undergoing cardiac surgery: a descriptive study

BACKGROUND

Total thrombus formation velocity calculated using amplitude parameters obtained at different times could be used to estimate the amplification and the propagation phases observed during coagulation processes, and therefore might be useful to predict postoperative hemostatic products administration in pediatric patients.

METHODS

We retrospectively analyzed data from 49 children <3 months of age who underwent cardiac surgery. Children ≤1 month of age routinely received fresh frozen plasma during bypass while children >1 month of age did not. The EXTEM parameters were used to calculate velocity curves using amplitudes obtained at different times, the area under the curve called total thrombus formation and the maximum rate of thrombus formation. These parameters were compared between children who received fresh frozen plasma and those who did not. Receiver operating characteristics curves were used to define variables that could be used to predict postoperative fresh frozen plasma transfusion.

RESULTS

Total thrombus formation and maximum rate of thrombus formation significantly increased in children who received fresh frozen plasma compared to those who did not. Both total thrombus formation and maximum rate of thrombus formation have a better specificity to predict postoperative fresh frozen plasma transfusion compared to clotting time or maximal clot firmness.

CONCLUSION

Based on this descriptive study, dynamic ROTEM(®) parameters of total thrombus formation could be used to estimate the amplification and the propagation phases of coagulation in children. These parameters might be used in further well-designed study to predict the need for hemostatic products in children undergoing cardiac surgery with cardiopulmonary bypass.

Correcting thrombin generation ex vivo using different haemostatic agents following cardiac surgery requiring the use of cardiopulmonary bypass

Recently, lower thrombin generation has been associated with excess bleeding post-cardiopulmonary bypass (CPB). Therefore, treatment to correct thrombin generation is a potentially important aspect of management of bleeding in this group of patients. The objective of the present study was to investigate the effects of fresh frozen plasma (FFP), recombinant factor VIIa (rFVIIa), prothrombin complex concentrate (PCC) and tissue factor pathway inhibitor (TFPI) inhibition on thrombin generation when added ex vivo to the plasma of patients who had undergone cardiac surgery requiring CPB. Patients undergoing elective cardiac surgery were recruited. Blood samples were collected before administration of heparin and 30 min after its reversal. Thrombin generation was measured in the presence and absence of different concentrations of FFP, rFVIIa, PCC and an anti-TFPI antibody. A total of 102 patients were recruited. Thrombin generation following CPB was lower compared with pre-CPB (median endogenous thrombin potential pre-CPB 339 nmol/l per min, post-CPB 155 nmol/l per min, P < 0.0001; median peak thrombin pre-CPB 35 nmol/l, post-CPB 11 nmol/l, P < 0.0001). Coagulation factors and anticoagulants decreased, apart from total TFPI, which increased (55-111 ng/ml, P < 0.0001), and VWF (144-170 IU/dl, P < 0.0001). Thrombin generation was corrected to pre-CPB levels by the equivalent of 15 ml/kg FFP, 45 μg/kg rFVIIa and 25 U/kg of PCC. Inhibition of TFPI resulted in an enhancement of thrombin generation significantly beyond pre-CPB levels. This study shows that FFP, rFVIIa, PCC and inhibition of TFPI correct thrombin generation in the plasma of patients who have undergone surgery requiring CPB. Inhibition of TFPI may be a further potential therapeutic strategy for managing bleeding in this group of patients.

INR vs. thrombin generation assays for guiding VKA reversal: a retrospective comparison

BACKGROUND

Prothrombin complex concentrate (PCC) is used to reverse vitamin K antagonist (VKA)-induced anticoagulation. Prothrombin time-derived international normalized ratio (INR) measurements are widely used in determining the required PCC dose, but this approach requires reappraisal. The aim of the present study was to determine the added value of the thrombin generation assay (TGA) compared with the INR in guidance of VKA reversal by PCC.

METHODS

In an open, observational study, INR and TGA measurements were carried out on plasma samples from phenprocoumon-treated patients receiving VKA reversal. Following both analytical methods, PCC dosing correlates were calculated and compared retrospectively. Alternatively, in vitro PCC spiking experiments were performed.

RESULTS

As expected, an exponential relationship between PCC dose and INR was found. For the TGA parameters peak thrombin and endogenous thrombin potential (ETP), however, this relationship was found to be linear throughout the full therapeutic range. Additional computational analysis showed a positive correlation (r²=0.7) between the initial INR and PCC dose required for a target INR of 2.1, which was completely lost at a lower target INR. In contrast, a positive correlation (r²=0.8) between initial ETP as well as peak height and PCC dose required to obtain parameter normalization was found. These correlates appeared useful for calculating PCC dose.

CONCLUSIONS

Our results support the current debate questioning the rationale for the use of the INR in the management of anticoagulation by VKA. Compared with INR, TGA-based calculations may enable a more accurate PCC dosing regimen for patients requiring VKA reversal.

Rotational thromboelastometry in prediction of bleeding after cardiac surgery

Background

Reexploration and its associated complications significantly affect hospital mortality and morbidity. Therefore, to prevent postoperative bleeding and its related complications, using an appropriate modality is essential during cardiac surgery.

Methods

Four hundred patients (296 males and 104 females, mean age 60.8 ± 9 years) scheduled for first-time coronary artery bypass graft surgery were prospectively enrolled. Blood samples were obtained for ROTEM testing before surgery and 30 min after heparin reversal. The patients were divided into 2 groups: group 1 was patients with no abnormal postoperative bleeding and group 2 was patients who required reexploration for abnormal postoperative bleeding. Group 2 patients were divided into 2 subgroups: 2a was patients with surgical bleeding and group 2b was patients with nonsurgical bleeding. Variables were compared between groups.

Results

Among the 400 patients, 42 were reexplored. Hospital stay was significantly longer and hospital deaths more frequent in group 2 patients ( p < 0.001 and p = 0.010, respectively). Ten (2.8%) patients had abnormal preoperative results of ROTEM in group 1 compared to 14 (33.3%) in group 2 ( p < 0.001). After surgery, the number of patients with abnormal ROTEM results was significantly different between the 2 groups: 6 (1.7%) in group 1 vs. 14 (33.3%) in group 2 ( p < 0.001). Four (12.5%) patients in group 2a had abnormal preoperative ROTEM results compared to 10 (100%) in group 2a ( p < 0.001).

Conclusion

Measuring coagulation factors by ROTEM both before surgery and after heparin reversal can identify patients at increased risk of postoperative bleeding.