Monitoring incomplete heparin reversal and heparin rebound after cardiac surgery

Thromboelastometry and two activated clotting tests in detecting residual heparin after protamine in cardiac surgical patients: A prospective cohort study

BACKGROUND

After cardiac surgery, complete heparin reversal with protamine is essential. Accordingly, there is a need for an accurate and precise point-of-care device to detect possible residual heparin after protamine administration.

OBJECTIVES

To compare two different activated clotting time (ACT) tests and thromboelastometry in detecting postprotamine heparin activity after cardiac surgery.

DESIGN

A single-centre prospective, observational study.

SETTING

University Hospital from September 2021 to February 2023.

PARTICIPANTS

Fifty-five adult, elective cardiac surgical patients.

INTERVENTIONS

The ACT-LR and ACT+ tests of Hemochron Signature Elite device, and the coagulation time (CT) ratio from INTEM and HEPTEM tests of ROTEM Sigma device, were analysed after protamine administration and compared to baseline values.

MAIN OUTCOME MEASURES

Based on postprotamine antifactor Xa (anti-fXa) activity, the patients were divided into heparin (anti-fXa ≥0.2 IU ml -1 ) and no heparin (anti-fXa ≤0.1 IU ml -1 ) groups.

RESULTS

There was a mean bias of 44 [95% confidence interval (CI) 40 to 47] celite seconds between ACT-LR and ACT+ measurements. The absolute changes in ACT-LR, ACT+ and INTEM:HEPTEM CT ratio were variable and did not differ between the groups. The mean ± SD percentage changes between postprotamine and baseline ACT-LR and ACT+ values were 5.9 ± 17.5 and 5.9 ± 16.9% in the no residual heparin group, compared to 1.4 ± 8.4 and 9.9 ± 12.5% in the residual heparin group. Receiver operator characteristic curves for postprotamine INTEM:HEPTEM CT ratio and for percentage changes in ACT-LR and ACT+ to detect an anti-fXa at least 0.2 IU ml -1 had areas under the curve of 0.496 (95% CI, 0.329 to 0.663), 0.425 (95% CI, 0.260 to 0.591) and 0.583 (95% CI, 0.417 to 0.749), respectively.

CONCLUSION

Both the ACT-LR and ACT+ tests of Hemochron Signature Elite device and the INTEM:HEPTEM CT ratio of ROTEM Sigma device have poor ability to detect residual heparin shortly after protamine administration.

Low-Range Heparin and Protamine Detection: A Single-Center Prospective Diagnostic Study

OBJECTIVES

The detection of low-range heparin activity is important to correctly assess heparin reversal and rebound, especially after cardiopulmonary bypass. Current parameters are either not available at point-of-care (anti-Xa activity [aXa] and activated partial thromboplastin time [aPTT]), insensitive (kaolin-activated clotting time [kACT]), or expensive (ROTEM viscoelastic test). We aimed to assess the performance of a recently proposed parameter from the Sonoclot viscoelastic test: the slope-45. We aimed to assess the effects of a range of low-dose heparin and protamine and their interaction on multiple proposed parameters.

DESIGN

Prospective in vitro volunteer study.

SETTING

Single-center university teaching hospital.

PARTICIPANTS

Healthy volunteers.

INTERVENTIONS

Blood samples from healthy volunteers (n = 10) were treated ex vivo with incremental low doses of heparin, protamine, or their combination. In the combination cycle, theoretical reversal ratios were 25%, 62.5%, 100%, and 200% of the highest heparin dose, based on a unit-for-unit reversal. We compared the effects on aXa, aPTT, iSTAT kACT, ROTEM clotting time ratio, and the novel Sonoclot slope-45 parameter, and we performed receiver operating curve analysis.

MEASUREMENTS AND MAIN RESULTS

In heparin-spiked blood, all parameters except iSTAT kACT were able to reliably detect low heparin activity. Protamine, both in isolation and combined with heparin, showed no impact on aXa, aPTT, iSTAT kACT, ROTEM clotting time ratio, and the novel Sonoclot slope-45 parameter.

CONCLUSIONS

We were able to confirm that the Sonoclot slope-45 has a high sensitivity for low-dose heparin, which is retained in the setting of interacting protamine. It was insensitive to protamine in itself.

Monitoring Hemostatic Function during Cardiac Surgery with Point-of-Care Viscoelastic Assays: A Narrative Review

Bleeding is a well-known and severe complication of cardiac surgery. Cardiopulmonary bypass, along with heparinization and hemodilution, is thought to affect all pathways of the hemostatic process, leading to excessive bleeding and worsened morbidity and mortality. The traditionally used standard laboratory tests (SLTs) were not designed for the surgical setting, have long turnaround times, and are poor predictors of bleeding. This review aims to give an overview of viscoelastic assays (VEAs), compare VEAs to conventional testing methods, and summarize the evidence for VEAs in cardiac surgery. A search of Medline via Pubmed, Scopus, and Embase yielded 2,868 papers, which we reviewed and summarized the key findings. VEAs such as rotational thromboelastometry and thromboelastography provide a quick turnaround, graphical, global impression of hemostasis in whole blood. VEAs allow for the analysis of specific contributors to the coagulation process and may facilitate cause-oriented hemostatic treatment and the development of treatment algorithms. VEAs have been found to have a high specificity and high negative predictive value for coagulopathic bleeding. Patients treated with VEA-based algorithms have been shown to have lower rates of bleeding, transfusion requirements, and exposure to allogeneic blood products. However, VEA-based algorithms have not demonstrated a mortality benefit and evidence for outcomes such as surgical re-exploration and hospital length of stay remains equivocal. In conclusion, VEAs have been shown to be comparable if not superior to SLTs in cardiac surgery. Further large-scale studies are needed to better evaluate the impact of VEAs on clinical outcomes.

Heparin rebound in patients undergoing off-pump coronary artery bypass grafting surgery: a single-center retrospective study

BACKGROUND

Heparin, an anticoagulant used in cardiac surgery, can result in heparin rebound (HR), where it returns postoperatively despite being neutralized with protamine. This study was designed to investigate the prevalence of HR in patients undergoing off-pump coronary artery bypass grafting (OPCAB) and evaluate the impact of HR on their short-term outcomes.

METHODS

HR was defined by a 10% increase in activated coagulation time (ACT) following two hours of heparin neutralization with protamine, bleeding over 200 mL/h, and abnormal laboratory coagulation examination results. We analyzed 503 OPCAB patients aged 31-80 years from September 2019 to June 2022, who were categorized into HR (n = 56) and Non-HR (n = 447) groups. The primary outcome was postoperative bleeding volume. Secondary outcomes included the incidence of postoperative reoperation for bleeding, allogenic blood transfusion incidences and volumes, and laboratory variables.

RESULTS

Significant differences were observed in preoperative platelet counts (P < 0.001) and the ACT measured 2 h post-heparin neutralization (P = 0.012). The group HR exhibited higher 24-hour bleeding volumes, increased reoperation rates, and greater total bleeding volumes (all P < 0.001).

CONCLUSIONS

Postoperative HR was found to be prevalent in OPCAB patients and increased bleeding risks. These findings indicate the need for future randomized controlled trials to confirm the impact of HR and guide patient blood management.

Does heparin rebound lead to postoperative blood loss in patients undergoing cardiac surgery with cardiopulmonary bypass?

BACKGROUND

Heparin rebound is a common observed phenomenon after cardiac surgery with CPB and is associated with increased postoperative blood loss. However, the administration of extra protamine may lead to increased blood loss as well. Therefore, we want to investigate the relation between heparin rebound and postoperative blood loss and the necessity to provide extra protamine to reverse heparin rebound.

METHODS

We searched PubMed, Cochrane, EMBASE, Google Scholar and Web of Science to review the question: "Does heparin rebound lead to postoperative blood loss in patients undergoing cardiac surgery with cardiopulmonary bypass." Combination of search words were framed within four major categories: heparin rebound, blood loss, cardiac surgery and cardiopulmonary bypass. All studies that met our question were included. Quality assessment was performed using the Cochrane risk of bias (RoB2) tool for randomized controlled trials and the risk of bias in non-randomized studies of intervention (ROBINS-I) for non-randomised trials.

RESULTS

4 randomized and 17 non-randomized studies were included. The mean incidence of heparin rebound was 40%. The postoperative heparin levels, due to heparin rebound, were often below or equal to 0.2 IU/mL. We could not demonstrate an association between heparin rebound and postoperative blood loss or transfusion requirements. However the quality of evidence was poor due to a broad variety of definitions of heparin rebound, measured by various coagulation tests and studies with small sample sizes.

CONCLUSION

The influence of heparin rebound on postoperative bleeding seems to be negligible, but might get significant in conjunction with incomplete heparin reversal or other coagulopathies. For that reason, it might be useful to get a picture of the entire coagulation spectrum after cardiac surgery, as can be done by the use of a viscoelastic test in conjunction with an aggregometry test.

Combination of bolus and continuous infusion of factor VIII in a patient with severe hemophilia A undergoing on-pump coronary artery bypass graft surgery

Patients with hemophilia A can safely undergo cardiac surgery. Combining continuous infusion and boluses of factor VIII is both safe and cost-effective. Interdisciplinary approach and meticulous planning are crucial in the prevention of bleeding complications.

Acetylsalicylic acid alone or in combination with either enoxaparin or unfractionated heparin for postoperative thromboprophylaxis in coronary artery bypass surgery patients. A randomised clinical trial assessing surrogate outcomes

INTRODUCTION

Coronary artery bypass graft surgery has considerable effects on patient haemostasis. Heparins as thromboprophylaxis may be beneficial but may also increase the risk of bleeding complications.

OBJECTIVES

To assess the effects of heparins on haemostasis in post-coronary artery bypass graft patients.

METHODS

Across one year, we randomised 60 participants scheduled for an elective coronary artery bypass graft-procedure with or without aortic valve replacement. The trial was a prospective, open-label (though blinded for the laboratory), randomised, single-centre trial with three intervention groups (n = 20 in each): group 1 received acetylsalicylic acid, group 2 received subcutaneous low molecular weight heparin and acetylsalicylic acid, and group 3 received intravenous unfractionated heparin and acetylsalicylic acid. Primary outcomes were platelet activation (Multiplate® ASPI-test) and time to clot initiation (TEG® R-time). We secondly assessed several additional Multiplate® and TEG® parameters.

RESULTS

Group 3 (intravenous unfractionated heparin) compared with group 1 (acetylsalicylic acid alone) showed evidence of 1) increased clot initiation time (R-time + 0.9 min; 95 % CI: +0.4 to +1.4 min; P = 0.009), and 2) decreased 30-min lysis (-1.3 %; 95 % CI: -2.1 to -0.5 %; P = 0.02). The remaining analyses of primary and secondary outcomes showed no evidence of a difference between the three groups.

DISCUSSION

Intravenous unfractionated heparins may increase the clot initiation time post-operatively after coronary artery bypass graft surgery and reduce lysis. Otherwise, there seems to be no effect of low molecular weight or unfractionated heparin on haemostatic parameters after coronary artery bypass surgery patients.

Protamine titration to optimize heparin antagonization after cardiopulmonary bypass

OBJECTIVES

To optimize protamine titration for heparin antagonization after weaning from cardiopulmonary bypass (CPB).

DESIGN

A prospective, observational trial.

SETTING

Single-center, non-university teaching hospital.

PARTICIPANTS

Forty patients presenting for elective on-pump coronary artery bypass grafting with or without single valve surgery.

INTERVENTIONS

At the end of CPB, the residual amount of heparin in the patient was estimated using a Bull-curve. The total protamine dose was calculated as 1 unit of protamine for 1 unit of heparin. Protamine was administered as 5 aliquots containing 20% of the total protamine dose each, with 2-min intervals.

MEASUREMENTS AND MAIN RESULTS

Activated Clotting Time (ACT) values were measured 2 min after administration of each aliquot. ROTEM(®)-analysis was performed after the full dose of protamine had been administered. After 60% of the total protamine dose had been administered, ACT values were normalized in 86.5% of patients. After the complete dose of protamine had been administered, 61.1% of patients displayed signs of protamine overdose on ROTEM(®)-analysis.

CONCLUSIONS

In patients who present for on-pump coronary artery bypass grafting with or without single valve surgery, a 0.6-to-1 ratio of protamine-to-heparin to antagonize heparin may be sufficient and beneficial for patients.

Management of Therapeutic-intensity Unfractionated Heparin: A Narrative Review on Critical Points

Nowadays, unfractionated heparin (UFH) use is limited to selected patient groups at high risk of both bleeding and thrombosis (patients in cardiac surgery, in intensive care unit, and patients with severe renal impairment), rendering its management extremely challenging, with many unresolved questions despite decades of use. In this narrative review, we revisit the fundamental concepts of therapeutic anticoagulation with UFH and address five key points, summarizing controversies underlying the use of UFH and discussing the few recent advances in the field: (1) laboratory tests for UFH monitoring have significant limitations; (2) therapeutic ranges are not well grounded; (3) the actual influence of antithrombin levels on UFH's anticoagulant activity is not well established; (4) the concept of UFH resistance lacks supporting data; (5) scarce data are available on UFH use beyond acute venous thromboembolism. We therefore identified key issues to be appropriately addressed in future clinical research: (1) while anti-Xa assays are often considered as the preferred option, we call for a vigorous action to improve understanding of the differences between types of anti-Xa assays and to solve the issue of the usefulness of added dextran; (2) therapeutic ranges for UFH, which were defined decades ago using reagents no longer available, have not been properly validated and need to be confirmed or reestablished; (3) UFH dose adjustment nomograms require full validation.

Factors Influencing Anti-Xa Assays: A Multicenter Prospective Study in Critically Ill and Noncritically Ill Patients Receiving Unfractionated Heparin

BACKGROUND

 The presence of dextran sulfate (DS) in reagents and the type of blood collection tube (citrate/citrated-theophylline-adenosine-dipyridamole [CTAD]) can lead to discrepancies between unfractionated heparin (UFH) anti-Xa levels.

OBJECTIVES

 To evaluate the extent of the effect (1) of different reagents containing or not containing DS and (2) of the blood collection tubes, on UFH anti-Xa levels, in various clinical situations (NCT04700670).

METHODS

 We prospectively included patients from eight centers: group (G)1, cardiopulmonary bypass (CPB) after heparin neutralization (n = 39); G2, cardiothoracic intensive care unit (ICU) after CPB (n = 35); G3, medical ICU (n = 53); G4, other medical inpatients (n = 38). Blood was collected into citrated and CTAD tubes. Chromogenic anti-Xa assays were centrally performed, using seven reagent/analyzer combinations including two without DS. The association between anti-Xa levels and covariates was tested using a linear mixed-effects model.

RESULTS

 We analyzed 4,546 anti-Xa values from 165 patients. Median anti-Xa levels were systematically higher with reagents containing DS, whatever the patient group, with the greatest effect observed in G1 (0.32 vs. 0.05 IU/mL). Anti-Xa levels were slightly higher in CTAD than in citrate samples, irrespective of the assay. The model showed: (1) a significant dextran-patient group interaction (p < 0.0001), the effect of DS on anti-Xa levels varying from 30.9% in G4 to 296% in G1, and (2) a significant effect of CTAD, varying between patient groups (p = 0.0302).

CONCLUSION

 The variability of anti-Xa levels with a great overestimation of the values, using a reagent containing DS, can lead to different treatment decisions, especially after heparin neutralization by protamine. Clinical consequences of these differences remain to be demonstrated.

Comparison of anticoagulation monitoring strategies for adults supported on extracorporeal membrane oxygenation: A systematic review

BACKGROUND

Anticoagulation is critical in patients supported on extracorporeal membrane oxygenation (ECMO). The appropriate monitoring strategies for heparin remain unclear.

OBJECTIVES

This systematic review aimed to compare the accuracy and safety of various monitoring strategies for patients supported on ECMO.

METHODS

The PubMed and Web of Science databases were searched for articles in March 2023 without restrictions on publication date. Anticoagulation monitoring strategies for adults supported on ECMO were compared across all included studies. The incidence of bleeding, thrombosis, mortality, blood transfusion, correlation between tests and heparin dose, and the discordance between different tests were discussed in the included studies. The risk of bias was assessed using the Newcastle-Ottawa Scale and Cochrane Collaboration's tool.

RESULTS

Twenty-six studies, including a total of 1,684 patients, met the inclusion criteria. The monitoring of anticoagulation by activated partial thromboplastin time (aPTT) resulted in less blood product transfusion than that by activated clotting time (ACT). Moreover, the monitoring of anticoagulation by anti-factor Xa (Anti-Xa) resulted in a more stable anticoagulation than that by aPTT. Anti-Xa and aPTT correlated with heparin dose better than ACT, and the discordance between different monitoring tests was common. Finally, combined monitoring showed some advantages in reducing mortality and blood product transfusion.

CONCLUSION

Anti-Xa and aPTT are more suitable for anticoagulation monitoring for patients supported on ECMO than ACT. Thromboelastography and combination strategies are less applied. Most of the studies were retrospective, and their sample sizes were relatively small; thus, more appropriate monitoring strategies and higher quality research are needed.

Heparin Rebound: An In-Depth Review

The common conception of "heparin rebound" invokes heparin returning to circulation in the postoperative period after apparently adequate intraoperative reversal with protamine. This is believed to portend increased postoperative bleeding and provides the rationale for administering additional empiric doses of protamine in response to prolonged coagulation tests and/or bleeding. However, the relevant literature of the last 60+ years provides only a weak level of evidence that "rebounded" heparin itself is a significant etiology of postoperative bleeding after cardiac surgery with cardiopulmonary bypass. Notably, many of the most frequently cited heparin rebound investigators ultimately concluded that although exceedingly low levels of heparin activity could be detected by anti-Xa assay in some (but not all) patients postoperatively, there was no correlation with actual bleeding. An understanding of the literature requires a careful reading of the details because the investigators lacked standardized definitions for "heparin rebound" and "adequate reversal" while studying the phenomenon with significantly different experimental methodologies and laboratory tests. This review was undertaken to provide a modern understanding of the "heparin rebound" phenomenon to encourage an evidence-based approach to postoperative bleeding. Literature searches were conducted via PubMed using the following MeSH terms: heparin rebound, heparin reversal, protamine, platelet factor 4, and polybrene. Relevant English language articles were reviewed, with subsequent references obtained from the internal citations. Perspective is provided for both those who use HepCon-guided management and those who do not, as are practical recommendations for the modern era based on the published data and conclusions of the various investigators.

Early Reexploration for Bleeding Is Associated With Improved Outcome in Cardiac Surgery

BACKGROUND

Reexploration after cardiac surgery, most frequently for bleeding, is a quality metric used to assess surgical performance. This may cause surgeons to delay return to the operating room in favor of attempting nonoperative management. This study investigated the impact of the timing of reexploration on morbidity and mortality.

METHODS

This study was a single-institution retrospective review of all adult cardiac surgery patients from July 2010 to June 2020. Time to reexploration was assessed, and outcomes were compared across increasing time intervals. Reported bleeding sites were classified into 5 groups, and bleeding rate (chest tube output) was compared across bleeding sites. Univariable analysis was performed using the Fisher exact and Kruskal-Wallis tests. Multivariable logistic regression models were used for risk-adjusted analyses.

RESULTS

Of 10 070 eligible patients, 251 (2.5%) required reexploration for postoperative bleeding. The most common site of bleeding was "any suture line" (n = 70; 28%). Interestingly, in 30% of cases (n = 75) "no active bleeding" site was reported. The highest rate of bleeding (mL/h) was observed in the "any mediastinal structure" group (median, 450; interquartile range [IQR], 185, 8878), and the lowest rate was noted in the "no active bleeding" group (median, 151.2; IQR, 102, 270). Both morbidity rates (0-4 hours, 12.3% vs 25-48 hours, 37.5%; P = .001) and mortality rates (0-4 hours, 3.1% vs 25-48 hours, 43.8%; P = .001) escalated significantly with increasing time to reexploration.

CONCLUSIONS

Delayed reexploration for bleeding after cardiac surgery is associated with increased risk for morbidity and mortality. Early surgical intervention, particularly within 4 hours, may improve outcomes. Implications from using reoperation as a performance metric may lead to unnecessary delay and patient harm.

Heparin Resistance During Cardiopulmonary Bypass in Adult Cardiac Surgery

The use of heparin for anticoagulation has changed the face of cardiac surgery by allowing a bloodless and motionless surgical field throughout the introduction of cardiopulmonary bypass (CPB). However, heparin is a drug with complex pharmacologic properties that can cause significant interpatient differences in terms of responsiveness. Heparin resistance during CPB is a weighty issue due to the catastrophic consequences stemming from inadequate anticoagulation, and the treatment of it necessitates a rationalized stepwise approach due to the multifactorial contributions toward this entity. The widespread use of activated clotting time (ACT) as a measurement of anticoagulation during CPB is examined, as it may be a false indicator of heparin resistance. Heparin resistance also has been repeatedly reported in patients infected with COVID-19, which deserves further exploration in this pandemic era. This review aims to examine the variability in heparin potency, underlying mechanisms, and limitations of using ACT for monitoring, as well as provide a framework towards the current management of heparin resistance.

Anti-factor X Activity Levels with Continuous Intravenous Infusion and Subcutaneous Administration of Enoxaparin after Coronary Artery Bypass Grafting: a Randomized Clinical Trial

BACKGROUND

Low-molecular-weight heparin enoxaparin is widely used in pharmacological thromboprophylaxis after coronary artery bypass grafting (CABG). The aim of this study was to compare anti-factor X activity (anti-Xa) levels when the thromboprophylactic dose of enoxaparin was provided after CABG, with two different administration routes: continuous intravenous infusion (CIV) and subcutaneous bolus (SCB) injection. We hypothesized that the current standard method of SCB administration might lead to lower anti-Xa levels than recommended in other patient groups, due to reduced bioavailability.

METHODS

In this prospective, randomized, controlled clinical trial, 40 patients scheduled for elective CABG were randomized to receive 40 mg of enoxaparin per day either as CIV or SCB for 72 h. Enoxaparin was initiated 6-10 h after CABG. Anti-Xa levels were measured 12-14 times during the study period. The primary outcome i.e. the maximum anti-Xa concentration over 0-24 h (C_max0-24h ), was calculated from these measured values. Secondary outcomes were C_max25-72h and the trough concentration of anti-Xa after 72 h of enoxaparin initiation (C_72h ).

RESULTS

Twenty patients were randomized to the CIV-group and 19 to the SCB-group. The median anti-Xa C_max0-24h was significantly lower in the CIV-group than in the SCB-group: 0.15 [interquartile range (IQR) 0.13-0.19] IU/mL versus 0.25 (IQR 0.18-0.32) IU/mL, p < 0.005. The median anti-Xa C_max25-72h was 0.12 (IQR, 0.1-0.17) IU/mL versus 0.23 (IQR 0.19-0.31) IU/mL, respectively, p < 0.005. At 72 h, there was no difference between the groups in their anti-Xa levels.

CONCLUSIONS

In this low-risk CABG patient population, SCB administration of a thromboprophylactic dose of enoxaparin provided anti-Xa levels that are considered sufficient for thromboprophylaxis in other patient groups. CIV administration resulted in lower anti-Xa levels compared to the SCB route.

Anticoagulation Monitoring for Perioperative Physicians

From preoperative medications to intraoperative needs to postoperative thromboprophylaxis, anticoagulants are encountered throughout the perioperative period. This review focuses on coagulation testing clinicians utilize to monitor the effects of these medications.

Optimization of Heparin Monitoring with Anti-FXa Assays and the Impact of Dextran Sulfate for Measuring All Drug Activity

Heparins, unfractionated or low molecular weight, are permanently in the spotlight of both clinical indications and laboratory monitoring. An accurate drug dosage is necessary for an efficient and safe therapy. The one-stage kinetic anti-FXa assays are the most widely and universally used with full automation for large series, without needing exogenous antithrombin. The WHO International Standards are available for UFH and LMWH, but external quality assessment surveys still report a high inter-assay variability. This heterogeneity results from the following: assay formulation, designed without or with dextran sulfate to measure all heparin in blood circulation; calibrators for testing UFH or LMWH with the same curve; and automation parameters. In this study, various factors which impact heparin measurements are reviewed, and we share our experience to optimize assays for testing all heparin anticoagulant activities in plasma. Evidence is provided on the usefulness of low molecular weight dextran sulfate to completely mobilize all of the drug present in blood circulation. Other key factors concern the adjustment of assay conditions to obtain fully superimposable calibration curves for UFH and LMWH, calibrators' formulations, and automation parameters. In this study, we illustrate the performances of different anti-FXa assays used for testing heparin on UFH or LMWH treated patients' plasmas and obtained using citrate or CTAD anticoagulants. Comparable results are obtained only when the CTAD anticoagulant is used. Using citrate as an anticoagulant, UFH is underestimated in the absence of dextran sulfate. Heparin calibrators, adjustment of automation parameters, and data treatment contribute to other smaller differences.

Antiplatelet and anticoagulation strategies for left ventricular assist devices

Left ventricular assist devices (LVAD) have revolutionized the management of advanced heart failure. However, complications rates remain high, among which hemorrhagic and thrombotic complications are the most important. Antiplatelet and anticoagulation strategies form a cornerstone of LVAD management and may directly affect LVAD complications. Concurrently, LVAD complications influence anticoagulation and anticoagulation management. A thorough understanding of device, patient, and management, including anticoagulation and antiplatelet therapies, are important in optimizing LVAD outcomes. This article provides a comprehensive state of the art review of issues related to antiplatelet and anticoagulation management in LVADs. We start with a historical overview, the epidemiology and pathophysiology of bleeding and thrombotic complications in LVADs. We then discuss platelet and anticoagulation biology followed by considerations prior to, during, and after LVAD implantation. This is followed by discussion of anticoagulation and the management of thrombotic and hemorrhagic complications. Specific problems, including management of heparin-induced thrombocytopenia, anticoagulant reversal, novel oral anticoagulants, artificial heart valves, and noncardiac surgeries are covered in detail.

Retrospective Analysis of Thromboelastography-Directed Transfusion in Isolated CABG: Impact on Blood Product Use, Cost, and Outcomes

Cardiac surgeries account for approximately 20% of blood use in the United States. Allogeneic transfusion has been associated with increased risk of morbidity and mortality, further justifying the need to reduce blood use. This study aimed at determining whether a point-of-care coagulation test, thromboelastography (TEG), impacted blood product administration and outcomes. Patients undergoing isolated coronary artery bypass grafting (CABG) were retrospectively reviewed before the use of TEG (2008-2009) (n = 640) and after implementation (2011-2012) (n = 458). Blood product use was compared between time frames. Logistic regression and generalized linear models were created to estimate the impact on outcomes including the reoperation rate, mortality, and cost. The mean use of each blood product was significantly reduced in the perioperative period. Overall blood product use was decreased by over 40%. Mediastinal re-exploration of bleeding was significantly reduced with TEG (4.8 vs. 1.5%). Six-month mortality was not impacted in this cohort nor was the readmission rate or hospital length of stay. However, blood cost and patient charges were significantly lower after TEG was introduced. The use of TEG to guide the administration of blood products during isolated CABG significantly affected the amounts and types of products given intra- and perioperatively. This resulted in less chest tube drainage, fewer returns to the operating room, and more accurate diagnosis of coagulopathic status. Cost savings to the patient and institution were appreciated as a consequence of these improved clinical outcomes.

Endogenous Heparin-Like Substances May Cause Coagulopathy in a Patient with Severe Postpartum Hemorrhage

Introduction

Postpartum hemorrhage (PPH) is associated with maternal morbidity and mortality. Accurate diagnosis of the cause of puerperal hemorrhage is as important as treatment strategies for resuscitation. We report a case of coagulation disorder caused by endogenous heparin-like substances in a PPH patient.

Case Presentation

A 30-year-old woman with no medical history of bleeding disorders suffered intractable hemorrhage following spontaneous delivery in a local hospital. The patient was transferred to the department of obstetrics of a superior hospital. On arrival, the patient was found to have severe hemorrhagic anemia, hemorrhagic shock, and disseminated intravascular coagulation. Active treatments were performed, but the patient continued bleeding. Laboratory testing, performed during early treatment, revealed that all coagulation factors were below normal. The differences between CK-TEG R-time (reaction time in citrated kaolin thromboelastography assay) and CKH-TEG R-time (reaction time in citrated kaolin with heparinase thromboelastography assay) suggested the presence of heparin activity. However, the patient's family denied heparin use prior to presentation. Thus, we deduced that endogenous heparin-like substances were the main cause of the coagulopathy. After receiving treatment with protamine, the patient stopped bleeding. Meanwhile, all coagulation parameters and the TEG assay results improved.

Conclusions

In this case report, TEG assay suggested the presence of heparin activity in a PPH patient, and treatment also highlighted the importance of analyzing different parameters in TEG.

Is There a "Blind Spot" in Point-of-Care Testing for Residual Heparin After Cardiopulmonary Bypass? A Prospective, Observational Cohort Study

Identifying the cause of a bleeding complication after cardiac surgery can be crucial. This study sought to clarify whether the application of unprocessed autologous pump blood influences anti-factor Xa activity after cardiac surgery and evaluated 2 point-of-care methods regarding their ability to identify an elevated anti-factor Xa activity at different timepoints after cardiopulmonary bypass. Anti-factor Xa activity, heparin/protamine titration and the clotting time ratio of thromboelastometry in the INTEM and HEPTEM were measured at baseline (T1), after the application of protamine (T2) and after the complete application of autologous pump blood (T3). Anti-factor Xa activity decreased significantly between T2 and T3 as well did the absolute number of patients with an elevated anti-factor Xa activity. Receiver Operating Curve analyses were performed for both point-of-care methods. At T2 neither could identify patients with an elevated anti-factor Xa activity, while both methods were able to do so at T3 with high sensitivity and specificity. This difference suggests that an interference in the detection of residual heparinization with point-of-care methods exists right after the application of protamine, which seems to subside after a short time span. Nevertheless, results of point-of-care testing for residual heparinization after cardiopulmonary bypass need to be interpreted considering the protamine-heparin ratio and the timepoint of protamine administration.

Effect of antithrombin in fresh frozen plasma on hemostasis after cardiopulmonary bypass surgery

INTRODUCTION

Supplementation of fresh frozen plasma immediately after cardiopulmonary bypass is an effective method to enhance clotting ability as coagulation factors are consumed in the extracorporeal circuit during cardiopulmonary bypass. On the other hand, the anticoagulation factors in fresh frozen plasma can also deter the clotting ability. This study investigated the effect of fresh frozen plasma administration on the comprehensive clotting ability following cardiopulmonary bypass.

METHODS

This prospective observational study included 22 patients scheduled for cardiac surgery. Clotting times and maximum clot firmness were evaluated using the types of rotational thromboelastometry, intrinsic rotational thromboelastometry, and heparinase thromboelastography preoperatively, immediately after cardiopulmonary bypass, and 1 hour after cardiopulmonary bypass. Activated clotting time, antithrombin activity, and heparin concentration were also measured at these time-points.

RESULTS

Antithrombin activity (62.9 ± 7.2% vs. 51.1 ± 7.4%, p < 0.0001) and activated clotting time (132.6 ± 9.6% vs. 120.0 ± 9.0%, p < 0.001) were significantly higher 1 hour after cardiopulmonary bypass compared to measurements taken immediately after cardiopulmonary bypass. Heparin concentration 1 hour after cardiopulmonary bypass was significantly decreased compared to that immediately after cardiopulmonary bypass. On the other hand, maximum clot firmness determined via intrinsic rotational thromboelastometry was significantly greater 1 hour after cardiopulmonary bypass (53.8 ± 4.8 mm) than that immediately after cardiopulmonary bypass (49.5 ± 4.8 mm). Clotting time determined via intrinsic rotational thromboelastometry and heparinase thromboelastography was also significantly shorter 1 hour after cardiopulmonary bypass than that immediately after cardiopulmonary bypass.

CONCLUSION

Fresh frozen plasma administration increased antithrombin activity and caused activated clotting time prolongation, but then increased clotting ability. Thus, testing by rotational thromboelastometry after cardiopulmonary bypass could be valuable in the detection of comprehensive clotting ability.

ACT Values after Neutralization Lower than Pre-heparinization ACT Leads to Lower Operative Times, Bleeding, and Post-Operative Transfusions in CABG Patients: an Observational Study

OBJECTIVE

To evaluate if lower activated coagulation time (ACT) value after neutralization than preoperative ACT value was effective in reducing bleeding, operative times, and post-operative transfusions in patients underwent coronary artery bypass grafting (CABG).

METHODS

Retrospective selection of 398 patients from January 2014 to May 2017. Patients were divided into 2 groups according to final ACT after neutralization: A - final ACT lower than preoperative ACT; and B - final ACT higher than or equal to preoperative ACT. Hemostatic time, intraoperative blood loss, ACT after final neutralization, mediastinal blood loss, and transfusion requirements were observed.

RESULTS

The hourly blood loss in the Group A was generally lower than in the Group B at first 3 hours, which has significant difference (P<0.05). However, there was no difference after 3 hours between the two groups. Operative time, intraoperative blood loss, mediastinal blood loss, transfusion requirements, and drainage in the first postoperative 12 hours in the Group A were lower than in Group B, which has significant difference (P<0.05).

CONCLUSION

As a result, final ACT values lower than pre-heparinization ACT values are safe and lead to lower operative times, bleeding, and post-operative transfusions.

The effect of protamine dosing variation on bleeding and transfusion after heparinisation for cardiopulmonary bypass

INTRODUCTION

Accurate dosing of protamine reversal following on-pump cardiac surgical procedures is challenging, with both excessive and inadequate administration recognised to increase bleeding risk. We aimed to examine the relationship between three ratios for heparin reversal and markers of haemostasis.

METHODS

A retrospective analysis of a prospectively collected database was undertaken at a single tertiary cardiac unit, reviewing all cases of on-pump coronary artery bypass grafts and single valve replacements from 01/01/2011 to 31/12/2015. The ratio between total intra-operative heparin and protamine was stratified to three groups (low: ≤0.6 mg per 100 IU of heparin, moderate: 0.6-1.0 and high: >1.0) and related to the primary outcome of red blood cell (RBC) transfusion, with secondary outcomes being the number of units transfused, the haemoglobin differential and mediastinal drain output at 4 hours.

RESULTS

Of the 803 patients identified, 338 received a blood transfusion, with 1035 units being used. Eighteen percent of individuals (145) received a low ratio, 50% (404) received a moderate ratio and 32% (254) a high ratio. Using the moderate group as a reference, the low dose group was 56.5% less likely to have received a RBC transfusion (OR 0.435; 95% CI 0.270:0.703 p=0.001) while the high dose group carried a 241% increased association with transfusion (OR 3.412; 95% CI 2.399:4.853 p<0.001). For those transfused, a lower protamine:heparin ratio was associated with a lower number of units transfused, lesser haemoglobin differential and less mediastinal drain output.

CONCLUSION

Higher doses of intra-operative protamine relative to heparin are associated with greater risk of transfusion and post-operative bleeding.

Diagnostic and therapeutic medical devices for safer blood management in cardiac surgery: systematic reviews, observational studies and randomised controlled trials

Background

Anaemia, coagulopathic bleeding and transfusion are strongly associated with organ failure, sepsis and death following cardiac surgery.

Objective

To evaluate the clinical effectiveness and cost-effectiveness of medical devices used as diagnostic and therapeutic tools for the management of anaemia and bleeding in cardiac surgery.

Methods and results

Workstream 1 – in the COagulation and Platelet laboratory Testing in Cardiac surgery (COPTIC) study we demonstrated that risk assessment using baseline clinical factors predicted bleeding with a high degree of accuracy. The results from point-of-care (POC) platelet aggregometry or viscoelastometry tests or an expanded range of laboratory reference tests for coagulopathy did not improve predictive accuracy beyond that achieved with the clinical risk score alone. The routine use of POC tests was not cost-effective. A systematic review concluded that POC-based algorithms are not clinically effective. We developed two new clinical risk prediction scores for transfusion and bleeding that are available as e-calculators. Workstream 2 – in the PAtient-SPecific Oxygen monitoring to Reduce blood Transfusion during heart surgery (PASPORT) trial and a systematic review we demonstrated that personalised near-infrared spectroscopy-based algorithms for the optimisation of tissue oxygenation, or as indicators for red cell transfusion, were neither clinically effective nor cost-effective. Workstream 3 – in the REDWASH trial we failed to demonstrate a reduction in inflammation or organ injury in recipients of mechanically washed red cells compared with standard (unwashed) red cells.

Limitations

Existing studies evaluating the predictive accuracy or effectiveness of POC tests of coagulopathy or near-infrared spectroscopy were at high risk of bias. Interventions that alter red cell transfusion exposure, a common surrogate outcome in most trials, were not found to be clinically effective.

Conclusions

A systematic assessment of devices in clinical use as blood management adjuncts in cardiac surgery did not demonstrate clinical effectiveness or cost-effectiveness. The contribution of anaemia and coagulopathy to adverse clinical outcomes following cardiac surgery remains poorly understood. Further research to define the pathogenesis of these conditions may lead to more accurate diagnoses, more effective treatments and potentially improved clinical outcomes.

Study registration

Current Controlled Trials ISRCTN20778544 (COPTIC study) and PROSPERO CRD42016033831 (systematic review) (workstream 1); Current Controlled Trials ISRCTN23557269 (PASPORT trial) and PROSPERO CRD4201502769 (systematic review) (workstream 2); and Current Controlled Trials ISRCTN27076315 (REDWASH trial) (workstream 3).

Funding

This project was funded by the National Institute for Health Research (NIHR) Programme Grants for Applied Research programme and will be published in full inProgramme Grants for Applied Research; Vol. 5, No. 17. See the NIHR Journals Library website for further project information.

Coagulation monitoring correlation with heparin dose in pediatric extracorporeal life support

Objectives:

Extracorporeal Life Support (ECLS) risks thrombotic and hemorrhagic complications. Optimal anti-coagulation monitoring is controversial. We compared coagulation tests evaluating the heparin effect in pediatric ECLS.

Methods:

A retrospective study of children (<18yrs) undergoing ECLS over 12 months in a tertiary pediatric intensive care unit (PICU). Variables included anti-Factor Xa activity (anti-Xa), activated partial thromboplastin time (aPTT), activated clotting time (ACT) and thromboelastogram (TEG®6s) parameters: ratio and delta reaction (R) times (the ratio and difference, respectively, between R times in kaolin assays with and without heparinase). Test results were correlated with unfractionated heparin infusion rate (IU/kg/hr) at the time of sampling. Mean test results of each ECLS run were evaluated according to the presence/absence of complications.

Results:

Thirty-two ECLS runs (31 patients) generated 695 data-points for correlation. PICU mortality was 22% and the thrombotic complication rate was 66%. The proportion of variation in coagulation test results explained by heparin dose was 13.3% for anti-Xa, 11.9% for ratio R time, and 9.9% for delta R time, compared with <1% for ACT and aPTT. Incorporating individual variation, age and antithrombin activity in a model with heparin dose explained less than 50% of the variation in test results. Correlation varied according to age, day of ECLS run and between individuals, with parallel dose-response lines noted between patients. Significantly lower mean anti-Xa was observed in PICU non-survivors and runs with thrombosis.

Conclusion:

Lower anti-Xa was observed in ECLS runs with complications. Although absolute results from anti-Xa and TEG6®s showed the best correlation with heparin dose, a large proportion of variation in results was unexplained by heparin, while dose response was similar between individuals. Population pharmacokinetic/pharmacodynamic modelling is required, as well as prospective trials to delineate the superior means of adjusting heparin therapy to prevent adverse clinical outcomes.

Postoperative Bleeding After Change in Heparin Supplier: A Cardiothoracic Center Experience

OBJECTIVE

Unfractionated heparin is a mixture of glycosaminoglycans with different pharmacologic and pharmacokinetic properties. The literature suggests that blood loss after cardiac surgery is related to both elevated postoperative heparin concentrations and the potency of different heparin brands.

DESIGN

An audit of the observed increase in the incidence of cardiac surgery-related bleeding after change in heparin supplier. Patient characteristics were compared between groups before and after a change in heparin brands.

SETTING

Tertiary cardiothoracic center.

PARTICIPANTS

All patients undergoing cardiac surgery between August 1, 2011, and April 30, 2012.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Two hundred eighty patients underwent surgery before a change in heparin brands and 216 after a change. Their preoperative and intraoperative characteristics were similar. Postoperative chest tube drainages and blood transfusions were significantly greater after the change in heparin brands (postoperative chest drainage 476.8 ± 393.1 v 344.8 ± 323.2 mL/6 h and 1,062.2 ± 738.8 v 841.8 ± 567.4 mL/24 h, respectively; both p < 0.001) despite the administration of larger amounts of protamine, fresh frozen plasma/platelet transfusions, and cryoprecipitate. Heparin recirculation within 24 hours of bypass was noted in about 70% of the samples tested using either anti-factor X activity or the thromboelastography ratio between nonheparinase R and heparinase-modified R and was not associated with the heparin brand. The likelihood ratio chi-square test for nested models identified an added predictive value of the heparin brand when included as a predictor of bleeding (chest drainage >800 mL/6 h) in a model comprising recirculation, assessed using either an elevated anti-factor X activity or ratio between nonheparinase R and heparinase-modified R.

CONCLUSION

It is likely that the observed increase in postoperative bleeding was related to the pharmacologic properties of the new heparin brand rather than a higher incidence of heparin recirculation.

An Adjusted Calculation Model of Reduced Heparin Doses in Cardiopulmonary Bypass Surgery in a Chinese Population

OBJECTIVE

To investigate the safety and efficacy of an adjusted regimen of heparin infusion in cardiopulmonary bypass (CPB) surgery in a Chinese population.

DESIGN

Prospective, single-center, observational study.

SETTING

University teaching hospital.

PARTICIPANTS

Patients having cardiac surgery with CPB were selected for this study using the following criteria: 18 to 75 years of age, undergoing first-time cardiac surgery with conventional median sternotomy, aortic clamping time between 40 and 120 minutes, and preoperative routine blood tests showing normal liver, renal, and coagulation functions. The exclusion criteria include salvage cases, a history of coagulopathy in the family, and long-term use of anticoagulation or antiplatelet drugs.

INTERVENTIONS

Sixty patients were divided randomly into a control group (n = 30) receiving a traditional heparin regimen and an experimental group (n = 30) receiving an adjusted regimen.

MEASUREMENTS AND MAIN RESULTS

Activated coagulation time (ACT) was monitored at different time points, ACT>480 seconds was set as the safety threshold of CPB. Heparin doses (initial dose, added dose, and total dose), protamine doses (initial dose, added dose, and total dose), CPB time, aortic clamping time, assisted circulation time, sternal closure time, blood transfusion volume, and drainage volume 24 hours after surgery were recorded. There was no significant difference in achieving target ACT after the initial dose of heparin between the 2 groups; CPB time, aortic clamping time, assisted circulation time, postoperative complication rate, and drainage volume between the 2 groups were not significantly different (p>0.05). However, initial and total dosage of heparin, initial and total dosage of protamine, sternal closure time, and intraoperative blood transfusion volume in the experimental group were significantly lower (p< 0.05).

CONCLUSIONS

Adjusted regimen of heparin infusion could be used safely and effectively in Chinese CPB patients, which might reduce the initial and total dosage of heparin and protamine as well as sternal closure time and intraoperative blood transfusion volume.

Management of anticoagulation and antiplatelet therapy in patients with left ventricular assist devices

Left ventricular assist devices (LVADs) have increased the survival of patients with advanced heart failure fourfold. Despite these advances, significant bleeding and thrombotic complications occur. Hemorrhage requiring surgery has been reported in up to 30% of adults and 50% of children after LVAD placement. LVAD thrombosis and embolic stroke lead to significant long-term morbidity. Adults are treated with antithrombotic therapy to prevent thrombotic complications, but the amount and intensity of treatment differs between institutions. The goal international normalized ratio for warfarin therapy varies from 1.5 to 3.0. Some physicians manage adult LVAD patients without antiplatelet medication, whereas other adults are treated with aspirin as a single agent or combined with dipyridamole. In contrast, physicians typically manage children with LVADs using the Edmonton Anticoagulation and Platelet Inhibition Protocol, a detailed algorithm for anticoagulation and antiplatelet treatment modified based on thromboelastography results. LVAD implantation causes consumption of coagulation proteins, activation of fibrinolysis, and loss of high molecular weight von Willebrand protein multimers. How these changes in the coagulation system influence the risk of hemorrhage and initiation of thrombosis is unknown. Prospective, controlled studies are needed to determine the antithrombotic regimen that most effectively balances bleeding and thrombosis in LVAD patients.

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.

Anticoagulation management during multivessel coronary artery bypass grafting: a randomized trial comparing individualized heparin management and conventional hemostasis management

BACKGROUND

Individualized heparin management (IHM) uses heparin dose-response curves to improve hemostasis management during cardiac surgery as compared with activated clotting time-based methods.

OBJECTIVES

IHM was compared with conventional hemostasis management (CHM) in a randomized, prospective study (ID DRKS00007580).

METHODS

One-hundred and twenty patients undergoing multivessel coronary artery bypass grafting (CABG) were enrolled. Heparin and protamine consumption, blood losses, blood transfusions and administration of hemostatic agents were recorded. Time courses of platelet counts and of coagulation parameters were determined. Coagulation was analyzed at intensive care unit (ICU) arrival by thromboelastometry.

RESULTS

IHM patients received significantly lower initial heparin doses (289.3IU kg(-1) [interquartile range (IQR) 221.5-376.2 IU kg(-1) ] versus 350.5 IU kg(-1) [IQR 346.8-353.7 IU kg(-1) ], P < 0.0001) but similar total heparin doses (418.5 IU kg(-1) [IQR 346.9-590.5 IU kg(-1) ] versus 435.8 IU kg(-1) [IQR 411.7-505.1 IU kg(-1) ]). IHM patients received significantly less protamine, resulting in protamine/total heparin ratios of 0.546 [IQR 0.469-0.597] versus 0.854 [IQR 0.760-0.911] in CHM patients (P < 0.0001). Activated partial thromboplastin time (50.5 s [IQR 40.0-60.0 s] versus 37.0 s [IQR 33.0-40.0 s], P < 0.0001), activated clotting time (136 s [IQR 129.0-150.5 s] versus 126.5 s [IQR 120.3-134.0 s], P = 0.0002) and INTEM clotting times (215 s [IQR 192-237] versus 201 s [IQR 191-216 s], P = 0.0397) were significantly longer in IHM patients than in CHM patients at ICU arrival, with no difference in prothrombin time (P = 0.538). IHM patients lost significantly more blood within 12 h postoperatively (420 mL [IQR 337.5-605.0 mL] versus 345 mL [IQR 230.0-482.5 mL], P = 0.0041), and required significantly more hemostatic agents to control bleeding. Red blood cell transfusion requirements and time courses of platelet counts did not differ between groups.

CONCLUSIONS

Multivessel CABG patients did not benefit from IHM in comparison with our established protocol based on activated clotting time.

A portable blood plasma clot micro-elastometry device based on resonant acoustic spectroscopy

Abnormal blood clot stiffness is an important indicator of coagulation disorders arising from a variety of cardiovascular diseases and drug treatments. Here, we present a portable instrument for elastometry of microliter volume blood samples based upon the principle of resonant acoustic spectroscopy, where a sample of well-defined dimensions exhibits a fundamental longitudinal resonance mode proportional to the square root of the Young's modulus. In contrast to commercial thromboelastography, the resonant acoustic method offers improved repeatability and accuracy due to the high signal-to-noise ratio of the resonant vibration. We review the measurement principles and the design of a magnetically actuated microbead force transducer applying between 23 pN and 6.7 nN, providing a wide dynamic range of elastic moduli (3 Pa-27 kPa) appropriate for measurement of clot elastic modulus (CEM). An automated and portable device, the CEMport, is introduced and implemented using a 2 nm resolution displacement sensor with demonstrated accuracy and precision of 3% and 2%, respectively, of CEM in biogels. Importantly, the small strains (<0.13%) and low strain rates (<1/s) employed by the CEMport maintain a linear stress-to-strain relationship which provides a perturbative measurement of the Young's modulus. Measurements of blood plasma CEM versus heparin concentration show that CEMport is sensitive to heparin levels below 0.050 U/ml, which suggests future applications in sensing heparin levels of post-surgical cardiopulmonary bypass patients. The portability, high accuracy, and high precision of this device enable new clinical and animal studies for associating CEM with blood coagulation disorders, potentially leading to improved diagnostics and therapeutic monitoring.

Activated coagulation time vs. intrinsically activated modified rotational thromboelastometry in assessment of hemostatic disturbances and blood loss after protamine administration in elective cardiac surgery: analysis from the clinical trial (NCT01281397)

BACKGROUND

Excessive bleeding after cardiopulmonary bypass (CPB) is risk factor for adverse outcomes after elective cardiac surgery (ECS). Although many different point-of-care devices to diagnose hemostatic disturbances after CPB are available, the best test is still unclear. The study aim was to compare the accuracy of hemostatic disorder detection between two point-of-care devices.

METHODS

We enrolled 148 patients (105 male and 43 female) undergoing ECS in a prospective observational study. Rotational thromboelastometry (TEM, with InTEM test), and Activated coagulation time (ACT) measurement were performed 15 min after protamine administration. The cohort group was divided into two subgroups according to occurrence of excessive postoperative bleeding. Endpoints were defined in two ways: as total amount of chest tube output (CTO) and blood product transfusion requirements.

RESULTS

Total amount of CTO value of 1507,50 mL presented 75th percentile of distribution, thus cut-off value for bleeder category. InTEM parameters, but not ACT, correlated significantly with CTO. InTEM parameters with the strongest correlation to CTO were tested for accuracy in predicting excessive postoperative bleeding using ROC analysis. InTEM A 10 value of 38 mm, InTEM A 20 value of 49 mm and InTEM A 30 value of 51 mm delineated bleeding tendency. Patients with total amount of CTO exceeding 75th percentile were more frequently transfused with fresh frozen plasma (51.4% vs. 9.9%, p < 0.001), fibrinogen concentrate (21.6% vs. 2.7%, p = 0.001) and platelet concentrate (13.5% vs. 0.9%, p = 0.004).

CONCLUSION

Our study showed that InTEM test, but not ACT is useful in prediction of bleeding tendency after protamine administration following weaning from CPB. InTEM test could be used as a first line test in screening of possible hemostatic disorder following protamine administration.

Heparinase thromboelastography compared with activated coagulation time for protamine titration after cardiopulmonary bypass

OBJECTIVE

The present study is a comparison of two point-of-care (POC) tests as endpoints of protamine titration after CPB. The authors hypothesized that using the heparinase-kaolin thromboelastography (TEG-HK) R-time difference would more readily identify residual heparin necessitating additional protamine than when using activated coagulation time (ACT). The primary endpoint was the between-group difference in protamine dose. Whether this approach would lessen postoperative bleeding and sequelae also was investigated.

DESIGN

Single center, blinded, prospective, randomized study.

SETTING

University teaching hospital.

PARTICIPANTS

Eighty-two adult patients for on-pump coronary artery bypass and/or valve surgery.

INTERVENTIONS

Patients were randomized. In the ACT group, protamine was titrated until ACT did not exceed baseline by more than 10%. In the TEG group, a TEG-HK R-time difference less than 20% was targeted. Protamine was repeated to achieve the endpoints. Clinicians in the ACT group were blinded to TEG data and vice versa.

MEASUREMENTS AND MAIN RESULTS

There was no between-group difference in total protamine dose (3.9 ± 0.6 and 4.2 ± 0.7; 95% CI of the difference between means: -0.544 to 0.008 mg/kg; p = 0.057) or protamine:heparin ratios (1.3:1 and 1.4:1; 95% CI of the difference between means: -0.05 to 0.03 mg/mg; p = 0.653). In the ACT group, 17% of patients required a second protamine dose, and in the TEG group, 24% of patients required a second protamine dose. No between-group differences in the postoperative transfusion requirements or intensive care unit length of stay were demonstrated.

CONCLUSION

No difference was identified in protamine dosing using either ACT or TEG-HK R-time difference as endpoints. Heparinase TEG may be useful for monitoring heparin reversal.