Use of fibrin-based thromboelastometry for cryoprecipitate transfusion in cardiac surgery involving deep hypothermic circulatory arrest during cardiopulmonary bypass

Comprehensive Coagulation Profiling at the Point-of-Care Using a Novel Laser-Based Approach

Delays in identifying internal bleeding are life-threatening, thus underscoring the need for rapid and comprehensive coagulation profiling at the bedside. The authors review a novel optical coagulation profiler that measures several coagulation metrics including prothrombin time, activated clotting time, clot polymerization rate (α-angle), clot stiffness (maximum amplitude), fibrinolysis (LY), and platelet function, using a single multifunctional instrument. The optical profiler is based on the principles of Laser Speckle Rheology that quantifies tissue viscoelasticity from light scattering patterns called laser speckle. To operate the optical profiler, whole blood (40 μL) is loaded into a disposable cartridge, laser speckle patterns are recorded via a camera, and the viscoelasticity of clotting blood is estimated from speckle intensity fluctuations. By monitoring alterations in viscoelastic moduli over time during clot initiation, thrombin generation, fibrin crosslinking, clot stabilization, and LY, global coagulation parameters are obtained within 10 minutes using a drop of whole blood. Clinical testing in over 500 patients to date has confirmed the accuracy of the optical profiler for comprehensively assessing coagulation status against conventional coagulation tests and thromboelastography. Recent studies have further demonstrated the capability to quantify platelet aggregation induced by adenosine diphosphate in a drop of platelet-rich-plasma in the absence of applied shear stress. Together, these studies demonstrate that global coagulation profiling in addition to platelet function may be accomplished using a single multifunctional device. Thus, by enabling rapid and comprehensive coagulation and platelet function profiling at the bedside, the optical profiler will likely advance the capability to identify and manage patients with an elevated risk for hemorrhage.

Can the Viscoelastic Parameter α-Angle Distinguish Fibrinogen from Platelet Deficiency and Guide Fibrinogen Supplementation?

Viscoelastic tests such as thrombelastography (TEG, Haemoscope Inc., Niles, IL) and thromboelastometry (ROTEM, Tem International GmbH, Munich, Germany), performed in whole blood, are increasingly used at the point-of-care to characterize coagulopathic states and guide hemostatic therapy. An algorithm, based on a mono-analysis (kaolin-activated assay) approach, was proposed in the TEG patent (issued in 2004) where the α-angle and the maximum amplitude parameters are used to guide fibrinogen supplementation and platelet administration, respectively. Although multiple assays for both the TEG and ROTEM devices are now available, algorithms based on TEG mono-analysis are still used in many institutions. In light of more recent findings, we discuss here the limitations and inaccuracies of the mono-analysis approach. Research shows that both α-angle and maximum amplitude parameters reflect the combined contribution of fibrinogen and platelets to clot strength. Therefore, although TEG mono-analysis is useful for identifying a coagulopathic state, it cannot be used to discriminate between fibrin/fibrinogen and/or platelet deficits, respectively. Conversely, the use of viscoelastic methods where 2 assays can be run simultaneously, one with platelet inhibitors and one without, can effectively allow for the identification of specific coagulopathic states, such as insufficient fibrin formation or an insufficient contribution of platelets to clot strength. Such information is critical for making the appropriate choice of hemostatic therapy.

Predictive value of rotational thromboelastometry during cardiopulmonary bypass for thrombocytopenia and hypofibrinogenemia after weaning of cardiopulmonary bypass

BACKGROUND

The early detection of coagulopathy helps guide decisions regarding optimal transfusion management during cardiac surgery. This study aimed to determine whether rotational thromboelastometry (ROTEM) analysis during cardiopulmonary bypass (CPB) could predict thrombocytopenia and hypofibrinogenemia after CPB.

METHODS

We analyzed 138 cardiac surgical patients for whom ROTEM tests and conventional laboratory tests were performed simultaneously both during and after CPB. An extrinsically activated ROTEM test (EXTEM), a fibrin-specific ROTEM test (FIBTEM) and PLTEM calculated by subtracting FIBTEM from EXTEM were evaluated. Correlations between clot amplitude at 10 min (A10), maximal clot firmness, platelet count, and fibrinogen concentrations at each time point were calculated. A receiver operating characteristic analysis with area under the curve (AUC) was used to assess the thresholds of EXTEM, PLTEM and FIBTEM parameters during CPB and for predicting thrombocytopenia and hypofibrinogenemia after weaning of CPB.

RESULTS

The A10 on EXTEM, PLTEM, and FIBTEM during CPB showed a good correlation with platelet counts (r = 0.622 on EXTEM and r = 0.637 on PLTEM; P < 0.0001 for each value) and fibrinogen levels (r = 0.780; P < 0.0001) after CPB. A10 on a FIBTEM threshold of 8 mm during the CPB predicted a fibrinogen concentration < 150 mg/dl (AUC = 0.853) after CPB. Additionally, the threshold level of A10 on EXTEM during CPB for predicting platelet counts < 100,000 /µl after CPB was 42 mm (AUC = 0.768).

CONCLUSIONS

EXTEM, PLTEM, and FIBTEM parameters during CPB may be useful for predicting thrombocytopenia and hypofibrinogenemia after weaning of CPB.

Cryoprecipitate therapy

Cryoprecipitate, originally developed as a therapy for patients with antihaemophilic factor deficiency, or haemophilia A, has been in use for almost 50 yr. However, cryoprecipitate is no longer administered according to its original purpose, and is now most commonly used to replenish fibrinogen levels in patients with acquired coagulopathy, such as in clinical settings with haemorrhage including cardiac surgery, trauma, liver transplantation (LT), or obstetric haemorrhage. Cryoprecipitate is a pooled product that does not undergo pathogen inactivation, and its administration has been associated with a number of adverse events, particularly transmission of blood-borne pathogens and transfusion-related acute lung injury. As a result of these safety concerns, along with emerging availability of alternative fibrinogen preparations, cryoprecipitate has been withdrawn from use in a number of European countries. Compared with the plasma from which it is prepared, cryoprecipitate contains a high concentration of coagulation factor VIII, coagulation factor XIII, and fibrinogen. Cryoprecipitate is usually licensed by regulatory authorities for the treatment of hypofibrinogenaemia, and recommended for supplementation when plasma fibrinogen levels decrease below 1 g litre(-1); however, this threshold is empiric and is not based on solid clinical evidence. Consequently, there is uncertainty over the appropriate dosing and optimal administration of cryoprecipitate, with some guidelines from professional societies to guide clinical practice. Randomized, controlled trials are needed to determine the clinical efficacy of cryoprecipitate, compared with the efficacy of alternative preparations. These trials will allow the development of evidence-based guidelines in order to inform physicians and guide clinical practice.

Introduction of an algorithm for ROTEM-guided fibrinogen concentrate administration in major obstetric haemorrhage

We compared blood component requirements during major obstetric haemorrhage, following the introduction of fibrinogen concentrate. A prospective study of transfusion requirements and patient outcomes was performed for 12 months to evaluate the major obstetric haemorrhage pathway using shock packs (Shock Pack phase). The study was repeated after the pathway was amended to include fibrinogen concentrate (Fibrinogen phase). The median (IQR [range]) number of blood components given was 8.0 (3.0-14.5 [0-32]) during the Shock Pack phase, and 3.0 (2.0-5.0 [0-26]) during the Fibrinogen phase (p = 0.0004). The median (IQR [range]) quantity of fibrinogen administered was significantly greater in the Shock Pack phase, 3.2 (0-7.1 [0-20.4]) g, than in the Fibrinogen phase, 0 (0-3.0 [0-12.4]) g, p = 0.0005. Four (9.5%) of 42 patients in the Shock Pack phase developed transfusion associated circulatory overload compared with none of 51 patients in the Fibrinogen phase (p = 0.038). Fibrinogen concentrate allows prompt correction of coagulation deficits associated with major obstetric haemorrhage, reducing the requirement for blood component therapy and the attendant risks of complications.

A 2014 Update on Coagulation Management for Cardiopulmonary Bypass

Coagulopathy after cardiac surgery with cardiopulmonary bypass is a serious complication that may result in massive bleeding requiring transfusion of significant amounts of blood products, plasma, and platelets. In addition to increased patient morbidity and mortality it is associated with longer hospital stay and increased resource utilization. The current review discusses aspects in cardiopulmonary bypass–induced coagulopathy with emphasis on point-of-care testing and individualized “goal-directed” therapy in patients who develop excessive bleeding after cardiac surgery.

Management of hemorrhage in cardiothoracic surgery

Bleeding is an important issue in cardiothoracic surgery, and about 20% of all blood products are transfused in this clinical setting worldwide. Transfusion practices, however, are highly variable among different hospitals and more than 25% of allogeneic blood transfusions have been considered inappropriate. Furthermore, both bleeding and allogeneic blood transfusion are associated with increased morbidity, mortality, and hospital costs. In the past decades, several attempts have been made to find a universal hemostatic agent to ensure hemostasis during and after cardiothoracic surgery. Most drugs studied in this context have either failed to reduce bleeding and transfusion requirements or were associated with severe adverse events, such as acute renal failure or thrombotic/thromboembolic events and, in some cases, increased mortality. Therefore, an individualized goal-directed hemostatic therapy ("theranostic" approach) seems to be more appropriate to stop bleeding in this complex clinical setting. The use of point-of-care (POC) transfusion and coagulation management algorithms guided by viscoelastic tests such as thromboelastometry/thromboelastography in combination with POC platelet function tests such as whole blood impedance aggregometry, and based on first-line therapy with fibrinogen and prothrombin complex concentrate have been associated with reduced allogeneic blood transfusion requirements, reduced incidence of thrombotic/thromboembolic and transfusion-related adverse events, and improved outcomes in cardiac surgery. This article reviews the current literature dealing with the management of hemorrhage in cardiothoracic surgery based on POC diagnostics and with specific coagulation factor concentrates and its impact on transfusion requirements and patients' outcomes.

Potential value of transfusion protocols in cardiac surgery

PURPOSE OF REVIEW

On the one hand, cardiac and aortic surgery is associated with a high rate of allogeneic blood transfusion. On the other hand, both bleeding and allogeneic blood transfusion is associated with increased morbidity, mortality, and hospital costs in cardiac and aortic surgery. This article reviews the current literature between 1995 and 2012 dealing with transfusion protocols in cardiovascular surgery. The 16 studies fitting these search criteria have evaluated the impact of the implementation of ROTEM/TEG based coagulation management algorithms on transfusion requirement and outcome in overall 8507 cardiovascular surgical patients.

RECENT FINDINGS

The use of point-of-care (POC) transfusion and coagulation management algorithms based on viscoelastic tests such as thromboelastometry (ROTEM) and thrombelastography (TEG) in combination with POC platelet function tests such as whole blood impedance aggregometry (Multiplate) have been shown to be associated with reduced allogeneic blood transfusion requirements, reduced incidence of thrombotic/thromboembolic and transfusion-related adverse events, and improved outcomes in cardiac surgery.

SUMMARY

Implementation of POC algorithms including a comprehensive bundle of POC diagnostics (thromboelastometry and whole blood impedance aggregometry) in combination with first-line therapy using immediately available specific coagulation factor concentrates (fibrinogen and prothrombin complex concentrate) and defining strict indications, calculated dosages, and clear sequences for each haemostatic intervention seems to be complex but most effective in reducing perioperative transfusion requirements and has been shown to be associated with a decreased incidence of thrombotic/thromboembolic events, transfusion-related adverse events, as well as with improved patients' outcomes including 6-month mortality.

Effect of haematocrit on fibrin-based clot firmness in the FIBTEM test

BACKGROUND

Point-of-care thromboelastometry (ROTEM(®)) can be used to assess coagulation in whole blood. In the ROTEM(®) FIBTEM test, cytochalasin D eliminates the contribution of platelets to the whole blood clot; hence, only the remaining elements, including fibrinogen/fibrin, red blood cells and factor XIII, contribute to clot strength. We investigated the relationships between FIBTEM maximum clot firmness (MCF), whole blood fibrinogen concentration and plasma fibrinogen concentration to determine the impact of haematocrit on these parameters during cardiac surgery.

MATERIALS AND METHODS

The relationships between FIBTEM MCF and both whole blood fibrinogen concentration and plasma fibrinogen concentration (Clauss assay) were evaluated pre-operatively and after cardiopulmonary bypass/protamine administration in haematocrit-based subgroups.

RESULTS

The study included 157 patients. The correlation coefficient rho between FIBTEM MCF and plasma fibrinogen concentration was 0.68 at baseline and 0.70 after protamine, while that between FIBTEM MCF and whole blood fibrinogen concentration was 0.74 at baseline and 0.72 after protamine (all P <0.001). In subgroup analyses based on haematocrit levels, pre-operative FIBTEM MCF and whole blood fibrinogen concentration were both significantly higher (P <0.05) for the lowest haematocrit subgroup, but plasma fibrinogen concentration was similar in all groups. After protamine, no significant differences were observed between the lowest haematocrit group and the other groups for any of the three parameters.

CONCLUSIONS

The effect of haematocrit on blood clotting is not reflected by plasma fibrinogen concentration, in contrast to FIBTEM MCF which incorporates the contribution of haematocrit to whole blood clot firmness. This effect does, however, appear to be negligible in haemodiluted patients.