Viscoelastic testing inside and beyond the operating room

Hemorrhage is a major contributor to morbidity and mortality during the perioperative period. Current methods of diagnosing coagulopathy have various limitations including long laboratory runtimes, lack of information on specific abnormalities of the coagulation cascade, lack of in vivo applicability, and lack of ability to guide the transfusion of blood products. Viscoelastic testing offers a promising solution to many of these problems. The two most-studied systems, thromboelastography (TEG) and rotational thromboelastometry (ROTEM), offer similar graphical and numerical representations of the initiation, formation, and lysis of clot. In systematic reviews on the clinical efficacy of viscoelastic tests, the majority of trials analyzed were in cardiac surgery patients. Reviews of the literature suggest that transfusions of packed red blood cells (pRBC), plasma, and platelets are all decreased in patients whose transfusions were guided by viscoelastic tests rather than by clinical judgement or conventional laboratory tests. Mortality appears to be lower in the viscoelastic testing groups, despite no difference in surgical re-intervention rates and massive transfusion rates. Cost-effectiveness studies also seem to favor viscoelastic testing. Viscoelastic testing has also been investigated in small studies in other clinical contexts, such as sepsis, obstetric hemorrhage, inherited bleeding disorders, perioperative thromboembolism risk assessment, and management of anticoagulation for patients on mechanical circulatory support systems or direct oral anticoagulants (DOACs). While the results are intriguing, no systematic, larger trials have taken place to date. Viscoelastic testing remains a relatively novel method to assess coagulation status, and evidence for its use appears favorable in reducing blood product transfusions, especially in cardiac surgery patients.

Coagulation management in patients undergoing mechanical circulatory support

The incidence of bleeding and thrombo-embolic complications in patients undergoing mechanical circulatory support therapy remains high and is associated with bad outcomes and increased costs. The need for anticoagulation and anti-platelet therapy varies widely between different pulsatile and non-pulsatile ventricular-assist devices (VADs) and extracorporeal membrane oxygenation (ECMO) systems. Therefore, a unique anticoagulation protocol cannot be recommended. Notably, most thrombo-embolic complications occur despite values of conventional coagulation tests being within the targeted range. This is due to the fact that conventional coagulation tests such as international normalised ratio (INR), activated partial thromboplastin time (aPTT) and platelet count cannot detect hyper- or hypofibrinolysis, hypercoagulability due to tissue factor expression on circulating cells or increased clot firmness, and platelet aggregation as well as response to anti-platelet drugs. By contrast, point-of-care (POC) whole blood viscoelastic tests (thromboelastometry/-graphy) and platelet function tests (impedance or turbidimetric aggregometry) reflect in detail the haemostatic status of patients undergoing mechanical circulatory support therapy and the efficacy of their anticoagulation and antiaggregation therapy. Therefore, monitoring of haemostasis using POC thromboelastometry/-graphy and platelet function analysis is recommended during mechanical circulatory support therapy to reduce the risk of bleeding and thrombo-embolic complications. Notably, these haemostatic tests should be performed repeatedly during mechanical circulatory support therapy since thrombin generation, clot firmness and platelet response may change significantly over time with a high inter- and intra-individual variability. Furthermore, coagulation management can be hampered in non-pulsatile VADs by acquired von Willebrand syndrome, and in general by acquired factor XIII deficiency as well as by heparin-induced thrombocytopenia. In addition, POC testing can be used in bleeding patients to guide calculated goal-directed therapy with allogeneic blood products, haemostatic drugs and coagulation factor concentrates to optimise the haemostasis and to minimise transfusion requirements, transfusion-associated adverse events and to avoid thrombo-embolic complications, as well. However, coagulation management in patients undergoing mechanical circulatory support therapy is somehow like navigating between Scylla and Charybdis, and development of protocols based on POC testing seems to be beneficial.

Pharmacotherapy for Mechanical Circulatory Support: A Comprehensive Review

Objective

To provide a comprehensive review of the pharmacotherapy associated with the provision of mechanical circulatory support (MCS) to patients with end-stage heart failure and guidance regarding the selection, assessment, and optimization of drug therapy for this population.

Data Sources:

The MEDLINE/PubMed, EMBASE, and Cochrane databases were searched from 1960 to July 2010 for articles published in English using the search terms mechanical circulatory support, ventricular assist system, ventricular assist device, left ventricular assist device, right ventricular assist device, biventricular assist device, total artificial heart, pulsatile, positive displacement, axial, centrifugal, hemostasis, bleeding, hemodynamic, blood pressure, thrombosis, antithrombotic therapy, anticoagulant, antiplatelet, right ventricular failure, ventricular arrhythmia, anemia, arteriovenous malformation, stroke, infection, and clinical pharmacist.

Study Selection And Data Extraction:

All relevant original studies, metaanalyses, systematic reviews, guidelines, and reviews were assessed for inclusion. References from pertinent articles were examined for content not found during the initial search.

Data Synthesis:

MCS has advanced significantly since the first left ventricular assist device was implanted in 1966. Further advancements in MCS technology that occurred in the tatter decade are changing the overall management of end-stage heart failure care and cardiac transplantation. These pumps allow for improved bridge-to-transplant rates, enhanced survival, and quality of life. Pharmacotherapy associated with MCS devices may optimize the performance of the pumps and improve patient outcomes, as well as minimize morbidity related to their adverse effects. This review highlights the knowledge needed to provide appropriate clinical pharmacy services for patients supported by MCS devices.

Conclusions:

The HeartMate II clinical investigators called for the involvement of pharmacists in MCS patient assessment and optimization. Pharmacotherapeutic management of patients supported with MCS devices requires individualized care, with pharmacists as part of the team, based on the characteristics of each pump and recipient.