Is it time to invest in a thromboelastograph?

Haemostatic management for aortic valve replacement in a patient with advanced liver disease

Redo-sternotomy and aortic valve replacement in patients with advanced liver disease is rare and associated with a prohibitive morbidity and mortality. Refractory coagulopathy is common and a consequence of intense activation of the coagulation system that can be triggered by contact of blood with the cardiopulmonary bypass circuitry, bypass-induced fibrinolysis, platelet activation and dysfunction, haemodilution, surgical trauma, hepatic decompensation and hypothermia. Management can be further complicated by right heart dysfunction, porto-pulmonary hypertension, poor myocardial protection, and hepato-renal syndrome. Complex interactions between coagulation/fibrinolysis and systemic inflammatory response syndrome reactions like “post-perfusion-syndrome” also compound haemostatic failure. Given the limited information available for the specific management and prevention of cardiopulmonary bypass-induced haemostatic failure, this report serves to guide the anaesthesia and medical management of future cases of a similar kind. We discuss our multimodal management of haemostatic failure using pharmacological strategies, thromboelastography, continuous cerebral and liver oximetry, and continuous cardiac output monitoring.

Can thrombelastography be a new tool to assess bleeding risk in patients with idiopathic thrombocytopenic purpura?

Thrombelastography (TEG) analyses the status of blood coagulation including abnormalities associated with low platelet count. The aim of this study was to investigate the changes in TEG parameters in idiopathic thrombocytopenic purpura (ITP) patients. Thirty nine patients with ITP (platelet count < 100 × 103  µl⁻¹) were included in the study. Age-matched 17 patients with thrombocytopenia due to chemotherapy were selected as a control group. Platelet count was positively correlated with maximum clot formation (MCF) in INTEM (r = 0.716, p < 0.001) and MCF in EXTEM (r = 0.679, p < 0.001); negatively correlated with clot formation time (CFT) in INTEM (r = -0.755, p < 0.001) and CFT in EXTEM (r = -0.585, p < 0.001) in ITP patients. Platelet count was positively correlated with MCF in INTEM (r = 0.776, p < 0.001) and MCF in EXTEM (r = 0.878, p < 0.001); negatively correlated with CFT in INTEM (r = -0.627, p < 0.001) in control group. Receiver operating characteristic curves to describe the critical platelet count and fibrinogen level that affect MCF revealed 31 × 103 µl⁻¹ and 375 mg dl⁻¹ as cut-off values, respectively. In conclusion, ROTEM determines the contribution of fibrinogen and platelets to clot strength in patients with ITP. MCF appears to be the most important TEG parameter in predicting bleeding in ITP patients that makes TEG superior to other hemostatic tests.

Host-guest composites for induced hemostasis and therapeutic healing in traumatic injuries

INTRODUCTION

The United States military currently outfits our soldiers with a zeolite-based hemostatic agent (HA) that is applied directly onto a traumatic wound to induce hemostasis and prevent loss of life from exsanguination. The goals of this work were to identify and implement strategies to attenuate a tissue burning side effect associated with the HA, resulting from a large release of heat upon hydration, without adversely affecting the wound healing properties. Five ion exchanged derivatives of the parent HA were prepared and characterized with regard to their material and thermal properties, in vitro hemostatic efficacy, and antibacterial activity.

METHODS

The five host-guest high-surface-area HAs were prepared by ion exchanging the zeolite linde type 5A with aqueous salt solutions under controlled conditions. The modified HAs were characterized by TGA, DSC, Thermal Imaging, SEM, XRD, XPS, BET, and a Thromboelastograph (TEG) was employed to assay the in vitro hemostatic efficacy. Antibacterial activity was assayed by measuring the zone of no growth of Pseudomonas aeruginosa biofilms growing in contact with the ion exchanged HAs.

RESULTS

The heat released during application of the HA can be minimized from 680 J/g to 420 J/g by ion exchanging the calcium ions in zeolite linde type 5A with cations of a reduced hydration enthalpy. Zeolite-based HAs that demonstrate in vitro clot induction time of R < or = 1.8 min, and with surfaces areas > or = 634 m2/g, correlate with 75% in vivo swine survivability of a universally lethal groin injury. Silver exchanged HA maintained a zone of no growth of P. aeruginosa with a surface area twice the geometrical surface area of an HA pressed pellet for 24 hours in an LB Agar assay.

CONCLUSIONS

Two strategies for reducing the large amount of heat released by a zeolite-based HA during application have been described and quantified: (1) ion exchange and (2) prehydration. Five ion-exchanged derivatives of the original HA have been prepared and assayed for hemostatic efficacy both in vitro, by TEG, and in vivo, by clinical swine trials. Contact activation coagulation rates, alpha, were found to increase with the amount of heat released by the HA. In Vitro clot induction time, R, and HA surface area have been identified as predictors of in vivo hemostatic performance. A proposed rationale for selecting hemostatic materials based on these parameters will likely reduce the quantity of experiments involving animals, and the associated labor and capital costs, necessary to test a new HA. A method for incorporating antibacterial activity against gram negative P. aeruginosa into the Ag-exchanged formulation of zeolite LTA-5A has been described and substantiated.

Provision for major obstetric haemorrhage: an Australian and New Zealand survey and review

Obstetric haemorrhage is a leading cause of maternal death and the most common contributor to serious obstetric morbidity. Maternal mortality audit data suggest that appropriate preparation and good emergency management leads to improved outcome. The aim of this study was to assess facilities relevant to major obstetric haemorrhage management in all units in Australia and New Zealand that offer operative obstetric services. The questionnaire was divided into ten sections: demographics, facilities, staffing, policies and guidelines, drugs, procedures, equipment, point of care testing, availability of O negative blood and free comments. Responses were received from 240 (76.4%) of the 314 hospitals surveyed (187 public and 53 private). One hundred and nine units (45%) had fewer than 500 deliveries per year Distances to referral facilities were frequently very large. Of the 90 hospitals (38.1%) without an onsite blood bank, 12 did not have a supply of blood for emergencies. Half of all units (n=121) had on-site intensive care or high dependency facilities and 72.9% (n=175) had an on-site cardiac arrest team. Only 58.8% of units (n=141) had a written haemorrhage protocol. Findings are presented in the context of other literature, including evidence-based guidelines. Haemorrhage responds well to appropriate treatment, although careful preparation and anticipation of problems is required. In our region geographical factors and different systems of healthcare complicate provision of obstetric services. Where facilities are limited, women should be offered antenatal transfer to a larger centre.

In vitro fertilization-induced alterations in coagulation and fibrinolysis as measured by thromboelastography

Supraphysiologic increases in estrogen produced by in vitro fertilization (IVF) promote the expression of hemostatic markers. Although quantitative studies of individual markers have been performed during IVF, their results are conflicting and do not reveal the qualitative effect of each marker on the overall coagulation and fibrinolytic processes. Thrombelastograph (TEG) coagulation analysis, by contrast, provides a global measure of coagulation and fibrinolysis and can indicate the relative contributions of clotting factors, fibrinogen, and platelets to each process. We studied the serum estrogen concentrations and TEG variables in 24 women at the beginning and conclusion of an IVF stimulation cycle. Serum estradiol (E(2)) concentrations (mean +/- SD) increased from 26.9 +/- 8.6 to 2098 +/- 913 pg/mL (P < 0.005) at baseline and oocyte retrieval, respectively. The measured TEG indices demonstrated alterations in coagulation rather than fibrinolysis. Although significant changes were noted in both the clot formation time and the coagulation index (P < 0.005), all TEG values remained within the normal range. In addition, an increased role of fibrinogen in promoting clot strength was observed. These findings may assist in the treatment of IVF patients who ultimately develop thromboembolic complications as a result of ovarian hyperstimulation. IMPLICATIONS. The dramatic changes in estrogen produced by in vitro fertilization therapies result in hemostatic marker alterations. Thrombelastograph coagulation analysis, which provides a global assessment of these changes, demonstrated significant alterations in two coagulation indices (clot formation time, coagulation index), although all variables remained within normal limits. The relative importance of fibrinogen versus platelets in determining clot strength was observed. No significant alterations in fibrinolysis were detected.

Thromboelastography

The Thromboelastograph has now been in use for over 50 years and has been largely regarded as a research tool. Increasing automation and refinement of the TEG and standardisation of results has led to decreased speculation regarding its validity as an assay of haemostasis. There are increasing clinical applications including cardiothoracic surgery and liver transplantation. This review discusses the principles and limitations of the TEG. It also focuses on the current clinical applications and potential research interests.