How to best monitor bivalirudin anticoagulant effect for ECMO and VAD-Comparison of four assay methods.

INTRODUCTION: Unfractionated heparin is widely used as an anticoagulant for extracorporeal life support (ECLS) and usually monitored with activated partial thromboplastin time (aPTT). Due to its limitations in pediatric populations and interferences with monitoring, bivalirudin is being utilized more frequently in these settings. For bivalirudin, other tests have emerged such as dilute thrombin time (dTT) and ecarin chromogenic assay (ECA); however, their utilities in pediatrics are unexplored. Development of suitable, accurate testing for bivalirudin monitoring is paramount to prevent complications. We sought to compare aPTT, aPTT with heparinase (HPTT), dTT1:4, modified dTT1:10, and ECA for monitoring of pediatric ECLS patients anticoagulated with bivalirudin. METHODS: aPTT, HPTT, dTT1:4, dTT1:10, and ECA were measured in 51 specimens from 17 children on bivalirudin-anticoagulated ECLS. Normal pooled plasma was spiked with various bivalirudin concentrations, and aPTT, dTT1:4, dTT1:10, and ECA were measured. In addition, dTT assays were performed using plasma from normal donors spiked with bivalirudin, heparin, and cryoprecipitate. RESULTS: dTT1:4 showed excellent correlation with ECA, while dTT1:4 correlated moderately with aPTT or HPTT. Fifty to 75% of specimens showed discordant results between dTT1:4 and HPTT. We found that dTT1:4 and ECA prolongations are associated with bivalirudin infusion rate; however, there are age-based differences that should be accounted for. The performance of dTT1:10 was similar to dTT1:4, though it was less sensitive to interfering factors (heparin or hyperfibrinogenemia). CONCLUSION: dTT1:10 appears to be more suitable for routine practice due to fewer variations and lower cost for monitoring bivalirudin in pediatric ECLS.

Trimester-specific thromboelastic values and coagulation activation markers in pregnancy compared across trimesters and compared to the nonpregnant state.

INTRODUCTION: Rotational thromboelastometry (ROTEM) rapidly identifies deficits underlying coagulopathy during massive hemorrhage. Prompt coagulopathy correction is balanced with the risk of blood product overutilization, making the ability to quickly target therapy highly desirable. However, data about ROTEM reference ranges in pregnancy are limited. We hypothesized that ROTEM parameters change across trimesters of pregnancy and differ from the nonpregnant state. Also, we sought to identify which hemostatic test best predicts coagulation activation during pregnancy. METHODS: A prospective cohort study in healthy pregnant patients in the first (n = 34), second (n = 34), and third trimesters (n = 41) against healthy, nonpregnant controls (n = 33) was performed. Citrated blood was collected, and ROTEM, complete blood count, and plasma-based assays of coagulation were performed. Mean ± SD or median [IQR] were compared across trimesters and between each trimester against the nonpregnant state. ROTEM parameters vs. plasma-based assays were also compared. RESULTS: Maximum clot firmness and A10 in FIBTEM correlated strongly with fibrinogen level. INTEM and EXTEM values demonstrated only weak to modest correlation with corresponding tests using plasma assays. Thrombin antithrombin complex (TAT) increased from the first trimester onward, whereas other coagulation activation markers did not show difference compared with control group. CONCLUSION: Rotational thromboelastometry parameters differ variably across trimesters of pregnancy and compared with the nonpregnant state. The development and use of pregnancy-specific values are critical to the proper clinical interpretation of ROTEM in women with serious hemorrhage during different stages in pregnancy. TAT was the earliest laboratory marker for coagulation activation among others.

C-reactive protein-induced activated partial thromboplastin time prolongation in heparinized samples is attenuated by elevated factor VIII.

INTRODUCTION: Activated partial thromboplastin time (aPTT) and antifactor Xa (anti-Xa) activity are used to monitor unfractionated heparin therapy in children on extracorporeal membrane oxygenation (ECMO). Elevated C-reactive protein (CRP) can prolong aPTT and cause discrepancy between these two assays. We aimed to evaluate CRP effect on aPTT and anti-Xa assays in the presence of heparin and to determine whether elevated CRP affects laboratory monitoring in pediatric ECMO patients. MATERIALS AND METHODS: Citrated normal specimens were spiked with CRP, heparin, and recombinant factor VIII (FVIII) and followed by measurement of aPTT and anti-Xa activity. Additionally, aPTT, anti-Xa activity, FVIII, fibrinogen, and CRP were measured in 18 ECMO specimens. RESULTS: Elevated CRP prolonged aPTT in normal specimens with or without heparin, but did not affect anti-Xa assay. In contrast, ECMO specimens showed similar aPTT and anti-Xa values regardless of CRP level. Elevated CRP in specimens was accompanied by increased fibrinogen and FVIII activity. Additional in vitro experiments confirmed that FVIII spiked simultaneously with CRP attenuated CRP-induced aPTT prolongation in heparinized specimens. CONCLUSION: In vitro CRP-induced aPTT prolongation is not observed in pediatric ECMO samples due to concomitant FVIII increase. Discordant changes of CRP and FVIII in plasma could contribute to aPTT/anti-Xa discrepancies observed during heparin therapy in the pediatric population. The anti-Xa assay is preferable for heparin monitoring in pediatric ECMO settings.

Low antithrombin levels in neonates and infants undergoing congenital heart surgery result in more red blood cell and plasma transfusion on cardiopulmonary bypass.

BACKGROUND: Neonates have lower levels of antithrombin (AT) due to immature liver synthetic function. AT deficiency may lead to inadequate anticoagulation with heparin during cardiac surgery resulting in consumption of coagulation factors and increased blood transfusion. The goal of this study is to examine the effect of AT level on the transfusion requirements of neonates and infants undergoing open heart surgery. STUDY DESIGN AND METHODS: This is a prospective, observational study at a tertiary pediatric referral center. Neonates and infants up to 6 months of age undergoing congenital heart surgery with cardiopulmonary bypass (CPB) were enrolled. Demographic, intraoperative, transfusion, and complications data were collected. Preoperative AT level was measured after induction of anesthesia. Prior to separation from CPB, a second blood sample was drawn and AT, thrombin antithrombin complex (TAT), D-dimer, and anti-Xa levels were measured. Linear and logistic regression were performed for data analysis. RESULTS: Preoperative low AT level was significantly associated with increased transfusion of red blood cells (RBCs) and fresh frozen plasma (FFP) during CPB, but not after separation from CPB. The incidence of thrombosis and re-operation were not associated with preoperative AT levels. There was no association between TAT, D-dimer, and anti-Xa levels at the end of CPB and preoperative AT levels. CONCLUSION: Low preoperative AT level is associated with increased transfusion of RBC and FFP on CPB in neonates and infants undergoing congenital heart surgery. Low preoperative AT level did not result in coagulation activation after CPB and after surgery.

Structural characterization of a clinically described heparin-like substance in plasma causing bleeding.

Heparin-like substances (HLS) have been described in various clinical situations, including in settings of liver disease associated with infection, transplant, and metastasis. HLS are generally attributed to circulating glycosaminoglycans. Initial results for this patient showed coagulopathy due to liver disease without HLS. Two weeks after liver transplantation, a 10 year-old female with liver failure patient began to bleed from catheter insertion sites, mouth, and nares and HLS was suspected. The patient subsequently died and these clinical samples resulted in the isolation of a single heparan sulfate (HS) present at high concentrations in the plasma. Analysis of this HS showed it had an intermediate between heparin and HS with low antithrombin-mediated anticoagulant activity. We speculate that this 10-year old patient might have a platelet function defect influenced by this unusual HS. Endothelial defects not measurable by our methods might have also contributed to the observed bleeding complications.

Monitoring bivalirudin therapy in children on extracorporeal circulatory support devices: Thromboelastometry versus routine coagulation testing.

INTRODUCTION: Bivalirudin is an alternative to heparin anticoagulation in infants and children in the setting of extracorporeal life support (ECLS). While activated partial thromboplastin time (aPTT) is widely accepted as the standard test to monitor bivalirudin therapy, the usefulness of thromboelastometry (ROTEM) to monitor bivalirudin infusion in the setting of ECLS is unknown. OBJECTIVE: We aimed to assess the utility of ROTEM in monitoring hemostasis and bivalirudin effect in children on either extracorporeal membrane oxygenation (ECMO) or ventricular assist devices (VAD) compared to standard plasma based coagulation assays. METHODS: A retrospective study of children undergoing bivalirudin infusion for ECMO/VAD support from a tertiary care pediatric hospital (January 2017-June 2018) was performed. ROTEM assays for extrinsic (EXTEM) and intrinsic (INTEM) coagulation pathways, INTEM with heparinase (HEPTEM), fibrin formation (FIBTEM) with measurement of the clotting time (CT) and maximum clot firmness (MCF) were compared to routine hemostasis testing including: aPTT, aPTT Hepzyme (HPTT), prothrombin time (PT), fibrinogen and platelet count. RESULTS: One hundred and six blood samples from 18 children were tested. There was a strong positive correlation between HPTT and HEPTEM CT, and moderate correlation between aPTT and INTEM CT. The bivalirudin dose did not correlate with any test, but displayed strong age-dependence, with infants requiring higher doses of bivalirudin to maintain therapeutic targets. Excellent correlation was found between FIBTEM MCF values and fibrinogen, but FIBTEM overestimated fibrinogen level when platelet count was >300 × 109/L. Heparin-like effect was identified in 39% of specimens, and an improved correlation between aPTT and INTEM CT was observed in specimens without heparinoids. CONCLUSIONS: In the setting of bivalirudin therapy, prolongation of CT on INTEM and HEPTEM showed moderate to strong correlation with aPTT and HPTT, and therefore, may provide a good alternative to these assays. In addition, HPTT and HEPTEM CT might be preferable for monitoring bivalirudin in the setting of ECLS due to frequent detection of heparin-like effect.