The History of Extracorporeal Membrane Oxygenation and the Development of Extracorporeal Membrane Oxygenation Anticoagulation

Extracorporeal membrane oxygenation (ECMO) was first started for humans in early 1970s by Robert Bartlett. Since its inception, there have been numerous challenges with extracorporeal circulation, such as coagulation and platelet activation, followed by consumption of coagulation factors and platelets, and biocompatibility of tubing, pump, and oxygenator. Unfractionated heparin (heparin hereafter) has historically been the defacto anticoagulant until recently. Also, coagulation monitoring was mainly based on bedside activated clotting time and activated partial thromboplastin time. In the past 50 years, the technology of ECMO has advanced tremendously, and thus, the survival rate has improved significantly. The indication for ECMO has also expanded. Among these are clinical conditions such as postcardiopulmonary bypass, sepsis, ECMO cardiopulmonary resuscitation, and even severe coronavirus disease 2019 (COVID-19). Not surprisingly, the number of ECMO cases has increased according to the Extracorporeal Life Support Organization Registry and prolonged ECMO support has become more prevalent. It is not uncommon for patients with COVID-19 to be on ECMO support for more than 1 year until recovery or lung transplant. With that being said, complications of bleeding, thrombosis, clot formation in the circuit, and intravascular hemolysis still remain and continue to be major challenges. Here, several clinical ECMO experts, including the "Father of ECMO"-Dr. Robert Bartlett, describe the history and advances of ECMO.

D-Dimer Elevation at Time of Admission is Associated with Need for Ventilator Support among Pediatric Patients with COVID-19 Infection

BACKGROUND

This study aims to determine if coagulation abnormalities at presentation are associated with clinical severity of pediatric COVID-19 infection.

METHODS

We retrospectively reviewed admission coagulation studies (D-dimer, prothrombin time (PT), partial thromboplastin time with hepzyme, fibrinogen, and platelet count) with disease severity defined by need for ICU admission, ventilator support, and length of stay (LOS).

RESULTS

There were 110 pediatric patients (0.5 months to 18 years) who had coagulation studies collected within 24 hours of admission. Patients who required ICU admission and ventilation support had significantly higher D-dimer and PT values at presentation compared to patients who required neither. In addition, D-dimer showed moderate correlation with LOS.

CONCLUSIONS

Elevated D-dimer correlated significantly with severity of disease and LOS, while prolonged PT only correlated with disease severity. Our data suggest that D-dimer at presentation may predict a pediatric patient's need for ICU care or ventilator support.

Is it time to switch to bivalirudin for ECMO anticoagulation?

For decades, unfractionated heparin (hereafter, heparin) has been the primary anticoagulant used for extracorporeal membrane oxygenation (ECMO) support. More recently, however, bivalirudin, a direct thrombin inhibitor, has emerged as an alternative. This systematic review based on PRISMA guidelines, aims to summarize 16 comparative studies and 8 meta-analysis and review articles published from January, 2011 till May, 2023 which directly compares ECMO courses using heparin versus bivalirudin as the anticoagulant. While this comparison is complicated by the lack of a standardized definition of major bleeding or thrombosis, our overall findings suggest there is no statistical difference between heparin and bivalirudin in incidence of bleeding and thrombosis. That said, some studies found a statistical significance favoring bivalirudin in reducing major bleeding, thrombosis, and the need for transfusions. We also offer essential guidance for appropriately selecting an anticoagulant and monitoring its effect in ECMO settings.

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.

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.

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.

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.

ABO-incompatible deceased donor pediatric liver transplantation: Novel titer-based management protocol and outcomes

ABO-ILT have re-emerged as an alternate option for select patients awaiting transplant. However, treatment protocols for children undergoing deceased donor ABO-ILT are not standardized. We implemented a novel IS protocol for children undergoing deceased donor ABO-ILT based on pretransplant IH titers. Children with high pretransplant IH titers (≥1:32) underwent an enhanced IS protocol including plasmapheresis, rituximab, IVIG, and mycophenolate, while children with IH titers ≤1:16 received steroids and tacrolimus. We retrospectively assessed our outcomes of ABO-ILT with ABO-compatible recipients of similar age and diagnosis over a 2-year period. Ten children with median age of 8.9 months underwent ABO-ILT, 4 of 10 patients underwent enhanced IS due to high IH titers. Rates of complications (rejection, infections, biliary, and vascular) at both 1 year and up to 3 years post-transplant were comparable between the groups. Patients with ABO-ILT had good graft function with 100% survival at a median follow-up of 3.3 years. In conclusion, IS tailored to pretransplant IH titers in pediatric deceased donor ABO-ILT is feasible and can achieve outcomes similar to ABO-CLT at 1 and 3 years post-transplantation.

Management of Hemostasis for Pediatric Patients on Ventricular-Assist Devices

Ventricular-assist devices (VADs) have seen increased utilization in the pediatric population. Formerly, this therapeutic modality was limited to only the pulsatile VAD, EXCOR (Berlin Heart GmbH). However, the continuous flow VAD devices, HeartMate II (Abbott Inc.) and HeartWare (Medtronic Inc.), are now increasingly used in this population. Postoperatively, VAD patients are acutely anticoagulated using unfractionated heparin, often beginning 24 to 48 hours after VAD placement. Once the patient is stabilized and ready to transition to a lower acuity or outpatient setting, low-molecular-weight heparin or warfarin therapy may be instituted. Also, because of the risk for thrombotic and thromboembolic complications, antiplatelet strategies are employed using medications such as aspirin, clopidogrel, or dipyridamole. Platelet-rich plasma or whole blood platelet aggregation studies, platelet function analyzer-100 (Siemens), VerifyNow (Accriva Diagnostics), or thromboelastography platelet mapping (Haemonetics) may be used to help monitor antiplatelet effects, though the interpretation of the strength of the antiplatelet effect remains difficult. Care must be taken to monitor the hematologic complications of VAD, including acquired von Willebrand syndrome, which increases the risk for bleeding, and intravascular hemolysis, which increases the risk of thrombosis. Appropriate device placement and anticoagulation management are imperative to help avoid neurological dysfunction and ischemic stroke, the most devastating potential complications of VAD therapy. As our experience grows, we continue to gain an increased understanding of the management of anticoagulation, need for antiplatelet medication, and appropriate monitoring for these critical patients.

Bleeding and Thrombotic Complications in the Use of Extracorporeal Membrane Oxygenation

Extracorporeal membrane oxygenation (ECMO) has been used for >40 years to support lung and heart failure; however, bleeding and thrombosis remain serious complications. The known etiologies of bleeding include heparin effect or overdose, coagulopathy, thrombocytopenia, platelet dysfunction, acquired von Willebrand syndrome, and hyperfibrinolysis. Bleeding sites may include cannula insertion sites, recent surgical incisions, vascular access sites, lung, gastrointestinal tract, mouth, nose, thoracic cavity, abdominal cavity, and brain. Massive bleeding in the brain, the most feared bleeding complication, can be rapidly fatal because it occurs in a rigid closed space, is difficult to drain, and cannot be stopped with direct pressure to the bleeding site. Pulmonary hemorrhage may cause irreversible lung damage. Management should be swift and precise to prevent fatal bleeding. In contrast, etiologies of thrombosis include high fibrinogen and factor VIII levels, heparin resistance, and platelet activation. Achieving the optimal anticoagulation balance to prevent bleeding and thrombosis in ECMO patients is extremely complex. Experts in hemostasis should be a part of an institutional ECMO team and continuously available for immediate management.

The Influence of Free Hemoglobin and Bilirubin on Heparin Monitoring by Activated Partial Thromboplastin Time and Anti-Xa Assay

Context

Elevated free hemoglobin (Hb) and bilirubinemia complicate extracorporeal membrane oxygenation and could affect unfractionated heparin (UH) therapy monitoring by anti-Xa assay and activated partial thromboplastin time (aPTT).

Objectives

To compare in vitro response of anti-Xa and aPTT assays to UH in samples with artificial hyperbilirubinemia and hyperhemoglobinemia and to estimate if this interference is also observed in vivo in pediatric extracorporeal membrane oxygenation.

Design

Measurement of aPTT and anti-Xa activity in plasma spiked with UH and increased concentration of free Hb and/or conjugated bilirubin. All samples with anti-Xa activity, antithrombin, free Hb, and bilirubin determination and infused dose of UH from inpatients on extracorporeal membrane oxygenation were extracted from the clinical patient database and analyzed.

Results

Each increment of free Hb by 100 mg/dL significantly shortened aPTT, whereas an increment of bilirubin by 6 mg/dL caused significant prolongation of aPTT and stepwise increase of free Hb and/or bilirubin in plasma decreased anti-Xa activity by 0.03 to 0.05 IU/mL. Extracorporeal membrane oxygenation samples with free Hb 50 mg/dL or greater had significantly lower anti-Xa activity compared with normal ones: 0.33 (0.25–0.42) versus 0.4 (0.31–0.48) IU/mL (P = .01), despite the identical UH infusion and similar antithrombin activity. Moderate increase of free Hb by 59 mg/dL was associated with absolute decrease of anti-Xa activity by 0.07 IU/mL.

Conclusions

Activated partial thromboplastin time and anti-Xa assay are affected by elevated level of free Hb and/or bilirubin in the presence of UH, and lower anti-Xa activity is noted in extracorporeal membrane oxygenation patients with elevated free Hb. Severe hemolysis and/or hyperbilirubinemia could compromise UH monitoring based on these assays.

Decline in platelet microparticles contributes to reduced hemostatic potential of stored plasma

INTRODUCTION

In an effort to administer life-saving transfusions quickly, some trauma centers maintain thawed plasma (TP). According to AABB, TP is approved for transfusion for up to five days when stored at 1-6° C. However, the alterations in microparticles (MP) contained in the plasma, which are an integral component of plasma's hemostatic capacity, are not well characterized. We report on MP changes in TP between its initial thaw (FFP-0) and five days (FFP-5) of storage.

MATERIALS AND METHODS

FFP units (n=30) were thawed at 37° C and kept refrigerated for five days. Phenotypes of residual cells, which include platelets, erythrocytes, leukocytes, monocytes, endothelial cells, and MP counterparts of each cell type, were analyzed by flow cytometry. Functional assays were used for MP procoagulant activity, plasma thrombin generation, and clotting properties (thromboelastography).

RESULTS

In FFP-0 the majority (94%) of residual cells were platelets, along with significant levels of platelet MPs (4408 × 10(3)/L). FFP-5 showed a decline in MP count by 50% (p<0.0001), and procoagulant activity by 29% (p<0.0001). FFP-5 exhibited only 54% (p<0.0001) of the potential for thrombin generation as FFP-0, while thromboelastography indicated a slower clotting response (p<0.0001) and a longer delay in reaching maximum clot (p<0.01). Removal of MP by filtration resulted in reduced thrombin generation, while the MP replacement restored it.

CONCLUSIONS

Decline in MP with storage contributes to FFP-5's reduced ability to provide the hemostatic potential exhibited by FFP-0, suggesting the presence of platelet MPs in freshly TP may be beneficial and protective in the initial treatment of hemorrhage.

Novel, semi-automated, 60-min-assay to determine von Willebrand factor cleaving activity of ADAMTS-13

INTRODUCTION

The clinical entity of idiopathic thrombotic thrombocytopenic purpura (TTP) has been closely associated with a severe deficiency of the von Willebrand factor (vWF)-cleaving protease (ADAMTS-13). Levels below 5% are highly specific for TTP basically excluding hemolytic uremic syndrome (HUS). Deficiency of ADAMTS-13 can either be inherited or caused by inhibitory IgG autoantibodies to ADAMTS-13. Diagnosis of TTP is often difficult since it often manifests oligosymptomatic exhibiting only laboratory signs of thrombocytopenia and hemolysis or involving atypical organs. In such cases rapid knowledge of the ADAMTS-13 activity is very useful in helping to establish a correct diagnosis rapidly and to initiate the appropriate therapy.

METHODS AND RESULTS

We have therefore designed a rapid, sensitive and simple assay for the determination of ADAMTS-13 activity and ADAMTS-13 inhibitors. The test is based on the measurement of the ristocetin-cofactor activity of purified, urea-denaturated vWF concentrate after incubation with diluted patient plasma that has been preactivated with barium chloride. While this assay has already previously been established, we have further modified and simplified the test thereby improving markedly the sensitivity, accuracy and turn-around time. A major improvement proved to be the change from buffer to heat-treated and vWF-replenished plasma as diluent for making the serial dilutions of normal pool plasma (NPP) for the calibration curve. Set up as a semi-automated assay the test is performed in only 50 to 60 min. Tested in 15 patients with ADAMTS-13 deficiency this new assay compared favorably and even more accurately with the classic electrophoretic ADAMTS-13 assay, especially in the low range below 10%. Mixing studies with patient plasma and NPP (ratio 1:1) revealed that a relatively short period of only 30 min at room temperature is sufficient for most samples to detect an inhibitor. With a single mixing experiment it is possible to discriminate inhibitor levels in the range of 0.5-4 Bethesda units.

CONCLUSION

Using this novel assay, determination of ADAMTS-13 activity and ADAMTS-13 inhibitors can be performed easily, rapidly (less than 2 h), and accurately, providing rapid information about the severity of ADAMTS-13 deficiency and the presence of an inhibitor. In addition, the test is suitable for full automation enabling to screen large populations and, thus, help to get further insights into the clinical significance of ADAMTS-13 deficiency in other diseases.