Bleeding and Thrombosis With Pediatric Extracorporeal Life Support: A Roadmap for Management, Research, and the Future From the Pediatric Cardiac Intensive Care Society: Part 2

Anti-Xa testing for pediatric and neonatal patients on extracorporeal membrane oxygenation

INTRODUCTION

To determine if anti-Xa testing is associated with improved outcomes for patients <19-years-old on ECMO.

METHODS

We evaluated the clinical benefit of anti-Xa heparin monitoring utilizing the Bleeding and Thrombosis during ECMO (BATE) database of 514 patients <19-years-old. The BATE database includes incidences of bleeding, thrombosis, and mortality. The database also describes anti-coagulation test utilization. We grouped and analyzed patients based on ECMO indication (cardiac, respiratory, or extracorporeal cardiopulmonary resuscitation [E-CPR]) and age (neonatal vs pediatric). We constructed multivariable logistic regression models to analyze the impact of anti-Xa testing on mortality, bleeding, and thrombosis in each group.

RESULTS

Across the entire population, anti-Xa testing did not have a significant effect on the incidence of mortality (43% with anti-Xa testing vs 49% without), bleeding (68% vs 74%), or thrombosis (37% vs 39%). However, among cardiac indicated patients on ECMO (n = 207), anti-Xa testing was significantly associated with reduced odds ratio (OR) of mortality (adjusted OR 0.527, p = .040) and bleeding (adjusted OR 0.369, p = .021). In addition, among neonatal patients on ECMO (n = 264), anti-Xa testing was associated with a significant reduction in the odds ratio of bleeding (adjusted OR 0.534, p = .046).

CONCLUSION

Anti-Xa testing is associated with improved outcomes among cardiac indicated and neonatal patients on ECMO. Additional research to find the optimal heparin monitoring regimen is needed to better support these critically ill patients. In the interim, we recommend clinicians consider utilizing anti-Xa assays as part of their heparin monitoring plan for neonatal and cardiac indicated patients on ECMO.

Anticoagulation-Free Pediatric Extracorporeal Membrane Oxygenation: Single-Center Retrospective Study

OBJECTIVES

To analyze hemorrhage and thrombosis data related to anticoagulation-free pediatric extracorporeal membrane oxygenation (ECMO).

DESIGN

Retrospective cohort study.

SETTINGS

High-volume ECMO single institution data.

PATIENTS

Children (0-18 yr) supported with ECMO (>24 hr) with initial anticoagulation-free period of greater than or equal to 6 hours.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Utilizing consensus American Thoracic Society definitions for hemorrhage and thrombosis on ECMO, we evaluated thrombosis and associated patient and ECMO characteristics during anticoagulation-free period. Thirty-five patients met inclusion criteria from 2018 to 2021 having a median age (interquartile range [IQR]) of 13.5 months (IQR, 3-91 mo), median ECMO duration of 135 hours (IQR, 64-217 hr), and 964 anticoagulation-free hours. Increased RBC transfusion needs were associated with longer anticoagulation-free periods ( p = 0.03). We identified 20 thrombotic events: only four during the anticoagulation-free period and occurring in three of 35 (8%) patients. Compared with those without thrombotic events, anticoagulation-free clotting events were associated with younger age (i.e., 0.3 mo [IQR, 0.2-0.3 mo] vs 22.9 mo [IQR, 3.6-112.9 mo]; p = 0.02), lower weight (2.7 kg [IQR, 2.7-3.25 kg] vs 13.2 kg [5.9-36.4 kg]; p = 0.006), support with lower median ECMO flow rate (0.5 kg [IQR, 0.45-0.55 kg] vs 1.25 kg [IQR, 0.65-2.5 kg]; p = 0.04), and longer anticoagulation-free ECMO duration (44.5 hr [IQR, 40-85 hr] vs 17.6 hr [IQR, 13-24.1]; p = 0.008).

CONCLUSIONS

In selected high-risk-for-bleeding patients, our experience is that we can use ECMO in our center for limited periods without systemic anticoagulation, with lower frequency of patient or circuit thrombosis. Larger multicentered studies are required to assess weight, age, ECMO flow, and anticoagulation-free time limitations that are likely to pose risk for thrombotic events.

Evaluation of acquired antithrombin deficiency in paediatric patients supported on extracorporeal membrane oxygenation

AIMS

There remains a paucity of literature regarding best practice for antithrombin (AT) monitoring, dosing and dose-response in paediatric extracorporeal membrane oxygenation (ECMO) patients.

METHODS

We conducted a retrospective cohort study at a quaternary care paediatric intensive care unit in all patients <18 years of age supported on ECMO from 1 June 2011 to 30 April 2020. Adverse events and outcomes were characterized for all ECMO runs. AT activity and replacement were characterized and compared between two clinical protocols. AT activities measured post- vs. pre-AT replacement were compared in order to characterize a dose-response relationship.

RESULTS

The final cohort included 191 patients with 201 ECMO runs and 2028 AT activity measurements. The median AT activity was 65% (interquartile range [IQR], 51-82) and 879 (43.3%) measurements met the criteria of deficient. The overall median AT dose and increase in AT activity were 50.6 units/kg/dose (IQR, 39.5-67.2) and 23.5% (IQR, 9.8-36.0), respectively. In the protocol that restricted AT activity measurements to clinical scenarios concerning for heparin resistance, there was significantly higher dosing in conjunction with significantly fewer overall administrations. Approximately one third of AT activity remained deficient after repletion. There was no difference in mechanical complications, reasons for discontinuation of ECMO support, time on ECMO or survival between protocols.

CONCLUSIONS

There was a high prevalence of AT deficiency in paediatric ECMO patients. An AT replacement protocol based on evaluating heparin resistance is associated with fewer AT administrations, with similar circuit and patient outcomes. Further data are needed to identify optimal dosing strategies.

Hemostatic complications and systemic heparinization in pediatric post-cardiotomy veno-arterial extracorporeal membrane oxygenation failed to wean from cardiopulmonary bypass

BACKGROUND

Hemostatic complications and the need for large amounts of blood products are major obstacles during veno-arterial extracorporeal membrane oxygenation (VA-ECMO). Additionally, the occurrence of coagulopathy after cardiopulmonary bypass (CPB) affects systemic heparinization in pediatric post-cardiotomy patients. This study compares hemostatic complications in pediatric post-cardiotomy VA-ECMO patients for failure to wean from CPB with those who received post-cardiotomy VA-ECMO for other indications, while also exploring the relationship between different stages-hemostatic complications and the timing of systemic heparinization.

METHODS

We retrospectively analyzed 146 pediatric patients who received post-cardiotomy VA-ECMO support (CPB-ECMO, n=96 vs. non-CPB-ECMO, n=50) from January 2005 to June 2020. Patients were divided into survivors (n=46) and non-survivors (n=50) according to in-hospital mortality in the CPB-ECMO group. We compared clinical outcomes between the groups, then examined the associations between the timing of systemic heparinization after ECMO implantation and different stages-hemostatic complications, in the CPB-ECMO group.

RESULTS

We found that the risk of early bleeding was significantly increased in patients who failed to wean from CPB. The presence of early bleeding was accompanied by the higher demand for blood products transfusion in the CPB-ECMO group, and for treatment the patients received a longer delayed continuous heparin infusion. As a result of using delayed systemic heparinization to avoid early bleeding, early hemolysis increased in the CPB-ECMO group. A delayed systemic heparinization of 9.5 hours showed the best Youden index results and the overall greatest accuracy in predicting early hemolysis.

CONCLUSIONS

A direct transition from CPB to ECMO in pediatric post-cardiotomy patients significantly increases early bleeding. Delayed systemic heparinization to reduce early bleeding has good discrimination for predicting early hemolysis in the CPB-ECMO group. Coagulopathy is complex in pediatric post-cardiotomy VA-ECMO patients who failed to wean from CPB, and, as such, it is extremely important to monitor coagulation-related indicators in multiple dimensions to determine the timing of systemic heparinization.

Poor Reliability of Common Measures of Anticoagulation in Pediatric Extracorporeal Membrane Oxygenation

Anticoagulation management in pediatric extracorporeal membrane oxygenation (ECMO) is challenging with multiple laboratory measures utilized across institutions without consensus guidelines. These include partial thromboplastin time (PTT), thromboelastography (TEG), and antifactor Xa (aXa). We aimed to evaluate the consistency of TEG R-time, PTT, and aXa correlation to bivalirudin and heparin dosing. We conducted a single-center restrospective review of pediatric ECMO cases from 2018 to 2020 anticoagulated with bivalirudin or heparin. We collected up to 14 serial simultaneous TEG R-time, PTT, and aXa measurements over a 7 day ECMO course with corresponding bivalirudin or heparin dosing. We analyzed the correlation between bivalirudin, heparin, and the three measurements of anticoagulation. A total of 67 ECMO runs, 32 bivalirudin, and 35 heparin, and more than 1,500 laboratory values, of which >80% simultaneous, were analyzed. When assessing correlations at the individual patient level, there was no consistent correlation between dosing and at least one laboratory parameter in the majority of patients. Furthermore, 44% of the bivalirudin cohort and 37% of the heparin cohort exhibited no correlation with any parameters. There were statistically significant correlations only between bivalirudin and heparin dosing and the sum total of the different laboratory tests. These inconsistencies highlight the importance of multimodality testing of anticoagulation in the management of pediatric ECMO anticoagulation and cannot be relied on in isolation from bedside clinical judgment.

Thrombosis in Extracorporeal Membrane Oxygenation (ECMO) Circuits

Thrombosis in extracorporeal membrane oxygenation (ECMO) circuits remains a frequent complication. We characterize the location, extent, structure, and clinical implications of thrombi in 53 ECMO circuits from 46 pediatric patients. The tubing, pump, and oxygenator were examined for visible thrombi. Representative samples of thrombi were collected for histologic, immunofluorescence, and immunohistochemical analysis. Thrombi were found in 81% of ECMO circuits. The most clinically significant were inflow oxygenator membrane surface thrombi (11% of circuits), arterial tubing thrombi (30%), and venous tubing (26%) or connector thrombi (26%). Oxygenator membrane surface thrombi resulted in rapidly increasing delta pressure across the oxygenator over 1-2 days, oxygenator failure, and circuit replacement. Oxygenator membrane surface thrombi were associated with intravascular venous thrombosis and bacterial infection before starting ECMO. Arterial cannula/tubing thrombi led in one case to aortic and mesenteric artery thrombosis followed by bowel infarction. In 11% of cases, venous tubing thrombi grew large enough to break off and embolize to the pump, resulting in increased hemolysis. Antifibrinolytic therapy during ECMO was associated with an increased risk of pump thromboembolism. Other less clinically significant thrombi included pump axle thrombi with thrombus fragments trapped in the oxygenator (45%), and deep oxygenator membrane thrombi (15%). Examination of ECMO circuits after removal is a useful quality improvement tool that can elucidate the cause of circuit problems, indicate patients at increased risk of thrombosis, and suggest areas for possible improvements.

Bivalirudin May Reduce the Need for Red Blood Cell Transfusion in Pediatric Cardiac Patients on Extracorporeal Membrane Oxygenation

We retrospectively compared anticoagulation with heparin and bivalirudin for 32 consecutive children under 18 years old during extracorporeal membrane oxygenation (ECMO) in our pediatric cardiac intensive care unit (PCICU). Between September 2015 and January 2018, 14 patients received heparin, 13 venoarterial (VA), and 1 venovenous (VV). From February 2018 to September 2019, 18 received bivalirudin (all VA). The mean (standard deviation [SD]) percentage of time with therapeutic activated partial thromboplastin time and activated clotting time was bivalirudin 54 (14%) and heparin 57 (11%), p = 0.4647, and percentage of time supratherapeutic was bivalirudin 18 (10%) and heparin 27 (12%), p = 0.0238. Phlebotomy-associated blood loss per hour of ECMO was double in the heparin compared with bivalirudin group 1.08 ml/h (0.20 ml/h), compared with 0.51 ml/h (0.07 ml/h), p = 0.0003, as well as interventions to control bleeding. Packed red blood cell (PRBC) transfusions significantly correlated with higher blood loss in the heparin group (Pearson correlation coefficient = 0.49, p = 0.0047). Overall amount of blood product utilization was not different between the groups. Survival to ECMO decannulation was 89% for bivalirudin and 57% for heparin, p = 0.0396, although 6 month survival was not significantly different (67% versus 57%, p = 0.5809). Heparin may increase the need for PRBC transfusions and strategies to attenuate bleeding when compared with bivalirudin for children receiving ECMO in PCICU.

Anticoagulation and Transfusion Management During Neonatal and Pediatric Extracorporeal Membrane Oxygenation: A Survey of Medical Directors in the United States

OBJECTIVES

To compare current practices within the United States of anticoagulation management and blood transfusion in neonatal and pediatric extracorporeal membrane oxygenation patients with a 2013 international report.

DESIGN

Cross-sectional survey distributed between August and December 2019.

SETTING

Extracorporeal Life Support Organization-registered neonatal and pediatric extracorporeal membrane oxygenation centers in the United States.

PARTICIPANTS

Extracorporeal membrane oxygenation medical directors.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Eighty-three medical directors at 108 centers responded. After removing four duplicate responses, 79 surveys were analyzed. Seventy-nine percent (n = 62) report a written extracorporeal membrane oxygenation protocol for both anticoagulation and blood product management. Ninety-four percent (n = 74) report unfractionated heparin as their primary anticoagulant; the remaining use the direct thrombin inhibitor, bivalirudin. Ninety percent (n = 71) report measuring antifactor Xa levels. Most centers report using a combination of assays to monitor heparin therapy, either antifactor Xa and activated partial thromboplastin time (54%) or more commonly antifactor Xa and activated clotting time (68%). Forty-one percent use viscoelastic tests to aid management. Goal monitoring levels and interventions generated by out of range values are variable. Fifty-one percent will replace antithrombin. Platelet transfusion thresholds vary by age and center with ranges from 50,000 to 100,000 cells/µL. Eighty-two percent of respondents are willing to participate in a randomized controlled trial comparing anticoagulation strategies for patients receiving extracorporeal membrane oxygenation.

CONCLUSIONS

Compared with the 2013 pediatric population, extracorporeal membrane oxygenation center anticoagulation and blood transfusion approaches continue to vary widely. Most report continued use of heparin as their primary anticoagulant and follow a combination of monitoring assays with the majority using the antifactor Xa assay in their practices, a significant shift from prior results. Antithrombin activity levels and viscoelastic tests are followed by a growing number of centers. Platelet transfusion thresholds continue to vary widely. Future research is needed to establish optimal anticoagulation and blood transfusion management.

Conversion From Activated Clotting Time to Anti-Xa Heparin Activity Assay for Heparin Monitoring During Extracorporeal Membrane Oxygenation

OBJECTIVES

Anticoagulation with unfractionated heparin remains the most common therapy used to prevent circuit thrombosis during extracorporeal membrane oxygenation, but no consensus exists on the optimal method or targets for heparin monitoring. From 2015 to 2018, we switched from monitoring heparin during extracorporeal membrane oxygenation using activated clotting times to anti-Xa heparin activity assays. This study describes the transition from activated clotting time to anti-Xa heparin activity assay monitoring and the associated clinical changes.

DESIGN

Retrospective analysis at single institution.

SETTING

Referral Children's Hospital.

PATIENTS

A total of 145 pediatric patients over 152 extracorporeal membrane oxygenation runs using 206 extracorporeal membrane oxygenation circuits.

INTERVENTIONS

Anticoagulation protocol quality improvement.

MEASUREMENTS AND MAIN RESULTS

From 2015 to 2018, heparin monitoring during extracorporeal membrane oxygenation changed from hourly activated clotting time to anti-Xa heparin activity assay every 6 hours with an associated 75% reduction in the circuit changes per extracorporeal membrane oxygenation day. Over the 4 years, patients with an average anti-Xa heparin activity assay of at least 0.25 U/mL showed a 59% reduction in circuit changes per extracorporeal membrane oxygenation day compared with less than 0.15 U/mL. In addition to its association with reduced circuit changes, anti-Xa heparin activity assay monitoring was also associated with reduced heparin dose changes per day from 11 ± 4 to 2 ± 1 (p < 0.001), smaller heparin dose changes (less variation in dose), and reduced diagnostic phlebotomy volumes from 41 ± 6 to 25 ± 11 mL/day (p < 0.001). The number of patients with reported bleeding decreased from 69% using activated clotting time to 51% (p = 0.03). Transfusion rates did not change.

CONCLUSIONS

Over 4 years, we replaced the activated clotting time assay with the anti-Xa heparin activity assay for heparin monitoring during extracorporeal membrane oxygenation. Minimum anti-Xa heparin activity assay levels of 0.25 U/mL were associated with reduced circuit changes. Further studies are needed to determine the optimum anti-Xa heparin activity assay therapeutic range during extracorporeal membrane oxygenation.

Bivalirudin and Alteplase for Pulmonary Embolism Requiring Veno-Arterial Extracorporeal Membrane Oxygenation in an Adolescent

Saddle pulmonary embolism (PE) remains a challenge to diagnose and manage in pediatric patients. Current literature encourages early consideration of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) in high-risk PE patients with impending right ventricular failure. We present a 17-year-old patient who was admitted to a pediatric cardiac intensive care unit with saddle PE requiring emergent VA-ECMO support because of cardiovascular collapse. Despite anticoagulation with bivalirudin and receiving systemic thrombolysis with alteplase, the clot burden was persistent with minimal improvement in right ventricular function. We proceeded to catheter thrombolysis while on VA-ECMO. This ultimately led to a successful resolution of the PE and allowed for weaning off VA-ECMO. PE is rare in children compared with adults, and pediatricians may be unaware of therapies becoming increasingly used in adults such as the use of VA-ECMO, with systemic and local thrombolysis. The concurrent use of a direct thrombin inhibitor for ECMO anticoagulation alongside the thrombolysis is a novel combination in this condition and age-group.

Anti-Xa versus time-guided anticoagulation strategies in extracorporeal membrane oxygenation: a systematic review and meta-analysis

The purpose was to compare time-based vs anti-Xa-based anticoagulation strategies in patients on ECMO. We conducted a systematic review and meta-analysis using multiple electronic databases and included studies from inception to July 19, 2019. The proportion of bleeding, thrombosis, and mortality were evaluated.

Twenty-six studies (2,086 patients) were included. Bleeding occurred in 34.2% (95%CI 25.1;43.9) of the patients with anti-Xa-based versus 41.6% (95%CI 24.9;59.4) of the patients with time-based anticoagulation strategies. Thrombosis occurred in 32.6% (95%CI 19.1;47.7) of the patients with anti-Xa-based versus 38.4% (95%CI 22.2;56.1) of the patients with time-based anticoagulation strategies. And mortality rate was 35.4% (95%CI 28.9;42.1) of the patients with anti-Xa-based versus 42.9% (95%CI 36.9;48.9) of the patients with time-based anticoagulation strategies. Among the seven studies providing results from both anticoagulation strategies, significantly fewer bleeding events occurred in the anti-Xa-based anticoagulation strategy (adjusted OR 0.49 (95%CI 0.32;0.74), p < 0.001) and a significantly lower mortality rate (adjusted OR 0.61 (95%CI 0.40;0.95), p = 0.03). There was no significant difference in thrombotic events (adjusted OR 0.91 (95%CI 0.56;1.49), p = 0.71). In these seven observational studies, only a small fraction of the patients were adults, and data were insufficient to analyze the effect of the type of ECMO.

In this meta-analysis of observational studies of patients on ECMO, an anti-Xa-based anticoagulation strategy, when compared to a time-based strategy, was associated with fewer bleeding events and mortality rate, without an increase in thrombotic events.

Epidemiology of Hemostatic Transfusions in Children Supported by Extracorporeal Membrane Oxygenation

OBJECTIVE

To evaluate the epidemiology of hemostatic transfusions (plasma, platelet, and cryoprecipitate) in children supported by extracorporeal membrane oxygenation.

DESIGN

Secondary analysis of a large observational cohort study.

SETTING

Eight pediatric institutions within the Eunice Kennedy Shriver National Institute of Child Health and Human Development's Collaborative Pediatric Critical Care Research Network.

PATIENTS

Critically ill children supported by extracorporeal membrane oxygenation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Extracorporeal membrane oxygenation was used in the care of 514 consecutive children. Platelets were transfused on 68% of extracorporeal membrane oxygenation days, plasma on 34% of the days on extracorporeal membrane oxygenation, and cryoprecipitate on 14%. Only 24% of the days on extracorporeal membrane oxygenation were free of any hemostatic transfusions. Daily platelet transfusion dose was independently associated with chest tube output (p < 0.001), other bleeding requiring RBC transfusion (p = 0.03), and daily set platelet goal (p = 0.009), but not with total platelet count (p = 0.75). Daily plasma transfusion dose was independently associated with chest tube output (p < 0.001), other bleeding requiring RBC transfusion (p = 0.01), activated clotting time (p = 0.001), and antithrombin levels (p = 0.02), but not with international normalized ratio (p = 0.99) or activated partial thromboplastin time (p = 0.29). Daily cryoprecipitate transfusion dose was independently associated with younger age (p = 0.009), but not with chest tube bleeding (p = 0.18), other bleeding requiring RBC transfusion (p = 0.75), fibrinogen level (p = 0.67), or daily fibrinogen goal (p = 0.81).

CONCLUSIONS

Platelets were transfused on two third of the days on extracorporeal membrane oxygenation, plasma on one third, and cryoprecipitate on one sixth of the days. Although most hemostatic transfusions were independently associated with bleeding, they were not independently associated with the majority of hemostatic testing. Further studies are warranted to evaluate the appropriateness of these transfusion strategies.

Hematologic concerns in extracorporeal membrane oxygenation

This ISTH "State of the Art" review aims to critically evaluate the hematologic considerations and complications in extracorporeal membrane oxygenation (ECMO). ECMO is experiencing a rapid increase in clinical use, but many questions remain unanswered. The existing literature does not address or explicitly state many pertinent details that may influence hematologic complications and, ultimately, patient outcomes. This review aims to broadly introduce modern ECMO practices, circuit designs, circuit materials, hematologic complications, transfusion-related considerations, age- and size-related differences, and considerations for choosing outcome measures. Relevant studies from the 2019 ISTH Congress in Melbourne, which further advanced our understanding of these processes, will also be highlighted.

Challenges in Maintaining the Hemostatic Balance in Children Undergoing Extracorporeal Membrane Oxygenation: A Systematic Literature Review

Background: Despite advances in technology and clinical experience, the incidence of hemostatic complications, including bleeding and thrombosis, remains high in children supported with extracorporeal membrane oxygenation (ECMO). These hemostatic complications are important to prevent, since they are associated with increased morbidity and mortality. This systematic literature review aims to outline the most important risk factors for hemostatic complications in children undergoing ECMO treatment, to summarize the reported alternative anticoagulant drugs used in pediatric ECMO and to describe studied associations between coagulation tests and hemostatic complications. Methods: A literature search was performed in Embase, Medline, Web of Science Core Collection, Cochrane Central Register of Controlled Trials, and Google Scholar in February 2020. Included studies were studies evaluating children (<18 years old) treated with ECMO, and studies evaluating risk factors for hemostatic complications, alternative anticoagulants, or the association between coagulation tests and hemostatic complications. Results: Out of 1,152 articles, 35 studies were included. Thirteen out of 49 risk factors were investigated in three or more studies. Most consistent results were found regarding ECMO duration and pH. However, evidence for risk factors was equivocal in the majority of studies, which is explained by the variability of populations studied, definitions of hemostatic complications, ECMO circuits, anticoagulation protocols, transfusion triggers and monitoring of anticoagulation. Five studies described alternative anticoagulants, including bivalirudin (n = 3), argatroban (n = 1) and FUT (n = 1). Higher anti-factor Xa levels were associated with less clotting events in one of nine studies, investigating the association between tests and hemostatic complications. Two studies revealed an association between anti-factor Xa assay-based protocols and a decreased number of transfusions, bleedings and need for circuit change. Conclusion: Studies regarding risk factors showed conflicting results and a few retrospective studies reported the use of new anticoagulants and data on coagulation tests in relation to hemostatic complications. To decrease hemostatic complications in ECMO children, prospective multicenter studies are needed with clear bleeding and thrombotic definitions, and the best possible standardization of ECMO circuits used, anticoagulation protocols, and transfusion triggers.