Augmentation of thrombin generation in neonates undergoing cardiopulmonary bypass

Contemporary tools for evaluation of hemostasis in neonates. Where are we and where are we headed?

The assessment of hemostatic disorders in neonates is crucial, but remains challenging for clinicians. Although the concept of developmental hemostasis is widely accepted among hemostasis specialists globally, it is probably under-recognized by clinicians and laboratory practitioners. In parallel with age-dependent hemostatic status maturation, comprehension of the differences between normal values is crucial for the accurate diagnosis of potential hemorrhagic and thrombotic disorders of the vulnerable neonatal population. This review outlines the basics of developmental hemostasis and the features of the available coagulation testing methods, with a focus on novel tools for evaluating the neonatal hemostatic profile. Common errors, issues, and pitfalls during the assessment of neonatal hemostasis are discussed, along with their impact on patient management. Current knowledge gaps and research areas are addressed. Further studying to improve our understanding of developmental hemostasis and its reflection on everyday clinical practice is warranted.

Activated 4-Factor Prothrombin Complex Concentrate as a Hemostatic Adjunct for Neonatal Cardiac Surgery: A Propensity Score-Matched Cohort Study

BACKGROUND

Prothrombin complex concentrates are an emerging "off-label" therapy to augment hemostasis after cardiopulmonary bypass (CPB), but data supporting their use for neonatal cardiac surgery are limited.

METHODS

We retrospectively reviewed neonates undergoing open heart surgery with first-time sternotomy between May 2014 and December 2018 from a hospital electronic health record database. Neonates who received activated 4-factor prothrombin complex concentrate (a4FPCC) after CPB were propensity score matched (PSM) to neonates who did not receive a4FPCC (control group). The primary efficacy outcome was total volume (mL/kg) of blood products transfused after CPB, including the first 24 hours on the cardiovascular intensive care unit (CVICU). The primary safety outcome was the incidence of 7- and 30-day postoperative thromboembolism. Secondary outcomes included 24 hours postoperative chest tube output, time to extubation, duration of CVICU stay, duration of hospital stay, 30-day mortality, and incidence of acute kidney injury on postoperative day 3. We used linear regression modeling on PSM data for the primary efficacy outcome. For the primary safety outcome, we tested for differences using McNemar test on PSM data. For secondary outcomes, we used linear regression, Fisher exact test, or survival analyses as appropriate, with false discovery rate-adjusted P values.

RESULTS

A total of 165 neonates were included in the final data analysis: 86 in the control group and 79 in the a4FPCC group. After PSM, there were 43 patients in the control group and 43 in the a4FPCC group. We found a statistically significant difference in mean total blood products transfused for the a4FPCC group (47.5 mL/kg) compared with the control group (63.7 mL/kg) for PSM patients (adjusted difference, 15.3; 95% CI, 29.4-1.3; P = .032). We did not find a statistically significant difference in 7- or 30-day thromboembolic rate, postoperative chest tube output, time to extubation, incidence of postoperative acute kidney injury (AKI), or 30-day mortality between the groups. The a4FPCC group had a significantly longer length of intensive care unit stay (32.9 vs 13.3 days; adjusted P = .049) and hospital stay (44.6 vs 24.1 days; adjusted P = .049) compared with the control group.

CONCLUSIONS

We found that the use of a4FPCC as a hemostatic adjunct for post-CPB bleeding in neonatal cardiac surgery was associated with a decrease in mean total blood products transfused after CPB without an increased rate of 7- or 30-day postoperative thromboembolism. Our findings suggest that a4FPCCs can be considered as part of a hemostasis pathway for refractory bleeding in neonatal cardiac surgery.

The role of the calibrated automated thrombogram in neonates: describing mechanisms of neonatal haemostasis and evaluating haemostatic drugs

Premature infants are at high risk of haemorrhage and thrombosis. Our understanding of the differences between the neonatal and adult haemostatic system is evolving. There are several limitations to the standard coagulation tests used in clinical practice, and there is currently a lack of evidence to support many of the transfusion practices in neonatal medicine. The evaluation of haemostasis is particularly challenging in neonates due to their limited blood volume. The calibrated automated thrombogram (CAT) is a global coagulation assay, first described in 2002, which evaluates both pro- and anti-coagulant pathways in platelet-rich or platelet-poor plasma. In this review, the current applications and limitations of CAT in the neonatal population are discussed.Conclusion: CAT has successfully elucidated several differences between haemostatic mechanisms in premature and term neonates compared with adults. Moreover, it has been used to evaluate the effect of a number of haemostatic drugs in a pre-clinical model. However, the lack of evidence of CAT as an accurate predictor of neonatal bleeding, blood volume required and the absence of an evidence-based treatment algorithm for abnormal CAT results limit its current application as a bedside clinical tool for the evaluation of sick neonates. What is Known: • The Calibrated automated thrombogram (CAT) is a global coagulation assay which evaluates pro- and anti-coagulant pathways. • CAT provides greater information than standard clotting tests and has been used in adults to evaluate bleeding risk. What is New: • This review summarises the physiological differences in haemostasis between neonates and adults described using CAT. • The haemostatic effect of several drugs has been evaluated in neonatal plasma using CAT.

Understanding and managing the complex balance between bleeding and thrombosis following cardiopulmonary bypass in paediatric cardiac surgical patients

Bleeding in the perioperative period of congenital heart surgery with cardiopulmonary bypass is associated with increased morbidity and mortality both from the direct effects of haemorrhage as well as the therapies deployed to restore haemostasis. Perioperative bleeding is complex and multifactorial with both patient and procedural contributions. Moreover, neonates and infants are especially at risk. The objective of this review is to summarise the evidence regarding bleeding management in paediatric surgical patients and identify strategies that might facilitate appropriate bleeding management while minimising the risk of thrombosis. We will address the use of standard and point-of-care tests, and the role of contemporary coagulation factors and other novel drugs.

Thrombin generation and bleeding in cardiac surgery: a clinical narrative review

This narrative review discusses the role of thrombin generation in coagulation and bleeding in cardiac surgery, the laboratory methods for clinical detection of impaired thrombin generation, and the available hemostatic interventions that can be used to improve thrombin generation. Coagulopathy after cardiopulmonary bypass (CPB) is associated with excessive blood loss and adverse patient outcomes. Thrombin plays a crucial role in primary hemostasis, and impaired thrombin generation can be an important cause of post-CPB coagulopathy. Existing coagulation assays have significant limitations in assessing thrombin generation, but whole-blood assays designed to measure thrombin generation at the bed-side are under development. Until then, clinicians may need to institute therapy empirically for non-surgical bleeding in the setting of normal coagulation measures. Available therapies for impaired thrombin generation include administration of plasma, prothrombin complex concentrate, and bypassing agents (recombinant activated factor VII and factor eight inhibitor bypassing activity). In vitro experiments have explored the relative potency of these therapies, but clinical studies are lacking. The potential incorporation of thrombin generation assays into clinical practice and treatment algorithms for impaired thrombin generation must await further clinical development.

Mathematical modelling indicates that lower activity of the haemostatic system in neonates is primarily due to lower prothrombin concentration

Haemostasis is governed by a highly complex system of interacting proteins. Due to the central role of thrombin, thrombin generation and specifically the thrombin generation curve (TGC) is commonly used as an indicator of haemostatic activity. Functional characteristics of the haemostatic system in neonates and children are significantly different compared with adults; at the same time plasma levels of haemostatic proteins vary considerably with age. However, relating one to the other has been difficult, both due to significant inter-individual differences for individuals of similar age and the complexity of the biochemical reactions underlying haemostasis. Mathematical modelling has been very successful at representing the biochemistry of blood clotting. In this study we address the challenge of large inter-individual variability by parameterising the Hockin-Mann model with data from individual patients, across different age groups from neonates to adults. Calculating TGCs for each patient of a specific age group provides us with insight into the variability of haemostatic activity across that age group. From our model we observe that two commonly used metrics for haemostatic activity are significantly lower in neonates than in older patients. Because both metrics are strongly determined by prothrombin and prothrombin levels are considerably lower in neonates we conclude that decreased haemostatic activity in neonates is due to lower prothrombin availability.

Prohemostatic Activity of Factor X in Combination With Activated Factor VII in Dilutional Coagulopathy

BACKGROUND

Recombinant activated factor VII (rFVIIa) concentrate reduces allogeneic blood transfusions, but it may increase thromboembolic complications in complex cardiac surgery. The mixture of activated factor VII (FVIIa) and factor X (FX) (FVIIa/FX) (FVIIa:FX = 1:10) is a novel bypassing agent for hemophilia patients. We hypothesized that the combination of FX and FVIIa could improve thrombin generation (TG) in acquired multifactorial coagulation defects such as seen in cardiac surgery and conducted in vitro evaluation of FVIIa/FX in parallel with other coagulation factor concentrates using in vitro and in vivo diluted plasma samples.

METHODS

Plasma samples were collected from 9 healthy volunteers and 12 cardiac surgical patients. We measured TG (Thrombinoscope) using in vitro 50% dilution plasma and in vivo dilution plasma after cardiopulmonary bypass, in parallel with thromboelastometry (ROTEM) and standard coagulation assays. In vitro additions of FVIIa/FX (0.35, 0.7, and 1.4 μg/mL, based on the FVIIa level), rFVIIa (1.4, 2.8, and 6.4 μg/mL), prothrombin complex concentrate (0.3 international unit), and 20% plasma replacement were evaluated.

RESULTS

In diluted plasma, the addition of either FVIIa/FX or rFVIIa shortened the lag time and increased the peak TG, but the effect in lag time of FVIIa/FX at 0.35 μg/mL was more extensive than rFVIIa at 6.4 μg/mL. Prothrombin complex concentrate increased peak TG by increasing the prothrombin level but failed to shorten the lag time. No improvement in any of the TG variables was observed after 20% volume replacement with plasma. The addition of factor concentrates normalized prothrombin time/international normalized ratio but not with plasma replacement. In cardiac patients, similar patterns were observed on TG in post-cardiopulmonary bypass samples. FVIIa/FX shortened clotting time (CT) in a concentration-dependent manner on CT on thromboelastometry. Plasma replacement did not improve CT, but a combination of plasma and FVIIa/FX (0.35 μg/mL) more effectively shortened CT than FVIIa/FX alone.

CONCLUSIONS

The combination of FVIIa and FX improved TG more efficiently than rFVIIa alone or plasma in dilutional coagulopathy models. The required FVIIa dose in FVIIa/FX was considerably lower than those reported during bypassing therapy in hemophilia patients (1.4-2.8 μg/mL). The combination of plasma could restore coagulation more efficiently compared to FVIIa/FX alone. Lesser FVIIa requirement to exert procoagulant activity may be favorable in terms of reducing systemic thromboembolic complications.

Effectiveness of prothrombin complex concentrate (PCC) in neonates and infants with bleeding or risk of bleeding: a systematic review and meta-analysis

To systematically evaluate the effectiveness of prothrombin complex concentrate (PCC) in neonates and infants, we performed a systematic review and meta-analysis based on current evidence. Quality of studies was assessed by Cochrane Collaboration's risk of bias tool and Newcastle-Ottawa quality assessment scale. For dichotomous data, we obtained the number of events and total number and calculated the relative risk (RR) with 95% confidence intervals (CI). For continuous variables, we obtained mean and standard deviation (SD) values and calculated mean difference (MD) with 95% CI. We identified six trials and two cohort studies. For trials, selection bias and performance bias were high, while detection bias, attrition bias, and reporting bias were relatively low. For cohort studies, selection bias was low. Both individual studies and meta-analysis failed to find any benefit of PCC on mortality. Meta-analysis also failed to show any benefit in reducing intracranial hemorrhage. The effectiveness of PCC on the correction of hemostatic defects was inconsistent among studies. In addition, PCC was not more effective than fresh frozen plasma (FFP) in correcting hemostatic defects.

CONCLUSION

There is insufficient evidence to allow a recommendation for use of PCC in neonates and infants. What is Known: • Prothrombin Complex Concentrate is becoming increasingly used off-label for treatment of neonates and infants with severe bleeding or risk of severe bleeding. • Some case reports showed PCC seemed to be effective for infants and children with coagulation factor deficiency, but evidence about the effectiveness of PCC to reverse serious Vitamin K Deficiency Bleeding is limited. What is New: • As far as we know, this is the first systematic review that evaluates the effectiveness of PPC in neonates with bleeding or risk of bleeding. • There is insufficient evidence to allow a recommendation for use of PCCs in neonates and infants.

Prothrombin Complex Concentrates for Bleeding in the Perioperative Setting

Prothrombin complex concentrates (PCCs) contain vitamin K-dependent clotting factors (II, VII, IX, and X) and are marketed as 3 or 4 factor-PCC formulations depending on the concentrations of factor VII. PCCs rapidly restore deficient coagulation factor concentrations to achieve hemostasis, but like with all procoagulants, the effect is balanced against thromboembolic risk. The latter is dependent on both the dose of PCCs and the individual patient prothrombotic predisposition. PCCs are approved by the US Food and Drug Administration for the reversal of vitamin K antagonists in the setting of coagulopathy or bleeding and, therefore, can be administered when urgent surgery is required in patients taking warfarin. However, there is growing experience with the off-label use of PCCs to treat patients with surgical coagulopathic bleeding. Despite their increasing use, there are limited prospective data related to the safety, efficacy, and dosing of PCCs for this indication. PCC administration in the perioperative setting may be tailored to the individual patient based on the laboratory and clinical variables, including point-of-care coagulation testing, to balance hemostatic benefits while minimizing the prothrombotic risk. Importantly, in patients with perioperative bleeding, other considerations should include treating additional sources of coagulopathy such as hypofibrinogenemia, thrombocytopenia, and platelet disorders or surgical sources of bleeding. Thromboembolic risk from excessive PCC dosing may be present well into the postoperative period after hemostasis is achieved owing to the relatively long half-life of prothrombin (factor II, 60-72 hours). The integration of PCCs into comprehensive perioperative coagulation treatment algorithms for refractory bleeding is increasingly reported, but further studies are needed to better evaluate the safe and effective administration of these factor concentrates.

Fibrin Network Changes in Neonates after Cardiopulmonary Bypass

BACKGROUND

Quantitative and qualitative differences in the hemostatic systems exist between neonates and adults, including the presence of "fetal" fibrinogen, a qualitatively dysfunctional form of fibrinogen that exists until 1 yr of age. The consequences of "fetal" fibrinogen on clot structure in neonates, particularly in the context of surgery-associated bleeding, have not been well characterized. Here, the authors examine the sequential changes in clotting components and resultant clot structure in a small sample of neonates undergoing cardiac surgery and cardiopulmonary bypass (CPB).

METHODS

Blood samples were collected from neonates (n = 10) before surgery, immediately after CPB, and after the transfusion of cryoprecipitate (i.e., adult fibrinogen component). Clots were formed from patient samples or purified neonatal and adult fibrinogen. Clot structure was analyzed using confocal microscopy.

RESULTS

Clots formed from plasma obtained after CPB and after transfusion were more porous than baseline clots. Analysis of clots formed from purified neonatal and adult fibrinogen demonstrated that at equivalent fibrinogen concentrations, neonatal clots lack three-dimensional structure, whereas adult clots were denser with significant three-dimensional structure. Clots formed from a combination of purified neonatal and adult fibrinogen were less homogenous than those formed from either purified adult or neonatal fibrinogen.

CONCLUSIONS

The results of this study confirm that significant differences exist in clot structure between neonates and adults and that neonatal and adult fibrinogen may not integrate well. These findings suggest that differential treatment strategies for neonates should be pursued to reduce the demonstrated morbidity of blood product transfusion.

Optimizing Thrombin Generation with 4-Factor Prothrombin Complex Concentrates in Neonatal Plasma After Cardiopulmonary Bypass

BACKGROUND

Bleeding is a serious complication after pediatric cardiopulmonary bypass (CPB) that is associated with an increase in perioperative morbidity and mortality. Four-factor prothrombin complex concentrates (4F-PCCs) have been used off-label to supplement transfusion protocols for bleeding after CPB in adults; however, data on their use in neonates are limited. In this study, we hypothesized that 4F-PCCs administered ex vivo to neonatal plasma after CPB will increase thrombin generation.

METHODS

Fifteen neonates undergoing complex cardiac repairs requiring CPB were enrolled in this prospective study. Arterial blood was obtained after anesthesia induction but before CPB (baseline), after CPB following heparin reversal, and after our standardized transfusion of a quarter of a platelet apheresis unit (approximately 20 mL·kg) and 3 units of cryoprecipitate. Kcentra (CSL Behring), a 4F-PCC with nonactivated factor VII (FVII), and factor 8 inhibitor bypassing activity (FEIBA; Baxter Healthcare Corporation), a 4F-PCC with activated FVII, were added ex vivo to plasma obtained after CPB to yield concentrations of 0.1 and 0.3 IU·mL. Calibrated automated thrombography was used to determine thrombin generation for each sample.

RESULTS

The addition of Kcentra to plasma obtained after CPB resulted in a dose-dependent increase in the median (99% confidence interval) peak amount of thrombin generation (42.0 [28.7-50.7] nM for Kcentra 0.1 IU·mL and 113.9 [99.0-142.1] nM for Kcentra 0.3 IU·mL). The rate of thrombin generation was also increased (15.4 [6.5-24.6] nM·min for Kcentra 0.1 IU·mL and 48.6 [29.9-66.6] nM·min for Kcentra 0.3 IU·mL). The same was true for FEIBA (increase in peak: 39.8 [27.5-49.2] nM for FEIBA 0.1 IU·mL and 104.6 [92.7-124.4] nM for FEIBA 0.3 IU·mL; increase in rate: 17.4 [7.4-28.8] nM·min FEIBA 0.1 IU·mL and 50.5 [26.7- 63.1] nM·min FEIBA 0.3 IU·mL). In the posttransfusion samples, there was a significant increase with Kcentra in the median (99% confidence interval) peak amount (41.1 [21.0-59.7] nM for Kcentra 0.1 IU·mL and 126.8 [106.6- 137.9] nM for Kcentra 0.3 IU·mL) and rate (18.1 [-6.2 to 29.2] nM·min for Kcentra 0.1 IU·mL and 53.2 [28.2-83.1] nM·min for Kcentra 0.3 IU·mL) of thrombin generation. Again, the results were similar for FEIBA (increase in peak: 43.0 [36.4-56.7] nM for FEIBA 0.1 IU·mL and 109.2 [90.3-136.1] nM for FEIBA 0.3 IU·mL; increase in rate: 25.0 [9.1-32.6] nM·min for FEIBA 0.1 IU·mL and 59.7 [38.5-68.7] nM·min for FEIBA 0.3 IU·mL). However, FEIBA produced in a greater median reduction in lag time of thrombin generation versus Kcentra in samples obtained after CPB (P = 0.003 and P = 0.0002 for FEIBA versus Kcentra at 0.1 and 0.3 IU·mL, respectively) and in samples obtained after transfusion (P < 0.0001 for FEIBA versus Kcentra at 0.1 and 0.3 IU·mL).

CONCLUSIONS

After CPB, thrombin generation in neonatal plasma was augmented by the addition of 4F-PCCs. The peak amount and rate of thrombin generation were enhanced in all conditions, whereas the lag time was shortened more with FEIBA. Our findings suggest that the use of 4F-PCCs containing activated FVII may be an effective adjunct to the initial transfusion of platelets and cryoprecipitate to augment coagulation and control bleeding in neonates after CPB.

Differential Contributions of Intrinsic and Extrinsic Pathways to Thrombin Generation in Adult, Maternal and Cord Plasma Samples

Background

Thrombin generation (TG) is a pivotal process in achieving hemostasis. Coagulation profiles during pregnancy and early neonatal period are different from that of normal (non-pregnant) adults. In this ex vivo study, the differences in TG in maternal and cord plasma relative to normal adult plasma were studied.

Methods

Twenty consented pregnant women and ten consented healthy adults were included in the study. Maternal and cord blood samples were collected at the time of delivery. Platelet-poor plasma was isolated for the measurement of TG. In some samples, anti-FIXa aptamer, RB006, or a TFPI inhibitor, BAX499 were added to elucidate the contribution of intrinsic and extrinsic pathway to TG. Additionally, procoagulant and inhibitor levels were measured in maternal and cord plasma, and these values were used to mathematically simulate TG.

Results

Peak TG was increased in maternal plasma (393.6±57.9 nM) compared to adult and cord samples (323.2±38.9 nM and 209.9±29.5 nM, respectively). Inhibitory effects of RB006 on TG were less robust in maternal or cord plasma (52% vs. 12% respectively) than in adult plasma (81%). Likewise the effectiveness of BAX499 as represented by the increase in peak TG was much greater in adult (21%) than in maternal (10%) or cord plasma (12%). Further, BAX499 was more effective in reversing RB006 in adult plasma than in maternal or cord plasma. Ex vivo data were reproducible with the results of the mathematical simulation of TG.

Conclusion

Normal parturient plasma shows a large intrinsic pathway reserve for TG compared to adult and cord plasma, while TG in cord plasma is sustained by extrinsic pathway, and low levels of TFPI and AT.

Correcting thrombin generation ex vivo using different haemostatic agents following cardiac surgery requiring the use of cardiopulmonary bypass

Recently, lower thrombin generation has been associated with excess bleeding post-cardiopulmonary bypass (CPB). Therefore, treatment to correct thrombin generation is a potentially important aspect of management of bleeding in this group of patients. The objective of the present study was to investigate the effects of fresh frozen plasma (FFP), recombinant factor VIIa (rFVIIa), prothrombin complex concentrate (PCC) and tissue factor pathway inhibitor (TFPI) inhibition on thrombin generation when added ex vivo to the plasma of patients who had undergone cardiac surgery requiring CPB. Patients undergoing elective cardiac surgery were recruited. Blood samples were collected before administration of heparin and 30 min after its reversal. Thrombin generation was measured in the presence and absence of different concentrations of FFP, rFVIIa, PCC and an anti-TFPI antibody. A total of 102 patients were recruited. Thrombin generation following CPB was lower compared with pre-CPB (median endogenous thrombin potential pre-CPB 339 nmol/l per min, post-CPB 155 nmol/l per min, P < 0.0001; median peak thrombin pre-CPB 35 nmol/l, post-CPB 11 nmol/l, P < 0.0001). Coagulation factors and anticoagulants decreased, apart from total TFPI, which increased (55-111 ng/ml, P < 0.0001), and VWF (144-170 IU/dl, P < 0.0001). Thrombin generation was corrected to pre-CPB levels by the equivalent of 15 ml/kg FFP, 45 μg/kg rFVIIa and 25 U/kg of PCC. Inhibition of TFPI resulted in an enhancement of thrombin generation significantly beyond pre-CPB levels. This study shows that FFP, rFVIIa, PCC and inhibition of TFPI correct thrombin generation in the plasma of patients who have undergone surgery requiring CPB. Inhibition of TFPI may be a further potential therapeutic strategy for managing bleeding in this group of patients.

Endogenous thrombin potential following hemostatic therapy with 4-factor prothrombin complex concentrate: a 7-day observational study of trauma patients

Introduction

Purified prothrombin complex concentrate (PCC) is increasingly used as hemostatic therapy for trauma-induced coagulopathy (TIC). However, the impact of PCC administration on coagulation status among patients with TIC has not been adequately investigated.

Methods

In this observational, descriptive study, data relating to thrombin generation were obtained from plasma samples gathered prospectively from trauma patients upon emergency room (ER) admission and over the following 7 days. Standard coagulation tests, including measurement of antithrombin (AT) and fibrinogen, were performed. Three groups were investigated: patients receiving no coagulation therapy (NCT group), patients receiving fibrinogen concentrate only (FC group), and patients treated with PCC and fibrinogen concentrate (FC-PCC group).

Results

The study population (77 patients) was predominantly male (84.4%); mean age was 40 ± 15 years and mean injury severity score was 25.6 ± 12.7. There were no significant differences between the three study groups in thrombin-related parameters upon ER admission. Endogenous thrombin potential (ETP) was significantly higher in the FC-PCC group compared with the NCT group on days 1 to 4 and the FC group on days 1 to 3. AT levels were significantly lower in the FC-PCC group from admission until day 3 (versus FC group) or day 4 (versus NCT group). Fibrinogen increased over time, with no significant between-group differences after ER admission. Despite ETP being higher, prothrombin time and activated partial thromboplastin time were significantly prolonged in the FC-PCC group from admission until day 3 to 4.

Conclusions

Treatment with PCC increased ETP for several days, and patients receiving PCC therapy had low AT concentrations. These findings imply a potential pro-thrombotic state not reflected by standard coagulation tests. This is probably important given the postoperative acute phase increase in fibrinogen levels, although studies with clinical endpoints are needed to ascertain the implications for patient outcomes. We recommend careful use of PCC among trauma patients, with monitoring and potentially supplementation of AT.