Thrombotic events in neonates receiving recombinant factor VIIa or fresh frozen plasma

Hemostatic Challenges in Neonates

The neonatal hemostatic system is strikingly different from that of adults. Among other differences, neonates exhibit hyporeactive platelets and decreased levels of coagulation factors, the latter translating into prolonged clotting times (PT and PTT). Since pre-term neonates have a high incidence of bleeding, particularly intraventricular hemorrhages, neonatologists frequently administer blood products (i.e., platelets and FFP) to non-bleeding neonates with low platelet counts or prolonged clotting times in an attempt to overcome these "deficiencies" and reduce bleeding risk. However, it has become increasingly clear that both the platelet hyporeactivity as well as the decreased coagulation factor levels are effectively counteracted by other factors in neonatal blood that promote hemostasis (i.e., high levels of vWF, high hematocrit and MCV, reduced levels of natural anticoagulants), resulting in a well-balanced neonatal hemostatic system, perhaps slightly tilted toward a prothrombotic phenotype. While life-saving in the presence of active major bleeding, the administration of platelets and/or FFP to non-bleeding neonates based on laboratory tests has not only failed to decrease bleeding, but has been associated with increased neonatal morbidity and mortality in the case of platelets. In this review, we will present a clinical overview of bleeding in neonates (incidence, sites, risk factors), followed by a description of the key developmental differences between neonates and adults in primary and secondary hemostasis. Next, we will review the clinical tests available for the evaluation of bleeding neonates and their limitations in the context of the developmentally unique neonatal hemostatic system, and will discuss current and emerging approaches to more accurately predict, evaluate and treat bleeding in neonates.

An overview of the role of microparticles/microvesicles in blood components: Are they clinically beneficial or harmful?

Blood cells and tissues generate heterogeneous populations of cell-derived vesicles, ranging from approximately 50 nm to 1 µm in diameter. Under normal physiological conditions and as an essential part of an energy-dependent natural process, microparticles (MPs) are continuously shed into the circulation from membranes of all viable cells such as megakaryocytes, platelets, red blood cells, white blood cells and endothelial cells. MP shedding can also be triggered by pathological activation of inflammatory processes and activation of coagulation or complement systems, or even by shear stress in the circulation. Structurally, MPs have a bilayered phospholipid structure exposing coagulant-active phosphatidylserine and expressing various membrane receptors, and they serve as cell-to-cell shuttles for bioactive molecules such as lipids, growth factors, microRNAs, and mitochondria. It was established that ex vivo processing of blood into its components, involving centrifugation, processing by various apheresis procedures, leucoreduction, pathogen reduction, and finally storage in different media and different types of blood bags, can impact MP generation and content. This is mostly due to exposure of the collected blood to anticoagulant/storage media and due to shear stresses or activation, contact with artificial surfaces, or exposure to various leucocyte-removal filters and pathogen-reduction treatments. Such artificially generated MPs, which are added to the original pool of MPs collected from the donor, may exhibit specific functional characteristics, as MPs are not an inert element of blood components. Not surprisingly, MPs' roles and functionality are therefore increasingly seen to be fully relevant to the field of transfusion medicine, and as a parameter of blood safety that must be considered in haemovigilance programmes. Continual advancements in assessment methods of MPs and storage lesions are gradually leading to a better understanding of the impacts of blood collection on MP generation, while clinical research should clarify links of MPs with transfusion reactions and certain clinical disorders. Harmonization and consensus in sampling protocols, sample handling and processing, and assessment methods are needed to achieve consensual interpretations. This review focuses on the role of MPs as an essential laboratory tool and as a most effective player in transfusion science and medicine and in health and disease.

Platelet-derived microparticles trigger THP-1 monocytic cell aggregation and release of pro-coagulant tissue factor-expressing microparticles in vitro

Microparticles (MPs) released by blood or endothelial cells are present in plasma for transfusion. They originate from the collected donor blood or are triggered by the variable steps taking place during collection and production/storage processes of blood components. While MPs may contribute to hemostasis, their presence in transfused plasma may lead to uncontrolled thrombin generation when transfused to susceptible cancer or hypercoagulable patients. Understanding the biochemical and cellular triggers of MP-mediated thrombogenesis is therefore crucial. We isolated platelet MPs (PMPs) present in platelet concentrate supernatant plasma (N-PMPs) or prepared by activation of isolated platelets using 0.1 IU/mL thrombin (T-PMPs). N-PMPs and T-PMPs were characterized by dynamic light scattering and counted by tunable resistive pulse sensing to determine population size and number. T-MPMs, but not N-PMPs, induced immediate, long-lasting, strong aggregation of THP-1 monocytic cells in vitro. In addition, co-cultures of THP-1 cells with both N-PMPs and T-PMPs triggered the generation of pro-coagulant tissue factor (TF)-bearing MPs from THP-1 cells. Therefore, some PMPs may induce THP-1 monocytic cell aggregation in vitro and trigger immune cell-mediated thrombogenicity linked to the release of pro-coagulant tissue factor-bearing MPs. Controlling the impact of the presence of PMPs in transfused blood components in certain patient population or critically ill patients deserves in-depth consideration.

Safety and efficacy of recombinant activated factor VII in nonhemophilia children with severe or life-threatening bleeding: a report from the SeveNBleeP registry

We evaluated efficacy and safety of recombinant activated factor VII (rFVIIa) in nonhemophilia children with life-threatening or severe bleeding. Using data from the SeveNBleeP registry, we analyzed demographic, clinical, laboratory, and treatment data for children who received rFVIIa to treat severe hemorrhage. The SeveNBleeP registry was international registry formed in 2005, to collect information on the use of rFVIIa in the off-label setting of severe bleeding in nonhemophilia patients. There were 191 patient records entered into this registry, of which 164 were validated. Of the 164 records, in 137 patient records, rFVIIa was used for treatment of bleeding episodes. Of these 137 treatment episodes, 42 were in neonates and infants under 1 year of age. Use of rFVIIa significantly improved laboratory parameters (prothrombin time, international normalized ratio, activated partial thromboplastin time, hematocrit), reduced estimated blood loss, and reduced requirements for blood products (packed red blood cells and fresh frozen plasma) in those more than 1 year of age. There was no significant reduction in requirements for blood products after rFVIIa administration in the neonates and infants, but there was a trend to lower frequency of FFP use after rFVIIa administration. There was one thromboembolic event in an infant that was related to administration of rFVIIa. No other serious adverse events were reported that were related to administration of rFVIIa. In nonhemophilia-associated bleeding in children, rFVIIa appears to be safe and efficacious in reducing estimated blood loss in children over 1 year of age, although its effectiveness in infants below 1 year of age was less clear.

Coagulation and the surgical neonate

Both coagulopathy and abnormal thrombosis can complicate the anesthetic and surgical management of neonatal patients; however, the patterns of bleeding and thrombosis in neonates differ from those in adults or older children. Severe coagulopathic bleeding most commonly occurs during heart surgery and almost certainly contributes to morbidity and mortality in this population. Such severe bleeding is rare during other surgery; the exception is babies presenting to the operating room with established coagulopathy secondary to severe sepsis. Alternatively, pathological thrombosis will mainly occur in association with indwelling vascular access devices or surgically created vascular shunts. There are important differences between the coagulation system in neonates and older patients. The implication of this is that therapies established in other patient groups will not be optimal for neonates without adaptation. While evidence from high-quality clinical trials is rarely available, an understanding of how coagulation in neonates differs can help to guide practice. This review will discuss important differences between the coagulation system of neonates and older patients and how these relate to newer models of coagulation. The emphasis will be on issues likely to impact on perioperative care. In particular, the management of severe bleeding, the manipulation of coagulation during heart surgery, and the management of coagulopathy in septic neonates will be discussed in detail.

Coagulopathies in the PICU: DIC and liver disease

Bleeding in patients in pediatric intensive care units is associated with an increased risk of mortality. Fortunately, most patients with an abnormal coagulation profile do not bleed because this is generally secondary to liver disease or dietary-induced vitamin K deficiency. When the laboratory markers of coagulopathy are the result of disseminated intravascular coagulation, bleeding is common and the risk of mortality extreme. Although interventions directed toward correcting the abnormal coagulation test results are generally initiated, they are also generally either not warranted or not fully successful.

Predicting response to rFVIIa in neonates with intractable bleeding or severe coagulation disturbances

BACKGROUND

To date, clinical experience with recombinant factor VIIa (rFVIIa) in neonates is rather limited because of the lack of controlled studies. ΑIM: The objective of this study was to present further experience from our center with regard to the use of rFVIIa in newborns with severe bleeding or coagulopathy resistant to conventional therapy and to determine factors affecting the clinical outcome.

METHODOLOGY

We performed a retrospective data analysis of 29 neonates with intractable bleeding or severe coagulation disturbances. All patients received 100 μg/kg of rFVIIa per dose bolus intravenously (maximum of 23 doses), as rescue procedure after other interventions had failed to achieve hemostasis.

RESULTS

Fourteen neonates survived (group A), whereas 15 died (group B). There was no difference in birth weight, gestational age, and bleeding site and causes between the 2 groups. In the neonates who survived, rFVIIa had been administered earlier in the disease process (<24 h of beginning of bleeding) compared with those who died (P=0.009). In all 29 neonates, international normalized ratio was directly restored (from 2.99±1.4 before rFVIIa administration to 1.6±1.1 afterward, P<0.001) and prothrombin time and activated partial thromboplastin time were significantly decreased after administration of rFVIIa (from 28 to 16.4 and from 180 to 67, respectively; P=0.001 and 0.05, respectively). Blood products administered were significantly less in group A than in group B, as time from the beginning of bleeding to the administration of rFVIIa was significantly less in group A than in group B. Neither acute adverse events nor thromboembolic complications were observed.

CONCLUSIONS

In this neonatal group with intractable bleeding and/or severe coagulation disturbances, rFVIIa was more effective in early intervention as rescue therapy, without any adverse events in all neonates. Upon failure to achieve hemostasis with initial administration of blood products, fast intervention with rFVIIa could be considered in neonates with serious bleeding and coagulation disorders.

Effects of in vitro adult platelet transfusions on neonatal hemostasis

BACKGROUND

Thrombocytopenia is frequent among neonates, and 20-25% of affected infants are treated with platelet transfusions. These are frequently given for mild thrombocytopenia (platelets: 50-100 × 10(9) L(-1)), largely because of the known hyporeactivity of neonatal platelets. In tests of primary hemostasis, however, neonates have shorter bleeding and closure times (CTs) than adults. This has been attributed to their higher hematocrits, higher von Willebrand factor (VWF) concentrations, and predominance of longer VWF polymers.

OBJECTIVE

To determine whether the 'transfusion' of adult (relatively hyperreactive) platelets into neonatal blood results in a hypercoagulable profile.

METHODS

Cord blood (CB) and adult peripheral blood (PB) were separated (with a modified buffy coat method) to generate miniaturized platelet concentrates (PCs) and thrombocytopenic blood. PB-derived and CB-derived PCs (n = 7 per group) were then 'transfused'in vitro into thrombocytopenic CB and PB. The effects of autologous vs. allogeneic (developmentally mismatched) 'transfusions' were evaluated with whole blood aggregometry, a platelet function analyzer (PFA-100), and thromboelastography (TEG).

RESULTS

Adult platelets aggregated significantly better than neonatal platelets in response to thrombin receptor-activating peptide, ADP, and collagen, regardless of the blood into which they were transfused. The 'transfusion' of adult platelets into thrombocytopenic CB resulted in shorter CTs-EPI (PFA-100) and higher clot strength and firmness (TEG) than 'transfusion' of neonatal autologous platelets.

CONCLUSIONS

In vitro'transfusion' of adult platelets into neonatal blood results in shorter CTs than 'transfusion' with neonatal platelets. Our findings should raise awareness of the differences between the neonatal and adult hemostatic system and the potential 'developmental mismatch' associated with platelet transfusions for neonatal hemostasis.

Recombinant activated factor VIIa treatment for refractory hemorrhage in infants

OBJECTIVE

Report clinical response to recombinant factor VIIa in a cohort of critically ill infants.

STUDY DESIGN

We identified all infants who received factor VIIa in the Duke Neonatal Intensive Care Unit between January 2005 and July 2008. Hematological data and volume of blood transfusions before and after factor VIIa treatment were compared. The precipitating diagnosis for each factor VIIa use, and the ensuing clinical outcomes of bleeding, thrombosis and mortality were noted.

RESULT

We identified 18 infants with median birth weight of 880 g and median gestational age of 26 weeks. One to six doses of factor VIIa (90 mcg kg(-1) per dose) were administered, with 13 (72%) infants receiving a single dose. Hemostasis was achieved in 13 (72%) of the infants. Prothrombin time and activated partial thromboplastin time significantly decreased following treatment with factor VIIa. Volume of plasma transfusions significantly decreased following treatment with factor VIIa (P=0.02). Thrombosis occurred in one (11%) infant. Six (33%) infants died within 72 h of treatment, and overall mortality was 10/18 (56%).

CONCLUSION

Treatment with factor VIIa at doses of 90 mcg kg(-1) improved coagulation studies and decreased the need for plasma transfusions in a group of critically ill infants without significant risk. Factor VIIa may be an effective addition to current treatment modalities for refractory hemorrhage in infants.

Optimal use of recombinant factor VIIa in the control of bleeding episodes in hemophilic patients

One of the last remaining clinical hurdles in the treatment of people with hemophilia is the development of inhibitors. Alloantibodies or autoantibodies directed at coagulation factors render the infusion of coagulation factor concentrates ineffective, and alternative means must be used to achieve hemostasis. Recombinant factor VIIa (rFVIIa) was developed to control bleeding episodes in hemophilic patients with inhibitors. Clinical efficacy in achieving hemostasis in inhibitor patients was demonstrated by a compassionate-use protocol, as well as in randomized controlled trials. To date, over 1.5 million doses of rFVIIa have been given to inhibitor patients, with an excellent efficacy and safety record. Because of its short half-life, alternative means of dosing and infusing rFVIIa have been explored and are reviewed here.