Primary hemostasis in neonates with thrombocytopenia

Implementing evidence-based restrictive neonatal intensive care unit platelet transfusion guidelines

Platelet transfusions are life-saving treatments for specific populations of neonates. However, recent evidence indicates that liberal prophylactic platelet transfusion practices cause harm to premature neonates. New efforts to better balance benefits and risks are leading to the adoption of more restrictive platelet transfusion guidelines in neonatal intensive care units (NICU). Although restrictive guidelines have the potential to improve outcomes, implementation barriers exist. We postulate that as neonatologists become more familiar with the data on the harm of liberal platelet transfusions, enthusiasm for restrictive guidelines will increase and barriers to implementation will decrease. Thus, we focused this educational review on; (1) the adverse effects of platelet transfusions to neonates, (2) awareness of platelet transfusion "refractoriness" in thrombocytopenic neonates and its association with poor outcomes, and (3) the impetus to find alternatives to transfusing platelets from adult donors to NICU patients.

Primary hemostasis in fetal growth restricted neonates studied via PFA-100 in cord blood samples

BACKGROUND

Platelet function of fetal growth restricted (FGR) neonates remains a field of debate. Platelet function analyzer (PFA-100) offers a quantitative in vitro assessment of primary, platelet-related hemostasis. Our aim was to examine platelet function using PFA-100 in FGR neonates and associate our results with perinatal parameters.

METHODS

PFA-100 was applied on 74 FGR neonates, 48 full-term (>37 weeks' gestation) and 26 preterm neonates (<37 weeks). The control group consisted of 118 healthy neonates. Two closure times (CTs) with COL/EPI and COL/ADP cartridges were determined on cord blood samples for each subject. Statistical analysis was performed by SAS 9.4. The statistical significance level was set at 0.05 and all tests were two-tailed.

RESULTS

COL/EPI CTs were prolonged in FGR (median 132 s, IQR 95-181 s) compared with control neonates (median 112.5 s, IQR 93-145 s), p = 0.04. Median COL/EPI CT for term and preterm FGR neonates was 126 s (IQR 90-157 s) and 137 s (IQR 104-203), respectively (p = 0.001), and COL/ADP CT was 70 s (IQR 62-80 s) for term and 75 s (IQR 68-82 s) for preterm FGR neonates (p = 0.08). Among FGR neonates, COL/EPI CT was related with delivery time (with preterm neonates exhibiting prolonged COL/EPI CTs), p = 0.05. No correlation was proved between both CTs and hematological parameters in FGR neonates.

CONCLUSION

FGR neonates showed impaired platelet function via PFA-100, with preterm FGR neonates confronting the greatest risk. Prolonged COL/EPI CTs in FGR neonates seemed to be independent of hematological parameters and could warn for closer evaluation during the first days of their lives.

Hemostasis in neonatal ECMO

Extracorporeal membrane oxygenation (ECMO) is a life-saving support for cardio-respiratory function. Over the last 50 years, the extracorporeal field has faced huge technological progress. However, despite the improvements in technique and materials, coagulation problems are still the main contributor to morbidity and mortality of ECMO patients. Indeed, the incidence and survival rates of the main hemorrhagic and thrombotic complications in neonatal respiratory ECMO are relevant. The main culprit is related to the intrinsic nature of ECMO: the contact phase activation. The exposure of the human blood to the non-endothelial surface triggers a systemic inflammatory response syndrome, which chronically activates the thrombin generation and ultimately leads to coagulative derangements. Pre-existing illness-related hemostatic dysfunction and the peculiarity of the neonatal clotting balance further complicate the picture. Systemic anticoagulation is the management's mainstay, aiming to prevent thrombosis within the circuit and bleeding complications in the patient. Although other agents (i.e., direct thrombin inhibitors) have been recently introduced, unfractionated heparin (UFH) is the standard of care worldwide. Currently, there are multiple tests exploring ECMO-induced coagulopathy. A combination of the parameters mentioned above and the evaluation of the patient's underlying clinical context should be used to provide a goal-directed antithrombotic strategy. However, the ideal algorithm for monitoring anticoagulation is currently unknown, resulting in a large inter-institutional diagnostic variability. In this review, we face the features of the available monitoring tests and approaches, mainly focusing on the role of point-of-care (POC) viscoelastic assays in neonatal ECMO. Current gaps in knowledge and areas that warrant further study will also be addressed.

Developmental hemostasis in the neonatal period

BACKGROUND

The hemostatic system is complex and evolves continuously since gestation and well into the adult years, in a process known as "developmental hemostasis."

DATA SOURCES

A comprehensive review was performed after an extensive literature search on PubMed/MEDLINE concerning developmental hemostasis during the neonatal period. Relevant cross references were also included.

RESULTS

Although part of a system, each component of the hemostatic system evolves differently, with many displaying both quantitative and qualitative age-related differences. This leads to drastic disparities between the coagulation system of neonates and both other children's and adults', while still maintaining a generally balanced and physiological hemostasis. The motives behind this process remain to be fully elucidated but may be, at least in part, related to non-hemostatic factors.

CONCLUSIONS

Knowledge regarding "developmental hemostasis" is essential for everyone caring for newborns or even children in general and in this review, we describe each hemostatic system component's neonatal characteristics and age-related progression as well as explore some of the possible physiological motives behind the process.

Transfusion in Neonatal Patients: Review of Evidence-Based Guidelines

Transfusion of red blood cells, platelets, and fresh frozen plasma in neonatal patients has not been well characterized in the literature, with guidelines varying greatly between institutions. However, anemia and thrombocytopenia are highly prevalent, especially in preterm neonates. When transfusing a neonatal patient, clinicians must take into consideration physiologic differences, gestational and postnatal age, congenital disorders, and maternal factors while weighing the risks and benefits of transfusion. This review of existing literature summarizes current evidence-based neonatal transfusion guidelines and highlights areas of current ongoing research and those in need of future studies.

Ontogeny of platelet function

Although the hemostatic potential of adult platelets has been investigated extensively, regulation of platelet function during fetal life is less clear. Recent studies have provided increasing evidence for a developmental control of platelet function during fetal ontogeny. Fetal platelets feature distinct differences in reactive properties compared with adults. These differences very likely reflect a modified hemostatic and homeostatic environment in which platelet hyporeactivity contributes to prevent pathological clot formation on the one hand but still ensures sufficient hemostasis on the other hand. In this review, recent findings on the ontogeny of platelet function and reactivity are summarized, and implications for clinical practice are critically discussed. This includes current platelet-transfusion practice and its potential risk in premature infants and neonates.

The Thromboelastographic Profile at Birth in Very Preterm Newborns with Patent Ductus Arteriosus

BACKGROUND

The role of hemostasis in the closure of patent ductus arteriosus (PDA) in preterm infants is controversial.

OBJECTIVE

To assess thromboelastography (TEG) at birth in very-low-birth-weight (VLBW) infants affected by PDA.

METHODS

This was an ancillary study of a prospective observational study aimed at defining the TEG profile in healthy VLBW infants in the first month of life. In this analysis, we included neonates of <33 weeks' gestational age (GA) with PDA and compared TEG traces based on (1) spontaneous closure versus the need for pharmacological treatment and (2) treatment response. We collected blood samples in the 1st day of life to perform recalcified native-blood TEG (reaction time, maximum amplitude, and lysis at 30 min [Ly30)]), standard coagulation tests, and a full blood count.

RESULTS

We enrolled 151 infants with a PDA at the first echocardiogram; 111 experienced spontaneous PDA closure while 40 required treatment. Mean GA was 29.7 ± 1.7 and 27.6 ± 2.1 weeks, and birth weight was 1,158 ± 256 and 933 ± 263 g in the 2 groups, respectively (p < 0.001). The hemostatic profile was similar between groups. Median hematocrit (44.6 and 48.7%; p = 0.01) and platelet count (187 and 216 × 103/μL; p = 0.04) were lower in the treated group, although differences lost significance after controlling for GA and illness severity in the multivariate analysis. Responders to PDA treatment (n = 20) had a significantly lower median Ly30 than nonresponders (0 and 0.7%; p = 0.02).

CONCLUSION

TEG at birth does not predict spontaneous PDA closure in preterm newborns. Fibrinolysis is enhanced in nonresponders to PDA treatment; this observation warrants further investigation.

Anticoagulation in Neonatal ECMO: An Enigma Despite a Lot of Effort!

Extracorporeal membrane oxygenation (ECMO) is a valuable modality used to support neonates, children, and adults with cardiorespiratory failure refractory to conventional therapy. It requires use of anticoagulation to prevent clotting in the extracorporeal circuit. Balancing bleeding from excessive anticoagulation with thrombotic risk remains a difficult aspect of ECMO care. Despite many advances in ECMO technology, better understanding of the coagulation cascade and new monitoring schemes to adjust anticoagulation, bleeding and thrombosis remain the most frequent complications in ECMO and are associated with morbidity and mortality. In neonates, ECMO is also complicated by the immature hemostatic system, laboratory testing norms which are not specific for neonates, lack of uniformity in management, and paucity of high-quality evidence to determine best practices. Traditional anticoagulation focuses on the use of unfractionated heparin. Direct thrombin inhibitors are also used but have not been well-studied in the neonatal ECMO population. Anticoagulation monitoring is complex and currently available assays do not take into account thrombin generation or platelet contribution to clot formation. Global assays may add valuable information to guide therapy. This review provides an overview of hemostatic alterations, anticoagulation, monitoring and management, novel anticoagulant use, and circuit modifications for neonatal ECMO. Future considerations are also presented.

Association Between In Vitro Bleeding Time and Bleeding in Preterm Infants With Thrombocytopenia

This cohort study examines the use of closure time following stimulation with collagen and adenosine diphosphate vs the platelet count as a marker of bleeding in premature neonates with thrombocytopenia.

Impaired platelet activity and hypercoagulation in healthy term and moderately preterm newborns during the early neonatal period

BACKGROUND

Preterm newborns are at thrombohemorrhagic risk during the early neonatal period. Taking into account the lack of informative tools for the laboratory diagnosis of hemostasis disorders in newborns, our goal was to determine the baseline values of thrombodynamics and platelet functional activity in healthy term and moderately preterm newborns during the early neonatal period future potential clinical use of these tests.

METHODS

Coagulation was assessed using an integral assay of thrombodynamics and standard coagulation assays, and platelet functional activity was estimated by flow cytometry.

RESULTS

Hypercoagulation of newborns, represented by a significantly higher clot growth velocity and the presence of spontaneous clots in the thrombodynamics, was combined with platelet hypoactivity. Granule release, phosphatidylserine exposure, and the ability to change shape upon activation were decreased in the platelets of moderately preterm newborns. The platelet function remained at the same level over the first four days of life, whereas the hypercoagulation became less pronounced.

CONCLUSIONS

The hemostasis of newborns is characterized by hypercoagulation combined with reduced platelet functional activity. Moderately preterm and term newborns do not differ in the parameters of coagulation, while some of the functional responses of platelets are lower in moderately preterm newborns than in term.

Influence of platelet count, platelet mass index, and platelet function on the spontaneous closure of ductus arteriosus in the prematurity

BACKGROUND

This study aims at evaluating the influence of platelet count, platelet mass index, and platelet function on the spontaneous closure of ductus arteriosus in prematurity.

METHODS

All preterm babies were divided into two groups, including Group 1 with "open PDA" and Group 2 with "closed PDA". The variables of platelet count, mean platelet volume, platelet mass index, and platelet function were analyzed and compared between two groups of patients to identify the factors that significantly influenced spontaneous closure of ductus arteriosus.

RESULTS

Twenty-four patients were in the "open PDA" group, whereas 36 patients were in the "closed PDA" group. Mean GA and BW were 27.6 ± 1.8 (23.1-30.4) and 28 ± 1.6 (23.4-30.6) weeks and 1009 ± 270 (585-1480) g and 1035 ± 298 (505-1500) g in "open PDA" and "closed PDA" groups, respectively (p > 0.05). The incidence of "Collagen-ADP > 130 s" was significantly higher in the "open PDA" group, and the levels of hemoglobin and hematocrit were significantly lower in the "open PDA" group (p < 0.05). Multivariate logistic regression analysis showed that respiratory distress syndrome (OR: 9, CI: 1.5-51.8) and collagen-ADP > 130 s (OR: 5.7 CI: 1.55-21.3) are two independent factors associated with ductal patency.

CONCLUSION

This is the first study in the English literature providing evidence of the influence of platelet dysfunction on the spontaneous closure of ductus arteriosus in prematurity. Longer collagen-ADP duration is identified as a risk factor of ductal closure.

Neonatal Platelet Transfusions and Future Areas of Research

Thrombocytopenia affects approximately one fourth of neonates admitted to neonatal intensive care units, and prophylactic platelet transfusions are commonly administered to reduce bleeding risk. However, there are few evidence-based guidelines to inform clinicians' decision-making process. Developmental differences in hemostasis and differences in underlying disease processes make it difficult to apply platelet transfusion practices from other patient populations to neonates. Thrombocytopenia is a risk factor for common preterm complications such as intraventricular hemorrhage; however, a causal link has not been established, and platelet transfusions have not been shown to reduce risk of developing intraventricular hemorrhage. Platelet count frequently drives the decision of whether to transfuse platelets, although there is little evidence to demonstrate what a safe platelet nadir is in preterm neonates. Current clinical assays of platelet function often require large sample volumes and are not valid in the setting of thrombocytopenia; however, evaluation of platelet function and/or global hemostasis may aid in the identification of neonates who are at the highest risk of bleeding. Although platelets' primary role is in establishing hemostasis, platelets also carry pro- and antiangiogenic factors in their granules. Aberrant angiogenesis underpins common complications of prematurity including intraventricular hemorrhage and retinopathy of prematurity. In addition, platelets play an important role in host immune defenses. Infectious and inflammatory conditions such as sepsis and necrotizing enterocolitis are commonly associated with late-onset thrombocytopenia in neonates. Severity of thrombocytopenia is correlated with mortality risk. The nature of this association is unclear, but preclinical data suggest that thrombocytopenia contributes to mortality rather than simply being a proxy for disease severity. Neonates are a distinct patient population in whom thrombocytopenia is common. Their unique physiology and associated complications make the risks and benefits of platelet transfusions difficult to understand. The goal of this review was to highlight research areas that need to be addressed to better understand the risks and benefits of platelet transfusions in neonates. Specifically, it will be important to identify neonates at risk of bleeding who would benefit from a platelet transfusion and to determine whether platelet transfusions either abrogate or exacerbate common neonatal complications such as sepsis, chronic lung disease, necrotizing enterocolitis, and retinopathy of prematurity.

Platelet Transfusions in the Neonatal Intensive Care Unit

There is significant world-wide variability in platelet transfusion thresholds used to transfuse thrombocytopenic neonates. A large multicenter randomized controlled trial comparing 2 different platelet transfusion thresholds in neonates is currently ongoing, and should provide data to guide transfusion practice. However, several studies have found that factors other than the degree of thrombocytopenia determine the bleeding risk. Thus, it will be important to develop better tests to assess primary hemostasis and bleeding risk in neonates.

Neonatal platelets: mediators of primary hemostasis in the developing hemostatic system

The human hemostatic system is developmentally regulated, resulting in qualitative and quantitative differences in the mediators of primary and secondary hemostasis as well as fibrinolysis in neonates and infants. Although gestational age-related differences in coagulation factor levels occur, the existence of a unique neonatal platelet phenotype remains controversial. Complicated by difficulties in obtaining adequate neonatal blood volumes with which to perform functional assays, ambiguity surrounds the characterization of neonatal platelets. Thus, much of the current knowledge of neonatal platelet function has been based on studies from cord blood samples. Studies suggest that cord blood-derived platelets, as a surrogate for neonatal platelets, are hypofunctional when compared with adult platelets. This relative platelet dysfunction, combined with a propensity toward thrombocytopenia in the neonatal intensive care unit population, creates a clinical conundrum regarding the appropriate administration of platelet transfusions. This review provides an appraisal of the distinct functional phenotype of neonatal platelets. Neonatal platelet transfusion practices and the impact of the relatively hypofunctional neonatal platelet on those practices will be considered.