Arachidonic acid-induced aggregation of platelets from human cord blood compared with platelets from adults

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.

Platelets in neonates: central mediators in haemostasis, antimicrobial defence and inflammation

Platelets are not only centrally involved in haemostasis, but also in antimicrobial defence and inflammation. Since evaluation of platelet physiology in the particular patient group of preterm and term neonatal infants is highly restricted for ethical reasons, there are hardly any data available in healthy and much less in extremely immature or ill neonates. By summarising current knowledge and addressing both platelet researchers and neonatologists, we describe neonatal platelet count and morphology, report on previous analyses of neonatal platelet function in primary haemostasis and provide insights into recent advances in platelet immunology that considerably impacts our clinical view on the critically ill neonatal infant. We conclude that neonatal platelets, originating from liver megakaryocytes, substantially differ from adult platelets and may play a pivotal role in the pathophysiology of neonatal sepsis or intraventricular haemorrhage, both complications which seriously augment perinatal morbidity and mortality.

Developmental haemostasis: secondary haemostasis

The haemostatic system is a complex interaction between the vasculature, cellular components and plasma proteins that interact to maintain haemostasis in the healthy body. The haemostatic system can be further defined as primary, secondary and tertiary haemostasis to better define the interdependent mechanisms that combine to maintain haemostasis. The term 'developmental haemostasis' was first introduced by Maureen Andrews in the 1980s to describe the age-related physiological changes of the coagulation system as it develops progressively over time from fetal, neonatal, paediatric to adult and geriatric systems. This paper will focus on developmental changes in secondary haemostasis, that is, the plasma protein changes that occur with age, particularly during the fetal and neonatal period, when the changes are most marked compared to the adult system.

Platelet aggregation in term and preterm newborns

The platelets of newborns have a hyporeactive period. This period, during which the platelet count is normal but their functions are deficient, is called transient platelet hyporeactivity of newborns. The platelet functions and their normalizing process of term and preterm neonates are investigated. Twenty term and 20 preterm (gestational age <37 weeks) newborns were enrolled in the study. Twenty-eight healthy children aged 2 months to 3 years old participated in the study as the control group. Healthy newborns were followed for 15 days after birth longitudinally in 3 periods: period 1 (0-4 days), period 2 (5-9 days), period 3 (10-15 days). Aggregation studies were performed from whole blood samples. Whole blood aggregation was measured by the impedance method. Transient hyporeactivity of platelets was found in term and preterm groups, and there was no difference between term and preterms. Platelets of newborns gained their normal functions at postnatal 10-14 days. The results show that hyporeactivity of platelets during the first 9 days of life is physiological and transient.

Platelet function in term and preterm neonates

Platelet dysfunction likely contributes to the pathophysiology of catastrophic hemorrhages in preterm neonates. In vitro studies have demonstrated that platelets of both term and preterm neonates are hyporesponsive to a variety of agonists. In contrast,template bleeding times of term neonates are shorter than those from adults. Very little is known about this and other tests of primary hemostasis in premature and sick neonates in the neonatal intensive care unit (NICU). This article covers the current knowledge of platelet function in preterm and term neonates and review show new agents (such as recombinant thrombopoietin and recombinant factor VIIa) may enhance neonatal platelet function.

An open-label randomized controlled trial of low molecular weight heparin for the prevention of central venous line-related thrombotic complications in children: the PROTEKT trial

OBJECTIVE(S)

Central venous lines (CVLs) are major risk factors for venous thromboembolism (VTE) in children. The objective of PROTEKT was to determine if a low molecular weight heparin (reviparin-sodium) safely prevents CVL-related VTE.

STUDY DESIGN

This multi-center, open-label study, with blinded central outcome adjudication, randomized patients with new CVLs to twice-daily reviparin-sodium or standard care. The efficacy outcome was based on an exit venogram at Day 30 (+14 days), or earlier in case of CVL removal, or confirmed symptomatic VTE. The safety outcomes were major bleeding and death. Due to slow and restricted patient accrual, PROTEKT was closed prematurely.

RESULTS

With reviparin-sodium, 14.1% (11:78) of patients had VTE compared to 12.5% (10:80) of control patients (odds ratio=1.15; 95% confidence interval 0.42, 3.23); 2P=0.82). One patient had a major bleed and there were two deaths, all three events occurring in the standard care group.

CONCLUSIONS

The use of reviparin-sodium for short-term prophylaxis of CVL-related VTE in children was safe but its efficacy remains unclear. Although underpowered, PROTEKT provided valuable information on event rates and predictors of CVL-related VTE.

Aggregation of and thromboxane B2 synthesis in platelets from newborn infants of smoking and non-smoking mothers

Cord blood platelet aggregation and thromboxane B2 (TxB2) synthesis were investigated in 20 healthy infants of drug-free healthy mothers with an uncomplicated pregnancy ending at term in a normal vaginal delivery. Eight of the mothers were habitual smokers and the remaining 12 were non-smokers. The platelet count was slightly lower in infants of smoking mothers than in the control infants. There were no differences between the two groups in the qualitative or quantitative aggregation responses (maximal change in optical density) to stimulation by 0.55, 1.1, 3.3 and 6.6 microM adenosine diphosphate, 0.5 and 1.0 mM arachidonic acid (AA) or collagen 1.0 and 5.5 mg/l. Nor was there any difference between the groups in regard to TxB2 synthesis after stimulation by these substances. The amount of TxB2 synthesized merely reflected the occurrence of reversible or irreversible platelet aggregation. Stimulation of platelets by AA induced by far the highest synthesis of TxB2. The generally decreased aggregability of platelets of newborn infants, compared with that in adults, was confirmed in this study. No effect of maternal smoking during pregnancy on the prostaglandin-dependent pathway of aggregation of cord blood platelets was demonstrated.