Neonatal antithrombin III deficiency

Antithrombin III Supplementation in a Premature Infant: Is There a Target Antithrombin Level?

The optimal antithrombin (AT) activity for low-molecular-weight heparin efficacy and the benefits of antithrombin III (ATIII) supplementation in premature infants diagnosed with venous thromboembolism are unknown. Currently, there are no neonatal-specific guidelines directing the appropriate target AT activity during supplementation. This case report describes a critically ill premature infant with a progressive, occlusive inferior vena cava thrombus who received supplemental ATIII during enoxaparin treatment. The patient did not achieve therapeutic anti-Xa levels despite increasing enoxaparin dosing to 3 mg/kg every 12 hours. ATIII supplementation sufficient to attain an AT activity of >40%, in combination with an enoxaparin dosing of >2 mg/kg every 12 hours, was needed to achieve therapeutic anti-Xa levels. Future large studies are needed to determine if there is an optimal target AT activity for critically ill premature infants.

Comparison of Bivalirudin Versus Heparin for Maintenance Systemic Anticoagulation During Adult and Pediatric Extracorporeal Membrane Oxygenation

OBJECTIVES

To provide a comparative analysis of conventional heparin-versus bivalirudin-based systemic anticoagulation in adult and pediatric patients supported on extracorporeal membrane oxygenation.

DESIGN

Retrospective chart review study of adult and pediatric patients receiving extracorporeal membrane oxygenation from January 1, 2014, to October 1, 2019.

SETTING

A large, high-volume tertiary referral adult and pediatric extracorporeal membrane oxygenation center.

PATIENTS

Four hundred twenty-four individuals requiring extracorporeal membrane oxygenation support and systemically anticoagulated with either unfractionated heparin (223 adult and 65 pediatric patients) or bivalirudin (110 adult and 24 pediatric patients) were included.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Digital data abstraction was used to retrospectively collect patient details. The majority of both groups were cannulated centrally (67%), and the extracorporeal membrane oxygenation type was predominantly venoarterial (84%). The adult bivalirudin group had a greater occurrence of heparin-induced thrombocytopenia (12% vs 1%; p < 0.01) and was more likely to require postcardiotomy extracorporeal membrane oxygenation (36% vs 55%; p < 0.01). There were no statistical differences between the groups in regards to age, sex, and extracorporeal membrane oxygenation initiation location. The main finding was a reduced mortality in the adult bivalirudin group (odds ratio, 0.39; p < 0.01), whereas no difference was noted in the pediatric group. A significant reduction in the composite transfusion requirement in the first 24 hours was noted in the pediatric bivaluridin group with an odds ratio of 0.28 (p = 0.02). Groups did not differ in regard to laboratories per day, anticoagulant dose adjustments, or ischemic complications.

CONCLUSIONS

When compared with heparin-based systemic anticoagulation, bivalirudin demonstrated feasibility and safety as established by the absence of increases in identifiable adverse outcomes while manifesting substantial improvements in hospital mortality in adult patients. Further studies are necessary to corroborate these findings and further elucidate the role of bivalirudin during extracorporeal membrane oxygenation support.

Role of platelets in neonatal necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is an inflammatory bowel necrosis of premature infants and is a leading cause of morbidity and mortality in infants born between 23 and 28 weeks of gestation. Fifty to 95% of all infants with NEC develop thrombocytopenia (platelet counts <150 × 109/L) within 24-72 h of receiving this diagnosis. In many patients, thrombocytopenia is severe and is treated with one or more platelet transfusions. However, the underlying mechanism(s) and biological implications of NEC-related thrombocytopenia remain unclear. This review presents current evidence from human and animal studies on the clinical features and mechanisms of platelet depletion in NEC. Anecdotal clinical experience is combined with evidence from laboratory studies and from an extensive literature search in databases PubMed, EMBASE, and Scopus and the electronic archives of abstracts presented at the annual meetings of the Pediatric Academic Societies. To avoid bias in identification of existing studies, key words were short-listed prior to the actual search both from anecdotal experience and from PubMed's Medical Subject Heading (MeSH) thesaurus. IMPACT: Fifty to 95% of infants with necrotizing enterocolitis (NEC) develop idiopathic thrombocytopenia (platelet counts <150 × 109/L) within 24-72 h of disease onset. Early clinical trials suggest that moderate thrombocytopenia may be protective in human NEC, although further work is needed to fully understand this relationship. We have developed a neonatal murine model of NEC-related thrombocytopenia, where enteral administration of an immunological stimulant, trinitrobenzene sulfonate, on postnatal day 10 induces an acute necrotizing ileocolitis resembling human NEC. In this murine model, thrombocytopenia is seen at 15-18 h due to platelet consumption and mild-moderate thrombocytopenia is protective.

Targeted inhibition of thrombin attenuates murine neonatal necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is an inflammatory bowel necrosis of premature infants and an orphan disease with no specific treatment. Most patients with confirmed NEC develop moderate-severe thrombocytopenia requiring one or more platelet transfusions. Here we used our neonatal murine model of NEC-related thrombocytopenia to investigate mechanisms of platelet depletion associated with this disease [K. Namachivayam, K. MohanKumar, L. Garg, B. A. Torres, A. Maheshwari, Pediatr. Res. 81, 817-824 (2017)]. In this model, enteral administration of immunogen trinitrobenzene sulfonate (TNBS) in 10-d-old mouse pups produces an acute necrotizing ileocolitis resembling human NEC within 24 h, and these mice developed thrombocytopenia at 12 to 15 h. We hypothesized that platelet activation and depletion occur during intestinal injury following exposure to bacterial products translocated across the damaged mucosa. Surprisingly, platelet activation began in our model 3 h after TNBS administration, antedating mucosal injury or endotoxinemia. Platelet activation was triggered by thrombin, which, in turn, was activated by tissue factor released from intestinal macrophages. Compared to adults, neonatal platelets showed enhanced sensitivity to thrombin due to higher expression of several downstream signaling mediators and the deficiency of endogenous thrombin antagonists. The expression of tissue factor in intestinal macrophages was also unique to the neonate. Targeted inhibition of thrombin by a nanomedicine-based approach was protective without increasing interstitial hemorrhages in the inflamed bowel or other organs. In support of these data, we detected increased circulating tissue factor and thrombin-antithrombin complexes in patients with NEC. Our findings show that platelet activation is an important pathophysiological event and a potential therapeutic target in NEC.

Updates in Pediatric Extracorporeal Membrane Oxygenation

Extracorporeal membrane oxygenation is an increasingly used mode of life support for patients with cardiac and/or respiratory failure refractory to conventional therapy. This review provides a synopsis of the evolution of extracorporeal life support in neonates, infants, and children and offers a framework for areas in need of research. Specific aspects addressed are the changing epidemiology; technologic advancements in extracorporeal membrane oxygenation circuitry; the current status and future direction of anticoagulation management; sedative and analgesic strategies; and outcomes, with special attention to the lessons learned from neonatal survivors.

Antithrombin replacement in neonates: is there any indication?

INTRODUCTION

Activation of the coagulation system and severe acquired antithrombin (AT) deficiency are common and prognostically important findings in sick and preterm neonates. It has been hypothesised that treatment of the acquired AT deficiency with AT concentrate may improve the outcome of conditions such as the neonatal respiratory distress syndrome (RDS), intracranial hemorrhage (ICH) and sepsis.

MATERIALS AND METHODS

We performed a systematic review of randomised controlled trials (RCTs) of AT replacement therapy in newborn infants.

RESULTS

Two full-length trial reports were found. Both were placebo-controlled. The first RCT examined the effects of AT therapy in 122 preterm infants with RDS. Administration of AT prolonged rather than shortened the duration of mechanical ventilation and oxygen therapy. The second RCT determined whether AT replacement decreased the incidence of ICH in 60 preterm infants who were born before 30 weeks of gestation. No beneficial effect on ICH was found.

CONCLUSIONS

Preterm infants with RDS do not benefit from therapy with AT concentrate and may be harmed. There is also little evidence that the administration of AT reduces the risk of ICH. The role of AT replacement during neonatal sepsis remains uncertain.

Antithrombin deficiency: issues in laboratory diagnosis

OBJECTIVE

To review the current understanding of the pathophysiology of antithrombin deficiency and its role in congenital thrombophilia. Recommendations for diagnostic testing of antithrombin function and concentration, derived from the medical literature and consensus opinions of recognized experts in the field, are included. These recommendations specify whom, how, and when to test.

DATA SOURCES

Review of the published medical literature.

DATA EXTRACTION AND SYNTHESIS

A summary of the medical literature and proposed testing recommendations were prepared and presented at the College of American Pathologists Conference XXXVI: Diagnostic Issues in Thrombophilia. After discussion at the conference, consensus recommendations presented in this article were accepted after a two-thirds majority vote by the participants.

CONCLUSIONS

Antithrombin deficiency is an infrequent genetic abnormality that may be a significant contributing cause of thrombophilia. Antithrombin deficiency also may be observed in conjunction with other genetic or acquired risk factors. Assay of antithrombin plasma levels is appropriate in the laboratory evaluation of individuals with thrombophilia, preferably using a functional, amidolytic antithrombin assay. The diagnosis of antithrombin deficiency should be established only after other acquired causes of antithrombin deficiency, such as liver disease, consumptive coagulopathy, or heparin therapy, are excluded. A low antithrombin level should be confirmed with a subsequent assay on a fresh specimen, and family studies may be helpful to establish the diagnosis. Antigenic antithrombin assays may be of benefit in subclassification of the type of antithrombin deficiency and to confirm the decreased antithrombin level in patients with type I deficiency.

Development of coagulation regulatory proteins in the fetal and neonatal lamb

To investigate the development of coagulation regulatory proteins-protein C (PC), protein S (PS), and antithrombin (AT)-in relationship to the procoagulant protein factor X (FX), a chronically catheterized fetal ovine model was used. Infusion and sampling catheters were placed into pregnant ewes and their fetuses and maintained from mid-gestation. From a total of 110 fetuses, 17 lambs, and 63 ewes that were studied on one to 15 occasions, 212 fetal, 88 neonatal, and 157 maternal samples were obtained. Liver tissue was obtained from 31 fetuses and 15 ewes. Plasma levels of all proteins studied were higher in the ewe than in the fetus (p < 0.0001). Plasma levels of FX, PC, and PS achieved neonatal levels by mid-gestation with mild but significant decreases during mid- and late gestation. Fetal and early neonatal plasma concentrations of these vitamin K-dependent proteins fit a model with both quadratic (p < 0.01) and linear (p < 0.01) components. The discrepant levels in mRNA relative to plasma concentration were consistent with regulatory control beyond the level of transcription. In contrast, a simple linear increase in plasma protein levels was determined for the vitamin K-independent coagulation regulatory protein, AT (p for quadratic component > 0.05). This study suggests that fetal regulation of coagulation proteins follows characteristic patterns relative to the vitamin K dependence of the protein rather than its role as a procoagulant versus regulatory protein.

Low preoperative antithrombin activity causes reduced response to heparin in adult but not in infant cardiac-surgical patients

We evaluated the interaction of preoperative antithrombin (AT) activity and intraoperative response to heparin in cardiac surgery. Heparin anticoagulation is essential during cardiopulmonary bypass (CPB). Heparin itself has no anticoagulant properties, however it causes a conformational change of the physiologic plasma inhibitor AT that converts this slow-acting serine protease inhibitor into a fast acting one. Thus, adequate AT activity is a prerequisite for sufficient heparin anticoagulation. AT activity is reduced by long-term heparin therapy. This prospective, observational study investigated 1516 consecutive cardiac-surgical patients (1304 patients >1 yr (Group A) and 212 patients < or = 1 yr (Group I)). AT activity was measured the day before surgery by a chromogenic substrate assay. The celite-activated activated clotting time (ACT) was used to guide intraoperative heparin administration. Heparin sensitivity was calculated and the postoperative blood loss and perioperative blood requirement was recorded. Infant patients had significantly less preoperative AT activity compared with older patients: 84 (33)% vs 97 (17)%, median (interquartile range) (P < 0. 05). The subgroup of patients aged <1 mo (n = 64) demonstrated a preoperative AT activity of 56 (27)% as compared with 90 (23)% in infant patients between one month and one year (n = 148). In adult patients, preoperative AT activity depended predominantly on preoperative heparin treatment: 62% of the patients with an AT activity <80% were pretreated with heparin. Five minutes after heparin but before CPB the ACT was 587 (334) s in Group A patients with AT activity > or = 80%, and 516 (232) in patients with AT activity < or = 80% (P < 0.05). The target ACT of 480 s was achieved in 70% of patients with normal AT activity in Group A compared with only 54% of patients with AT activity <80% (P < 0.05). In Group A patients with decreased AT activity, 18% demonstrated an inadequate ACT response-defined as ACT <400 s-to the first bolus injection of heparin. In Group I, preoperative AT activity did not influence the ACT response (ACT 5 min after heparin: 846 [447] s in patients with AT activity > or = 80% vs 1000 [364] s in patients with decreased AT activity). The heparin sensitivity was 2.4 (1.1) s/unit heparin/kg compared with 1.5 (0.8) s/unit heparin/KG in group A (P < 0.05). These results suggest that preoperative diminished AT activity causes reduced response to heparin in adult but not in infant patients. Infant patients demonstrate a higher heparin sensitivity despite lower preoperative AT activity. Measurement of preoperative AT activity identifies adult patients at risk of reduced sensitivity to heparin.

IMPLICATIONS

In patients less than one year of age, low antithrombin (AT) activity is caused by the immature coagulation system. Despite low AT activity, these young patients demonstrate a normal or increased response to heparin anticoagulation before cardiopulmonary bypass (CPB). In contrast, in patients older than one year of age and adult patients decreased preoperative AT activity is mainly caused by preoperative heparin therapy and causes insufficient response to heparin anticoagulation with a standard heparin dosage. Measurement of preoperative AT activity identifies patients at risk of inadequate anticoagulation during CPB.

Heparin and the risk of intraventricular hemorrhage in premature infants

OBJECTIVE

This study was carried out to determine whether the routine use of low-dose heparin in umbilical catheter infusates increases the risk of intraventricular hemorrhage or alters the coagulation profile in premature infants.

METHODS

In a randomized, blinded trial, 113 infants born at less than 31 weeks' gestation were assigned to receive, in their umbilical catheter infusate, either 1 unit of heparin per milliliter (n = 55) or no heparin (n = 58). Prothrombin time, activated partial thromboplastin time, fibrinogen concentration, and antithrombin III activity levels were determined at the start and the completion of the study. Cranial ultrasonography was performed during the first week of life.

RESULTS

There was no difference in the incidence of intraventricular hemorrhage between the heparin and no heparin groups, 35.8% and 31.5%, respectively (p = 0.6). Similarly, no difference was detected in the incidence of severe intraventricular hemorrhage (grades III/IV). Prothrombin time, activated partial thromboplastin time, and fibrinogen levels were not significantly different between the two groups. However, the use of heparin was associated with a lower antithrombin III activity level. Antenatal indomethacin use was associated with a 2.9 increased risk of intraventricular hemorrhage (95% confidence interval, 1.15 to 7.17).

CONCLUSION

A low dose of heparin added to umbilical catheter infusates does not increase the incidence or severity of intraventricular hemorrhage or significantly alter the coagulation profile in premature infants.

Central venous thrombosis after cardiac operations in children

To evaluate the incidence, mortality, late outcome, and cause of central venous thrombosis after pediatric heart operations and other operations performed with cardiopulmonary bypass, we identified patients with postoperative central venous thrombosis during a 10-year period at a single pediatric hospital. There had been 1591 open heart (with bypass) and 1086 closed heart (no bypass) procedures and 13 operations with cardiopulmonary bypass for extracardiac indications. There were 20 patients with central venous thrombosis, yielding incidences of 1.1% and 0.2% after cardiopulmonary bypass and after closed heart operations, respectively. When neonates were compared with older children (1 to 119 months of age) undergoing heart procedures, a tenfold increase (5.8% vs 0.6%) (p < 0.001) in the incidence of central venous thrombosis was observed. The mortality was eight of 20 (40%). Central venous thrombosis contributed to seven deaths and it was a direct cause of one death. Ten patients were reinvestigated 5 to 108 months after central venous thrombosis. The outcome of surgery was excellent in eight. Two had residual thrombosis, but this was not hemodynamically significant to the cardiorespiratory condition of the patients. During or preceding thrombosis, low levels of antithrombin III and/or protein C and high levels of the plasminogen activator inhibitor were observed in five of the patients. A congenital thrombotic risk factor, "resistance to activated protein C," was found in two of 12 tested patients with central venous thrombosis (17%). In conclusion, central venous thrombosis, especially in neonates, is an important cause of morbidity and mortality after cardiac operations. The cause is multifactorial, with contributions from multiple acquired thrombophilic coagulation abnormalities, and resistance to activated protein C may act as a risk factor for thrombosis already during neonatal period.

Fibrinolysis, antithrombin III, and protein C in neonates during cardiac operations

Fibrinolysis and coagulation were studied in 10 neonates undergoing cardiac operations for congenital heart defects. Coagulation was activated during cardiopulmonary bypass as evidenced by highly increased prothrombin fragment 1 + 2 levels compared with preoperative values. Prothrombin fragment 1 + 2 levels remained elevated until postoperative day 3. Unlike coagulation, fibrinolysis was not activated during cardiopulmonary bypass but did show late activation on postoperative day 3, as evidenced by elevated levels of the fibrin degradation product D-dimer. Lack of fibrinolytic activation during bypass and its appearance on postoperative day 3 were partly explained by changes observed in tissue plasminogen activator and its inhibitor. During bypass, levels of tissue plasminogen activator and its inhibitor increased by 3.4-fold and 3.2-fold, respectively. In the postoperative period, levels of plasminogen activator inhibitor normalized rapidly whereas tissue plasminogen activator remained elevated, resulting in late fibrinolytic activation on postoperative day 3. In accordance with elevated prothrombin fragment 1 + 2, platelet count, antithrombin III, protein C, prothrombin, and factor VII were decreased on postoperative day 2, indicating ongoing consumptive coagulopathy. Nine patients had antithrombin III and six had protein C levels below age-specific normal ranges, consistent with an acquired deficiency state. Three had central venous thrombosis by postoperative day 4 or 5. In all three, thrombosis was preceded by antithrombin III deficiency, protein C deficiency, and highly elevated plasminogen activator inhibitor (3.7 to 37 times the mean of the other patients) on postoperative days 1 to 3. In conclusion, cardiopulmonary bypass in neonates caused rapid and profound alterations in the coagulation and fibrinolytic systems and initiated consumptive coagulopathy lasting until at least postoperative day 3. Thrombophilic abnormalities in antithrombin III, protein C, and fibrinolysis were frequently found and were associated with serious thrombotic complications.

Bleeding and use of blood products after heart operations in infants

Recent studies have suggested that postoperative bleeding is decreased in pediatric heart operations if fresh whole blood instead of blood component therapy is used for postoperative transfusions. Because this is in contrast to our practice to use whole blood for only the priming of the cardiopulmonary bypass circuit and then to use blood components for additional transfusion requirements, it was our interest to analyze the bleeding complications and the use of blood products after heart operations in infants. The patient records of the 73 infants operated on in 1992 were reviewed. The chest tube drainage varied from 3 to 51 ml/kg per 6 hours (mean 10 ml/kg) and it did not correlate with any of the tested clinical or laboratory parameters. One infant underwent reoperation because of surgical bleeding. Disseminated intravascular coagulation developed in another patient. Sixty-eight patients (93%) needed red blood cell supplementation. Sixty-eight percent of patients between 1 month and 1 year old could be treated without any other postoperative transfusion except for red blood cell supplementation. In contrast, in the neonates, platelet concentrates or fresh frozen plasma, or both, were used in 61% of the patients. In addition to the known immaturity of the hemostatic system, the increased need for platelet concentrates in the neonates was attributed to longer cardiopulmonary bypass time, deeper hypothermia in association with circulatory arrest, larger dosages of heparin, and more extensive plasma dilution during cardiopulmonary bypass. In conclusion, a low rate of bleeding complications and acceptably low general blood loss can be achieved postoperatively with blood component therapy.