Thrombosis in Children: Current Perspective and Distinct Challenges

Deep Vein Thrombosis of the Left Lower Limb in a Sudanese Child with Sickle Cell Disease

This is a case of an eleven-year-old female Sudanese child, a known Sickle Cell Anemia (SCA) patient, who presented with fever, as well as left thigh and leg swelling that was associated with pain and warmness, which was diagnosed as Deep Vein Thrombosis (DVT) of her left lower limb. She had a previous history of admissions to the emergency room, during which she once received blood. The patient was managed by carrying out a basic routine initial laboratory investigation. A Doppler ultrasound scan showed features consistent with DVT. Based on the clinical findings and investigation results, management began by providing the patient with intravenous fluid, analgesia, packed Red Blood Cells (RBCs), intravenous antibiotics, and low-molecular-weight heparin. Further consultations showed that there was no need for vascular surgery or surgical intervention. This case highlights the need for more studies on DVT and Venous Thromboembolism (VTE) complications in children with SCA, so as to develop strategies for diagnosis and management in order to reduce the risk of life-threatening complications of VTE in patients with Sickle Cell Disease SCD.

Tissue Plasminogen Activator Use in Pediatric Patients: A Single Center Experience

INTRODUCTION

Thrombosis is rare in children and antithrombolytic treatment is controversial. Most commonly used thrombolytic agent is tissue plasminogen activator (t-PA) in pediatrics. In this study, we report our experience in the use of thrombolytic treatment.

METHODS

Eighteen patients who had received systemic t-PA between January 2006 and December 2013 were recorded. The response to t-PA was evaluated as complete, partial, and no. The bleeding complication during t-PA administration was graded as minor or major.

RESULTS

There were 18 patients (2 mo to 12 y) who received systemic t-PA. Three patients had venous, 14 patients had arterial, and 1 patient had intracardiac thrombosis. Thrombosis was related to cardiac catheterization (61.1%), central venous catheterization (16.7%), cardiac surgery (11.1%), and arrhythmia (5.5%). In 1 patient thrombosis occurred spontaneously (5.5%). Eighteen patients received 25 courses of systemic t-PA (0.15 to 0.3 mg/kg/h). A total of 55.6% of cases had complete, 27.8% had partial, and 16.6% showed no resolution.

CONCLUSION

t-PA infusion at doses of median 0.2 mg/kg/h (0.15 to 0.3) seems effective and safe. There is still no consensus on indications and dosing of antithrombolytic treatment in children but in selected patients it decreases long-term complications due to thrombosis.

Pediatric Hospital Acquired Venous Thromboembolism

Pediatric hospital acquired venous thromboembolism (HA-VTE) is an increasing problem with an estimated increase from 5.3 events per 10,000 pediatric hospital admissions in the early 1990s to a current estimate of 30-58 events per 10,000 pediatric hospital admissions. Pediatric HA-VTE is associated with significant morbidity and mortality. The etiology is multifactorial but central venous catheters remain the predominant risk factor. Additional HA-VTE risk factors include both acquired (recent surgery, immobility, inflammation, and critical illness) and inherited risk factors. Questions remain regarding the most effective method to assess for HA-VTE risk in hospitalized pediatric patients and what preventative strategies should be implemented. While several risk-assessment models have been published in pediatric patients, these studies have limited power due to small sample size and require prospective validation. Potential thromboprophylactic measures include mechanical and pharmacologic methods both of which have associated harms, the most significant of which is bleeding from anticoagulation. Standard anticoagulation options in pediatric patients currently include unfractionated heparin, low molecular weight heparin, or warfarin all of which pose a monitoring burden. Ongoing pediatric studies with direct oral anticoagulants could potentially revolutionize the prevention and treatment of pediatric thrombosis with the possibility of a convenient route of administration and no requirement for monitoring. Further studies assessing clinical outcomes of venous thromboembolism (VTE) prevention strategies are critical to evaluate the effectiveness and harm of prophylactic interventions in children. Despite HA-VTE prevention efforts, thrombotic events can still occur, and it is important that clinicians have a high clinical suspicion to ensure prompt diagnosis and treatment to prevent further associated harms.

Overview of Heparin and Protamine Management and Dosing Regimens in Pediatric Cardiac Surgical Patients

Compared with adults, infants and children who undergo cardiopulmonary bypass for cardiac surgery present with a myriad of anticoagulation considerations. Inadequate anticoagulation during cardiopulmonary bypass may cause “subclinical” or “overt” thrombosis, while effective anticoagulation decreases excessive bleeding and transfusions. Current strategies for heparinization and its neutralization in pediatric patients undergoing congenital heart repair requiring cardiopulmonary bypass are examined. The coagulation system of the neonate and infant is immature and is further weakened by congenital heart disease. Changes in coagulation and fibrinolytic activity occur during cardiopulmonary bypass as a result of hemodilution and exposure of the blood to the extracorporeal circuit. Adequate anticoagulation is essential to minimize the thrombin generation that will result. The extent of excessive thrombin formation in pediatric patients undergoing cardiopulmonary bypass is better appreciated today than in the past, but no controlled study defines the optimal dose or technique for heparin dosing in these patients. Heparin concentration may even fall to 1.5 U/mL during cardiopulmonary bypass. However, the activated clotting time and heparin concentration correlate poorly. The ideal method to achieve adequate thrombin inhibition is unknown. Additionally, the dangers of excessive protamine are becoming more apparent. Heparin continues to be the most effective agent to achieve anticoagulation and protamine the most effective agent to neutralize it. A technique for heparin and protamine dosing with determination of heparin concentrations, may remove many variables associated with pediatric cardiac surgery that requires cardiopulmonary bypass and may provide clinicians with new therapies to achieve better anticoagulation for patients and consequently better outcomes.

Evaluation and Management of Patients With Thrombotic Thrombocytopenic Purpura

Thrombotic thrombocytopenic purpura (TTP) describes syndromes with multiple etiologies, some of which are rapidly fatal without plasma exchange treatment. Although there have been advances in understanding the pathogenesis of TTP, evaluation and management remain difficult because there are no specific diagnostic criteria, as TTP can be clinically similar to other acute disorders, such as sepsis, disseminated malignancy, malignant hypertension, and preeclampsia, and because urgent treatment is required. An unexpected observation of anemia and thrombocytopenia should trigger consideration of TTP; evidence that the anemia is due to microangiopathic hemolysis, suggested by the presence of red cell fragmentation on the blood smear, supports the diagnosis. When the diagnostic criteria of microangiopathic hemolytic anemia and thrombocytopenia without an apparent alternative etiology are fulfilled, plasma exchange treatment is appropriate. However, plasma exchange has risks for severe complications and death; therefore, this management decision must be balanced against the confidence in the diagnosis. With plasma exchange treatment, approximately 80% of patients survive, in contrast to only 10% in the era prior to the availability of plasma exchange. The continuing mortality from TTP, the risks of plasma exchange treatment, and the potential for recurrent episodes of TTP are clinical challenges that remain to be solved.

Thromboembolism and anticoagulation management in the preterm infant

The incidence of preterm thromboembolism has been increasing due to advances in diagnostic imaging which allow better detection of thrombi in sick preterm infants. At the same time, improvement in neonatal intensive care unit supportive care has increased the number of surviving and living preterm infants with thromboembolic risk factors. Disruption in the fine balance of hemostasis with potential risk factors, specifically septicemia and indwelling catheters, increase the occurrence of thromboembolic events. Treatment strategies in preterm infants are challenging due to limited data.

Deep venous thrombosis in children with sickle cell disease

BACKGROUND

Deep venous thrombosis (DVT) is rare in children compared to adults. Its incidence and risk factors in children are not well known. This study determined these aspects of DVT in children with sickle cell disease (SCD).

PROCEDURE

A retrospective, observational and descriptive study was performed. Patients born between October 2000 and October 2012 with SCD and registered in HEMORIO, including those who died in HEMORIO, were included in this study. Patients whose medical records were inaccessible, who died in institutions other than HEMORIO, who died with implanted deep venous catheters, and those who were not monitored in HEMORIO for a period of 1 year or more were excluded from the study. Of a total of 1,519 patients, 456 were excluded and 1,063 patients were included in the study. Data were obtained from the computer system and the medical records at HEMORIO.

RESULTS

Of the 1,063 patients, 2 (0.2%) developed DVT with both cases being related to central venous catheters (CVCs) (P-value <0.001). Of the patients who required CVCs, the prevalence of DVT was 10%. No other variable was clinically or statistically significant with respect to DVT.

CONCLUSION

The establishment of CVCs in children with SCD poses a high risk for DVT. If this procedure is necessary, the internal jugular vein should be utilized instead of the subclavian and femoral veins. The identification of associated risk factors may justify antithrombotic prophylaxis.

Chebulagic acid inhibits the LPS-induced expression of TNF-α and IL-1β in endothelial cells by suppressing MAPK activation

Inflammatory response in the vasculature, including the overexpression of tumor necrosis factor (TNF)-α and interleukin (IL)-1β, has been demonstrated to increase the risk of thrombosis development. Chebulagic acid (CA) is a key chemical component in the traditional Mongolian anti-thrombotic drug Garidi-13, and has been suggested to exert anti-inflammatory and anti-infective effects. The present study aimed to evaluate the regulatory impact of CA on a number of biological processes, including lipopolysaccharide (LPS)-induced inflammation, LPS-promoted mitogen-activated protein kinase (MAPK) activation and the expression of toll-like receptor (TLR)4 in EA.hy926 human endothelial cells. The results indicated that CA significantly inhibited the LPS-induced upregulation of TNF-α and IL-1β in a dose- and time-dependent manner. Furthermore, LPS-activated MAPK signaling was inhibited by CA treatment in the EA.hy926 cells. However, TLR4, which serves a key function in LPS-induced inflammation as the receptor of LPS, was not regulated by the CA treatment. In summary, the results of the present study indicate that CA inhibits the LPS-induced promotion of TNF-α and IL-1β in endothelial cells by suppressing MAPK activation, which may contribute to the anti-thrombotic effect of Garidi-13.

Elevated lipoprotein(a) in a newborn with thrombosis and a family history of dyslipidemia

This paper reports a rare case of elevated lipoproteinemia(a) that evolved into thrombosis during the neonatal period. During the first days of life, the patient presented with an intracardiac thrombus, pulmonary thromboembolism and a hemorrhagic stroke. Initially, the results of the blood tests performed to screen for thrombophilic diseases were normal for the patient's age. The maternal dyslipidemia and the family's positive history of thromboembolism drew attention to an underlying, inherited, thrombophilic defect. Upon further investigation of the thrombophilia, the increase in lipoprotein(a) levels found in the mother and infant enabled the diagnosis of hyperlipoprotein(a) and the administration of appropriate therapy.

Retrospective evaluation of antithrombin III supplementation in neonates and infants receiving enoxaparin for treatment of thrombosis

BACKGROUND

Thromboembolic events are occurring at increasing rates in neonates and infants. At Children's Mercy Hospitals and Clinics, antithrombin III (AT3) concentrates are often used in combination with enoxaparin to supplement physiologically low AT3 levels. Theoretically, AT3 enhances the anticoagulant activity of enoxaparin and results in decreased time to therapeutic anti-Xa levels. No data exist on use of AT3 for this indication.

PROCEDURE

This retrospective study compared time to therapeutic anti-Xa levels in patients <1 year of age receiving enoxaparin with AT3 (Group 1) and without AT3 (Group 2) for treatment of thrombosis. Primary objective was to compare time to therapeutic anti-Xa levels (0.5-1 U/ml) between groups. Secondary objectives included comparison of the initial and therapeutic dose of enoxaparin, enoxaparin dose changes, AT3 supplementation, and level monitoring. Bleeding events and cost were also evaluated. Statistical tests included Schuirmann's two one-sided tests for equivalence and general linear models/logistic regression for independent effects of age, critical illness, and timing of AT3.

RESULTS

Mean time to therapeutic anti-Xa levels were not equivalent between Groups 1 and 2 (80.7 vs. 65.2 hours; P = 0.28). Initial enoxaparin dose and number of dose changes were equivalent. Group 1 required higher doses of enoxaparin to achieve therapeutic anti-Xa levels. Age, critical illness, and timing of AT3 had no effect on time to therapeutic anti-Xa levels. Bleeding events were not equivalent between Groups 1 and 2 (14.3% vs. 3.9%; P = 0.55).

CONCLUSION

Supplementation with AT3 did not decrease time to therapeutic anti-Xa levels, added significant cost, and was associated with increased bleeding events.

Thrombophilia testing in children: a 7 year experience

BACKGROUND

Incidence of venous thromboembolism (VTE) in children is reported to be increasing. We examined thrombophilia testing results in children with VTE that presented in inpatient and outpatient settings to explore patterns of thrombophilia testing.

PATIENTS/METHODS

Children, ages 0-20 years with VTE seen at our institution from Jan 2005 to Apr 2012 were studied retrospectively. All patients with VTE confirmed by imaging were eligible and the presence of significant risk factors was evaluated. Thrombophilia was diagnosed if >1 tests confirmed: persistently low protein C (PC), protein S (PS), and antithrombin (AT) following VTE resolution, persistent antiphospholipid antibodies (APA) positivity >12 weeks from first test, factor V Leiden (FVL) and prothrombin mutation (PTm) hetero- or homozygosity, elevated plasminogen activator inhibitor (PAI-1) levels with 4G/5G or 4G/4G polymorphisms, methylene tetrahydrofolate reductase (MTHFR) polymorphisms with elevated fasting homocysteine levels.

RESULTS

Three hundred ninety-two patients met inclusion criteria. At least one test was ordered in 157/239 inpatients. All 153 outpatients had >1 test ordered. Thrombophilia rate differences between inpatients and outpatients did not reach statistical significance except for PC deficiency, which was significantly higher in outpatients. Of inpatients, central venous line (CVL) was significantly associated with not having tests done (P < 0.0022).

CONCLUSIONS

This study of pediatric VTE demonstrated a low thrombophilia rate in both inpatient and outpatient populations. The role of testing in other pediatric patients should be further explored.

Current and future antithrombotic agents in children

Thromboembolic complications are increasing in children, and the use of anticoagulation has seen a dramatic increase despite the lack of randomized clinical trials. The most widely used agents in children are heparin and warfarin, however these agents have limitations that are exaggerated in children. This has led to the use of newer agents with improved pharmacologic properties such as low-molecular-weight heparin, however, the use of novel agents such as direct thrombin inhibitors has been limited to case reports. These agents, however, have potential advantages over heparin, low-molecular-weight heparin and warfarin. Current clinical trials are in progress to define the proper dose of two such agents--argatroban (Argatroban, GlaxoSmithKline) and bivalirudin (Angiomax, The Medicines Company). The selective Factor Xa inhibitor fondaparinux (Arixtra, Sanofi-Synthelabo) has not been used in children; however, there are situations in which this agent may be advantageous. This review will discuss the currently available agents, with an emphasis on those that are novel and their potential uses in children.

An unusual presentation of May-Thurner syndrome in a pediatric patient with a pelvic kidney

We report a case of an adolescent who presented with a deep vein thrombosis (DVT) and clinical findings consistent with May-Thurner Syndrome. Specific imaging demonstrated direct compression of the left common iliac vein by an overlying pelvic kidney. The patient's history and clinical presentation is detailed. The discussion focuses on the potential implications for care and management of a patient with an ectopic left pelvic kidney.

Successful treatment of arterial thrombus in an extremely low-birth-weight preterm neonate

Arterial thromboembolism in the pediatric population frequently occurs secondary to arterial catheterization. Catheterization-related complications are more common in smaller and sicker infants, due to high prothrombotic activity, low levels of natural anticoagulants, and various fibrinolytic imbalances. Arterial thrombus management in neonates remains controversial. Recombinant tissue plasminogen activator is the most commonly used thrombolytic agent in children, however there is very little experience with recombinant tissue plasminogen activator therapy in small prematures, especially in the first week of life. This case study reports catheter-related femoral artery occlusion in an extremely low-birth-weight preterm infant. Despite continuous heparin infusion for 6 hours, no resolution of the thrombus was seen by clinicians. Heparin was stopped, and recombinant tissue plasminogen activator therapy enabled complete recovery from the thrombus. The risk of bleeding (including intracranial hemorrhage) with recombinant tissue plasminogen activator treatment, especially in small preterm neonates is unknown. However, in this extremely low-birth-weight preterm infant, recombinant tissue plasminogen activator therapy was effective, and limiting the infusion rate to ≤0.4 mg/kg/hour was safe.

Assessment of the standard pediatric unfractionated heparin dosing protocol

Current dosing guidelines for unfractionated heparin therapy in pediatric patients are based on recommendations of only one study that evaluated a weight-based dosing nomogram. To test the hypothesis that adhering to a strict weight-based nomogram yields better therapeutic results in pediatric patients, we prospectively monitored 25 consecutive pediatric patients who received unfractionated heparin based on the nomogram, and compared them to control patients whose treatment did not follow the standard nomogram. The mean time needed to achieve the target activated partial thromboplastin time was significantly shorter in the study group than the control group (18.32 ± 9.98 vs. 43.8 ± 30 h). A higher proportion of the study group reached the target activated partial thromboplastin time at 12, 24, and 36 h, compared to controls: 44% vs. 6%, 72% vs. 28%, 100% vs. 58%, respectively. Within the study group, patients under 1 year of age needed more time to achieve the target activated partial thromboplastin time than those over 1-year old. The performance of the standard dosing nomogram was excellent with regard to early anticoagulation target achievement, without increasing the risk of bleeding. Further studies are warranted to refine this nomogram for pediatric patients who are less than 1-year old.

Hematology and Oncology in Critical Illness

This chapter will focus on a variety of hematologic issues pertinent to the care of critically ill children. This is an area of intense research with the pathophysiology underlying these clinical conditions becoming progressively better understood. This improved understanding has resulted in new therapeutic strategies that are being assessed in multicenter clinical trials. The chapter will begin by describing the incidence and pathophysiologic significance of anemia in the pediatric intensive care unit (PICU) providing a differential diagnosis of the many conditions that may present with anemia in this setting. The chapter will next consider disseminated intravascular coagulation (DIC) focusing on the pathophysiology of a condition that has been associated with much morbidity and mortality. The underlying conditions predisposing to DIC will be detailed as well as a number of treatment options that have been implemented in clinical trials. In addition to DIC, thrombocytopenia may be caused by a number of other clinical conditions important to the pediatric critical care provider. The clinical and prognostic significance of thrombocytopenia will be addressed and a focused differential diagnosis will be provided. Thrombotic disorders are becoming increasingly recognized in children and are a particular concern for the pediatric intensivist. The epidemiology of thromboembolism in children will be reviewed focusing on the conditions most commonly associated with these thromboses. Finally, a chapter on hematologic issues in the critically ill child would not be complete without a discussion of sickle cell disease. Acute chest syndrome, one of the most frequent complications of sickle cell disease resulting in the need for intensive care services, will be discussed in detail.

Anticoagulation and coagulation management for ECMO

Advances in extracorporeal membrane oxygenation (ECMO) management have helped to reduce complications compared with its inception but they remain high. The principal causes of mortality and morbidity are bleeding and thrombosis. The nonbiologic surface of an extracorporeal circuit provokes a massive inflammatory response leading to consumption and activation of procoagulant and anticoagulant components. The vast differences in neonatal and adult anticoagulation and transfusion requirements demands tremendous clinical knowledge to provide the best care. Increased use of thrombelastogram will complement other methods currently being used to improved care. Methods to recognize the level of thrombin formation at the bedside could help reduce neurologic complications. ECMO requires a multidisciplinary team approach to achieve the best outcomes.

Defining the role of recombinant activated factor VII in pediatric cardiac surgery: where should we go from here?

OBJECTIVES

Postoperative hemorrhage is a recognized complication of pediatric cardiac surgery. Both the immature coagulation system and increased susceptibility to hemodilution increase the likelihood of pediatric patients developing coagulopathy when compared with adult counterparts. Treatment options remain limited. Recombinant factor VII (rFVIIa) is a hemostatic agent increasingly used to reduce hemorrhage in other surgical settings, the role of which is unclear in this population. This article systematically reviews the published literature on the use of rFVIIa in pediatric cardiac surgery.

DATA SOURCES AND STUDY SELECTION

A systematic literature search identified reports of rFVIIa administration in pediatric patients undergoing cardiac surgery. Where possible, individual patient-specific data were extracted and pooled statistical analysis was performed.

DATA EXTRACTION AND SYNTHESIS

Twenty-nine articles reporting on the administration of rFVIIa to 169 patients were identified. rFVIIa has been administered to patients with predefined congenital abnormalities of hemostasis to arrest hemorrhage refractory to other interventions and prophylactically in the hope of reducing blood loss. Treatment regimens vary widely, in terms of both first and cumulative dose. Data on chest tube blood loss and two markers of coagulation were pooled and analyzed, and significant improvements were demonstrated. Mortality was 4.4% for the entire cohort but 20% of patients on extracorporeal membrane oxygenation suffered significant thromboembolic complications.

CONCLUSIONS

rFVIIa has an increasingly accepted role in the management of patients with congenital coagulopathies undergoing major surgery. However, randomized trials are required to define the role of rFVIIa as an adjunct to control major hemorrhage in the pediatric cardiac surgical population. Any future work must focus not only on benefits but also on patient safety, particularly, risk of morbid thromboembolic complication.

Pulmonary thrombosis as the first manifestation of systemic lupus erythematosus in a 14-year-old boy

We describe the case of a 14-year-old boy who presented with pulmonary embolism and who was subsequently found to have nephrotic syndrome due to lupus membranous nephropathy. He had no other signs of nephrotic syndrome or of systemic lupus erythematosus, such as edema or circulating lupus anticoagulants (antiphospholipid or anticardiolipin antibodies), and no hereditary coagulopathy. This case contributes to our understanding of unusual clinical presentations of systemic lupus erythematosus in children.

Clinical outcomes after platelet transfusions in patients with thrombotic thrombocytopenic purpura

BACKGROUND

Reports of deterioration and death after platelet (PLT) transfusions in patients with thrombotic thrombocytopenic purpura (TTP) have led to recommendations that they should not be given except for life-threatening hemorrhage.

STUDY DESIGN AND METHODS

Published reports of PLT transfusions in patients with TTP were systematically reviewed and data from the Oklahoma TTP-HUS Registry, an inception cohort of 382 consecutive patients, 1989 through 2007, were analyzed.

RESULTS

A systematic review identified 34 publications describing outcomes of patients with TTP after PLT transfusions: 9 articles attributed complications to PLT transfusions, 4 suggested that they may be safe, and 21 articles did not comment about a relation between PLT transfusions and outcomes. Fifty-four consecutive patients from the Oklahoma TTP-HUS Registry were prospectively analyzed. ADAMTS13 activity was less than 10 percent in 47 patients; also included were 7 patients whose activity was not measured but who may have been deficient. Thirty-three (61%) patients received PLT transfusions. The frequency of death was not different between the two groups (p = 0.971): 8 (24%) patients who received PLT transfusions died (thrombosis, 5; hemorrhage, 1; sepsis, 2) and 5 (24%) patients who did not receive PLT transfusions died (thrombosis, 4; hemorrhage, 1). The frequency of severe neurologic events was also not different (p = 0.190): 17 (52%) patients who received PLT transfusions (in 5 of these 17 patients, neurologic events only occurred before PLT transfusions) and 7 (33%) patients who did not receive PLT transfusions.

CONCLUSION

Evidence for harm from PLT transfusions in patients with TTP is uncertain.

Prevention and management of central venous catheter occlusion and thrombosis in children with cancer

BACKGROUND

The views and clinical practice of children's cancer units were surveyed regarding management of central venous catheter (CVC) occlusion (CVC-occlusion), CVC-related thrombosis (CVC-thrombosis) and thromboembolism (CVC-thromboembolism).

PROCEDURE

A questionnaire was sent to all 22 United Kingdom Children's Cancer Study Group centres, requesting information about their views of the importance of, and their practices regarding, prophylaxis, diagnosis and treatment of CVC-occlusion/thrombosis.

RESULTS

Twenty (91%) centres responded. Eighty percent, 80% and 70%, respectively, stated that CVC-occlusion, CVC-thrombosis and CVC-thromboembolism were clinically important concerns. All centres used heparinised saline flushes as prophylaxis against CVC-occlusion, with little variation (</=30% centres) in frequency, volume and heparin concentration. Symptoms or signs suggesting partial CVC-occlusion, total CVC-occlusion, or CVC-thrombosis/thromboembolism were always investigated in 20%, 55% and 85% of centres, respectively, but with considerable variability in the nature and sequence of investigations performed, which included (depending on the clinical scenario) chest X-ray, contrast linography or venography, ultrasonography, echocardiography and magnetic resonance venography. A fibrinolytic lock was administered before investigation of CVC-occlusion in 75% of centres. Although 45%, 60% and 80%, respectively, always treated partial CVC-occlusion, total CVC-occlusion or CVC-thrombosis/thromboembolism, the type and order of treatments differed greatly between centres, especially for CVC-thrombosis/thromboembolism, in which CVC removal, systemic anticoagulation (heparin or warfarin), local or systemic fibrinolysis, or thrombectomy were performed in at least some centres.

CONCLUSIONS

The clinical practice of UKCCSG centres regarding prevention, investigation and treatment of CVC-occlusion/thrombosis varies greatly. Additional trials should facilitate development of evidence-based guidelines.

Interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha) levels and IL-6, TNF-polymorphisms in children with thrombosis

Infection has an important role in the pathogenesis of thrombosis and it becomes more prominent in childhood cases, in whom the infection frequency is higher. It has been suggested that patients with high tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 levels might be at increased risk of developing thrombotic complications owing to the effects of these cytokines on the coagulation pathway. Functional polymorphisms in the promoter regions of the genes coding for TNF-alpha and IL-6 are associated with increased plasma levels of these cytokines. The aims of this study were to evaluate the serum levels of acute phase reactants, such as C-reactive protein, and of cytokines (TNF-alpha and IL-6) and to investigate the association between the TNF-alpha-308 G/A and IL-6-174 G/C polymorphisms in Turkish pediatric patients with thrombosis. Fifty-eight children with thrombosis (group 1) and 89 controls (group 2) were included in the study. Patients who had a history of infection within the 15 days before thrombosis were classified as group 1a and those who had no infection history before thrombosis were classified as group 1b. Serum TNF-alpha did not differ significantly between the groups. However, the IL-6 level was higher in group 1a than in group 1b (P<0.05). The genotype distribution and allele frequencies of TNF-alpha G/A polymorphism were significantly higher in the thrombotic children without infection and in the control group than in the thrombotic children with an infection history (P<0.05). The IL-6-174 C/C genotype was significantly higher in thrombotic children with an infection history (P<0.05); there were no differences between the groups in mean allele frequency (Table 2). On the basis of our results, patients with a history of infection seem to have higher C-reactive protein and IL-6 levels and IL-6-174 C/C genotype. Furthermore, venous thrombosis is more frequent in this group than arterial thrombosis (P<0.05).

New Anticoagulants in Children

Thromboembolic complications are increasing in children and the use of anticoagulation has seen a dramatic increase despite the lack of randomized clinical trials. The most widely used agents in children are heparin, low-molecular-weight heparins (LMWH), and warfarin. These agents, however, have significant limitations that are exaggerated in children. Novel anticoagulants such as direct thrombin inhibitors and the selective factor Xa inhibitor, fondaparinux, have been approved for use in adults and have properties that suggest they may be safer and more efficacious than the standard agents; however, until recently, publications using these agents in children were limited to case reports. Recently, clinical trials for two direct thrombin inhibitors, bivalirudin and argatroban, have been completed and a clinical trial of fondaparinux is under way. This review will compare the standard agents with the novel agents and briefly review the results of the clinical trials.

Clinical Measures of Heparin’s Effect and Thrombin Inhibitor Levels in Pediatric Patients with Congenital Heart Disease

In this investigation, we examined the relationship among three thrombin inhibitors, antithrombin III (ATIII), heparin cofactor II (HCII), and alpha-2-macroglobulin (alpha2M), and several clinical tests of heparin's effect in pediatric patients with congenital heart disease undergoing cardiopulmonary bypass. One hundred eighteen children were stratified into six age groups: <1 mo, 1-3 mo, 3-6 mo, 6-12 mo, 12-24 mo, and >10 yr. Baseline ATIII, HCII, and alpha2M values were measured. Baseline celite- and kaolin-activated clotting times (ACT) were also measured and repeated 3 min after a standard heparin dose of 400 U/kg. Differences in ACT values before and after heparin administration and a heparin dose-response relationship were calculated for each patient. Kaolin-activated ACT tests showed less variation after heparin administration than celite-activated tests. In contrast to what has been demonstrated in adults, ATIII showed no positive correlation with the clinical tests of heparin's effect nor did the other thrombin inhibitors. Additionally, patients <1 mo old had unexpectedly low levels of alpha2M accompanying their expected low levels of ATIII and HCII. Our findings raise concerns about the ability of heparin to adequately anticoagulate these neonates during cardiopulmonary bypass and, consequently, challenge the accuracy of ACT prolongation to truly reflect the extent of their anticoagulation.

Diagnosis and treatment of thrombosis in children: general principles

Thrombosis is an increasingly recognized complication occurring primarily in children with serious underlying conditions and most often associated with intravenous catheters. There are few clinical trials available to guide the decision-making in the diagnosis and treatment of thrombosis. Although there are published guidelines which suggest how to manage such patients, they are based on data from adult studies and uncontrolled pediatric studies and it is unclear how widely these guidelines are utilized in clinical practice. What is clear is that many additional studies are needed to provide the data required to make evidence-based decisions. Nevertheless, patients today are being diagnosed with thrombosis and must be treated. Diagnosis is based largely on various diagnostic-imaging methods. While Doppler ultrasonography is non-invasive and relatively inexpensive, its sensitivity for the upper venous system is poor. Venography/angiography, the most sensitive method to diagnose venous/arterial thrombosis is underutilized due to the need for peripheral venous access for venography and arterial catheterization for angiography as well as interventional radiology. Newer methods such as computed tomography and magnetic resonance imaging are useful for large vessel disease but are not validated in pediatrics. Treatment is based on the methods that are best at restoring circulation rapidly balanced by the risk for bleeding. Both thrombolysis and anticoagulation can be utilized with the circumstances of each individual patient dictating the choice. The field of pediatric thrombosis continues to advance with numerous new studies currently underway or being planned. In the near future, the results of these studies will allow for better management of pediatric patients with thrombosis.

3' end processing of the prothrombin mRNA in thrombophilia

Clinical and genetic studies have led to the discovery of specific genotypes that predispose to thromboembolism in adults and children. The exploration of the underlying pathologies has revealed a broad variety of affected molecular mechanisms. Most recently, the functional analysis of the prothrombin (F2) 20210*A variant revealed increased efficiency of 3' end processing as a novel genetic mechanism predisposing to human disease. Here, we review the 3' end processing of the human F2 mRNA and demonstrate how clinically relevant mutations in the F2 gene contribute to thrombophilia by interfering with a tightly balanced architecture of noncanonical 3' end formation signals.

Post-thrombotic syndrome is uncommon in childhood cancer survivors

Deep vein thrombosis occurs in up to 50% of children with tunneled central venous catheters (CVCs). CVC-related deep vein thrombosis involving the upper extremity is usually asymptomatic but can result in post-thrombotic syndrome (swelling, pain, skin changes, and functional impairment). In a cohort of childhood cancer survivors evaluated clinically a mean of 7.5 +/- 2.8 years after completion of therapy who previously had CVCs in place for a median 15.5 months, none of 50 patients (95% CI = 0% to 6%) had these features diagnostic of post-thrombotic syndrome. Five patients had arm circumference 3% to 5% greater ipsilateral to the prior CVC.

Analysis of some clinical and laboratory aspects of adolescent patients with thrombosis

A total of 360 pediatric patients aged 1 month to 18 years were diagnosed as having thrombosis between January 1998 and April 2003. Of these patients, those aged 11-18 years (n=131) were regarded as adolescents and the rest as children. The proportion of adolescents in the whole group excluding the neonates was 36%. The peak age of diagnosis in adolescents was 11-14 years, comprising 58% of all thrombotic events in adolescents. In 73% of the adolescents, there was at least one risk factor. The four most common underlying disorders were infection, malignancy, connective tissue and cardiac disorders, in decreasing order of frequency. In children, on the other hand, infection was followed by congenital heart disease, malignancy and liver disease. Three common types of thrombosis in adolescents were deep venous thrombosis, cerebro-vascular events and portal venous thrombosis, while cerebro-vascular events were the most common in children. The frequency of factor V G1691A mutation in the adolescents (22.1%) was significantly higher than that found in a group of healthy controls (7.4%) and this mutation was associated with a 3.6-fold increase in the risk of developing thrombosis (95% confidence interval, 1.4-9.0). The carrier frequency of prothrombin G20210A mutation (3.1%) in adolescents did not differ significantly from that of the healthy population (2.3%) and no association was observed between this mutation and a risk of developing thrombosis in this group (odds ratio, 1.3; 95% confidence interval, 0.2-7.5). The rate of recurrent thrombosis was 6%.

Thrombosis during infancy and childhood: what we know and what we do not know

Despite underlying illnesses, children have a greater chance to survive and are expected to live 6 to 8 decades following an episode of venous or arterial thrombosis. The disproportionate benefits of preventing thrombosis and its sequelae in pediatric patients are evident. Therefore, it is necessary to develop appropriate strategies for diagnosis and management of thromboembolic events in children and to understand their acute and long-term effects. There still are many unanswered questions and clinical trials are being designed to help study these important issues.

Analysis of pediatric thrombotic patients in Turkey

This study analyzes the data of thrombotic children who were followed up in different pediatric referral centers of Turkey, to obtain more general data on the diagnosis, risk factors, management, and outcome of thrombosis in Turkish children. A simple two-page questionnaire was distributed among contact people from each center to standardize data collection. Thirteen pediatric referral centers responded to the invitation and the total number of cases was 271. All children were diagnosed with thromboembolic disease between January 1995 and October 2001. Median age at time of first thrombotic event was 7.0 years. Of the children 4% of the cases were neonates, 12% were infants less than 1 year old, and 17% were adolescents. Thromboembolic event was mostly located in the cerebral vascular system (32%), deep venous system of the limbs, femoral and iliac veins (24%), portal veins (10%), and intracardiac region (9%). Acquired risk factors were present in 86% of the children. Infection was the most common underlying risk factor. Inherited risk factors were present in 30% of the children. FVL was the most common inherited risk factor. Acquired and inherited risk factors were present simultaneously in 19% of the patients. Eleven children had a history of familial thrombosis. Due to the local treatment preferences, the treatment of the children varied greatly. Outcome of the 142 patients (52%) was reported: 88 (62%) patients had complete resolution, 47 (33%) had complications, 12 (9%) had recurrent thrombosis, and 34 (24%) died. Three children (2.1%) died as a direct consequence of their thromboembolic disease. The significant morbidity and mortality found in this study supports the need for multicentric prospective clinical trials to obtain more generalizable data on management and outcome of thrombosis in Turkish children.

Thrombotic complications of central venous catheters in children

Use of central venous catheters has become standard in the treatment of many chronic conditions during childhood and for the acute treatment of critically ill infants and children. However, these catheters can be associated with numerous complications, including thrombosis at the tip or in the lumen causing difficulty with its overall function. Even more concerning is the occlusion of large veins into which the catheter is placed, which could predispose patients to pulmonary embolism or postthrombotic syndrome. Recent research has focused on identifying risk factors for catheter-related thrombosis in children and determining methods for diagnosing deep venous thrombosis associated with a catheter in the upper extremities. Evidence now exists that as many as 50% of children with catheters develop deep venous thrombosis; however, most events are clinically silent. Few clinical trials have studied prevention of catheter-related thrombosis in pediatric patients. Data regarding incidence, treatment, and long-term outcome of catheter-related thrombosis in children are limited. Although central venous catheters are extremely important in the supportive care of sick children, concerns remain about their immediate and long-term safety.