Pediatric heparin-induced thrombocytopenia: management with Danaparoid (orgaran)

Heparin-induced thrombocytopenia: natural history, diagnosis, and management

Heparin-induced thrombocytopenia (HIT) is an under-recognized, limb- and life-threatening complication of pharmacologic heparin administration. Antibody formation against heparin complexed to platelet factor 4 (PF4) is central to the pathogenesis of HIT. Heparin: PF4 antibodies promote platelet activation and aggregation as well as excess thrombin generation which may lead to clinical thrombosis. HIT should be suspected in patients who develop thrombocytopenia with or without associated arterial or venous thrombosis while on heparin. HIT is a clinical diagnosis. Specialized HIT assays should be interpreted with care. The cornerstone of HIT management is the discontinuation of all forms of heparin exposure and the institution of anticoagulation with an alternative agent. The direct thrombin inhibitors lepirudin and argatroban are currently available and approved for use in patients with HIT.

Antithrombotic therapy in neonates and children: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

Neonates and children differ from adults in physiology, pharmacologic responses to drugs, epidemiology, and long-term consequences of thrombosis. This guideline addresses optimal strategies for the management of thrombosis in neonates and children.

METHODS

The methods of this guideline follow those described in the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines.

RESULTS

We suggest that where possible, pediatric hematologists with experience in thromboembolism manage pediatric patients with thromboembolism (Grade 2C). When this is not possible, we suggest a combination of a neonatologist/pediatrician and adult hematologist supported by consultation with an experienced pediatric hematologist (Grade 2C). We suggest that therapeutic unfractionated heparin in children is titrated to achieve a target anti-Xa range of 0.35 to 0.7 units/mL or an activated partial thromboplastin time range that correlates to this anti-Xa range or to a protamine titration range of 0.2 to 0.4 units/mL (Grade 2C). For neonates and children receiving either daily or bid therapeutic low-molecular-weight heparin, we suggest that the drug be monitored to a target range of 0.5 to 1.0 units/mL in a sample taken 4 to 6 h after subcutaneous injection or, alternatively, 0.5 to 0.8 units/mL in a sample taken 2 to 6 h after subcutaneous injection (Grade 2C).

CONCLUSIONS

The evidence supporting most recommendations for antithrombotic therapy in neonates and children remains weak. Studies addressing appropriate drug target ranges and monitoring requirements are urgently required in addition to site- and clinical situation-specific thrombosis management strategies.

Heparin-induced thrombocytopenia in the pediatric population: a review of current literature

Heparin-induced thrombocytopenia is a rare and serious reaction to unfractionated heparin and low-molecular-weight heparins in children. Quick recognition, discontinuation of heparin, and subsequent treatment with an alternative anticoagulant are essential steps to prevent serious complications such as thrombus and limb amputation. The purpose of this review is to describe the clinical features of heparin-induced thrombocytopenia in children and to summarize the data available for its management. This paper summarizes data and relates the use of direct thrombin inhibitors with clinical outcomes. A literature search was conducted with Ovid, using the key terms argatroban, bivalirudin, hirulog, danaparoid, lepirudin, direct thrombin inhibitor, heparin-induced thrombocytopenia, thrombosis, warfarin, and fondaparinux. Articles were excluded if they were classified as editorials, review articles, or conference abstracts or if they involved patients 18 years of age or older or described disease states not related to thrombosis. Nineteen articles containing 33 case reports were identified and evaluated for this review. Of the 33 cases, 14, 10, 4, and 2 cases described the use of lepirudin, danaparoid, argatroban, and bivalirudin, respectively. Two cases did not report the type of anticoagulant used, and 1 case used aspirin. The most commonly reported complication was bleeding.

Anticoagulation in neonates and children: Pitfalls and dilemmas

Anticoagulation in children is problematic for many reasons, related to the patient population as well as the anticoagulant drugs themselves. This paper describes the multitude of reasons why providing anticoagulation therapy in children is different from anticoagulation therapy in adults, and hence why dedicated paediatric anticoagulant services are the ideal structure to provide this service. The paper then describes the three most common anticoagulants used in children, and details specifically what is and is not known about them in the paediatric population. Finally the paper addresses the issue of how best to introduce newer anticoagulant drugs into the paediatric population. There remains much research to be done in this field, in the meantime clinicians need to carefully consider the evidence available to them and manage each individual patient accordingly.

Aspects of anticoagulation in children

The number of children receiving anticoagulation is increasing. Thromboembolic events are associated with significant risk of morbidity and mortality although the optimal management of asymptomatic events remains unclear. Specific challenges in paediatrics include the diagnosis of thrombosis, delivery and monitoring of anticoagulation in a wide range of ages from neonates through to adolescents. The development of the haemostatic system as children age results in changing pathophysiology of thrombosis and response to anticoagulation agents. Although registry and observational studies have provided vital information, specific paediatric, prospective anticoagulation studies have been few and limited in design. The result is that much of current practice is extrapolated from adult studies. Traditional anticoagulants have significant limitations. Both heparin and warfarin are in widespread use but many fundamental questions regarding dose, therapeutic range, efficacy and optimum duration have not been fully answered. Alternative agents, such as direct thrombin inhibitors and the selective anti-factor Xa inhibitor fondaparinux, may have advantages for children. Clinical trials in adults and preliminary data in children are promising but caution should be applied until specific paediatric studies have demonstrated safety and efficacy.

Antithrombotic therapy in neonates and children: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This chapter about antithrombotic therapy in neonates and children is part of the Antithrombotic and Thrombolytic Therapy: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs, and Grade 2 suggests that individual patient values may lead to different choices (for a full understanding of the grading, see Guyatt et al in this supplement, pages 123S-131S). In this chapter, many recommendations are based on extrapolation of adult data, and the reader is referred to the appropriate chapters relating to guidelines for adult populations. Within this chapter, the majority of recommendations are separate for neonates and children, reflecting the significant differences in epidemiology of thrombosis and safety and efficacy of therapy in these two populations. Among the key recommendations in this chapter are the following: In children with first episode of venous thromboembolism (VTE), we recommend anticoagulant therapy with either unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) [Grade 1B]. Dosing of IV UFH should prolong the activated partial thromboplastin time (aPTT) to a range that corresponds to an anti-factor Xa assay (anti-FXa) level of 0.35 to 0.7 U/mL, whereas LMWH should achieve an anti-FXa level of 0.5 to 1.0 U/mL 4 h after an injection for twice-daily dosing. In neonates with first VTE, we suggest either anticoagulation or supportive care with radiologic monitoring and subsequent anticoagulation if extension of the thrombosis occurs during supportive care (Grade 2C). We recommend against the use of routine systemic thromboprophylaxis for children with central venous lines (Grade 1B). For children with cerebral sinovenous thrombosis (CSVT) without significant intracranial hemorrhage (ICH), we recommend anticoagulation initially with UFH, or LMWH and subsequently with LMWH or vitamin K antagonists (VKAs) for a minimum of 3 months (Grade 1B). For children with non-sickle-cell disease-related acute arterial ischemic stroke (AIS), we recommend UFH or LMWH or aspirin (1 to 5 mg/kg/d) as initial therapy until dissection and embolic causes have been excluded (Grade 1B). For neonates with a first AIS, in the absence of a documented ongoing cardioembolic source, we recommend against anticoagulation or aspirin therapy (Grade 1B).

Prevalence of heparin-dependent platelet antibodies in children after cardiopulmonary bypass

OBJECTIVE

To determine the prevalence of heparin-dependent platelet antibodies (HDPA) in children requiring heparin for >5 days after cardiopulmonary bypass surgery.

DESIGN

Prospective, observational study.

SETTING

Tertiary care pediatric intensive care unit.

PATIENTS

Thirty children were enrolled: 15 patients <30 days old and 15 patients between 30 days and 12 yrs of age.

INTERVENTIONS

Detection of HDPA by heparin-platelet factor 4 enzyme-linked immunosorbent assay after 5-10 days of postoperative heparin exposure. Positive or equivocal results were confirmed with serotonin release assay.

MEASUREMENTS AND MAIN RESULTS

There were no confirmed cases of HDPA in this study (95% confidence interval 0-11.6%). Despite the lack of HDPA, the study population was at high risk of thrombosis with symptomatic clot developing in six patients (20%). Clinical models developed in adults to determine the pretest risk of heparin-induced thrombocytopenia were not valid in this study population.

CONCLUSIONS

The prevalence of HDPA in children after cardiopulmonary bypass surgery is low. After bypass surgery, critically ill children are at risk of developing thrombosis from multiple etiologies, and suspicion of heparin-induced thrombocytopenia needs to be confirmed with laboratory testing including a functional assay.

Heparin-induced Thrombocytopenia, a Prothrombotic Disease

Heparin-induced thrombocytopenia (HIT) is a serious, yet treatable prothrombotic disease that develops in approximately 0.5% to 5% of heparin-treated patients and dramatically increases their risk of thrombosis (odds ratio, 37). The antibodies that mediate HIT (ie, heparin-platelet factor 4 antibodies) occur more frequently than the overt disease itself, and, even in the absence of thrombocytopenia, are associated with increased thrombotic morbidity and mortality. HIT should be suspected whenever the platelet count drops more than 50% from baseline (or to <150 x 10(9)/L) beginning 5 to 14 days after starting heparin (or sooner if there was prior heparin exposure) or new thrombosis occurs during, or soon after heparin treatment, with other causes excluded. When HIT is strongly suspected, with or without complicating thrombosis, heparins should be discontinued, and a fast-acting, nonheparin alternative anticoagulant such as argatroban should be initiated immediately. With prompt recognition, diagnosis, and treatment of HIT, the clinical outcomes and health economic burdens of this prothrombotic disease are improved significantly.

Recognition and Management of Heparin-Induced Thrombocytopenia in Pediatric Cardiopulmonary Bypass Patients

Repeated exposure to unfractionated heparin is the rule in many congenital heart disease patients. Heparin-induced thrombocytopenia occurs in 1% to 3% of adult cardiac surgeries, and carries high thrombotic morbidity (38% to 81%) and mortality (approximately 28%). Although heparin-induced thrombocytopenia appears to be infrequent in pediatric patients, particularly neonates, our evolving experience suggests postcardiopulmonary bypass congenital heart disease patients may be at increased risk. Diagnostic and therapeutic challenges include frequency of thrombocytopenia after cardiopulmonary bypass, imperfect laboratory testing, lack of established dosing of alternative anticoagulants (such as argatroban and lepirudin), and increased anticoagulant-related bleeding in young children.

Safety and efficacy of danaparoid (Orgaran) use in children

Immune-mediated heparin-induced thrombocytopenia (HIT) is an uncommon but serious complication of therapy with heparins. It affects all ages and requires replacement of the causative anticoagulant. However, information on alternative antithrombotic use in children with HIT is limited. This paper reviews 27 published and 7 unpublished case reports of children aged 2 weeks to 17 years treated with danaparoid. Thirty-three suffered from HIT or suspected HIT, and 1 child without HIT had a high bleeding risk. All children had severe underlying problems increasing their thrombotic and/or bleeding risk. HIT diagnosis was confirmed serologically or clinically in 26 cases (78.8%). Danaparoid regimens were similar to those used in adults, but in general, younger children needed higher daily doses of danaparoid to achieve the same target plasma anti-Xa levels than teenagers or adults. Of those with a known outcome 28/33 children (84.8%) survived, 7 having suffered from a serious adverse event. Five deaths occurred including 1 thrombotic and 2 major bleeds. Three of the in total 4 major bleeding events occurred in children undergoing surgery with cardiopulmonary bypass. We conclude that despite the reported adverse events danaparoid can be used as an alternative antithrombotic for children who are intolerant of the heparins, except in cases requiring cardiopulmonary bypass surgery.

Bidirectional Glenn Shunt Surgery Using Lepirudin Anticoagulation in an Infant with Heparin-Induced Thrombocytopenia with Thrombosis

There are few reports of the management of pediatric patients with heparin-induced thrombocytopenia (HIT) requiring cardiac surgery using currently available anticoagulants. We report a case of an infant with HIT requiring a bidirectional Glenn shunt who was successfully managed using lepirudin (r-hirudin, Refludan; Aventis, Bridgewater, NJ). Dosing and monitoring of anticoagulation were difficult, and we suggest caution in the use of lepirudin for cardiac surgery unless reliable monitoring of the degree of anticoagulation becomes available.

Argatroban for anticoagulation during cardiopulmonary bypass in an infant

Heparin induced thrombocytopenia (HIT) is a rare, but potentially life-threatening complication of heparin therapy. In patients with HIT, alternative means of anticoagulation are necessary. The authors present an infant with HIT who required anticoagulation during cardiopulmonary bypass for tricuspid valve excision in the treatment of bacterial endocarditis. The direct thrombin inhibitor, argatroban, was successfully used. Previous reports regarding the use of argatroban and other nonheparin anticoagulants for anticoagulation are reviewed and suggestions regarding argatroban dosing in infants are presented.

Heparin-induced thrombocytopenia in the pediatric intensive care unit population

OBJECTIVES

To report the occurrence of heparin-induced thrombocytopenia (HIT), discuss its pathophysiology, and outline an approach to management in the pediatric intensive care unit (ICU) patient.

DESIGN

Retrospective case reports.

SETTING

Pediatric ICU in a tertiary-care center.

PATIENTS AND RESULTS

Two pediatric ICU patients (2 and 6 mos of age) who developed HIT in the pediatric ICU. One was receiving heparin as a flush solution through a central line and the other had full heparinization during cardiopulmonary bypass. Both had received heparin during their neonatal course and developed thrombocytopenia; however, HIT was not considered as a possible diagnosis. HIT was diagnosed using a heparin-induced platelet aggregation study. The thrombocytopenia resolved with the cessation of heparin administration. One of the patients developed a deep vein thrombosis around a femoral venous catheter.

CONCLUSION

Although well described in the adult literature, there have been a limited number of reports of HIT in pediatric-aged patients. Given its potential for morbidity, HIT should be considered in the differential diagnosis of thrombocytopenia in the pediatric ICU patient.

Diagnosis and treatment of heparin-induced thrombocytopenia in neonates and children

Heparin-induced thrombocytopenia (HIT), a well-known side effect of heparin therapy, occurs with an incidence of 1-2% in certain pediatric patient groups. In affected children, HIT markedly increases the risk of venous and arterial thromboembolism. The use of alternative anticoagulation with danaparoid, lepirudin and argatroban in adults and children has demonstrated to be safe and could reduce morbidity and mortality also in affected pediatric patients. Thus, in children and neonates, an early diagnosis and accurate management is crucial to avoid the deleterious consequences of HIT. This review article will focus on the presentation of HIT in neonates and children. It reviews the pathophysiology of HIT and it summarizes epidemiological data. Finally important diagnostic and therapeutic issues are discussed.

Incidence of Heparin-Induced Thrombocytopenia and Therapeutic Strategies in Pediatric Cardiac Surgery

BACKGROUND

We identified the incidence of heparin-induced thrombocytopenia and the antiheparin-platelet factor 4 (PF4) antibody in pediatric patients undergoing cardiac surgery and documented the differences in the anticoagulation management for the extracorporeal circulation.

METHODS

Between January 2001 and September 2003, 559 cardiac procedures with extracorporeal circulation in 415 patients with congenital heart defects were performed in our institution. Because the development of heparin-induced thrombocytopenia requires previous exposition to heparin, only the 144 patients undergoing a scheduled second procedure on extracorporeal circulation were screened preoperatively. Of these 144 patients, 41 underwent also a third procedure and were screened before each procedure for presence of antiheparin-PF4 antibodies and for clinical signs of heparin-induced thrombocytopenia.

RESULTS

The incidence of antiheparin-PF4 antibodies during the study period was 1.4% (2 of 144 patients). Patients with clinically significant heparin-induced thrombocytopenia could not be identified. Outside the study protocol, 2 more patients with antiheparin-PF4 antibodies were found. In these 4 patients, surgery was performed using lepirudin (Schering, Berlin, Germany) instead of the usual heparin management for extracorporeal circulation. Three of these 4 patients had an uneventful procedure and postoperative course. In 1 patient after total cavopulmonary connection, a reoperation was necessary on the seventh postoperative day owing to partial thrombosis of the lateral tunnel.

CONCLUSIONS

The incidence of heparin-induced thrombocytopenia and of antiheparin-PF4 antibodies in patients undergoing repeated cardiac surgery is low. In antiheparin-PF4 antibody positive patients, the complete avoidance of heparin can be achieved and may account for an uneventful perioperative course.

Heparin-induced thrombocytopenia (HIT) in pediatric cardiac surgery: an emerging cause of morbidity and mortality

Unfractionated heparin (UFH) is immunogenic, and heparin-dependent antibodies can be demonstrated 5 to 10 days postoperatively in 25% to 50% of adult postcardiac surgery patients. In a minority of these cases (1% to 3% if UFH is continued longer than 1 week) these antibodies strongly activate platelets, causing thrombocytopenia and massive thrombin generation (HIT syndrome). HIT is an intensely procoagulant disorder, and in adult cardiac surgery patients carries both significant thrombotic morbidity (38% to 81%) and mortality (28%). Despite the ubiquitous use of UFH in pediatric intensive care units, and the repeated and sustained exposures to UFH in neonates and young children with congenital heart disease, HIT has been infrequently recognized and reported in this patient population. However, emerging experience at our institution and elsewhere suggests that HIT is significantly under-recognized in pediatric congenital heart disease patients, and may in fact have an incidence and associated thrombotic morbidity and mortality in this patient group comparable to that seen in adult cardiac surgery patients. This article will review HIT in pediatric patients with congenital heart disease and emphasize the special challenges posed in clinical recognition, laboratory diagnosis, and treatment of HIT in this patient group. We will also outline our experience with the off-label use of the direct thrombin inhibitor, argatroban, in pediatric patients with HIT.

Antithrombotic Therapy in Children*

This article about antithrombotic therapy in children is part of the 7th American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh the risks, burden, and costs. Grade 2 suggests that individual patients' values may lead to different choices (for a full understanding of the grading see Guyatt et al, CHEST 2004; 126:179S-187S). Among the key recommendations in this article are the following. In neonates with venous thromboembolism (VTE), we suggest treatment with either unfractionated heparin or low-molecular-weight heparin (LMWH), or radiographic monitoring and anticoagulation therapy if extension occurs (Grade 2C). We suggest that clinicians not use thrombolytic therapy for treating VTE in neonates, unless there is major vessel occlusion that is causing the critical compromise of organs or limbs (Grade 2C). For children (ie, > 2 months of age) with an initial VTE, we recommend treatment with i.v. heparin or LMWH (Grade 1C+). We suggest continuing anticoagulant therapy for idiopathic thromboembolic events (TEs) for at least 6 months using vitamin K antagonists (target international normalized ratio [INR], 2.5; INR range, 2.0 to 3.0) or alternatively LMWH (Grade 2C). We suggest that clinicians not use thrombolytic therapy routinely for VTE in children (Grade 2C). For neonates and children requiring cardiac catheterization (CC) via an artery, we recommend i.v. heparin prophylaxis (Grade 1A). We suggest the use of heparin doses of 100 to 150 U/kg as a bolus and that further doses may be required in prolonged procedures (both Grade 2 B). For prophylaxis for CC, we recommend against aspirin therapy (Grade 1B). For neonates and children with peripheral arterial catheters in situ, we recommend the administration of low-dose heparin through a catheter, preferably by continuous infusion to prolong the catheter patency (Grade 1A). For children with a peripheral arterial catheter-related TE, we suggest the immediate removal of the catheter (Grade 2C). For prevention of aortic thrombosis secondary to the use of umbilical artery catheters in neonates, we suggest low-dose heparin infusion (1 to 5 U/h) (Grade 2A). In children with Kawasaki disease, we recommend therapy with aspirin in high doses initially (80 to 100 mg/kg/d during the acute phase, for up to 14 days) and then in lower doses (3 to 5 mg/kg/d for > or = 7 weeks) [Grade 1C+], as well as therapy with i.v. gammaglobulin within 10 days of the onset of symptoms (Grade 1A).

Low-Molecular-Weight Heparin–Induced Thrombocytopenia in a Child

OBJECTIVE

To report a case of probable acute venous thrombosis caused by heparin-induced thrombocytopenia (HIT) in a pediatric patient with a normal platelet count after prolonged enoxaparin therapy.

CASE SUMMARY

An 11-year-old African American female with Crohn's disease developed extensive vena cava thrombosis. Her deep vein thrombosis (DVT) was treated with intravenous unfractionated heparin followed by extended outpatient warfarin therapy. Four months later, the warfarin was stopped and subcutaneous enoxaparin 1.5 mg/kg once daily was substituted prior to an elective colonoscopy. She was readmitted 6 weeks later with acute DVT with a platelet count of 233 × 10 3 /mm 3 , significantly lower than the count of 550–700 × 10 3 /mm 3 5 months previously and the count of 433 × 10 3 /mm 3 3 months earlier. An enzyme-linked immunosorbent assay for heparin-platelet factor 4 antibodies was strongly positive and a d-dimer was elevated at 2.9 mg/L (normal <1.5). She was treated with lepirudin followed by warfarin when repeat d-dimer on day 3 was normal. An ultrasound at that time showed no clot extension, and the platelet count had risen to >300 × 10 3 /mm 3 . Over the next 4 months, there was no further thrombosis.

DISCUSSION

HIT appears to be rare in the pediatric population, and only a few cases treated with a direct thrombin inhibitor have been reported. This is the first case report to our knowledge of a pediatric patient developing HIT secondary to enoxaparin. An interesting feature of this case is the development of HIT in the face of a normal platelet count, which is rare but has been reported in adults.

CONCLUSIONS

Pediatric patients receiving low-molecular-weight heparin are still at risk for developing HIT. Treatment of HIT should involve the initial use of a direct thrombin inhibitor to manage thrombosis until the platelet count returns to higher values. Once the platelet count returns, warfarin can be used for long-term thrombosis management.

Use of low molecular mass heparin (enoxaparin) in newborn infants: a prospective cohort study of 62 patients

OBJECTIVE

To detail low molecular mass heparin (enoxaparin) use in the first few months of life.

DESIGN

Prospective, consecutive cohort of unselected newborn infants.

METHODS

Newborn infants were divided into groups by gestational age, underlying condition, hepatic and renal function, thrombocytopenia, and prothrombin time (PT/INR). Groups were analysed with respect to many aspects of enoxaparin treatment using multivariate methods.

RESULTS

Sixty two newborn infants received enoxaparin representing 5.39 treatment years. Thromboembolic events (TEs) occurred predominantly in the lower and upper venous system in the presence of indwelling catheters (69%). Preterm infants required longer than full term infants to achieve an anti-(factor Xa) level in the target range (six versus two days). Preterm infants required higher doses of enoxaparin than full term infants to maintain anti-(factor Xa) levels in the target range (2.1 v 1.7 mg/kg/12 h). Infants with congenital heart disease (CHD) required less enoxaparin than those without CHD to maintain an anti-(factor Xa) level in the target range (1.7 v 2.1 mg/kg/12 h). Impaired renal and liver function influenced the number of dose changes needed (three versus one a month). Complete or partial resolution of TE was accomplished in 59% of newborn infants. Four infants developed major bleeds (1.2% per patient year). Recurrent TE and clot extension occurred in three infants (0.9% per patient year).

CONCLUSIONS

Preterm infants are more difficult to treat with enoxaparin than full term infants. Enoxaparin appears to be an alternative to treatment with standard heparin or no treatment.

Heparin-induced thrombocytopenia in children

OBJECTIVE

To audit the frequency of heparinoid (standard heparin and low molecular weight heparin) use in a tertiary paediatric hospital, and to determine the occurrence of heparin-induced thrombocytopenia (HIT).

METHODS

A 1-week cross-sectional audit of all heparinoids given to inpatients at a tertiary paediatric hospital was undertaken and a retrospective medical record review of all suspected HIT cases at the tertiary paediatric centre over a 2-year period was carried out.

RESULTS

One hundred and sixteen patients received heparinoid medications over a 7-day period. An average of 29 children received heparin daily. The retrospective medical record review identified four patients with suspected HIT over a 2-year period. Two patients developed thrombotic complications, which were fatal in one patient.

CONCLUSION

Heparin is used frequently in paediatric tertiary hospitals, yet the occurrence of HIT in children is much lower than that reported in adults. Improved laboratory techniques could facilitate improved screening and diagnosis of this serious adverse drug reaction.

Diagnosis and treatment of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a major side effect secondary to the administration of heparin. This syndrome is serious and potentially life threatening. This response is the result of antibodies formed against the platelet factor 4 (PF4)/heparin complex. The incidence of this immune-mediated syndrome has been estimated to be 1-3% of all patients receiving heparin therapy. The occurrence of HIT in patients requiring full anticoagulation for cardiopulmonary bypass (CPB), therefore, presents a serious challenge to the cardiac surgery team. The diagnosis of HIT should be based on both clinical and laboratory evidence. While functional assays, platelet aggregation tests, and the serotonin release assay can be used to support the diagnosis, the negative predictive value of these tests is generally less than 50%. In contrast, although non-functional antibody detection assays are more sensitive, they have a low specificity. HIT can be treated in several ways, including cessation of all heparin and giving an alternative thrombin inhibitor, platelet inhibition followed by heparin infusion, and the use of low molecular weight heparins. In this presentation, the pathology and current diagnostic tests, as well as the successful management of patients with HIT undergoing CPB at New York Presbyterian Hospital, are reviewed.

Lepirudin anticoagulation for heparin-induced thrombocytopenia

Lepirudin is indicated for anticoagulation in patients with heparin-induced thrombocytopenia (HIT). We describe 2 cases of HIT and thrombosis in children with heart disease, including one that required extracorporeal membrane oxygenation. Lepirudin, dosed in the recommended adult weight--based fashion, was an effective antithrombotic agent in pediatric patients with HIT.

Clinical experiences with low-molecular weight heparins in pediatric patients

The courses of 79 children (2 weeks to 19 years old) treated with two different low-molecular weight heparins (LMWHs)--nadroparin (n=66) and enoxaparin (n=13)--were retrospectively analysed. In 62 patients, LMWHs were given for short-term prophylaxis (1-2 weeks) during immobilization after surgery or trauma. Thirteen children with thromboembolic events received long-term prophylaxis with LMWHs for 2-18 months--six after thrombolytic therapy and seven after therapy with unfractionated heparin (UFH). Because of thromboembolic events, four patients were initially treated with LMWHs. In all patients with short-term prophylaxis, no thrombosis occurred. After thrombolytic therapy, three children had no reocclusion, two had no thrombus apposition and one had complete recanalization. In the seven patients treated with LMWHs after UFH, four had no reocclusion, two had recanalization and one had reocclusion. In all patients receiving LMWHs for initial treatment of thrombosis, no thrombus apposition, but also no recanalization, occurred. For short-term prophylaxis, nadroparin was used independent of the body weight and without determination of anti-factor Xa (anti-FXa) activity. Long-term prophylaxis was given mainly as doses of 45-100 anti-FXa U/kg resulting in anti-FXa activities between 0.2 and 0.4 U/ml. For treatment of thrombosis, doses of 200-300 anti-FXa U/kg corresponded to 0.5-1.0 anti-FXa U/ml. Side effects--slight gastrointestinal bleeding and temporary reversible hair loss--were seen in two patients. In conclusion, LMWHs proved to be efficacious and safe especially in prophylaxis of thromboembolic events in children.

Low-dose danaparoid sodium catheter flushes in an intensive care infant suffering from heparin-induced thrombocytopenia

OBJECTIVE: Despite controversy about whether peripheral and central venous catheters should be locked with heparin to prevent catheter-associated clotting, the practice is widespread. We describe a severe side effect of the practice: a case of heparin-induced thrombocytopenia occurring with catheter flushes using unfractionated heparin (UFH) in a 10-month-old boy successfully treated with danaparoid. Patient: A preterm-born patient (33 wks gestational age, birth weight 1200 g) suffering from VACTERL syndrome was repeatedly treated with UFH in the context of several invasive procedures. On day 310 of age, a central venous catheter was inserted to provide total parenteral nutrition. The central catheter was flushed with a continuous infusion of UFH at 100 U/day, and a decrease in platelet counts from 150,000/&mgr;L (on day 310 of age) to 45,000/&mgr;L (on day 319 of age) was observed. Clinically suspected heparin-induced thrombocytopenia (HIT) was serologically confirmed by demonstrating HIT antibodies with platelet factor 4/heparin complex specificity. Main Result: Catheter flushing was switched to low-dose danaparoid sodium as a continuous infusion at 15 anti-factor Xa units per day. Two days later, platelet counts recovered. Neither catheter thrombosis nor systemic thromboembolic complications occurred during the follow up period. CONCLUSIONS: Even continuous infusion of low-dose heparin to provide patency of central venous port catheters may trigger the primary immune response of HIT. Low-dose danaparoid sodium, a heparinoid, can prevent in-catheter thrombus formation and allows normalization of platelet counts in acute HIT.