Primary Thromboprophylaxis with Heparins for Arteriovenous Fistula Failure in Pediatric Patients

Background

To reduce the incidence of early arteriovenous fistula failure (AVF) due to thrombosis in pediatric hemodialysis (HD) patients, a primary thromboprophylaxis (PTP) protocol was initiated at author's institution in June 2005. The goal of this study is to report author's experience with this protocol one year later.

Methods and Results

19 AVFs (14 patients, Historical group) and 8 AVFs (7 patients, PTP group) were created prior to and after initiation of PTP respectively. PTP consisted of unfractionated heparin (5–10 units/kg/hr) infusion postoperatively, followed by subcutaneous low molecular weigh heparin (LMWH) until AVF was matured. LMWH dosing was “Prophylactic” (0.5 mg/kg/d, anti-factor Xa levels: peak 0.25–0.5 and trough < 0.3 units/mL) and “Therapeutic” (1 mg/kg/d, anti-factor Xa level: peak 0.5-1 and trough < 0.5 units/mL) based on thrombosis predisposition. In Historical group, 12 AVFs did not receive thromboprophylaxis (No-treatment group), 5 received 81 mg aspirin/day (Aspirin group), and 2 received LMWH. In No-treatment group 10/12 AVFs failed: 9 thromboses and 1 stenosis. In Aspirin group 1/5 AVFs failed due to thrombosis. In PTP group 1/8 AVFs failed due to stenosis; the first 2 AVFs developed hematoma prompting a reduction in LMWH dose and monitoring trough anti-factor Xa levels, one AVF required thrombectomy after LMWH was transiently held. The incidence of thrombosis was less in PTP group (12.5%) when comparing to No-treatment group (83%) (p < 0.05).

Conclusion

PTP is a feasible option to prevent early thrombosis at AVF. Close clinical and laboratory monitoring including trough anti-factor Xa levels is required to adjust optimum anticoagulation. Larger studies are needed to clarify safety and efficacy of our PTP protocol.

Switching clotting factor concentrates: considerations in estimating the risk of immunogenicity

The development of neutralizing antibodies to factor VIII (FVIII) is the most serious complication of therapy for haemophilia A. There is now excellent documentation that a large number of both genetic and environmental factors contribute to the risk of FVIII inhibitor incidence. One of the environmental factors that has been proposed as an influence on this complication is the occurrence of FVIII product switching. There are only a small number of clinical studies that have addressed this question, and thus, the amount of objective information available to assess this association is limited. In this review, in addition to summarizing past evidence pertinent to this subject, we present the results of a complementary strategy, a Delphi analysis, to add to the considerations of product switching and FVIII immunogenicity. With the imminent arrival in the clinic of several new FVIII products, the haemophilia community must be prepared to collect prospectively controlled data to better address this important management issue.

Primary thromboprophylaxis with heparins for arteriovenous fistula failure in pediatric patients

BACKGROUND

To reduce the incidence of early arteriovenous fistula failure (AVF) due to thrombosis in pediatric hemodialysis (HD) patients, a primary thromboprophylaxis (PTP) protocol was initiated at author's institution in June 2005. The goal of this study is to report author's experience with this protocol one year later.

METHODS AND RESULTS

19 AVFs (14 patients, Historical group) and 8 AVFs (7 patients, PTP group) were created prior to and after initiation of PTP respectively. PTP consisted of unfractionated heparin (5-10 units/kg/hr) infusion postoperatively, followed by subcutaneous low molecular weigh heparin (LMWH) until AVF was matured. LMWH dosing was 'Prophylactic' (0.5 mg/kg/d, anti-factor Xa levels: peak 0.25-0.5 and trough < 0.3 units/mL) and 'Therapeutic' (1 mg/kg/d, anti-factor Xa level: peak 0.5-1 and trough < 0.5 units/mL) based on thrombosis predisposition. In Historical group, 12 AVFs did not receive thromboprophylaxis (No-treatment group), 5 received 81 mg aspirin/day (Aspirin group), and 2 received LMWH. In No-treatment group 10/12 AVFs failed: 9 thromboses and 1 stenosis. In Aspirin group 1/5 AVFs failed due to thrombosis. In PTP group 1/8 AVFs failed due to stenosis; the first 2 AVFs developed hematoma prompting a reduction in LMWH dose and monitoring trough anti-factor Xa levels, one AVF required thrombectomy after LMWH was transiently held. The incidence of thrombosis was less in PTP group (12.5%) when comparing to No-treatment group (83%) (p < 0.05).

CONCLUSION

PTP is a feasible option to prevent early thrombosis at AVF. Close clinical and laboratory monitoring including trough anti-factor Xa levels is required to adjust optimum anticoagulation. Larger studies are needed to clarify safety and efficacy of our PTP protocol.

The U.S. Thrombosis and Hemostasis Centers pilot sites program

Venous thromboembolism (VTE) is a common disorder associated with significant morbidity and mortality. Despite important advances in understanding the etiology of VTE, delivery of care to patients with thrombosis and thrombophilia is frequently incomplete and highly variable. A comprehensive model of health care has been used successfully to treat and prevent complications for people with hemophilia and other chronic disorders. The effectiveness of an integrated healthcare model for patients with all coagulation disorders has yet to be evaluated. The Division of Hereditary Blood Disorders of the Centers for Disease Control and Prevention (CDC) is collaborating with eight Thrombosis and Hemostasis Centers (pilot sites) to provide health-related services and conduct research directed toward the reduction or prevention of complications of thrombosis and thrombophilia. The initial objectives of the collaboration are to (1) determine the efficacy of integrated multidisciplinary care and prevention services for people with hemostatic disorders, (2) assess unmet needs for service delivery and identify outreach strategies to improve access to care, (3) develop effective messages aimed at disease management and prevention, and (4) foster the development of training programs to enhance provider skills for the delivery of patient care. To address these objectives, the investigators and CDC have developed and implemented a web-based patient registry to follow prospectively service allocation and patient outcomes. Funding for the program began in October 2001. All eight funded centers are affiliated with U.S. medical schools. Principal investigators at the centers are hematologists (five adult, two pediatric) or cardiologists. Faculty in obstetrics-gynecology, surgery, and multiple other specialties are integral to the model of care at the centers. Other critical components at the centers are clinical laboratory services, training programs, research networks, and education and outreach programs. From August 2003 to March 2006, over 2,600 patients were enrolled in the registry, accounting for a total of more than 5,000 visits to the centers. Immediate goals of the data collection at the centers are to characterize patients receiving care at centers and document the state of health services provided. Long-term goals are to evaluate prospectively clinical outcomes for patients receiving multidisciplinary care and prevention services at centers. The network of data collection across centers will facilitate future collaborative clinical and epidemiologic investigations and enhance collective expertise in hemostasis and coagulation disorders.

Combined factor V and factor VIII deficiency in a Thai patient: a case report of genotype and phenotype characteristics

A Thai woman, with no family history of bleeding disorders, presented with excessive bleeding after minor trauma and tooth extraction. The screening coagulogram revealed prolonged activated partial thromboplastin time and prothrombin time. The specific-factor assay confirmed the diagnosis of combined factor V and factor VIII deficiency (F5F8D). Her plasma levels of factor V and factor VIII were 10% and 12.5% respectively. The medications and blood product treatment to prevent bleeding from invasive procedure included 1-deamino-8-d-arginine vasopressin, cryoprecipitate, factor VIII concentrate, fresh frozen plasma and antifibrinolytic agent. Gene analysis of the proband identified two LMAN1 gene mutations; one of which is 823-1 G --> C, a novel splice acceptor site mutation that is inherited from her father, the other is 1366 C --> T, a nonsense mutation that is inherited from her mother. Thus, the compound heterozygote of these two mutations in LMAN1 cause combined F5F8D.

Molecular defects in coagulation Factor VIII and their impact on Factor VIII function

Molecular defects in Factor VIII (FVIII), such as haemophilia A-related mutations or denaturative conformational changes, may affect the stability of FVIII as well as its interactions with physiological activators, von Willebrand Factor, phospholipid, or conformationally sensitive antibodies. We summarize the contemporary assays which allow identification of impaired functional interactions of FVIII that cause a reduction or loss of its cofactor activity and/or increased immunogenicity. These assays can potentially be used for detection of molecular defects in FVIII and elucidation of the function impaired by these defects.

Optimal management of patent ductus arteriosus in the neonate weighing less than 800 g

Between January 1988 and December 1990, 132 neonates weighing < 800 g were admitted to our neonatal intensive care unit. Of the 76 who survived initial resuscitation, 42 had developed a hemodynamically significant patent ductus arteriosus (PDA) (mean +/- SD): gestational age 25.3 +/- 1.9 weeks, birth weight 650 +/- 93 g. Two infants were referred for primary surgical ligation because of contraindications to indomethacin. Forty infants were initially treated with indomethacin. Seventeen of 40 (43%) were subsequently referred for surgical ligation because of indomethacin failure. Infants requiring surgical duct closure were a lower gestational age (24.6 +/- 1.3 v 25.7 +/- 2.0 weeks, P = 0.49) and had a greater left atrial-aortic (LA/Ao) ratio on echocardiography (1.71 +/- 0.28 v 1.46 +/- 0.26, P = .04) compared with those treated successfully with indomethacin. There were 6 deaths (15%), all of which occurred in infants receiving indomethacin (5 indomethacin alone, 1 indomethacin+ligation). Indomethacin was directly associated with intestinal perforation in 3 patients, and acute renal failure in 1; all 4 died. Surgery was associated with minimal morbidity (intraoperative transfusion in 1, postoperative pneumothorax requiring chest tube in 1). These data suggest that in the extremely premature neonate with a hemodynamically significant PDA: (1) indomethacin therapy is associated with a high failure rate and significant complications; (2) PDA associated with a large LA/Ao ratio is unlikely to close with indomethacin therapy; and (3) surgical duct closure is associated with minimal morbidity. We conclude that primary surgical ligation may provide the optimal management for PDA in carefully selected patients.