The influence of age on in vitro plasmin generation in the presence of fibrin monomer

Pediatric Thrombolysis: A Practical Approach

The incidence of pediatric venous thromboembolic disease is increasing in hospitalized children. While the mainstay of treatment of pediatric thrombosis is anticoagulation, reports on the use of systemic thrombolysis, endovascular thrombolysis, and mechanical thrombectomy have steadily been increasing in this population. Thrombolysis is indicated in the setting of life- or limb-threatening thrombosis. Thrombolysis can rapidly improve venous patency thereby quickly ameliorating acute signs and symptoms of thrombosis and may improve long-term outcomes such as postthrombotic syndrome. Systemic and endovascular thrombolysis can result in an increase in minor bleeding in pediatric patients, compared with anticoagulation alone, and major bleeding events are a continued concern. Also, endovascular treatment is invasive and requires technical expertise by interventional radiology or vascular surgery, and such expertise may be lacking at many pediatric centers. The goal of this mini-review is to summarize the current state of knowledge of thrombolysis/thrombectomy techniques, benefits, and challenges in pediatric thrombosis.

Plasmin generation and fibrinolysis in pediatric patients undergoing cardiopulmonary bypass surgery

This prospective, single-centre cohort study aimed to evaluate plasmin generation and fibrinolysis during and after cardiopulmonary bypass (CPB) surgery in a cohort of children up to 6 years of age. Blood samples were drawn at eight time points: after induction of anesthesia, before unfractionated heparin (UFH), after UFH, after initiation of bypass, before protamine, after protamine, after chest closure, and 6 h after chest closure. The study identified an increase in fibrinolysis during CPB and particularly up to 6 h afterward in children. This could be the mechanism for the significant bleeding events observed in this young population after CPB. This study establishes the foundation for future studies in this area, particularly those focusing on clinical outcomes after CPB surgery.

Hemostatic response in paediatric patients undergoing cardiopulmonary bypass surgery

This prospective, single-center cohort study aimed to evaluate the hemostatic response during and after Cardiopulmonary Bypass (CPB) surgery in a large cohort of children up to 6 years of age. Blood samples were drawn at eight time points: post-induction of anesthesia, pre-unfractionated heparin (UFH), post-UFH, post-initiation of bypass, pre-protamine, post-protamine, post-chest-closure, and 6 h post-chest-closure. As expected, all measures of the UFH effect increased significantly post-UFH bolus and decreased post-protamine administration. However, thrombin generation remained inhibited compared to baseline values despite the post-UFH reversal by protamine. We also demonstrate that residual UFH effect is not responsible for the ongoing inhibition of thrombin observed post-protamine administration. The significant increase in both free and total tissue factor pathway inhibitor levels during the CPB surgery might contribute to the persistent thrombin generation/endogenous thrombin potential inhibition post-protamine administration. This study makes a significant and novel contribution by investigating the physiological mechanisms behind the degree of thrombin inhibition by UFH and the residual levels of thrombin inhibition that continue despite protamine reversal and provides a new foundation for future interventional studies in the setting of paediatric CPB surgery.

Evaluation and Treatment of Neonatal Thrombus Formation in 17 Patients

Introduction: Thrombosis is a rare but serious event in neonates. Perinatal risk factors associated with the developing hemostatic system increase the risk of thromboembolism. Treatment protocols vary between different centers. In this study, thrombosis and subsequent treatment were evaluated in 17 neonates hospitalized in a neonatal intensive care unit. This is the largest series reported to date. Method: From January 2007 to December 2009, thrombosis was diagnosed in 17 newborns hospitalized in a neonatal intensive care unit. Most were treated with recombinant tissue plasminogen activator (r-tPA) and enoxaparin as anticoagulant therapy. Results: Eleven courses of r-tPA therapy were administered to 10 patients. Sixteen patients received low-molecular-weight heparin (LMWH) treatment. None of the patients had hemorrhagic complications due to therapy. Recurrence was observed in 1 patient 1.5 months after the first course of r-tPA and retreatment was performed. A complete decrease in thrombus size was achieved in 9 patients and a partial decrease in 5 patients. One patient died before treatment was initiated; another died at the end of the first day of treatment and thus could not be evaluated. One patient who had a homozygous mutation for factor V Leiden did not respond to treatment and the extremity involved was amputated. Conclusions: Thrombosis in neonates is a multifactorial disorder. Treatment consisting of r-tPA and an anticoagulant was shown to be a safe and effective approach to clot dissolution in neonates.

Efficacy of local instillation of recombinant tissue plasminogen activator for restoring occluded central venous catheters in neonates

OBJECTIVE

To evaluate the efficacy of local instillation of tissue plasminogen activator (tPA) for restoring function to occluded central venous catheters (CVCs) in the neonatal population.

STUDY DESIGN

This was a retrospective review of patients admitted to the neonatal intensive care unit during September 2000 to April 2006 who received instillation of tPA for occluded CVCs.

RESULTS

Among 18 infants who received tPA for occluded CVCs, gestational age at birth was 32.5 weeks, birth weight was 1550 g, and gestational age at tPA administration was 39 weeks, with 4 neonates < or =32 weeks' gestational age at tPA administration; age at tPA use was 39 days (medians reported). Ten of 18 (55%) of CVC occlusions were successfully opened after using tPA. No bleeding complications of tPA were noted, including increased or new-onset intraventricular hemorrhage, overt bleeding, or changes in INR or partial thromboplastin time attributed to tPA use. Three patients (16.5%) had bacteremia within 7 days of tPA administration, and no catheter ruptures occurred.

CONCLUSIONS

Local instillation of tPA was successful in restoring function to occluded CVCs in a significant proportion of neonates, although success rates were lower than that reported in populations of older age. Despite the vulnerability of neonates to the potential complications of tPA, no major complications were detected even among premature infants.

Thrombolysis for intravascular thrombosis in neonates and children

PURPOSE OF REVIEW

Plasminogen activators stimulate the fibrinolytic pathway to accelerate thrombus resolution and can be used to treat serious and life-threatening arterial and venous thrombosis in neonates and children. The main disadvantage of these drugs is the risk of bleeding associated with their use. This article reviews the fibrinolytic pathway and discusses the current agents available for thrombolytic therapy, as well as indications for their use, dosing regimens, safety, and efficacy.

RECENT FINDINGS

There is great variation in the drug dosing regimens used for thrombolysis and in the incidence of bleeding complications that have been reported in pediatric series. Increased experience with these drugs, appropriate patient selection, and careful monitoring appear to have reduced the risk of major bleeding over time. The use of thrombolysis for occlusive deep vein thrombosis, in attempt to reduce the long-term complication of postthrombotic syndrome, is controversial and deserves further investigation.

SUMMARY

The use of thrombolytic therapy in pediatrics has increased over the past two decades. Urokinase and recombinant tissue plasminogen activator are the currently available thrombolytic agents. Catheter-related arterial thrombi that threaten life, organ or limb are the most common indication for their use. There is a tremendous need for well designed clinical studies to improve the safety and efficacy of these drugs in neonates and children.