An Evaluation of the Effects of a Standard Heparin Dose on Thrombin Inhibition During Cardiopulmonary Bypass in Neonates

Recent achievements and future developments in neonatal cardiopulmonary bypass

A primary goal of improving neonatal cardiopulmonary bypass has been making the circuit smaller and reduce the blood contacting surfaces. As bypass circuit size has decreased, bloodless surgery has become possible even in neonates. Since transfusion guidelines are difficult to construct based on existing literature, these technical advances should be taken advantage of in conjunction with an individualized transfusion scheme, based on monitoring of oxygen availability to the tissues. For the majority of neonatal heart operations, several centers have shifted toward normothermic bypass even for complex neonatal surgeries, in order to avoid the adverse effects of hypothermia. Deep hypothermic circulatory arrest is no longer a necessity but an option, and selective antegrade cerebral perfusion has become common practice; however, technical uncertainties with regard to this technique have to be addressed, based on reliable neurologic monitoring. Maintenance of patient-specific heparin concentrations during bypass is another key goal, since neonates have lower baseline antithrombin concentrations and, therefore, a higher risk for inadequate thrombin inhibition and postoperative bleeding. Due to the immaturity of their hemostatic system, the standard coagulation tests alone are inappropriate to guide hemostatic therapy in neonates. The use of indirect heparin concentration assays and global viscoelastic assays in the operating room is likely to represent the optimal strategy, and requires validation in neonates. Monitoring of global and regional indexes of oxygen availability and consumption on bypass have become possible; however, their use in neonates still has outstanding technical issues which should be addressed and hence needs further validation. Due to the immaturity of the neonatal myocardium, single-shot cold cardioplegia solutions are thought to confer the best myocardial protection; their superiority when compared to more conventional modalities, however, remains to be demonstrated.

The Norwood Stage 1 procedure - conduct of perfusion: 2017 Survey results from NPC-QIC member institutions

Hypoplastic left heart syndrome (HLHS) is a rare and severe congenital cardiac defect. Approximately 1000 infants are born with HLHS in the United States every year. Healthcare collaboratives over the last decade have focused on sharing patient experiences and techniques in an effort to improve outcomes. In 2010, cardiologists and patient families joined together to improve the care of HLHS patients by forming the National Pediatric Cardiology Quality Improvement Collaborative (NPC-QIC). Sixty-six of the approximately 110 institutions caring for patients with HLHS in the United States and Canada are now members of NPC-QIC. In 2017, cardiovascular perfusionists joined the collaborative as another specialty involved in the care of HLHS patients. Perfusionists and cardiac surgeons developed the collaborative’s first conduct of perfusion survey for the Norwood Stage 1 procedure, specifically targeting the provision of cardiopulmonary bypass for patients with HLHS. This manuscript discusses the results of this survey, unveiling a significant variance in the conduct of perfusion for this patient population.

Anti-activated factor II assay for monitoring unfractionated heparin in children: results of the HEARTCAT study

Essentials Unfractionated heparin has variable effects in children and therefore, monitoring is essential. A randomized controlled trial substudy investigating an anti-IIa assay in children was conducted. Anti-IIa values are lower in younger children, an effect more pronounced at low-dose heparin. Heparin effect on Xa and IIa is not equal, particularly in infants and after high-dose heparin.

SUMMARY

Background Unfractionated heparin (UFH) is used for the prophylaxis and treatment of thrombosis in children. Laboratory monitoring of UFH is needed to prevent over-anticoagulation or under-anticoagulation. Objectives To investigate the association between UFH dose and UFH effect as monitored with the anti-activated factor II (FIIa) assay, the relationship between anti-FIIa and anti-activated factor X (FXa) effects, and the influence of patient age and other factors on UFH effect. Patients and methods This was a randomized controlled trial in children during cardiac catheterization, comparing high-dose UFH (100 units kg-1 bolus) with low-dose UFH (50 units kg-1 bolus). Blood samples were drawn at baseline, and after 30 min, 60 min, and 90 min. For the purpose of this study, 49 children and 117 blood samples were evaluated. Results The anti-FIIa assay discriminated well between high-dose and low-dose UFH. Multiple regression demonstrated significant influences of UFH dose and age on anti-FIIa levels. Younger children had lower anti-FIIa levels than older children, an effect that was more pronounced with low-dose UFH. Anti-FXa/anti-FIIa ratios were equal with low-dose UFH. However, anti-FXa levels were relatively increased over anti-FIIa levels in infants and after high-dose UFH bolus administration. Conclusion The UFH effect on anti-FIIa levels is lower in infants than in older children. This influence of age appears to be dose-dependent, being more pronounced with low-dose UFH. Anti-FXa and anti-FIIa levels are not equal, particularly in infants and after high-dose UFH. Monitoring UFH solely with anti-FXa assays may not be sufficient in children, and the anti-FIIa assay may provide important complementary information.

Development of a population pharmacokinetic-pharmacodynamic model of a single bolus dose of unfractionated heparin in paediatric patients

BACKGROUND

Unfractionated heparin (UFH) is the anticoagulant of choice in paediatric patients undergoing a variety of cardiac procedures. There are currently no population pharmacokinetic-pharmacodynamic (PKPD) models for UFH in paediatrics.

OBJECTIVE

The aim of the present study was to develop and evaluate a PKPD model of UFH in paediatrics.

METHODS

Data from 64 children who received 75-100 IU kg(-1) of UFH during cardiac angiography were analysed. Five blood samples were collected at baseline and at 15, 30, 45 and 120 min postdose. The UFH concentration was quantified using a protamine titration assay. The UFH effect was quantified using activated partial thromboplastin time (aPTT). A PKPD model was fitted using nonlinear mixed-effects modelling. Patient covariates such as gender, weight (WT) and fat-free mass (FFM) were tested. The final model was evaluated using the likelihood ratio test and visual predictive checks (VPCs).

RESULTS

A one-compartment model with linear elimination provided the best fit for the dose-concentration data. FFM was a significant covariate on clearance. A linear model provided the best fit for the concentration-effect data using aPTT as a biomarker for effect. The models performed well using VPCs. However, when used to simulate UFH infusion (at a much lower dose), the model overpredicted target aPTT responses.

CONCLUSIONS

A PKPD model to describe the time course of the UFH effect was developed in a paediatric population. FFM was shown to describe drug disposition well. However, when applied to smaller UFH infusion doses, the model overpredicted target aPTT responses. This unsuccessful extrapolation may be attributed to a possible nonlinear relationship for heparin PKPD.

Cyanotic congenital heart disease (CCHD): focus on hypoxemia, secondary erythrocytosis, and coagulation alterations

Children with cyanotic congenital heart disease (CCHD) have complex alterations in their whole blood composition and coagulation profile due to long-standing hypoxemia. Secondary erythrocytosis is an associated physiological response intended to increase circulating red blood cells and oxygen carrying capacity. However, this response is frequently offset by an increase in whole blood viscosity that paradoxically reduces blood flow and tissue perfusion. In addition, the accompanying reduction in plasma volume leads to significant deficiencies in multiple coagulation proteins including platelets, fibrinogen and other clotting factors. On the one hand, these patients may suffer from severe hyperviscosity and subclinical 'sludging' in the peripheral vasculature with an increased risk of thrombosis. On the other hand, they are at an increased risk for postoperative hemorrhage due to a complex derangement in their hemostatic profile. Anesthesiologists caring for children with CCHD and secondary erythrocytosis need to understand the pathophysiology of these alterations and be aware of available strategies that lessen the risk of bleeding and/or thrombosis. The aim of this review is to provide an updated analysis of the systemic effects of long-standing hypoxemia in children with primary congenital heart disease with a specific focus on secondary erythrocytosis and hemostasis.

Monitoring unfractionated heparin in children: a parallel-cohort randomized controlled trial comparing 2 dose protocols

Monitoring unfractionated heparin (UFH) is crucial to prevent over- or under-anticoagulation. However, the optimal parameters for monitoring UFH in children are not well established. The study objectives were to investigate (1) the relationship between UFH dose and its anticoagulant effect as assessed by anti-Xa, activated partial thromboplastin time (aPTT) and activated clotting time (ACT); (2) other factors influencing UFH effect; (3) the agreement between the assays; and (4) the association between UFH effect and clinical outcome. HEARTCAT was a parallel-cohort randomized controlled trial comparing high-dose (100 U/kg bolus followed by age-based continuous infusion in randomized children) vs low-dose UFH (50 U/kg bolus) during cardiac catheterization in children. Blood samples were drawn before and after UFH administration at 30, 60, and 90 minutes. Four-hundred and two samples of 149 patients were evaluable. Anti-Xa, aPTT, and ACT all showed good discrimination between UFH doses. Regression models demonstrated the following determinants of UFH effect: UFH dose, age, baseline antithrombin (for anti-Xa), and baseline levels of aPTT and ACT, respectively. UFH effects were lower in infants compared with older children, which was more pronounced at low-dose than at high-dose UFH. Agreement between the 3 assays was poor. Most aPTT values were above therapeutic range or beyond measuring limit and thus of limited value for UFH monitoring. No association of UFH dose or effect with clinical outcome could be observed. In conclusion, all assays reflected a significant UFH dose-effect relationship, however, with poor agreement between the respective tests. The age-dependency of UFH effect was confirmed. Notably, the influence of age on UFH effect was dose-dependent.

In vitro evaluation and in vivo demonstration of a biomimetic, hemocompatible, microfluidic artificial lung

Despite the promising potential of microfluidic artificial lungs, current designs suffer from short functional lifetimes due to surface chemistry and blood flow patterns that act to reduce hemocompatibility. Here, we present the first microfluidic artificial lung featuring a hemocompatible surface coating and a biomimetic blood path. The polyethylene-glycol (PEG) coated microfluidic lung exhibited a significantly improved in vitro lifetime compared to uncoated controls as well as consistent and significantly improved gas exchange over the entire testing period. Enabled by our hemocompatible PEG coating, we additionally describe the first extended (3 h) in vivo demonstration of a microfluidic artificial lung.

Pharmacokinetics and pharmacodynamics of anticoagulants in paediatric patients

Given the rising incidence of thrombotic complications in paediatric patients, understanding of the pharmacologic behaviour of anticoagulant drugs in children has gained importance. Significant developmental differences between children and adults in the haemostatic system and pharmacologic parameters for individual drugs highlight potentially unique aspects of anticoagulant pharmacology in this special and vulnerable population. This review focuses on pharmacologic information relevant to the dosing of unfractionated heparin, low molecular weight heparin, warfarin, bivalirudin, argatroban and fondaparinux in paediatric patients. The bulk of clinical experience with paediatric anticoagulation rests with the first three of these agents, each of which requires higher bodyweight-based dosing for the youngest patients, compared with adults, in order to achieve comparable pharmacodynamic effects, likely related to an inverse correlation between age and bodyweight-normalized clearance of these drugs. Whether extrapolation of therapeutic ranges targeted for adult patients prescribed these agents is valid for children, however, is unknown and a high priority for future research. Novel oral anticoagulants, such as dabigatran, rivaroxaban and apixaban, hold promise for future use in paediatrics but require further pharmacologic study in infants, children and adolescents.

Use of Confidex to control perioperative bleeding in pediatric heart surgery: prospective cohort study

Bleeding during and after cardiac surgery is a major issue in pediatric patients. A prospective cohort study was conducted to evaluate the effect of a commercially available prothrombin complex (Confidex) administered in cardiac surgery after weaning from cardiopulmonary bypass of infants with nonsurgical bleeding. In this study, 14 patients younger than 1 year received a Confidex bolus and were matched with 11 patients of a similar age who did not receive the drug. The preoperative coagulation profile was similar in the two groups. No side effects, including anaphylaxis or thrombotic events, were observed. The numbers of units of packed red blood cells and fresh frozen plasma administered both intra- and postoperatively were similar. The postoperative coagulation examination results and thromboelastographic parameters did not differ significantly between the two groups. However, the Confidex patients bled significantly less than the control subjects during the first 24 postoperative hours. The median volume of drained blood was 0.0 ml/kg h (range 0-1.9 ml/kg h) compared with 1.9 ml/kg h (range 1-3 ml/kg h) (p = 0.009). At least one unit of packed red blood cells in the postoperative phase was required by 2 patients (14 %) in the Confidex group and six patients (54 %) in the control group (odds ratio [OR], 0.13; 95 % confidence interval [CI], 0.02-0.9; p = 0.03). The median duration of mechanical ventilation was 3 days (range 2-4 days) in the Confidex group and 4 days (range 0-8 days) in the control group (p = 0.66). The median stay in the intensive care unit was 6 days (range 5-9 days) in the Confidex group and 7 days (range 4-12 days) in the control group (p = 0.88). The use of Confidex for infants undergoing cardiac surgery was safe and effective. It reduced postoperative bleeding and allowed fewer units of packed red blood cells to be infused in the postoperative phase without major side effects.

Coagulation and the surgical neonate

Both coagulopathy and abnormal thrombosis can complicate the anesthetic and surgical management of neonatal patients; however, the patterns of bleeding and thrombosis in neonates differ from those in adults or older children. Severe coagulopathic bleeding most commonly occurs during heart surgery and almost certainly contributes to morbidity and mortality in this population. Such severe bleeding is rare during other surgery; the exception is babies presenting to the operating room with established coagulopathy secondary to severe sepsis. Alternatively, pathological thrombosis will mainly occur in association with indwelling vascular access devices or surgically created vascular shunts. There are important differences between the coagulation system in neonates and older patients. The implication of this is that therapies established in other patient groups will not be optimal for neonates without adaptation. While evidence from high-quality clinical trials is rarely available, an understanding of how coagulation in neonates differs can help to guide practice. This review will discuss important differences between the coagulation system of neonates and older patients and how these relate to newer models of coagulation. The emphasis will be on issues likely to impact on perioperative care. In particular, the management of severe bleeding, the manipulation of coagulation during heart surgery, and the management of coagulopathy in septic neonates will be discussed in detail.

Changes in fibrinopeptide A peptides in the sera of rats chronically exposed to low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a ubiquitously distributed endocrine disruptors. To investigate peptide changes in the sera of rats chronically exposed to TCDD and to explore the association of these changes with liver morphology, TCDD was administrated to male rats at doses of 140, 350, and 875 ng/kg/week for 29 weeks. Serum was collected and proteomic analysis was performed using automated Bruker Daltonics ClinProt with matrix-assisted laser desorption/ionization time-of-flight mass spectrometer. One peptide at 1740.89 was found to be significantly decreased and further identified with nano LC-MS/MS system. The MS BLAST homology search engine reported the peptide to be a partial sequence of fibrinopeptide A. Liver fatty degeneration and necrosis were assessed by hematoxylin and eosin staining. Liver fatty degeneration and necrosis were both found to be significantly increased after TCDD exposure. Levels of fibrinopeptide A were significantly correlated with liver fatty degeneration and necrosis.

Coagulation considerations for infants and children undergoing cardiopulmonary bypass

Cardiac surgery involving cardiopulmonary bypass imposes a significant pathophysiologic burden on patients. Pediatric patients are especially predisposed to the adverse effects of surgery and bypass on the coagulation system, with resultant bleeding, transfusion, and poor outcomes. These risks accrue to pediatric patients in inverse proportion to their weight and are attributable to hematologic immaturity, coagulation defects associated with congenital heart disease, bypass equipment, and the nature of congenital heart surgery. Standard anticoagulation does not completely inhibit thrombin generation, and continuous consumption of coagulation factor continues throughout bypass. Conventional measurements of anticoagulation during bypass poorly reflect this incomplete anticoagulation, and alternate methods may improve anticoagulant therapy. Emerging therapies for blocking the effects of bypass on the coagulation system hold promise for decreasing bleeding and related complications, and improving outcomes in congenital heart surgery.

The relationship among thromboelastography, hemostatic variables, and bleeding after cardiopulmonary bypass surgery in children

BACKGROUND

Mediastinal bleeding is common after pediatric cardiopulmonary bypass (CPB) surgery. Thromboelastography (TEG) may predict bleeding and provide insight into likely mechanisms. We aimed to (a) compare perioperative temporal profiles of TEG and laboratory hemostatic variables between patients with significant hemorrhage (BLEED) and those without (CONTROL), (b) investigate the relationship between TEG variables and routine hemostatic variables, and (c) develop a model for prediction of bleeding.

METHODS

TEG and laboratory hemostatic variables were measured prospectively at 8 predefined times for 50 children weighing <20 kg undergoing CPB.

RESULTS

Patients who bled demonstrated different TEG profiles than those who did not. This was most apparent after protamine administration and was partly attributable to inadequate heparin reversal, but was also associated with a significantly lower nadir in mean (sd) fibrinogen for the BLEED group compared with CONTROL group: 0.44 (0.18) and 0.71 (0.40) g/L, respectively (P = 0.01). Significant nonlinear relationships were found between the majority of TEG and laboratory hemostatic variables. The strongest relationship was between the maximal amplitude and the platelet-fibrinogen product (logarithmic r(2) = 0.71). Clot strength decreased rapidly when (a) fibrinogen concentration was <1 g/L, (b) platelets were <120 x 10(9)/L, and (c) platelet-fibrinogen product was <100. A 2-variable model including the activated partial thromboplastin time at induction of anesthesia and TEG mean amplitude postprotamine discriminated well for subsequent bleeding (C statistic 0.859).

CONCLUSIONS

Hypofibrinogenemia and inadequate heparin reversal are 2 important factors contributing to clot strength and perioperative hemorrhage after pediatric CPB. TEG may be a useful tool for predicting and guiding early treatment of mediastinal bleeding in this group.

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.

Monitoring Unfractionated Heparin (UFH) therapy: Which Anti Factor Xa assay is appropriate?

INTRODUCTION

Anti-Factor Xa (Anti-Xa) assays specifically determine the anticoagulant activity of UFH by measuring the ability of heparin-bound Antithrombin (AT) to inhibit a single enzyme, Factor Xa (FXa). Recent improvements in the automation, cost-effectiveness and accessibility of the assay to clinicians, have resulted in the Anti-Xa assay becoming a part of daily clinical practice in many institutions.

OBJECTIVES

We hypothesized that different Anti-Xa assays have different applicability for use in clinical settings, depending on the amount of UFH administered. This was investigated in a tertiary paediatric institution.

MATERIALS AND METHODS

Samples were collected from children receiving Low-dose of UFH of at least 10 IU/kg/h, with or without a previous bolus of up to 25 IU/kg/h, within the previous 6 h in the PICU and HDU. High-dose UFH population consisted of children undergoing Cardiac Catheterization (CC), who received a bolus of UFH of 100 IU/kg body weight, 30 min prior to sampling.

RESULTS AND CONCLUSIONS

The Anti-Xa activity for a given dose of UFH was found to vary significantly based on the Anti-Xa assay and the population being monitored. Our study suggests that the MODIFIED COMATIC Anti-Xa assay provides the best physiological measure of the UFH effect in children, as it does not introduce sources of error, such as exogenous AT, which may increase the measured ant Factor Xa activity, nor Dextran Sulphate which can displace plasma protein bound heparin and once again leading to falsely elevated assay results. Further studies that include assessment of clinical outcomes are required to confirm the applicability of use of this particular assay in monitoring UFH therapy.

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.