Heparin Therapy during Cardiopulmonary Bypass in Children Requires Ongoing Quality Control

Use of Coagulation Point-of-Care Tests in the Management of Anticoagulation and Bleeding in Pediatric Cardiac Surgery: A Systematic Review

Bleeding and coagulation management are essential aspects in the management of neonates and children undergoing cardiac surgery. The use of point-of-care tests (POCTs) in a pediatric setting is not as widely used as in the adult setting. This systematic review aims to summarize the evidence showed by the literature regarding the use of POCTs in children undergoing cardiac surgery. We included all studies examining the pediatric population (<18 years old) undergoing cardiac surgery in which the coagulation profile was assessed with POCTs. Three electronic databases (PubMed, Embase, and the Cochrane Controlled Clinical Trials register) were searched. Tests involved were heparin effect tests, viscoelastic tests, and platelet function tests. Due to the wide heterogeneity of the patients and tests studied, a formal meta-analysis was impossible, and the results are therefore presented through a systematic review. Eighty articles were found, of which 47 are presented in this review. At present, literature data are too weak to define POCTs as a "gold standard" for the treatment of perioperative bleeding in pediatric cardiac surgery. Nevertheless, introduction of POCTs into postoperative algorithms has shown to improve bleeding management, patient outcome, and cost efficiency.

Hematologic concerns in extracorporeal membrane oxygenation

This ISTH "State of the Art" review aims to critically evaluate the hematologic considerations and complications in extracorporeal membrane oxygenation (ECMO). ECMO is experiencing a rapid increase in clinical use, but many questions remain unanswered. The existing literature does not address or explicitly state many pertinent details that may influence hematologic complications and, ultimately, patient outcomes. This review aims to broadly introduce modern ECMO practices, circuit designs, circuit materials, hematologic complications, transfusion-related considerations, age- and size-related differences, and considerations for choosing outcome measures. Relevant studies from the 2019 ISTH Congress in Melbourne, which further advanced our understanding of these processes, will also be highlighted.

Anticoagulation during ECMO in neonatal and paediatric patients

Extracorporeal Membrane Oxygenation (ECMO) is a form of Extracorporeal Life Support (ECLS) which is used frequently in the paediatric and neonatal setting to support either the pulmonary, or both the pulmonary and cardiac systems. Management of ECMO requires the use of systemic anticoagulation to prevent patient and circuit based thrombosis, which in turn increases the risk of haemorrhage. A number of coagulation tests, laboratory and point of care based, are used to monitor anticoagulation, however the evidence for correlation of the test results with level of anticoagulant and clinical outcomes in children remains poor.

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.

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.

Change in heparin potency and effects on the activated clotting time in children undergoing cardiopulmonary bypass

BACKGROUND

Heparin is the anticoagulant most commonly used for cardiopulmonary bypass (CPB), and the activated clotting time (ACT) is its primary monitor. In October 2009, the Food and Drug Administration changed the United States Pharmacopeia (USP) monograph for unfractionated heparin to incorporate new quality tests and a new potency assay and reference standard. This latter change was anticipated by in vitro tests to reduce heparin potency by 10% in each USP unit dose. After integration of the "new" heparin into our practice, we subjectively noticed less prolongation of the ACT with our routine heparin bolus before the initiation of CPB. We performed this investigation to provide objective evidence of a reduction in the level of anticoagulation achieved with use of the new heparin as assessed by ACT values and to document the occurrence of having an ACT below our institutional threshold before the initiation of CPB.

METHODS

A retrospective chart review was performed on all children who underwent CPB at Children's Healthcare of Atlanta between July 1, 2008, and June 30, 2009, before the release of the new heparin ("old heparin" [OH] group) and between June 1, 2010, and May 31, 2011, after complete integration of the new heparin ("new heparin" [NH] group). Baseline ACTs and ACTs after the administration of 400 U/kg of heparin were recorded for both the OH and NH groups. We determined the number of patients in each group having an ACT <480 seconds after the initial heparin bolus but before the initiation of CPB. Additionally, patients were divided into 3 age groups (<1 month, 1 to 12 months, and >1 year) to analyze similar ACT changes.

RESULTS

Postheparin ACTs were significantly lower in the NH group than in the OH group. There were significantly more patients having an ACT <480 seconds after the initial heparin bolus in the NH group (OH: 68 of 557 [12.2%] versus NH: 140 of 491 patients [28.5%]; P < 0.0001). The change remained significant when assessed across the age groups.

CONCLUSIONS

In this investigation we provide objective evidence that the level of anticoagulation after the initial pre-CPB heparin bolus as assessed by the ACT is significantly less with use of the new heparin. This reduction remained consistent across 3 age groups and was associated with a more frequent occurrence of ACTs below our institutional threshold for the initiation of CPB. Consideration should be given to increasing the initial weight-based heparin dose administered before CPB.

Point-of-care testing for anticoagulation monitoring in neuroendovascular procedures

POC testing is defined as diagnostic testing at or near the site of patient care. Rapid measurement of the intensity of anticoagulation and, more recently, platelet inhibition allows dose titration of adjuvant medications such a heparin and antiplatelet agents during neuroendovascular procedures. However, knowledge among practicing physicians regarding the pathophysiologic basis of these measurements and variations in knowledge about the differences among devices is often limited. This review discusses the role of anticoagulation in endovascular procedures and the currently available POC tests for anticoagulation monitoring.

Measurement of activated coagulation time in children: evaluation of the blood-saving kaolin i-STAT activated coagulation time technique in pediatric cardiac anesthesia

OBJECTIVE

To compare the activated coagulation times (ACTs) measured with the blood-saving kaolin i-STAT 1 ACT technique (Abbott Point of Care Inc, Princeton, NJ) with ACTs obtained from the widely used ACTR II device (Medtronic, Inc, Minneapolis, MN) in children undergoing cardiac surgery.

DESIGN

A prospective, observational single-center study.

PARTICIPANTS

Forty-four pediatric cardiac surgery patients.

INTERVENTION

Surgery was performed with cardiopulmonary bypass (CPB) necessitating heparinization.

METHODS AND MAIN RESULTS

ACTs measured on the i-STAT 1 device (2 × 95 μL) were compared with those obtained from the Medtronic ACTR II device (2 × 0.5 mL). Blood samples were drawn before, during, and after heparinization for CPB and paired for statistical analysis. The 2 techniques were compared using simple and multiregression analyses and the Bland-Altman method. In total, 179 intrarater and 142 interrater data pairs were analyzed. The intrarater reliability of the 2 devices was good, with a mean bias and limits of agreement of +2.0 and -55.5/+59.5 seconds for the Medtronic ACTR II and +0.5 and -59.9/+60.9 seconds for the i-STAT 1. An interrater reliability analysis of the mean of simultaneously measured ACT of the Medtronic ACTR II and both i-STAT 1 devices yielded a mean bias of -5.3 seconds and limits of agreement of -210.1/+199.5 seconds. A comparison of the higher of the paired ACT values from both devices showed similar results. After the removal of heparin, the i-STAT 1's ACT values became significantly lower than those measured on the Medtronic ACTR II (p < 0.001). Simple and multiregression analyses revealed that base excess independently influenced the mean bias of the ACT values from the Medtronic ACTR II (p = 0.037) and i-STAT 1 devices (p = 0.036).

CONCLUSION

The kaolin i-STAT 1 ACT technique agreed well with the Medtronic ACTR II technique during the nonheparinized phase that preceded CPB. The overall agreement between the ACT obtained from the 2 devices was poor. The routine use of i-STAT 1 measured ACT values cannot be recommended as a reliable alternative to the Medtronic ACTR II.

Establishing an association between a peri-operative perfusion score system (PerfSCORE) and post-operative patient morbidity/mortality during CPB cardiac surgery

BACKGROUND

To date, there is no quality assurance program that correlates patient outcome to perfusion service provided during cardiopulmonary bypass (CPB). A score was devised, incorporating objective parameters that would reflect the likelihood to influence patient outcome. The purpose was to create a new method for evaluating the quality of care the perfusionist provides during CPB procedures and to deduce whether it predicts patient morbidity and mortality.

METHODS

We analysed 295 consecutive elective patients. We chose 10 parameters: fluid balance, blood transfused, Hct, ACT, PaO2, PaCO2, pH, BE, potassium and CPB time. Distribution analysis was performed using the Shapiro-Wilcoxon test. This made up the PerfSCORE and we tried to find a correlation to mortality rate, patient stay in the ICU and length of mechanical ventilation. Univariate analysis (UA) using linear regression was established for each parameter. Statistical significance was established when p < 0.05. Multivariate analysis (MA) was performed with the same parameters.

RESULTS

The mean age was 63.8 +/- 12.6 years with 70% males. There were 180 CABG, 88 valves, and 27 combined CABG/valve procedures. The PerfSCORE of 6.6 +/- 2.4 (0-20), mortality of 2.7% (8/295), CPB time 100 +/- 41 min (19-313), ICU stay 52 +/- 62 hrs (7-564) and mechanical ventilation of 10.5 +/- 14.8 hrs (0-564) was calculated. CPB time, fluid balance, PaO2, PerfSCORE and blood transfused were significantly correlated to mortality (UA, p < 0.05). Also, CPB time, blood transfused and PaO2 were parameters predicting mortality (MA, p < 0.01). Only pH was significantly correlated for predicting ICU stay (UA). Ultrafiltration (UF) and CPB time were significantly correlated (UA, p < 0.01) while UF (p < 0.05) was the only parameter predicting mechanical ventilation duration (MA).

CONCLUSIONS

CPB time, blood transfused and PaO2 are independent risk factors of mortality. Fluid balance, blood transfusion, PaO2, PerfSCORE and CPB time are independent parameters for predicting morbidity. PerfSCORE is a quality of perfusion measure that objectively quantifies perfusion performance.

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.

Devices for Monitoring Heparin and Protamine in the Operating Room

Ongoing monitoring of heparin anticoagulation is an essential component of many cardiothoracic and vascular surgical procedures in order to prevent significant thrombotic and hemorrhagic complications. The classic test to assess high-dose (>1 unitlmL) heparin anticoagulation is the activated clotting time. Although simple to perform, the activated clotting time has many variations and can be affected by a number of nonanalytical and patient-related factors. Correlation with the heparin concentration may be poor. Alternatively, other test systems assess the individual patient's responsiveness to heparin in order to customize the heparin administration and subsequent protamine neutralization. The choice of test and system depends on the clinical application and the desired outcome. Regulatory and accreditation standards govern this type of testing; modern instrumentation can facilitate compliance with these standards. Understanding of the nature of the test and its performance under a variety of conditions is critical for proper interpretation.

Monitoring anticoagulation and hemostasis in cardiac surgery

The need to monitor anticoagulation and hemostasis during and after cardiac surgery has led to recognition of the importance of evaluation and use of hemostasis monitors in this setting. Consequently, rapid and accurate identification of abnormal hemostasis has been the major impetus for the development of point-of-care tests and their use in transfusion algorithms for cardiac surgical and other critically ill patients.

Whole blood heparin concentrations do not correlate with plasma antifactor Xa heparin concentrations in pediatric patients undergoing cardiopulmonary bypass

This study was designed to test the validity of whole blood heparin concentration (WHBC) measurements using an on-site protamine titration assay with the Hepcon instrument (Medtronic Blood Management, Parker, CO, USA) in pediatric patients less than 1 year old undergoing cardiopulmonary bypass (CPB). The validity of the Hepcon measurements was examined via a test of correlation with the gold standard plasma antifactor Xa activity (anti-Xa) assay. Fifty-one patients (23 females and 28 males) under 1 year old (mean age 5.3 months) were studied prospectively. Blood samples were taken at 5 min into CPB and at the end of CPB for the WBHC, plasma anti-Xa activity, and hematocrit (Hct). The WBHC was converted to plasma heparin level using a formula taking into account the collection of blood into citrate solution and the effect of the citrate on the hematocrit. While a nonparametric statistical analysis revealed that the mean corrected values from the Hepcon instrument were not significantly different from the mean anti-Xa values (p = 0.070 at 5 min on CPB, p = 0.518 at the end of CPB), there was no significant correlation between these values at either 5 min into CPB (r = 0.113, p = 0.429) or at the end of CPB (r = -0.247, p = 0.080). The lack of correlation between the two assays may be related to the extreme hemodilution observed during CPB in small children, which leads to very low concentrations of coagulation proteins. Due to this discrepancy, whole blood heparin monitors should be further evaluated in children undergoing CPB.

Low Molecular Weight Heparin: An Evaluation of Current and Potential Clinical Utility in Surgery

Heparin, a mixture of glycosaminoglycans of various sizes, is a potent natural anticoagulant. Low molecular weight heparins (LMWH) contain only the polymers of smaller size, which appear to possess most of the antithrombotic potential. Pharmacological differences between the two suggest a number of advantages with LMWH therapy. Our objective was to establish the utility of LMWHs in comparison to the current practice of anticoagulation in surgical patients. Articles were obtained through MEDLINE and CURRENT CONTENTS queries. The searches were limited to English and French-language articles and included published overviews containing relevant individual trials. We examined the current literature, consisting of 1,730 published reports from 1979-1998, regarding the biochemistry, pharmacology, physiology, and clinical applications of LMWH in comparison with current therapy. Studies were selected based on their relevance to LMWHs, the size and methods of trials, and their application to clinical care. Peer-reviewed published data were critically evaluated by independent extraction by several authors. Established rules for levels of evidence were used to objectively evaluate the strength of evidence supporting recommendations in each clinical area. LMWHs provide superior anticoagulation in the prophylaxis of DVT following orthopedic, general, and trauma surgery. Further studies should establish which other patients may benefit from such prophylaxis. Current evidence does not support the use of LMWHs in patients with mechanical heart valves or those on mechanical cardiac support devices; however, it may have a role in the maintenance of vascular graft patency. Further studies should examine the role of LMWHs in transplant atherosclerosis, and in patients requiring long-term anticoagulation at high risk for bleeding with warfarin therapy. The economic implications of LMWH administration remain unclear. On the basis of the information presented in this review, LMWHs are promising new agents in prophylaxis and treatment of both arterial and venous thrombosis. In the near future, LMWHs are likely to supplant UFH and perhaps warfarin in many applications.http://link.springer-ny.com/link/service/journals/00547/bibs/8n4p203.html</hea

Comparison of the effects of red cell separation and ultrafiltration on heparin concentration during pediatric cardiac surgery

OBJECTIVE

To determine the effects of red cell separation and ultrafiltration on heparin concentration.

DESIGN

Prospective study.

SETTING

University-affiliated, pediatric medical center.

PARTICIPANTS

Thirty-one children undergoing cardiac surgery.

INTERVENTIONS

Blood sampled for heparin concentration and coagulation tests.

MEASUREMENTS AND MAIN RESULTS

Thirteen infants under-went modified veno-venous ultrafiltration (UF) after cardiopulmonary bypass (CPB). In addition, residual blood in the CPB circuit was hemoconcentrated by UF and reinfused (UF group). Heparin concentration increased from 2.0 +/- 0.6 to 2.5 +/- 0.8 U/mL, following modified UF; while activated coagulation time (ACT) decreased from 701 +/- 177 to 627 +/- 107 seconds. Heparin concentration of CPB circuit residual increased from 1.9 +/- 0.7 to 3.1 +/- 1.0 U/mL. In 18 children (older than 1 year old), the residual blood in the CPB circuit was hemoconcentrated by cell separation (CS) and reinfused (CS group). Heparin concentration of CPB circuit residual decreased from 2.6 +/- 0.6 to 0.3 +/- 0.2 U/mL. After reinfusion, patient heparin concentration remained unchanged at < 0.05 U/mL. Thrombin time increased from 28 +/- 6 to 48 +/- 29 seconds and did not correlate with H.

CONCLUSIONS

The plasma concentration of heparin increased after veno-venous modified UF of the patient. Heparin concentration also increased after UF of residual CPB circuit blood. In contrast, circuit blood hemoconcentrated by CS contained minimal heparin, and, when infused, did not increase patient's heparin concentration. ACT and thrombin time did not correlate with heparin concentration.

Age-related differences in heparin sensitivity and heparin-protamine interactions in cardiac surgery patients

OBJECTIVE

The present study was conducted to determine how children and adults differ (it at all) with respect to sensitivity to heparin activity and heparin-protamine interactions during cardiac surgery requiring cardiopulmonary bypass (CPB).

DESIGN

A prospective study of both children and adults undergoing CPB.

SETTING

A tertiary care academic medical center between July 1992 and October 1994.

PARTICIPANTS

Ninety patients who had cardiac or aortic arch surgery using CPB. The median age of the entire study sample was 15.8 years (range 2 months to 72 years).

INTERVENTION

Data were obtained using the Medtronic Hemotec Hepcon Hemostasis Management System (Englewood, CO). An ex vivo heparin dose-response (HDR) curve was generated for each patient before skin incision to determine the target heparin concentration (THC) needed to achieve an activated coagulation time (ACT) of at least 480 seconds. Protamine dose was determined on the basis of whole blood heparin concentration estimated by means of a heparin-protamine titration.

MEASUREMENTS AND MAIN RESULTS

The study population was divided into four groups based on age: infants (< 1 year), preschool (1 to 5 years), school-age (5 to 14 years) and adults (> 14 years). The mean +/- SD THC for the preschool group was 4.0 +/- 1.1; for infants, 3.3 +/- 0.7; for school-age, 3.1 +/- 0.7; and for adults, 3.4 +/- 0.7. The initial dose of heparin needed to achieve this THC (mean +/- SD) was significantly higher in infants (578 +/- 220 U/kg) and preschool children (477 +/- 159 U/kg) than in school-age children (327 +/- 57 U/kg) and adults (332 +/- 64 U/kg). The ratio of protamine to heparin was significantly higher in adults (1.4 +/- 0.5) and school-age children (1.3 +/- 0.6) than in infants (1.1 +/- 0.7) and preschool children (1.1 +/- 0.4).

CONCLUSIONS

Pre-school children are less sensitive to heparin but also display a wider range of sensitivity. The data in this study support the use of 300 U/kg of heparin before CPB in patients > or = 5 years but suggest that heparin requirements may be greater in the younger patient who may require as much as 500 U/kg to achieve what is believed to be an appropriate target heparin concentration for initiating CPB.

The activated coagulation time: suitability for monitoring heparin effect and neutralization during pediatric cardiac surgery

OBJECTIVES

To determine how the stage of surgery affects the relationship between activated clotting time (ACT) and heparin effect in children undergoing cardiac surgery using cardiopulmonary bypass (CPB) and to compare the results of ACT determinations made with two different coagulation timers using different clot detection technologies and activator compositions.

DESIGN

Prospective, paired observation.

SETTING

Tertiary care children's hospital affiliated with an academic medical center.

PARTICIPANTS

Fifty-eight children scheduled for nonprimary cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

ACTs were measured by two different commercially available automated coagulation timers (Hepcon Hemostasis Management System [HP] and the Hemochron model 801 [HM]) at four different time points over the course of cardiac surgery requiring CPB in patients ranging in age from 0.16 to 19 years. Simultaneous determinations of whole blood heparin concentration using heparin-protamine titrations were made as well. When the two methods of ACT determination were compared, baseline ACTs were not significantly different. HP ACT prolongation after heparin administration but before bypass was significantly less than HM ACT prolongation (median ACT range HM > or = 999 seconds; HP, 560 to 679; p = 0.006). Twenty-one percent of the HP ACTs and none of the HM ACTs fell below the 480 seconds required at this institution for the initiation of CPB (p = 0.008). Both instruments showed a significant further prolongation of ACT after initiation of bypass (median ACT range HP > or = 999 seconds; HM > or = 999; p < 0.001 for both), whereas the heparin concentration decreased significantly (before, 3.5 +/- 0.2 U/mL; after, 2.7 +/- 0.1; p < 0.001). After termination of CPB and heparin neutralization, no significant difference between the ACTs was found. However, four HP ACTs were > or = 999 seconds despite simultaneous HM baseline values and whole blood heparin concentrations of zero. Heparin concentration correlated with ACT prolongation using both the HM (Spearman p = 0.36; p = 0.02) and the HP (Spearman p = 0.57; p = 0.0025) instruments before, but not 10 minutes after, initiation of bypass.

CONCLUSIONS

In pediatric cardiac surgery, the relationship between ACT and heparin concentration changes depending on when during the surgery the ACT is measured. ACT prolongation in children anticoagulated for CPB correlates poorly with heparin concentrations during CPB. HP and HM ACT tests are not interchangeable. The HM ACT is a better indicator of heparin neutralization than the HP ACT. On the other hand, continued prolongation of the HP ACT after heparin neutralization may be related to risk of postoperative hemorrhagic complications. If devices from different manufactures are freely substituted for each other, clinical practice may be altered in an uncontrolled manner.