Variability of the Activated Coagulation Time

Does heparin rebound lead to postoperative blood loss in patients undergoing cardiac surgery with cardiopulmonary bypass?

BACKGROUND

Heparin rebound is a common observed phenomenon after cardiac surgery with CPB and is associated with increased postoperative blood loss. However, the administration of extra protamine may lead to increased blood loss as well. Therefore, we want to investigate the relation between heparin rebound and postoperative blood loss and the necessity to provide extra protamine to reverse heparin rebound.

METHODS

We searched PubMed, Cochrane, EMBASE, Google Scholar and Web of Science to review the question: "Does heparin rebound lead to postoperative blood loss in patients undergoing cardiac surgery with cardiopulmonary bypass." Combination of search words were framed within four major categories: heparin rebound, blood loss, cardiac surgery and cardiopulmonary bypass. All studies that met our question were included. Quality assessment was performed using the Cochrane risk of bias (RoB2) tool for randomized controlled trials and the risk of bias in non-randomized studies of intervention (ROBINS-I) for non-randomised trials.

RESULTS

4 randomized and 17 non-randomized studies were included. The mean incidence of heparin rebound was 40%. The postoperative heparin levels, due to heparin rebound, were often below or equal to 0.2 IU/mL. We could not demonstrate an association between heparin rebound and postoperative blood loss or transfusion requirements. However the quality of evidence was poor due to a broad variety of definitions of heparin rebound, measured by various coagulation tests and studies with small sample sizes.

CONCLUSION

The influence of heparin rebound on postoperative bleeding seems to be negligible, but might get significant in conjunction with incomplete heparin reversal or other coagulopathies. For that reason, it might be useful to get a picture of the entire coagulation spectrum after cardiac surgery, as can be done by the use of a viscoelastic test in conjunction with an aggregometry test.

Accurate protamine:heparin matching (not just smaller protamine doses) decreases postoperative bleeding in cardiac surgery; results from a high-volume academic medical center

BACKGROUND

A multidisciplinary Quality Assurance/Performance Improvement study to identify the incidence of "heparin rebound" in our adult cardiac surgical population instead detected a thromboelastometry pattern suggestive of initial protamine overdose in 34% despite Hepcon-guided anticoagulation management. Analysis of our practice led to an intervention that made an additional lower-range Hepcon cartridge available to the perfusionists.

METHODS

One year later, an IRB-approved retrospective study was conducted in >500 patients to analyze the effects of the intervention, specifically focusing on the impact of the initial protamine dose accuracy and 18-h mediastinal chest tube drainage (MCTd).

RESULTS

No differences were observed between group demographics, surgical procedures, duration of CPB or perioperative blood product transfusion. Both groups were managed using the same perfusion and anesthesia equipment, strategies, and protocols. The median initial protamine dose decreased by 19% (p < .001) in the intervention group (170 [IQR 140-220] mg; n = 295) versus the control group (210 [180-250] mg; n = 257). Mean 18-h MCTd decreased by 13% (p < .001) in the intervention group (405.15 ± 231.54 mL; n = 295) versus the control group (466.13 ± 286.73 mL; n = 257). Covariate-adjusted mixed effects model showed a significant reduction of MCTd in the intervention group, starting from hour 11 after surgery (group by time interaction p = .002).

CONCLUSION

Though previous investigators have associated lower protamine doses with less MCTd, this study demonstrates that more accurately matching the initial protamine dose to the remaining circulating heparin concentration reduces postoperative bleeding.

Heparin Rebound: An In-Depth Review

The common conception of "heparin rebound" invokes heparin returning to circulation in the postoperative period after apparently adequate intraoperative reversal with protamine. This is believed to portend increased postoperative bleeding and provides the rationale for administering additional empiric doses of protamine in response to prolonged coagulation tests and/or bleeding. However, the relevant literature of the last 60+ years provides only a weak level of evidence that "rebounded" heparin itself is a significant etiology of postoperative bleeding after cardiac surgery with cardiopulmonary bypass. Notably, many of the most frequently cited heparin rebound investigators ultimately concluded that although exceedingly low levels of heparin activity could be detected by anti-Xa assay in some (but not all) patients postoperatively, there was no correlation with actual bleeding. An understanding of the literature requires a careful reading of the details because the investigators lacked standardized definitions for "heparin rebound" and "adequate reversal" while studying the phenomenon with significantly different experimental methodologies and laboratory tests. This review was undertaken to provide a modern understanding of the "heparin rebound" phenomenon to encourage an evidence-based approach to postoperative bleeding. Literature searches were conducted via PubMed using the following MeSH terms: heparin rebound, heparin reversal, protamine, platelet factor 4, and polybrene. Relevant English language articles were reviewed, with subsequent references obtained from the internal citations. Perspective is provided for both those who use HepCon-guided management and those who do not, as are practical recommendations for the modern era based on the published data and conclusions of the various investigators.

Clinical monitoring of activated clotting time during cardiothoracic surgery: comparing the Hemochron® Response and Hemochron® Signature Elite

INTRODUCTION

The Activated Clotting Time (ACT) is commonly used to manage anticoagulation during cardiac surgery. The aim of this study was to compare the older manually operated Hemochron^® Response and the automated Hemochron^® Signature Elite.

METHODS

In this observational study the clinically relevant differences of both devices were investigated simultaneously, using duplicate measurements, in 29 patients who underwent a Coronary Artery Bypass Grafting (CABG) or Aortic Valve Replacement (AVR) in order to determine reliability, bias, and to detect which method has the lowest variation. Blood samples were obtained from the arterial line prior to surgery, after administration of 300 IU/kg heparin, 5 minutes after initiation of cardiopulmonary bypass and successively every 30 minutes, and after protamine administration.

RESULTS

A total of 202 measurements were performed. Of these 10 measurements were out of range in the Response and 9 in the Elite. About 27 single unstable magnet errors were seen in the Response versus no measurement errors in the Elite. No statistically significant differences between the Response (p = 0.22, Wilcoxon rank) and Elite (p = 0.064) duplicates were observed. The Response values were consistently higher during heparinization than the Elite measurements (p = 0.002, repeated measurements) with an average positive bias of around 56 seconds during heparinization (Bland-Altman). Overall, the coefficient of variation (CoV) increased during heparinization.

CONCLUSION

The Elite was more reliable, but the variation was higher for the Elite than the Response. The observed positive bias in the Response compared to the Elite could affect heparin administration during surgery making the two systems not interchangeable.

Protamine titration to optimize heparin antagonization after cardiopulmonary bypass

OBJECTIVES

To optimize protamine titration for heparin antagonization after weaning from cardiopulmonary bypass (CPB).

DESIGN

A prospective, observational trial.

SETTING

Single-center, non-university teaching hospital.

PARTICIPANTS

Forty patients presenting for elective on-pump coronary artery bypass grafting with or without single valve surgery.

INTERVENTIONS

At the end of CPB, the residual amount of heparin in the patient was estimated using a Bull-curve. The total protamine dose was calculated as 1 unit of protamine for 1 unit of heparin. Protamine was administered as 5 aliquots containing 20% of the total protamine dose each, with 2-min intervals.

MEASUREMENTS AND MAIN RESULTS

Activated Clotting Time (ACT) values were measured 2 min after administration of each aliquot. ROTEM(®)-analysis was performed after the full dose of protamine had been administered. After 60% of the total protamine dose had been administered, ACT values were normalized in 86.5% of patients. After the complete dose of protamine had been administered, 61.1% of patients displayed signs of protamine overdose on ROTEM(®)-analysis.

CONCLUSIONS

In patients who present for on-pump coronary artery bypass grafting with or without single valve surgery, a 0.6-to-1 ratio of protamine-to-heparin to antagonize heparin may be sufficient and beneficial for patients.

A Pilot Study to Assess the Clinical Onset of IV Heparin in Interventional Cardiology and Cardiac Surgery

OBJECTIVES

To determine the onset of heparin anticoagulation, using 2 different measures of activated clotting times (ACT), thromboelastography (TEG; R-time), and anti-Xa levels, after administering low- (100 U/kg) and high- (300 U/kg) dose intravenous (IV) heparin to patients undergoing transcatheter aortic valve replacement (TAVR) and cardiac surgery, respectively.

DESIGN

Prospective study.

SETTING

Single academic institution.

PARTICIPANTS

Patients with normal baseline coagulation presenting for TAVR or cardiac valve surgery.

INTERVENTIONS

Coagulation studies were performed at baseline, 30 seconds, 90 seconds, and 180 seconds after IV heparin administration. The tests included iSTAT (iACT) and Hemochron ACT (hACT), TEG R-Time, and anti-Xa levels. At the authors' institution, anti-Xa is the preferred measure of heparin anticoagulation when time permits. ACT, a rapid point- of-care test, is used to assess intraprocedural anticoagulation.

MEASUREMENTS AND MAIN RESULTS

After both low- and high-dose heparin, there are peak increases in ACT and anti-Xa at 30 seconds, followed by a decline at 90 seconds and plateau at 180 seconds. The TEG R-time remained elevated (>80 minutes) throughout. For TAVR cases, all anti-Xa was >1.5 IU/mL, and was associated with an iACT >180 seconds and an hACT >200 seconds. For cardiac valve surgery cases, all anti-Xa was >2.4 and associated with an iACT >420 seconds and and hACT >340 seconds. Compared with hACT, iACTs were significantly lower at all time points after low-dose heparin, but not after high-dose heparin.

CONCLUSIONS

In this pilot study, heparin anticoagulation was detected as early as 30 seconds after IV administration, based on ACT, anti-Xa levels, and TEG R-time.

"In Less than No Time": Feasibility of Rotational Thromboelastometry to Detect Anticoagulant Drugs Activity and to Guide Reversal Therapy

Anticoagulant drugs (i.e., unfractionated heparin, low-molecular-weight heparins, vitamin K antagonists, and direct oral anticoagulants) are widely employed in preventing and treating venous thromboembolism (VTE), in preventing arterial thromboembolism in nonvalvular atrial fibrillation (NVAF), and in treating acute coronary diseases early. In certain situations, such as bleeding, urgent invasive procedures, and surgical settings, the evaluation of anticoagulant levels and the monitoring of reversal therapy appear essential. Standard coagulation tests (i.e., activated partial thromboplastin time (aPTT) and prothrombin time (PT)) can be normal, and the turnaround time can be long. While the role of viscoelastic hemostatic assays (VHAs), such as rotational thromboelastometry (ROTEM), has successfully increased over the years in the management of bleeding and thrombotic complications, its usefulness in detecting anticoagulants and their reversal still appears unclear.

Adjusted calculation model of heparin management during cardiopulmonary bypass in obese patients: A randomised controlled trial

BACKGROUND

Anticoagulation during cardiopulmonary bypass (CPB) is usually adapted to total body weight (TBW). This may be inaccurate in obese patients and lead to heparin overdose with a risk of bleeding.

OBJECTIVES

To validate the efficacy and safety of an adjusted calculation model of heparin dosing based on ideal body weight (IBW) rather than TBW in obese CPB patients, with an expected target mean plasma heparin concentration of 4.5 IU ml after onset of CPB in the experimental group.

DESIGN

Randomised controlled study.

SETTING

University hospital.

PATIENTS

Sixty obese patients (BMI ≥ 30 kg m) scheduled for CPB were included from January to June 2016.

INTERVENTIONS

Patients received a bolus dose of unfractionated heparin of either 300 IU kg of TBW or 340 IU kg of IBW before onset of CPB. Additional adjusted boluses were injected to maintain an activated clotting time (ACT) of at least 400 s.

MAIN OUTCOME MEASURES

Plasma heparin concentration and ACT were measured at different time points. Total heparin doses and transfusion requirements were recorded.

RESULTS

The target heparin concentration of 4.5 IU ml was reached in the IBW group at the onset of CPB and maintained at all time points during CPB. Heparin concentrations were significantly higher in the TBW group after the bolus (6.52 ± 0.97 vs. 4.54 ± 1.13 IU ml, P < 0.001) and after cardioplegia (5.10 ± 1.03 vs. 4.31 ± 1.00 IU ml, P = 0.02). Total heparin doses were significantly higher in the TBW group. Mean ACT was significantly lower in the IBW group but remained over 400 s during CPB. The correlation between heparin and ACT was poor. Peri-operative bleeding and transfusion requirements were comparable. No thrombotic event occurred in the CPB circuit.

CONCLUSION

The current IBW-adjusted regimen of heparin administration may be used efficiently in obese CPB patients, thereby avoiding overdose which cannot be accurately assessed by ACT monitoring alone.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02675647.

The activated clotting time in cardiac surgery: should Celite or kaolin be used?

Objectives

Both kaolin- and Celite-activated clotting times (ACT) are used to guide anticoagulation during cardiopulmonary bypass. It is unknown whether these methods lead to similar management procedures for anticoagulation in patients and are thus interchangeable in terms of bias, precision and variability.

Methods

We randomized 97 patients undergoing coronary artery bypass grafting or aortic valve replacement to either kaolin- or Celite-guided anticoagulation. The ACT was measured simultaneously with the other method. We administered 300 IU/kg heparin to obtain initial ACT values greater than 400 s and additional heparin in each group using the minimum value of duplicate measurements according to a predefined protocol. The primary end point was the total heparin dose and the number of heparin supplements.

Results

The total heparin dose per patient in the 48 Celite-guided patients was 35 271 ± 12 406 IU with 51 supplements and in the 49 kaolin-guided patients, 35 997 ± 11 540 IU ( P  = 0.77) with 56 supplements ( P  = 0.53). Postoperative thrombin generation time, fibrinolytic response time, chest tube loss and transfusion requirements were not different between the two groups. However, the methods differed in individual patients with regard to supplemental heparin ( P  = 0.002). Bias between methods at baseline was +10.3%, Celite being higher, and changed to a value of -12.9% at 2 h bypass. The coefficient of variation at baseline for individual patients was 2.6 times larger with kaolin than with Celite ( P  < 0.001). Correlation between ACT values at baseline was only 45%.

Conclusions

Kaolin- and Celite-guided management of anticoagulation is clinically not different, but the methods are not interchangeable.

Clinical registration number

www.trialregister.nl identifier 1738.

Anticoagulation management in patients undergoing open heart surgery by activated clotting time and whole blood heparin concentration

Objective: To investigate the changes in perioperative anticoagulation management using a heparin-concentration-based system (HMS), and its effect on postoperative outcome. Methods: A total of 39 patients undergoing elective primary open heart surgery were randomly assigned to a heparin-concentration-based system approach (study group: 17 patients) or a standard ACT-based anticoagulation system (control group: 22 patients). Measurements and main results: Patients in the study group received a statistically significant higher dose of heparin (median 29 000 IU with IQR 22 500 33 500 IU versus median 19 000 IU with IQR 17 775 21 500 IU; p <0.001) and a smaller dose of protamine (median 170 mg with IQR 145 190 mg versus median 200 mg with IQR 180-250 mg; p=0.008) compared to the control group. Postoperative platelet count was significantly higher in the study group (164± 45×109/L versus 125±27 × 109/L, p=0.002). None of the study patients, but six patients in the control group required transfusion of blood products (p=0.02). No differences were recorded in postoperative antithrombin activity, bleeding, and other clinical outcomes. Conclusion: he HMS system, by facilitating maintenance of a stable heparin concentration, and by determining an appropriate dose of protamine, is associated with reduced platelet consumption and does not increase AT-III consumption and postoperative bleeding.

A portable blood plasma clot micro-elastometry device based on resonant acoustic spectroscopy

Abnormal blood clot stiffness is an important indicator of coagulation disorders arising from a variety of cardiovascular diseases and drug treatments. Here, we present a portable instrument for elastometry of microliter volume blood samples based upon the principle of resonant acoustic spectroscopy, where a sample of well-defined dimensions exhibits a fundamental longitudinal resonance mode proportional to the square root of the Young's modulus. In contrast to commercial thromboelastography, the resonant acoustic method offers improved repeatability and accuracy due to the high signal-to-noise ratio of the resonant vibration. We review the measurement principles and the design of a magnetically actuated microbead force transducer applying between 23 pN and 6.7 nN, providing a wide dynamic range of elastic moduli (3 Pa-27 kPa) appropriate for measurement of clot elastic modulus (CEM). An automated and portable device, the CEMport, is introduced and implemented using a 2 nm resolution displacement sensor with demonstrated accuracy and precision of 3% and 2%, respectively, of CEM in biogels. Importantly, the small strains (<0.13%) and low strain rates (<1/s) employed by the CEMport maintain a linear stress-to-strain relationship which provides a perturbative measurement of the Young's modulus. Measurements of blood plasma CEM versus heparin concentration show that CEMport is sensitive to heparin levels below 0.050 U/ml, which suggests future applications in sensing heparin levels of post-surgical cardiopulmonary bypass patients. The portability, high accuracy, and high precision of this device enable new clinical and animal studies for associating CEM with blood coagulation disorders, potentially leading to improved diagnostics and therapeutic monitoring.

Coagulation-induced resistance to fluid flow in small-diameter vascular grafts and graft mimics measured by purging pressure

In this study, the coagulation-induced resistance to flow in small-diameter nonpermeable Tygon tubes and permeable expanded polytetrafluoroethylene (ePTFE) vascular grafts was characterized by measuring the upstream pressure needed to purge the coagulum from the tube lumen. This purging pressure was monitored using a closed system that compressed the contents of the tubes at a constant rate. The pressure system was validated using a glycerin series with well-defined viscosities and precisely controlled reductions in cross-sectional area available for flow. This system was then used to systematically probe the upstream pressure buildup as fibrin glue, platelet-rich plasma (PRP) or whole blood coagulated in small-diameter Tygon tubing and or ePTFE grafts. The maximum purging pressures rose with increased clot maturity for fibrin glue, PRP, and whole blood in both Tygon and ePTFE tubes. Although the rapidly coagulating fibrin glue in nonpermeable Tygon tubing yielded highly consistent purging curves, the significantly longer and more variable clotting times of PRP and whole blood, and the porosity of ePTFE grafts, significantly diminished the consistency of the purging curves.

Reappearance of circulating heparin in whole blood heparin concentration-based management does not correlate with postoperative bleeding after cardiac surgery

OBJECTIVE

The Hepcon Heparin Management System (HMS) facilitates administration of higher heparin and lower protamine doses, which may affect bleeding potential due to heparin rebound. The present study evaluated heparin rebound in patients for whom the Hepcon HMS was used to determine whether point-of-care tests detect residual heparin and residual heparin is associated with postoperative blood loss.

DESIGN

Prospective study.

SETTING

Tertiary care center affiliated with a university hospital.

PARTICIPANTS

Adults undergoing elective cardiac surgery requiring cardiopulmonary bypass.

INTERVENTIONS

In blood samples obtained at baseline, at 2 minutes, and at 1, 2, 4, 6, and 24 hours after heparin neutralization, heparin concentrations were measured using an automated chromogenic assay. Activated coagulation time (ACT), activated partial thromboplastin time (APTT), and thromboelastometry 2 hours after heparin neutralization also were examined in the last 22 study patients enrolled.

MEASUREMENTS AND MAIN RESULTS

All 31 patients had measurable heparin levels 2 hours after protamine administration; 22 patients exhibited a primary failure to reverse heparin after protamine administration, and 9 patients had measureable heparin levels 2 hours after complete heparin reversal (ie, heparin rebound). The thromboelastometric variable, INTEM-CT:HEPTEM-CT ratio, correlated with heparin concentration (r=0.72), but ACT (r=-0.12), APTT (r=0.36), and whole blood heparin concentration, determined using the Hepcon HMS, did not. Peak heparin concentration (0.18±0.07 U/mL) at 4 hours was not correlated with mediastinal blood loss.

CONCLUSION

Circulating heparin detected by the chromogenic assay was too low to be clinically significant based on postoperative bleeding, although all 31 patients had residual heparin or heparin rebound at 2 hours after protamine administration with use of the Hepcon HMS.

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.

Practical management of anticoagulation, bleeding and blood product support for cardiac surgery. Part one: bleeding and anticoagulation issues

There are many challenging problems related to bleeding and anticoagulation in cardiac surgery. Practical guidelines, which are based on available evidence, can help to direct management issues of post-bypass bleeding, perioperative anticoagulation and the use of haemostatic agents. The patient's bleeding history is the most useful preoperative screening test of haemostasis. The input of a haematologist is often valuable in a number of areas, such as preoperative assessment of patients with a significant history of bleeding, or past history of heparin-induced thrombocytopenia, a lupus anticoagulant, or recent venous thromboembolism. Cardiothoracic surgeons, anaesthetists, perfusionists and haematologists can ensure 'best practice' by being actively involved in the development of 'local' transfusion and anticoagulation guidelines, hospital transfusion committee policies, and audits.

Surveillance de l'anticoagulation des circulations extracorporelles par l'héparine non fractionnée : quels sont les problèmes non résolus ?

Cardiac surgery with extracorporeal circulation induces major alterations of haemostasis and requires high level of anticoagulation, usually achieved by unfractionated heparin infusion. Optimization of anticoagulant regimen, through adapted biological monitoring, can probably improve postoperative course, at least for postoperative haemostatic status. Despite increasing knowledge on extracorporeal circulation-induced haemostatic abnormalities and the development of new biological devices for heparin monitoring, the optimal level of anticoagulation remains matter of debate, as well as the monitoring procedures. This critical review presents the current available data on heparin anticoagulation and monitoring in this specific context, and underlines the pending issues about anticoagulation management during extracorporeal bypass.

The Clinical Onset of Heparin Is Rapid

This study used the activated clotting time (ACT) to determine the clinical onset of four different doses of heparin after bolus injection into the central circulation. Ten consenting adults (Group A) undergoing coronary artery bypass grafting were given 350 U/kg of bovine lung heparin and had simultaneous duplicate arterial and venous ACT determinations at baseline and at 30, 60, 90, 120, 180, and 600 s after heparin injection. Twenty additional coronary artery bypass grafting patients were alternately assigned to one of two 10-patient groups (B and C), which were given 200 and 300 U/kg of bovine lung heparin, respectively. Group D consisted of 10 abdominal aortic aneurysmectomy patients who received 70 U/kg of bovine lung heparin. In Groups B, C, and D, duplicate ACT measurements were taken from an indwelling arterial catheter at baseline and at 30, 60, 90, 120, 180, and 300 s after completion of a bolus injection of heparin into the central circulation. After a 70 U/kg heparin dose, all patients had significant ACT prolongation within 30 s, and 8 of 10 had effectively achieved their peak anticoagulation response by that time. In all patients receiving 200, 300, and 350 U/kg of heparin, arterial anticoagulation (ACT > 300 s) occurred and in most patients peaked within 30 s after heparin administration (P < 0.05). Arterial and venous ACTs did not differ significantly from each other at any measurement period, but venous ACTs peaked slightly later than arterial ACTs (within 60 s in 9 of 10 patients). When 200 U/kg or more of heparin is administered into the central venous circulation in hemodynamically stable anesthetized patients, peak arterial ACT prolongation occurs within 30 s and peak venous ACT prolongation within 60 s.

Management approaches to platelet-related microvascular bleeding in cardiothoracic surgery

Patients undergoing cardiac surgery with cardiopulmonary bypass are at increased risk for microvascular bleeding that requires perioperative transfusion of blood components. Platelet-related defects have been shown to be the most important hemostatic abnormality in this setting. The exact association between preoperative use of potent platelet inhibitors and either bleeding or transfusion in patients undergoing cardiac surgical procedures is currently being defined. Laboratory evaluation of platelets and coagulation factors can facilitate the optimal administration of pharmacologic and transfusion-based therapy. However, their turnaround time makes laboratory-based methods impractical for concurrent management of surgical patients, which has led many investigators to study the role of point-of-care coagulation tests in this setting. Use of point-of-care tests of hemostatic function can optimize the management of excessive bleeding and reduce transfusion. Accordingly, point-of-care tests that assess platelet function may also identify patients at risk for acquired, platelet-related bleeding. The ability to reduce the unnecessary use of blood products and to decrease operative time or reexploration rates has important consequences for blood inventory, blood costs, and overall health care costs.

Assessment of heparin anticoagulation: comparison of two commercially available methods

BACKGROUND

The activated clotting time is a bedside method routinely used to monitor heparin anticoagulation during operations requiring cardiopulmonary bypass. The thrombolytic assessment system heparin management test is a new bedside method for monitoring heparin effect. We compared these methods with respect to their ability to reflect the actual heparin concentration in plasma determined by an anti-FXa method.

METHODS

Two studies were done, an ex vivo study on ten patients who had coronary artery bypass using non-heparin-coated cardiopulmonary bypass circuits and full systemic heparinization and an in vitro study on single donor plasma spiked with heparin 0 to 10 IU/mL.

RESULTS

Ex vivo study correlation coefficients of activated clotting time and the thrombolytic assessment system heparin management test clotting times versus anti-FXa-based heparin assay were low (r = 0.53, p = 0.002/r = 0.64, p<0.001) in contrast with the corresponding correlation coefficients for the in vitro study (r = 0.98, p<0.001/r = 0.99, p<0.001). A substantial variability in duplicate activated clotting time determinations was noted, which was less pronounced with the thrombolytic assessment system heparin management test.

CONCLUSIONS

The thrombolytic assessment system method does not correlate better to the actual amount of heparin during cardiopulmonary bypass procedures than the activated clotting time method, which should be performed in duplicate.

Optimal management of bleeding and transfusion in patients undergoing cardiac surgery

Patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) are at increased risk for excessive perioperative blood loss requiring transfusion of blood products. Point-of-care evaluation of platelets, coagulation factors, and fibrinogen can enable physicians to rapidly assess bleeding abnormalities, facilitate the optimal administration of pharmacological and transfusion-based therapy, and also identify patients with surgical bleeding. The ability to reduce the unnecessary use of blood products in this setting has important implications for emerging issues in blood inventory and blood costs. The ability to decrease surgical time, along with exploration rates, has important consequences for health care costs in an increasingly managed health care environment.

Heparin management test versus activated coagulation time during cardiovascular surgery: correlation with anti-Xa activity

OBJECTIVE

To compare the abilities of the heparin management test (HMT) and the activated coagulation time (ACT) to provide a measurement of heparin effect in patients undergoing cardiac or peripheral vascular surgery. These measurements of heparin effect were also compared with measurements of heparin concentrations tested by anti-Xa activity. A secondary objective was to compare the performance of the noncitrated HMT with that of the citrated HMT.

DESIGN

A prospective study.

SETTING

A single-center study conducted in a university hospital.

PARTICIPANTS

After human investigation committee approval and informed consent were obtained, adult patients undergoing cardiac or peripheral vascular surgery were included in this study.

INTERVENTIONS

In both surgical groups, blood was sampled for ACT, HMT, and anti-Xa activity. Each HMT was performed on both noncitrated and citrated samples.

MEASUREMENTS AND MAIN RESULTS

As an indicator of heparin effect, the HMT had a strong correlation with the ACT (r = 0.899; p < 0.01). In addition, the HMT had a significantly stronger correlation with anti-Xa activity than the ACT (p < 0.01). The correlation obtained from the noncitrated samples was identical with that obtained from the citrated samples (r = 0.819; p < 0.001 for both groups).

CONCLUSION

The ability of the HMT and the ACT to measure heparin effect was similar. The HMT performed better than the ACT when using anti-Xa activity as a measure of heparin concentration. Noncitrated HMT results were similar to citrated HMT results, thus supporting the use of fresh whole blood for testing purposes.

Effect of heparin-bonded pulmonary artery catheters on the activated coagulation time

OBJECTIVE

This study evaluated the effect of a heparin-bonded pulmonary artery catheter (PAC) on the activated coagulation time (ACT).

DESIGN

A prospective, controlled comparison.

SETTING

A tertiary care university hospital.

PARTICIPANTS

Adult cardiac surgery patients.

INTERVENTIONS

Celite ACTs were measured from arterial and central venous blood samples before and after the insertion of a heparin-bonded PAC. Thromboelastograms were also obtained from central venous blood samples before and 2 minutes after PAC insertion.

MEASUREMENTS AND MAIN RESULTS

There was no significant difference between the sample sites before PAC insertion. After PAC insertion, the central venous ACTs were significantly increased compared with the corresponding arterial measurements at 2, 5, 10, and 20 minutes (p < 0.005, analysis of variance [ANOVA] for repeated measures, Fisher's protected least significant difference [PLSD]). The 2-minute post-PAC reaction time from the central venous blood sample was greater than 60 minutes in all cases.

CONCLUSION

The heparin-bonded PAC was associated with a localized, time-dependent alteration in the ACT. Whenever possible, blood samples for baseline ACT measurements should be obtained from an arterial catheter to minimize the anticoagulant effects from the PAC.

Heparin detection by the activated coagulation time: a comparison of the sensitivity of coagulation tests and heparin assays

OBJECTIVE

Laboratory and point-of-care coagulation tests are frequently obtained to determine the presence of heparin after surgical procedures. The objective of this study was (1) to compare the sensitivity of the activated coagulation time (ACT), activated partial thromboplastin time (aPTT), protamine titration (Hepcon; HMS Medtronic, Hemotec, Englewood, CO), and thromboelastography (TEG) with heparin anticoagulation and (2) to determine how frequently residual heparin is present in the 24-hour period after heparin neutralization in cardiopulmonary bypass (CPB) patients.

DESIGN

A prospective study.

SETTING

A tertiary care university teaching center that performs more than 15,000 surgical procedures per year.

PARTICIPANTS

Vascular surgical (n = 17) and CPB (n = 29).

INTERVENTIONS

In vascular surgical patients, coagulation tests (ACT, protamine titration [Hepcon], and TEG) were obtained before and 90 minutes after heparin (50 to 60 U/kg IV) and compared with heparin concentration determined by factor Xa inhibition assay. In cardiac surgical patients, ACT and heparin concentrations were measured after anesthesia induction, during CPB, after protamine neutralization, and 3 as well as 6 hours after CPB. In addition to heparin concentrations and ACT measures, platelet counts, fibrinogen levels, and bleeding times were determined before and 3 and 24 hours after CPB.

MEASUREMENTS AND MAIN RESULTS

Ninety minutes after heparin, significant heparin concentrations were present in all vascular surgical patients, but ACT was elevated in only 4 of 17 patients. Protamine titration (Hepcon) correlated with the factor Xa inhibitory assay for heparin (r2 = 0.76). All 17 patients had an abnormal TEG (mean "R" time = 81 +/- 39 minutes) and a marked elevation of aPTT (135 +/- 35 sec [normal 22 to 33 seconds]) 90 minutes after heparin. In CPB patients, ACT did not correlate with heparin assays. After protamine neutralization of heparin in CPB patients, ACT returned to baseline despite the presence of heparin in 3 of 29 patients (0.22, 0.18, and 0.33 U/mL).

CONCLUSIONS

ACT was less sensitive to residual heparin anticoagulation than aPTT, TEG, and whole blood heparin assay. The whole blood heparin assay (Hepcon) provided sensitive and specific data about the presence of residual heparin. Despite the limitation of ACT in detecting heparin, the investigators found that residual heparin was not common in the period after uncomplicated CPB.

Activated coagulation time: one tube or two?

OBJECTIVES

To compare activated coagulation time (ACT) management directed by a single ACT determination to that of the average of two simultaneously obtained ACT values.

DESIGN

Prospective study.

SETTING

Cardiac operating rooms of a university hospital.

PARTICIPANTS

Patients undergoing surgery requiring cardiopulmonary bypass.

INTERVENTIONS

All ACT determinations were performed in duplicate; patients were managed based on the average of the duplicate values, as is customary. Results of all tests were recorded on a spreadsheet, and the management dictated by a randomly chosen single result of each pair was compared with the management directed by the average value of each pair. Predetermined criteria were set for preference of one testing method over the other. Patients were grouped according to preoperative heparin exposure, and results of the two groups were compared.

MEASUREMENTS AND MAIN RESULTS

One hundred patients underwent 683 paired celite ACT determinations. In 565/683 tests (83%), both methods called for identical heparin management responses. Management by the single-tube method would have resulted in supplemental heparin administration 34% more often than management by the average method. The single-tube method would have resulted in withholding supplemental heparin 13 times when the average method called for supplemental heparin administration, a 16% occurrence. The results of the patients with and without preoperative heparin exposure were not significantly different.

CONCLUSIONS

The results of this study suggest the use of a two-tube average method to guide heparin administration for cardiopulmonary bypass. Preoperative heparin exposure did not influence this outcome.

Heparin and antithrombin III levels during cardiopulmonary bypass: correlation with subclinical plasma coagulation

The anticoagulant effect of heparin in the milieu of altered antithrombin III levels was investigated in adult (n = 7) and pediatric (n = 14) patients undergoing open heart operations. The pediatric patients were subdivided into a control group (n = 8) and an antithrombin III group (n = 6), which received 1,000 units of antithrombin III. The reduction in antithrombin III levels during cardiopulmonary bypass was obvious in patients of all ages, showing a greater reduction (although not statistically significant) in the pediatric patients. However, the antithrombin III group patients maintained their preoperative levels of antithrombin III. The elevated fibrinopeptide A levels in pediatric and adult control group patients suggested that considerable subclinical plasma coagulation occurred during open heart operations, especially during the normothermic period of cardiopulmonary bypass and after the administration of protamine. Antithrombin III levels in the children were the most predictive (r = -0.58; p < 0.001) for production of fibrinopeptide A during moderate hypothermic cardiopulmonary bypass, but the heparin levels were most predictive (r = -0.57, p < 0.03) in the adults. This result may be related to the different actions of heparin when antithrombin III levels are reduced. Supplementation with antithrombin III succeeded in suppressing the activation of the coagulation cascade and resulted in no statistical change in fibrinopeptide A levels at any time. We conclude that heparin and (in some patients) antithrombin III levels are important variables for the inhibition of fibrin formation and the possible preservation of coagulation proteins.

The use of activated clotting times to monitor heparin therapy during and after interventional procedures

Use of the activated clotting time (ACT) was recommended in the mid 1970s to guide administration and reversal of heparin during cardiopulmonary bypass. As the applications of cardiopulmonary bypass spread, so too did the need for more efficient techniques to assess coagulation status. This led to the development of automated ACT measurements. Today, the importance of coagulation and anticoagulation has been further highlighted by recent advances in the field of interventional cardiology. More and more cardiologists are using in-laboratory bedside coagulation monitoring to assess heparin requirements during interventional procedures such as percutaneous transluminal coronary angioplasty (PTCA). This review focuses on the development of anticoagulation monitoring and provides historic information on the clinical use of heparin. The application of ACTs in the catheterization laboratory and in other clinical situations is discussed, along with alternative methods for bedside assessment of coagulation status. No definite guidelines have been established for ACT monitoring during invasive intravascular procedures; thus its role continues to be refined. In the meantime, the ACT appears to be an extremely useful method for monitoring heparin therapy and the adequacy of anticoagulation.

Masking of heparin activity in the activated coagulation time (ACT) by platelet procoagulant activity

The effect of platelet procoagulant activity in the Activated Coagulation Time (ACT) was measured in whole blood anticoagulated with various levels of heparin before or after reversal with protamine. Similar studies were carried out on blood anticoagulated with hirudin to distinguish procoagulant activity from heparin neutralization in platelet preparations. At 0.5-1.0 units/mL antithrombin activity with heparin or hirudin, the ACT was lowered progressively by the addition of increasing concentrations of lysed platelets to as much as 20 seconds below the baseline clotting time obtained with unanticoagulated blood samples. Neutralization of higher concentrations of heparin with protamine produced an ACT below baseline in the presence of lysed platelets. Aprotinin (400 KIU/mL) prolonged the ACT slightly in heparinized whole blood, but did not prevent the lowering of the ACT by lysed platelets to baseline or below. Recirculation of heparinized whole blood in a simulated cardiopulmonary bypass circuit generated platelet microparticles detected by flow cytometry. An increase in platelet microparticles was associated with a decrease in the amount of protamine needed to reach the baseline ACT in blood samples removed from the circuit at various time points during recirculation. A chromogenic anti-Factor Xa assay of heparin did not show a change with increasing microparticle concentration during recirculation. These findings indicate a masking of heparin activity by the procoagulant activity of platelet membrane microparticles that could affect reversal of heparin based on the ACT.

Intraoperative measurement of activated partial thromboplastin time and prothrombin time by a portable laser photometer in patients following cardiopulmonary bypass

Intraoperative capabilities to rapidly assess coagulation status following cardiopulmonary bypass (CPB) may be of benefit in providing optimal hemostasis and transfusion management, because CPB causes abnormalities in coagulation that may increase morbidity and mortality. The Ciba Corning 512 coagulation monitor (Ciba Corning, Medfield, MA) is a compact and portable device that rapidly determines the prothrombin time (PT) and activated partial thromboplastin time (APTT) in whole blood samples. One hundred patients requiring CPB had APTT and PT determined in whole blood specimens by the 512 coagulation monitor and in plasma specimens by the hospital laboratory from the same arterial blood sample obtained after protamine administration. Correlation coefficients of 0.95 and 0.77 were obtained for the paired APTT and PT tests, respectively (P < 0.01). A bias of 12.6 seconds and 0.77 seconds was determined for the APTT and PT, respectively. The 95% confidence intervals of the bias of the APTT and PT were 9.7 seconds to 15.5 seconds and 0.3 seconds to 1.16 seconds, respectively. The 512 coagulation monitor provided APTT and PT results in less than 3 minutes compared to approximately 45 minutes for the hospital laboratory. A reduction in accuracy was associated with the 512 coagulation monitor PT and APTT when different sampling sites were used. The 512 coagulation monitor accuracy was not affected by a variation of hemoglobin concentration or platelet count between 6 and 12 gm/dL and 15 to 300 x 10(9)/L, respectively. In conclusion, the 512 coagulation monitor provided a rapid APTT and PT result, but the APTT was less accurate. Speeding access to hospital laboratory results would be even more efficacious and accurate.

Response to heparinization in adults and children undergoing cardiac operations

The activated clotting time is an unreliable index of anticoagulation status during cardiopulmonary bypass procedures. However, modern instrumentation (Hemotec Hepcon HMS) now allows the monitoring of free heparin levels via automated protamine titration. In the present study, the standard procedure of anticoagulation at Killingbeck Hospital, Leeds, was investigated. Twenty-two pediatric patients and 20 adult patients undergoing open heart procedures involving cardiopulmonary bypass were given empirical doses of heparin (3 mg/kg body weight bolus), and activated clotting time was maintained at a level greater than 450 seconds using the Hemochron Timer. Heparin neutralization was performed at the termination of the bypass period using an empirical equivalent (3 mg/kg) of protamine sulfate. Mean free heparin concentration (+/- standard deviation) fell from 2.26 (+/- 0.45) mg/kg to 1.39 (+/- 0.34) mg/kg over the period 10 to 40 minutes on bypass in children. In adults, free heparin level declined from 2.56 (+/- 0.58) mg/kg to 1.81 (+/- 0.58) mg/kg over the same period. The biological half-life for heparin was 60 minutes in adults and 35 minutes in pediatric patients. Empirical protamine dosing resulted in excess protamine administration when compared with Hepcon titrated dose requirements: for children: median (range), 80 (12 to 350) versus 33 (12 to 97) mg, p less than 0.001; and for adults: 350 (200 to 500) versus 130 (61 to 237) mg, p less than 0.001. In conclusion, empirical heparin administration (3 mg/kg) does not result in "steady-state" anticoagulation during cardiopulmonary bypass, and empirical administration of protamine takes no account of interindividual differences in heparin sensitivity and biological half-life, which may be assessed using the Hepcon HMS.

Hemostatic effects of tranexamic acid and desmopressin during cardiac surgery

BACKGROUND

Desmopressin-induced release of tissue plasminogen activator from endothelial cells may explain the absence of its hemostatic effect in patients undergoing cardiac surgery. Prior administration of the antifibrinolytic drug tranexamic acid might unmask such an effect, and combination therapy might thereby improve postoperative hemostasis.

METHODS AND RESULTS

A double-blinded design randomly allocated 163 adult patients undergoing coronary revascularization, valve replacement, both procedures, or repair of atrial septal defect to four treatment groups: placebo, tranexamic acid given as 10 mg/kg over 30 minutes followed by 1 mg.kg-1.hr-1 for 12 hours initiated before skin incision, desmopressin given as 0.3 micrograms/kg over 20 minutes after protamine infusion, and both drugs. One surgeon performed all operations. Blood loss consisted of mediastinal tube drainage over 12 hours. Follow-up visits sought evidence of myocardial infarction and stroke. Desmopressin decreased neither the 12-hour blood loss nor the amount of homologous red cells transfused. Tranexamic acid alone significantly reduced 12-hour blood loss, by 30% (mean, 318 versus 453 ml; p less than 0.0001), without enhancement by desmopressin. Tranexamic acid also decreased the proportion of patients receiving homologous blood within 12 hours of operation (8% versus 21%, p = 0.024) and within 5 days of operation (22% versus 41%, p = 0.011).

CONCLUSIONS

Desmopressin exerts no hemostatic effect, with or without prior administration of antifibrinolytic drug. Prophylactic tranexamic acid alone appears economical and safe in decreasing blood loss and transfusion requirement after cardiac surgery.

Does the preparation of heparin influence anticoagulation during cardiopulmonary bypass?

Various preparations of heparin from different manufacturers are commercially available. The influence of bovine lung heparin (BLH) and porcine mucosal heparin (PMH) on anticoagulation and heparin plasma concentration was investigated in four groups of 10 patients undergoing elective aortocoronary bypass grafting either after single dose or repetitive dose (after 60 minutes) of one of these heparin preparations. Heparin plasma concentration increased significantly after injection of heparin (BLH: minimum, 1.67 U/mL; maximum, 2.10 U/mL; PMH: minimum, 1.69 U/mL; maximum, 2.15 U/mL). Sixty minutes after the initial dose, heparin plasma levels were higher in the patients who received PMH. Supplemental heparin doses 60 minutes after the loading dose increased plasma heparin concentration only with porcine mucosal heparin. Elimination of heparin in the urine was not different among the groups. Fibrinogen and antithrombin III concentrations, as well as activated clotting time (ACT; always greater than 400 seconds) and partial thromboplastin time (PTT; always greater than 300 seconds), did not differ among the groups, indicating effective anticoagulation during the bypass period with both types of heparin. It can be concluded that sufficient anticoagulation can be achieved with either kind of heparin. PMH seems to be longer acting and a repeat dose in these patients seems to be necessary only if cardiopulmonary bypass lasts longer than 90 minutes.

Heparin rebound: a comparative study of protamine chloride and protamine sulfate in patients undergoing coronary artery bypass surgery

Heparin rebound has been suggested to occur when protamine sulfate, but not protamine chloride, is used to neutralize heparin. This study was undertaken to compare these two protamine salts in 32 patients undergoing coronary artery bypass surgery. Initial heparin and subsequent protamine doses were determined by constructing a heparin-activated coagulation time response curve. Heparin was neutralized either with protamine sulfate or protamine chloride. The total protamine/heparin dose ratio was 0.71 +/- 0.05 for protamine sulfate and 0.77 +/- 0.07 (mg/100 U) for protamine chloride. The initial neutralization effect, the subsequent behavior of the plasma heparin level, and the various coagulation parameters did not differ significantly between the groups. Two hours after neutralization, a small and temporary increase of plasma heparin level was observed in both groups. The postoperative blood losses were comparable in both groups. Thus, protamine chloride was not a clinically superior antidote to heparin than protamine sulfate. The observed heparin rebound levels were low and clinically insignificant in terms of blood loss, but they were associated with slight changes in coagulation monitoring.

Blood coagulation and autologous blood transfusion in cardiac surgery

STUDY OBJECTIVE

To review the basic pathophysiology of altered coagulation associated with cardiopulmonary bypass and autologous blood transfusion in cardiac surgery.

DESIGN

Review of rational use of heparin, mechanisms and treatment of coagulation disorders, and autologous blood transfusion.

SETTING

Cardiac surgery in community and academic hospitals.

PATIENTS

Adult cardiac surgical patients.

MAIN RESULTS

Heparin is most commonly used for anticoagulation during cardiopulmonary bypass. Although activated clotting time is widely used to assess heparin-induced anticoagulation, the minimum time to prevent clotting during cardiopulmonary bypass remains unclear. Activated clotting time is affected by many factors other than heparin, such as antithrombin III, blood temperature, platelet count, and age. The rational use of activated clotting time still must be defined. The frequency of abnormal bleeding after cardiopulmonary bypass is significant. Although inadequate surgical hemostasis is the most frequent cause of bleeding, altered coagulation often is present. A decreased number of functional platelets is one of the important causes of bleeding diathesis. Platelet dysfunction is induced by perioperative medication such as aspirin. Cardiopulmonary bypass decreases functional platelets by degranulation, fragmentation, and loss of fibrinogen receptors. Medications such as prostacyclin and iloprost may be useful to protect these platelets. Desmopressin increases factor VIII:C and von Willebrand's factor, leading to a decrease in bleeding time. Desmopressin may be useful to decrease blood loss in repeat cardiac operations, complex cardiac surgery, and abnormal postoperative bleeding. Patients undergoing coronary artery bypass grafting immediately after streptokinase infusion also are at risk for abnormal bleeding. Transfusion of fresh-frozen plasma and cryoprecipitate may be necessary. Autologous blood transfusion is cost-effective and the safest way to avoid or decrease homologous blood transfusion. Predonation, intraoperative salvage, and postoperative salvage are encouraged. Erythropoietin may be useful in increasing the amount of predonation red cells.

CONCLUSIONS

Coagulation disorders in cardiac surgery are caused by many factors, such as heparin, platelet dysfunction, and fibrinolysis. Rational use of blood component therapy and medications such as heparin, protamine, and desmopressin are mandatory. Autologous blood transfusion is very useful in decreasing or obviating the use of homologous blood transfusion.

Low activated coagulation time during cardiopulmonary bypass does not increase postoperative bleeding

The activated coagulation time (ACT) is widely used to monitor adequacy of anticoagulation during cardiopulmonary bypass despite absence of data establishing an ACT below which adverse outcomes occur. For anticoagulation before cardiopulmonary bypass, we administered a single dose of heparin (300 U/kg) to 193 patients and measured ACT and heparin levels at intervals after administration. No additional heparin was administered to any patient. Clot formation in the cardiopulmonary bypass circuit and excessive postoperative chest tube drainage were considered outcomes indicating inadequate anticoagulation. Cardiopulmonary bypass averaged 59 +/- 23 minutes (range, 30 to 138 minutes). Activated coagulation time values at every sampling period were normally distributed. In 51 patients (26.4%) ACT values were less than 400 seconds, including 4 less than 300 seconds, at some sampling time after heparinization. Patients with low ACT values did not bleed more postoperatively than those with high ACT values, nor was bleeding related to heparin level. No clots were found in any perfusion circuit. We conclude that a minimum ACT value for adequacy of heparinization is not yet defined but that it is less than 400 seconds.