Low preoperative antithrombin activity causes reduced response to heparin in adult but not in infant cardiac-surgical patients

Investigation of real-world heparin resistance and anticoagulation management prior to cardiopulmonary bypass: report from a nationwide survey by the Japanese Association for Thoracic Surgery heparin resistance working group

OBJECTIVE

Heparin resistance is often encountered during cardiopulmonary bypass. Heparin dose and activated clotting time target values for the initiation of cardiopulmonary bypass are not yet universally standardized; further no consensus exists on the management of heparin resistance. This study aimed to investigate the current real-world practice on heparin management and anticoagulant treatment for heparin resistance in Japan.

METHODS

A questionnaire survey was conducted at medical institutions nationwide with which The Japanese Society of Extra-Corporeal Technology in Medicine members are affiliated, targeting surgical cases with cardiopulmonary bypass performed from January 2019 through December 2019.

RESULTS

Among 69% (230/332) of the participating institutions, the criterion for heparin resistance was defined as "the target activated clotting time value not reached even with an additional dose of heparin administration". Cases of heparin resistance were reported in 89.8% (202/225) of the responded institutions. Of note, 75% (106/141) of the responded institutions reported heparin resistance associated with antithrombin activity ≥ 80%. Antithrombin concentrate was used in 38.4% (238/619 responses) or third dose of heparin in 37.8% (234/619 responses) for advanced heparin resistance treatment. Antithrombin concentrate was found to be effective in resolving heparin resistance in patients having normal, as well as lower antithrombin activity.

CONCLUSION

Heparin resistance has occurred in many cardiovascular centers, even among patients with normal antithrombin activities. Interestingly, the administration of antithrombin concentrate resolved heparin resistance, regardless of the baseline antithrombin activity value.

Thromboprophylaxis in Extracorporeal Circuits: Current Pharmacological Strategies and Future Directions

The development of extracorporeal devices for organ support has been a part of medical history and progression since the late 1900s. These types of technology are primarily used and developed in the field of critical care medicine. Unfractionated heparin, discovered in 1916, has really been the only consistent form of thromboprophylaxis for attenuating or even preventing the blood-biomaterial reaction that occurs when such technologies are initiated. The advent of regional anticoagulation for procedures such as continuous renal replacement therapy and plasmapheresis have certainly removed the risks of systemic heparinization and heparin effect, but the challenges of the blood-biomaterial reaction and downstream effects remain. In addition, regional anticoagulation cannot realistically be applied in a system such as extracorporeal membrane oxygenation because of the high blood flow rates needed to support the patient. More recently, advances in the technology itself have resulted in smaller, more compact extracorporeal life support (ECLS) systems that can-at certain times and in certain patients-run without any form of anticoagulation. However, the majority of patients on ECLS systems require some type of systemic anticoagulation; therefore, the risks of bleeding and thrombosis persist, the most devastating of which is intracranial hemorrhage. We provide a concise overview of the primary and alternate agents and monitoring used for thromboprophylaxis during use of ECLS. In addition, we explore the potential for further biomaterial and technologic developments and what they could provide when applied in the clinical arena.

Comparison of activated clotting times measured using the Hemochron Jr. Signature and Medtronic ACT Plus during cardiopulmonary bypass with acute normovolemic haemodilution

Objective

This study compared the activated clotting time (ACT) measured using the Hemochron Jr. Signature (HACT) with the ACT measured using the Medtronic ACT Plus (MACT) during cardiopulmonary bypass (CPB) with acute normovolemic haemodilution (ANH) in patients undergoing cardiac surgery.

Methods

The ACT was checked at baseline with both devices after inducing anaesthesia, and 400 to 800 mL of whole blood was withdrawn to induce moderate ANH. Before initiating CPB, a 300-IU/kg bolus dose of heparin was administered to maintain the HACT at >400 s; protamine was later given to reverse the anticoagulation. The ACT was checked using both devices at baseline, during heparinisation, and after protamine administration.

Results

In total, 106 pairs of samples from 29 patients were analysed. The ACT showed a good correlation between the two devices (r = 0.956). However, Bland–Altman analysis showed that the MACT was higher, particularly at baseline and during heparinisation. Multiple regression analysis showed that the blood glucose concentration significantly influenced the differences between the two ACT devices.

Conclusions

The HACT was lower than the MACT during CPB with ANH in patients undergoing cardiac surgery. Clinicians should be cautious when using each ACT device within generally accepted reference ACT values.

Complete antithrombin replacement for anticoagulation for cardiopulmonary bypass to repair severe infective mitral valve endocarditis

: We present a case of a 26-year-old patient with severe infective endocarditis complicated with cerebral septic emboli that required essentially complete replacement of his circulating antithrombin activity to achieve an activated coagulation time near 480 s. The need for this degree of antithrombin administration may have been secondary to ongoing systemic inflammation and consequent thrombin generation despite blood culture results demonstrating no bacteremia. In sum, ongoing loss of endogenous antithrombin activity secondary to inflammation and the need for more than 80% normal activity to conduct safe cardiopulmonary bypass may require extraordinary administration of exogenous antithrombin in similar settings.

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.

Use and Future Investigations of Recombinant and Plasma-Derived Coagulation and Anticoagulant Products in the Neonate

Although congenital bleeding disorders can manifest in the newborn period, the most common causes of bleeding and thrombosis in neonates are acquired conditions. Factor concentrates are used for specific diagnoses (hemophilia with inhibitors, specific factor deficiency, von Willebrand disease) and approved indications, and increasingly for off-label indications (bleeding in surgery cardiopulmonary bypass, extracorporeal membrane oxygenation). We will review the approved indications for factor products in the neonate and discuss the evidence and rationale for off-label use of factor products in management of bleeding and thrombosis in the neonate.

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.

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.

Review article: heparin sensitivity and resistance: management during cardiopulmonary bypass

Heparin resistance during cardiac surgery is defined as the inability of an adequate heparin dose to increase the activated clotting time (ACT) to the desired level. Failure to attain the target ACT raises concerns that the patient is not fully anticoagulated and initiating cardiopulmonary bypass may result in excessive activation of the hemostatic system. Although antithrombin deficiency has generally been thought to be the primary mechanism of heparin resistance, the reasons for heparin resistance are both complex and multifactorial. Furthermore, the ACT is not specific to heparin's anticoagulant effect and is affected by multiple variables that are commonly present during cardiac surgery. Due to these many variables, it remains unclear whether decreased heparin responsiveness as measured by the ACT represents inadequate anticoagulation. Nevertheless, many clinicians choose a target ACT to assess anticoagulation, and interventions aimed at achieving the target ACT are routinely performed in the setting of heparin resistance. Treatments for heparin resistance/alterations in heparin responsiveness include additional heparin or antithrombin supplementation. In this review, we discuss the variability of heparin potency, heparin responsiveness as measured by the ACT, and the current management of heparin resistance.

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.

Heparin dose response is independent of preoperative antithrombin activity in patients undergoing coronary artery bypass graft surgery using low heparin concentrations

BACKGROUND

Unfractionated heparin's primary mechanism of action is to enhance the enzymatic activity of antithrombin (AT). We hypothesized that there would be a direct association between preoperative AT activity and both heparin dose response (HDR) and heparin sensitivity index (HSI) in patients undergoing coronary artery bypass graft surgery.

METHODS

Demographic and perioperative data were collected from 304 patients undergoing primary coronary artery bypass graft surgery. AT activity was measured after induction of general anesthesia using a colorimetric method (Siemens Healthcare Diagnostics, Tarrytown, NY). Activated coagulation time (ACT), HDR, and HSI were measured using the Hepcon HMS Plus system (Medtronic, Minneapolis, MN). Heparin dose was calculated for a target ACT using measured HDR by the same system. Multivariate linear regression was performed to identify independent predictors of HDR. Subgroup analysis of patients with low AT activity (<80% normal; <0.813 U/mL) who may be at risk for heparin resistance was also performed.

RESULTS

Mean baseline ACT was 135 ± 18 seconds. Mean calculated HDR was 98 ± 21 s/U/mL. Mean baseline AT activity was 0.93 ± 0.13 U/mL. Baseline AT activity was not significantly associated with baseline or postheparin ACT, HDR, or HSI. Addition of AT activity to multivariable linear regression models of both HDR and HSI did not significantly improve model performance. Subgroup analysis of 49 patients with baseline AT <80% of normal levels did not reveal a relationship between low AT activity and HDR or HSI. Preoperative AT activity, HDR, and HSI were not associated with cardiac troponin I levels on the first postoperative day, intensive care unit duration, or hospital length of stay.

CONCLUSION

Although enhancing AT activity is the primary mechanism by which heparin facilitates cardiopulmonary bypass anticoagulation, low preoperative AT activity is not associated with impaired response to heparin or to clinical outcomes when using target ACTs of 300 to 350 seconds.

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.

Preoperative low molecular weight heparin reduces heparin responsiveness during cardiac surgery

PURPOSE

Cardiac surgery with cardiopulmonary bypass requires systemic anticoagulation, defined by an activated clotting time (ACT) of 400-480 sec. Patients with altered heparin responsiveness require disproportionately higher doses of heparin to achieve this target ACT. A common risk factor for heparin resistance is preoperative heparin therapy. Recently, therapy with low molecular weight heparin (LMWH) has become an acceptable substitute for prolonged heparin therapy. The current study examines the effect of preoperative LMWH therapy on subsequent heparin responsiveness during cardiac surgery.

METHODS

Records of patients undergoing cardiac surgery with cardiopulmonary bypass over a period of four months were reviewed. We identified patients who, during the week preceding surgery, had received prolonged (>24 hr) therapy with either sc LMWH (LMWH group) or continuous iv unfractionated heparin (Heparin group). A Control group consisted of patients who received neither heparin nor LMWH preoperatively. The heparin sensitivity index (calculated as the first change in ACT from baseline divided by the first intraoperative heparin dose, normalized to body weight), was compared among groups using ANOVA.

RESULTS

One hundred and thirty-nine patients were included in the analysis. The heparin sensitivity index was 33-45% higher in the Control group (1.6+/-0.7 sec.IU-1.kg-1; P<0.0001) compared to the LMWH (1.2+/-0.4 sec.IU-1.kg-1) and Heparin (1.1+/-0.5 sec.IU-1.kg-1) groups. In a multivariable model, the use of preoperative LMWH remained a significant predictor of reduced intraoperative heparin responsiveness (P=0.002).

CONCLUSION

Prolonged preoperative LMWH therapy, similar to the known effect of prolonged unfractionated heparin infusion, reduces subsequent intraoperative response to heparin.

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

We compared the adequacy of heparinization in neonates and older children undergoing cardiopulmonary bypass (CPB) by measuring heparin activity, thrombin formation, and thrombin activity. Ten neonates and 10 older children were administered 400 U/kg of heparin before CPB. Heparin anti-Xa activity, prothrombin fragment 1.2 (F1.2), and fibrinopeptide A (FPA) were measured at baseline, after 30 min on CPB, immediately post-CPB, and 3 and 24 h post-CPB. Heparin anti-Xa activity was significantly decreased during and immediately post-CPB in the neonatal group. F1.2 and FPA levels in neonates were significantly higher at baseline, decreased with the commencement of CPB, and increased to levels higher than those in older children after CPB. Our data show that with standard heparin doses, neonates exhibit less heparin anti-Xa activity during CPB. Higher baseline levels of F1.2 and FPA present in neonates indicate preoperative activation of their coagulation systems as compared with older children. Although F1.2 and FPA levels initially decrease with the commencement of CPB, probably representing hemodilution, the subsequent increase in these markers indicates significantly more thrombin formation and activity during and after CPB. These results raise the concern that 400 U/kg of heparin may not adequately suppress thrombin formation and activity in neonates undergoing CPB.

Acute normovolemic hemodilution does not reduce antithrombin concentration for cardiac surgery

BACKGROUND

Acute normovolemic hemodilution (ANH) is used to reduce allogeneic blood transfusion with cardiac surgery. This procedure involves pre-operatively removing and storing a volume of whole blood and replacing the volume with crystalloid. The stored blood is then available for transfusion, if required. Hemodilution associated with ANH may reduce the effectiveness of heparin anticoagulation due to dilution of antithrombin. The aim of this study was to determine if antithrombin concentrations are reduced in patients who undergo one unit of ANH during cardiac surgery.

METHODS

Patients scheduled for cardiac surgery (n = 71) were grouped according to whether they did or did not undergo ANH pre-operatively. Antithrombin concentrations were measured before and after ANH. This study had 80% power to detect a difference in reduction of antithrombin concentration of 6% between groups following ANH with an alpha error of <0.05. The effect of one unit ANH was expected to cause a difference of 12% or greater.

RESULTS

No significant difference in the concentration of antithrombin between ANH patients and those that did not have ANH, nor was there a difference in the decrease in antithrombin between groups.

CONCLUSIONS

The results indicate that one unit of ANH does not significantly reduce the concentration of antithrombin prior to cardiac surgery. Thus patients who undergo one unit of ANH are not at increased risk due to dilution of antithrombin.

The Effects of Argatroban on Thrombin Generation and Hemostatic Activation In Vitro

We evaluated argatroban, a direct thrombin inhibitor, as a heparin adjunct for anticoagulation. Platelet-poor plasma (PPP) was isolated from blood collected from 12 volunteers. Thrombin generation measurements were performed in donor PPP that was mixed with antithrombin (AT)-poor plasma to yield AT levels of 0%, 20%, 60%, and 100%. Effects of argatroban (0-1.0 microg/mL), heparin (0.25 U/mL), or the combination of argatroban (0.5 microg/mL) and heparin were also studied. The addition of increasing concentrations of argatroban, heparin, or both to donor PPP (AT level approximately 100%) caused progressive decreases in the lag time and peak formation of thrombin generation. Heparin (0.25 U/mL) at small AT concentrations had a minimal effect on lag time or peak thrombin formation; its effectiveness of inhibiting thrombin was directly correlated with the concentration of AT. Argatroban at 0.5 microg/mL was effective in decreasing thrombin formation at both low and normal AT levels, but it was most effective when combined with heparin. Additionally, blood samples were obtained from 47 cardiac surgical patients, and the interaction of heparin (>1.5 U/mL) and AT or argatroban on clot formation was evaluated with kaolin activated clotting times (ACTs). Significant increases of ACTs at all heparin levels were observed with the addition of argatroban (0.125 and 0.25 microg/mL). The addition of AT (0.2 U/mL) to heparinized blood samples further prolonged ACTs. In summary, we showed that argatroban, unlike heparin, could effectively reduce thrombin generation regardless of AT levels and could prolong ACTs in vitro at clinically used concentrations.

Effects of tirofiban on haemostatic activation in vitro

BACKGROUND

Thrombin plays a critical role in normal haemostasis and pathological thrombosis. Heparin has long been a mainstay choice of antithrombotic regimen in cardiac patients, but persistent thrombin generation seems to occur during heparin therapy. Because platelets are integral to primary haemostasis and clot formation, we evaluated the use of tirofiban (Aggrastat),a platelet inhibitor, as a therapy to improve heparin sensitivity and delay thrombin formation.

METHODS

Blood samples were obtained from healthy subjects (n=8) and cardiac surgical patients (n=34). Thrombin formation was measured in platelet-rich plasma with a Thrombogram-Ascent fluorescent plate reader system. Platelet inhibition by tirofiban was evaluated with Plateletworks, and the interaction of tirofiban and heparin (>1.5 U ml(-1)) on clot formation was evaluated with Sonoclot Analyzer or kaolin activated clotting times (ACTs).

RESULTS

Addition of tirofiban (70-280 ng ml(-1)) progressively delayed onset of thrombin generation triggered by adenosine diphosphate (ADP). Plateletworks showed platelet inhibition with tirofiban (>35 ng ml(-1)), whereas heparin per se failed to produce platelet inhibition at 7 U ml(-1). Heparin (1.5 U ml(-1)) slowed the onset and rate of fibrin formation on Sonoclot analyses, and this was further slowed after addition of tirofiban (70 ng ml(-1)) to heparin-containing blood samples. Significant increases in ACT at all heparin concentrations were observed with the addition of tirofiban (70 ng ml(-1)). The addition of antithrombin (0.2 units/ml) to heparinized blood samples further prolonged ACTs, but the difference was not statistically significant when compared with heparin alone.

CONCLUSION

Tirofiban delays platelet activation-mediated thrombin generation and prolongs ACT in heparinized blood.

Decreased concentration of antithrombin after preoperative therapeutic heparin does not cause heparin resistance during cardiopulmonary bypass

OBJECTIVE

To determine if preoperative heparin therapy causes an increase in the incidence of intraoperative heparin resistance by reducing the concentration of antithrombin in plasma.

DESIGN

Prospective laboratory investigation of clinical samples.

SETTING

Public tertiary care hospital and public pathology service.

PARTICIPANTS

Forty-six patients undergoing cardiac surgery involving cardiopulmonary bypass.

INTERVENTIONS

Fourteen patients received preoperative heparin therapy (POHI group) and 32 patients were controls (CONT group).

MEASUREMENTS AND MAIN RESULTS

The concentration of antithrombin, activated coagulation time (ACT), and clinical parameters were measured at intervals. More POHI patients had on-bypass heparin resistance than CONT (43% and 3%, respectively, p < 0.01). The POHI group had a lower concentration of antithrombin than the CONT group before (80.9% and 92.6%, respectively, p < 0.01) and while on cardiopulmonary bypass (51.6% and 57.5%, respectively, p = 0.04). Comparison of heparin-resistant and heparin-responsive POHI patients showed that the concentration of antithrombin did not differ before bypass (82.4% and 79.8%, respectively, p = 0.53) or during bypass (51.8% and 51.4%, respectively, p = 0.91). In fact, antithrombin concentrations were slightly higher in the heparin-resistant POHI patients (not significant). POHI patients received more heparin than CONT patients (medians 787 U/kg and 600 U/kg, respectively, p = 0.01) and were transfused with more fresh frozen plasma on bypass (p = 0.03).

CONCLUSIONS

Preoperative heparin causes an increased incidence of heparin resistance and reduced antithrombin concentrations. However, heparin resistance was not causally related to reduced antithrombin because antithrombin concentrations were not different between heparin-resistant and heparin-responsive patients in the POHI group.

Sonoclot analysis in cardiac surgery in dialysis-dependent patients

BACKGROUND

Dialysis-dependent patients have multiple disorders of hemostasis; however, there are no reports of viscoelastic changes during cardiac surgery in such patients.

METHODS

Hemostasis in dialysis-dependent patients during cardiac operations was evaluated. Thirty patients who underwent cardiopulmonary bypass (CPB) were studied: 6 with chronic renal failure undergoing dialysis (HD group), and 24 without hemodialysis. Blood samples were obtained at four points: before sternotomy, 30 and 90 minutes after the start of CPB, and after protamine administration.

RESULTS

Activated clotting time (ACT) measured with Sonoclot analyzer was significantly correlated with ACT measured traditionally (r = 0.92; p < 0.001; y = 36.1 + 0.95x). Values for ACT measured with Sonoclot analyzer as well as traditional ACT increased significantly during CPB. Values for ACT measured with Sonoclot analyzer in the HD group were significantly longer than those in the control group. Before CPB, both ACT measured with Sonoclot analyzer and traditional ACT in the HD group were significantly longer than those in the control group; however, there were no significant differences in ACT measured with Sonoclot analyzer between the groups after CPB. Clot rates and peak signal values were significantly decreased during CPB in both groups, and returned to preoperative values after protamine administration. There were no significant differences in clot rate and peak signal values between the two groups. There were no differences between the two groups in changes of time to peak. Platelet counts in the HD group were significantly higher (p < 0.05) than those in the control group. There were no differences in platelet counts after CPB between the two groups. Antithrombin III levels decreased below 50% during and after CPB. Antithrombin III in the HD group was significantly lower (p < 0.01) than those in the control group. A significant time-group interaction was observed in antithrombin III levels.

CONCLUSIONS

Sonoclot signatures in HD patients showed no significant differences in viscoelastic changes compared with non-HD patients.