Evaluation of a New Point-of-care Celite-activated Clotting Time Analyzer in Different Clinical Settings: The i-STAT Celite-activated Clotting Time Test

Background: Activated clotting time (ACT) is used to monitor heparin therapy during cardiopulmonary bypass, interventional cardiology, and hemodialysis. Traditionally, ACT is performed by use of the Hemochron system. Recently, a new device, the i-STAT system, has been introduced to measure ACT. The aim of this study was to correlate the performances of these two systems and to compare ACT values with heparin levels.

Methods: One hundred sixty-five samples from 29 patients undergoing cardiopulmonary bypass or hemodialysis were assayed in duplicate with two Hemochron and two i-STAT devices. Heparin levels were determined by anti-factor Xa assay.

Results: The Hemochron ACT ranged from 88 to 1,028 s, and the i-STAT ACT ranged from 80 to 786 s. Heparin plasma levels ranged from 0.01 to 10.8 U/mL. Bland-Altman analysis showed a mean difference between the two methods of 24 +/- 101 s. Strong relationships between anti-factor Xa activity and Hemochron ACTs (r2 = 0.69, P < 0.001) and i-STAT ACTs (r2 = 0.79, P < 0.001) were observed. During cardiac surgery, significant correlations were found: Hemochron, r2 = 0.61, P < 0.001 and i-STAT, r2 = 0.74, P < 0.001. During hemodialysis, relationships between anti-factor Xa activity and ACTs were found: Hemochron, r2 = 0.62, P < 0.001 and i-STAT, r2 = 0.55, P < 0.001.     

A novel thrombelastograph tissue factor/kaolin assay of activated clotting times for monitoring heparin anticoagulation during cardiopulmonary bypass

We used a thrombelastograph (TEG) assay with tissue factor and kaolin (TEG TF/K) to measure activated clotting time (ACT) in 31 patients during cardiopulmonary bypass. For comparison, ACTs were also determined by a Hemochron Jr. Signature and a Hepcon HMS. The TEG TF/K correlated with both the Hepcon (r(2) = 0.789) and Hemochron (r(2) = 0.743) ACTs. The average ACT after heparin was 319 +/- 119 s (mean +/- sd) for the TEG TF/K compared with 624 +/- 118 s for the Hepcon instrument. To evaluate the effects of hemodilution on TEG TF/K and Hemochron assays, ACT assays were performed on blood diluted to 50% and titrated with heparin from 0 to 6 U/mL. Both instruments showed significant (P < 0.01) changes in the ACT-versus-heparin slope, but the 0 heparin intercept for the TEG TF/K ACTs was not significantly changed (P = 0.292), in contrast to that for the Hemochron device (P = 0.041). Both instruments also indicated the same 1.3:1 ratio of protamine to heparin for optimum heparin neutralization, with increasing ACTs at ratios >2.6:1. The TEG TF/K ACT assay rapidly monitors heparin anticoagulation, in addition to the capabilities of this instrument to monitor platelet function, clotting factors, and fibrinolysis.     

The plasma supplemented modified activated clotting time for monitoring of heparinization during cardiopulmonary bypass: a pilot investigation

The standard celite or kaolin activated clotting time (ACT) correlates poorly with heparin levels during cardiopulmonary bypass (CPB). We compared a modified kaolin ACT, in which plasma was supplemented, to a standard undiluted kaolin ACT for monitoring heparin levels during CPB. Fifteen patients undergoing normothermic CPB were enrolled in this prospective study. Heparin management was performed according to the Hepcon HMS results (Medtronic, Minneapolis, MN). The ACTs were performed with the ACT II device (Medtronic). Hepcon HMS calculations, standard kaolin ACTs, and plasma supplemented modified ACTs (mACTs), prepared by diluting blood samples 1:1 with human plasma (Behring, Marburg, Germany), were measured every 30 min during CPB. The data obtained were correlated to the plasma chromogenic anti-Xa activity as a reference assay for heparin levels. A total of 64 samples were evaluated. The chromogenic anti-Xa activity ranged from 0.2 to 5.5 IU/mL. The Hepcon HMS calculations ranged from 2.7-8.2 IU/mL of heparin, the standard ACT ranged from 424 to >999 s, and the mACT ranged from 210 to 801 s. The correlation to the chromogenic anti-Xa method was r = 0.43 for the standard kaolin ACT and r = 0.69 for the plasma mACT. The plasma mACT provided an improved correlation to chromogenically measured levels of anti-Xa activity during CPB. The improved correlation most likely results from a correction of the effects of the impairment of the coagulation system caused by hemodilution and consumption of procoagulants on extracorporeal surfaces. IMPLICATIONS: During cardiopulmonary bypass, the plasma modified kaolin activated clotting time (ACT) provides a better correlation with heparin levels than the standard kaolin ACT.     

Evaluation of Point-of-Care ACT Coagulometers and Anti-Xa Activity During Cardiopulmonary Bypass

Objective: The activated clotting time (ACT) is used worldwide to confirm safe heparin anticoagulation for cardiopulmonary bypass. For the present study, the performances of 2 commonly used ACT devices were compared with each other and with anti-Xa levels throughout the surgical procedure in order to understand whether they can be used interchangeably.Design: Prospective study.Setting: Tertiary care center.Participants: The study comprised 33 elective adult cardiac surgical patients.Interventions: Blood samples were taken at standard times throughout the surgery (after induction, after heparin bolus, 4 samples at 30-minute intervals during cardiopulmonary bypass, after protamine), and ACTs and anti-Xa levels were analyzed. Data were compared using receiver operating characteristics and LOESS regression.Measurements and Main Results: The correlation between anti-Xa levels and the Hemochron ACT (Instrumentation Laboratory, Bedford, MA) was acceptable (r = 0.82, 95% confidence interval [CI] 0.757-0.868; p < 0.0001), as was the correlation between anti-Xa levels and the i-STAT (Abbott Point of Care, Abbott Park, IL) (r = 0.81, 95% CI 0.738-0.858; p < 0.0001). The correlation between the 2 ACT methods was poorer (r = 0.77, 95% CI 0.707-0.828; p < 0.0001) than their correlation to anti-Xa levels. When compared with anti-Xa levels, the sensitivity and specificity were mediocre for both devices, although the i-STAT performed better than the Hemochron ACT. The Hemochron ACT read higher values than the i-STAT ACT throughout the course of the surgery.Conclusion: The correlation between the Hemochron ACT and i-STAT ACT is moderate, and they have different sensitivity and specificity when compared with anti-Xa levels. This suggests that ACT devices should not be used interchangeably, but cut-off values for safe anticoagulation during cardiopulmonary bypass should be determined for each type of device, particularly when switching supplier.     

Bedside testing with the new CoaguChek Pro activated clotting time assay in dialysis

The objective of this study was to assess the analytical performance of CoaguChek Pro activated clotting time (ACT) assay using 2 lots versus Hemochron Celite and glass ACT regarding ACT values and correlations versus heparin levels. Determinations were performed using 4 CoaguChek Pro meters and 1 Hemochron 801 meter. Samples were collected during hemodialysis before, after start of heparinization, and 2 h later. Agreement between CoaguChek Pro ACT and Hemochron Celite was good (r = 0.82, slope = 1.12) and moderate with Hemochron glass (r = 0.83, slope = 0.97). Agreement between both CoaguChek Pro lots was r = 0.98. Agreement between the activators, Hemochron Celite, and glass was r = 0.73. Correlation between CoaguChek Pro ACT and heparin concentration was r = 0.88 and 0.94; for Hemochron the correlation was r = 0.75 (Celite) and r = 0.73 (glass). CoaguChek Pro ACT is therefore suitable for monitoring heparin administration during dialysis.     

Heparin monitoring during cardiopulmonary bypass surgery using the one-step point-of-care whole blood anti-factor-Xa clotting assay heptest-POC-Hi

The activated clotting time (ACT) generally used for monitoring heparinization during cardiopulmonary bypass (CPB) surgery does not specifically measure heparin anticoagulant activities. This may result in heparin over- or under-dose and subsequent severe adverse events. A new point-of-care whole blood clotting assay (Heptest POC-Hi [HPOCH]) for quantifying heparin anticoagulant activity specifically was compared with ACT and anti-factor Xa (anti-Xa) heparin plasma levels (Coatest heparin) in 125 patients undergoing CPB surgery. The analytical reliability of the HPOCH and the influence of preanalytical variables on assay results were also examined. The ACT and HPOCH clotting times determined throughout the entire observation period correlated closely (n=683; r = 0.80; p < .0001). Similarly, there was a significant linear correlation between HPOCH and Coatest anti-Xa levels (n=352; r = 0.87; p < .0001). Pre- and post-CBP values of HPOCH, ACT, and anti-Xa plasma levels correlated closely with each other (correlation coefficients between r = 0.90 and r = 0.99; p < .0001). During CPB, there was no significant relationship between ACT and whole blood or plasma heparin levels determined by HPOCH (n=157; r = 0.19) and the chromogenic anti-Xa assay (n=157; r = 0.04), respectively. In contrast, HPOCH and anti-Xa plasma levels correlated strongly during CPB (n=157; r = 0.57; p < .0001). However, bias analysis showed that the HPOCH and Coatest heparin could not be used interchangeably. The HPOCH was well reproducible and not influenced by aprotinin, hemodilution, or other factors affecting ACT. The HPOCH seems to be a promising new tool for specific on-site measurement of heparin activities in whole blood during CPB.     

Monitoring of heparin-induced anticoagulation with kaolin-activated clotting time in cardiac surgical patients treated with aprotinin.

High-dose aprotinin appears to enhance the anticoagulant effects of heparin, as documented by increases in the activated clotting times (ACTs) during cardiopulmonary bypass; hence, some authorities have advocated reducing the dose of heparin in patients treated with aprotinin. An in vitro study by our group suggested that the increase of the ACT in the presence of aprotinin and heparin may be due to the use of celite as surface activator. We compared celite and kaolin as surface activators for the measurement of the ACT in cardiac surgical patients treated with aprotinin and in patients given no aprotinin. This double-blind, randomized, placebo-controlled study included 30 patients, of whom 14 received aprotinin and 16 received a placebo. Before, during, and after cardiopulmonary bypass, the ACT was measured with two Hemochron 400 systems with 12 mg of either celite (C-ACT) or kaolin (K-ACT) used as surface activator and with one Hepcon HMS system (HR-ACT), which uses kaolin as activator. The latter also was used for measurement of the blood heparin concentration. The ACTs of blood without heparin did not differ between aprotinin and control patients. During anticoagulation with heparin and cardiopulmonary bypass, the average C-ACTs were 784 +/- 301 s (aprotinin) and 496 +/- 120 s (control) (P < .001); the K-ACTs were 502 +/- 131 s (aprotinin) and 458 +/- 101 s (control) (P > .05); the HR-ACTs were 406 +/- 87 s (aprotinin) and 423 +/- 82 s (control) (P > .05), which was consistently less than C-ACT and K-ACT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lack of correlation between activated clotting time and plasma heparin during cardiopulmonary bypass.

The activated clotting time (ACT) with a Hemochron system for determining heparin requirements during cardiopulmonary bypass surgery, (CPB) accompanied by hemodilution and hypothermia was evaluated using plasma heparin levels as a standard. In 28 patients who were administered a standard heparin regimen (300 units/kg prebypass, 8000 units in the pump prime and 100 units/kg hourly during CPB) mean prebypass plasma heparin was 4 units/ml, and ACT was 493 seconds. During CPB mean plasma heparin decreased significantly (p < 0.001) to 3.1 units/ml, whereas mean ACT increased significantly (p < 0.001) to 674 seconds. The mean protamine requirement predicted from ACT was significantly higher (43%) than predicted from plasma heparin levels or actual protamine administered. The ACT neither accurately reflected plasma heparin during CPB nor predicted protamine requirements. The fixed-dose regimen employed, however, prevented both intraoperative thrombosis, assessed clinically in all patients, and clotting on six arterial line filters, as determined by scanning EM, despite wide variations in ACT and plasma heparin levels during surgery.     

An investigation of a new activated clotting time "MAX-ACT" in patients undergoing extracorporeal circulation

Activated clotting time (ACT) is a test used in the operating room for monitoring heparin effect. However, ACT does not correlate with heparin levels because of its lack of specificity for heparin and its variability during hypothermia and hemodilution on cardiopulmonary bypass (CPB). A modified ACT using maximal activation of Factor XII, MAX-ACT (Actalyke MAX-ACT; Array Medical, Somerville, NJ), may be less variable and more closely related to heparin levels. We compared MAX-ACT with ACT in 27 patients undergoing CPB. We measured ACT, MAX-ACT, temperature, and hematocrit at six time points: baseline; postheparin; on CPB 30, 60, and 90 min; and postprotamine. Additionally, we assessed anti-Factor Xa heparin activity and antithrombin III activity at four of these six time points. With institution of CPB and hemodilution, MAX-ACT and ACT did not change significantly but had a tendency to increase, whereas concomitant heparin levels decreased (P = 0.065). Neither test correlated with heparin levels. ACT and MAX-ACT did not differ during normothermia but did during hypothermia, and ACT was significantly longer than MAX-ACT (P = 0.009). At the postheparin time point, ACT-heparin sensitivity (defined as [ACT postheparin - ACT baseline]/[heparin concentration postheparin - heparin concentration baseline]) was greater than MAX-ACT-heparin sensitivity (analogous calculation for MAX-ACT; 520 [266 - 9366] s. U(-1). mL(-1) vs 468 [203 - 8833] s. U(-1). mL(-1); P = 0.022). IMPLICATIONS: MAX-ACT (a new activated clotting time [ACT] test) uses more maximal clotting activation in vitro and, although it is less susceptible to increase because of hypothermia and hemodilution than ACT, lack of correlation with heparin levels remains a persistent limitation.     

Activated clotting time for control of anticoagulation during surgery

Two groups of patients undergoing extracorporeal bypass were compared for heparin activity and for heparin and protamine dosage. In group I (18 patients), a uniform dosage pattern was neutralized at the end to a normal clotting time. In group II (43 patients), heparin and terminal protamine doses were regulated by activated clotting times (ACT) using a Hemochron (International Technidyne Corp., Metuchen, NJ). In group II there was a 39 per cent reduction of total heparin dose per case, protamine was reduced 76 per cent, and if the initial heparin doses were excluded, maintenance heparin was reduced 73 per cent. No pattern of heparin administration could be applied to all patients. Heparin half-life varied from 43 to 220 minutes. Other factors that alter heparin activity during bypass revealed no statistical differences. Plasma Hgb was significantly higher in group I, and platelet counts the day following operation were higher in group II. ACT allows tailoring heparin and protamine without the unnecessary dangers of variations in patient response and drug potency.     

Correlation of ACT as measured with three commercially available devices with circulating heparin level during cardiac surgery

Automated activated clotting time (ACT) is utilized as the primary means of assessing anticoagulation status for cardiopulmonary bypass (CPB) procedures. Influences on the clotting cascade during CPB such as hypothermia, hemodilution, and platelet dysfunction are known to affect ACT. The recently introduced Thrombolytic Assessment System (TAS) has been reported to be less sensitive to changes in hemodilution and hypothermia during CPB than more conventional ACT devices. This study evaluated the ability of TAS, and two other commercially available automated ACT systems, the HemoTec and Hemochron, to correlate with circulating heparin levels. Reference standards for circulating heparin were determined by inactivation of factor Xa assay. Nineteen patients undergoing moderate hypothermic CPB served as subjects for this investigation. Blood samples were obtained for study at four time periods: 1) baseline (control), 2) post heparin administration (300-400 U/kg) prior to CPB, 3) during CPB, and 4) post protamine. Study results demonstrated a high correlation between the HemoTec and Hemochron (r = 0.99), increased heparin dose response on CPB compared to pre-CPB activity (p < 0.05), and a significant (p < 0.05) negative correlation between devices and patient hematocrit during CPB. Additionally, device correlation with anti-Xa assay during collection periods 2 and 3 showed negative correlations in each of the three devices evaluated. We conclude that all automated devices tested demonstrated an inability to predict circulating heparin at levels necessary for CPB, and that these discrepancies become magnified during CPB procedures.     

Anti-factor Xa monitoring of anticoagulation during cardiopulmonary bypass in a patient with antiphospholipid syndrome

The activated clotting time (ACT) may be an unreliable monitor of coagulation for patients with the antiphospholipid syndrome. We describe a patient with antiphospholipid syndrome in whom adequate anticoagulation during cardiopulmonary bypass was confirmed by monitoring both the ACT and anti-factor Xa levels. The cardiopulmonary bypass was uneventful, and there were no thrombotic or bleeding complications. The use of anti-factor Xa levels provided confirmation of adequate anticoagulation (and reversal of anticoagulation) that was not possible using the ACT alone.     

Arterial versus venous sampling for activated coagulation time measurements during cardiac surgery: a comparative study

OBJECTIVE: Activated coagulation times (ACTs) are widely used for monitoring anticoagulation during cardiac surgery. Significant variability of this test is well known. Variability in test results was studied, which may arise from the sample drawing site. DESIGN: Prospective study. SETTING: University hospital. PARTICIPANTS: Sixty-five patients scheduled for surgery requiring cardiopulmonary bypass were enrolled in the study. INTERVENTION: ACTs were assessed using the Hemochron 801 ACT machine. Samples were collected (1) baseline I from the arterial catheter before anesthetic induction, (2) baseline II from the arterial and venous collection sites after pulmonary artery catheterization, (3) after heparin administration, (4) 10 minutes after blood collection number 3, and (5) after protamine administration. MEASUREMENTS AND MAIN RESULTS: At the baseline II, the ACT measures using venous blood were significantly higher than that obtained using an arterial sample (p = 0.001). There was no significant difference in ACT measures obtained using either arterial or venous blood samples at the other time points. After heparin administration, the ACT variability in individual patients was quite striking, with ranges of up to 600 seconds in repeated measures. CONCLUSION: During the period of systemic anticoagulation, there is great individual variability between ACT measures obtained from venous and arterial samples. Further studies are required to analyze the cause of differences at the baseline and the source of variable coagulation times after heparin.     

Alternative methods for anticoagulation monitoring in pediatric patients with applicability to a patient with severe hemophilia A and circulating inhibitor.

Anticoagulation monitoring in pediatric patients can be problematic because of the immaturity of the coagulation system in this population. In addition, the hemodilution required to place a small patient on bypass can interfere with standard monitoring methods. In this institution, the Hemochron Jr. ACT (activated clotting time)+ assay has been the standard of care for anticoagulation monitoring since 1997. This assay, with a target ACT of 400 s for initiating bypass, was compared to both the Medtronic HMS system (N = 7) and the Hemochron HiTT assay (N = 6) in pediatric patients. All three assays were then employed to monitor a pediatric Hemophilia A patient (Factor VIII <1%) with high inhibitor titer. Both the HiTT clotting time and the HMS heparin level showed statistically significant correlation to the ACT+ (HiTT, N = 24, r = 0.761; HMS, N = 31, r = 0.818). An HMS target heparin level of 1.5 mg/kg and a HiTT target clotting time of 180 s were found to be clinically equivalent to the 400-s ACT+ as indicators of the need for additional heparin. When a 7-year-old male with severe hemophilia A and high inhibitor titer required tricuspid valve replacement, all three assays were used to ensure appropriate anticoagulation management. During bypass, this patient's ACT+ remained out of range (>1005 s). The HiTT was maintained at >180 s and the HMS heparin level at >1.5 mg/kg. Heparin was administered when any single parameter was below the cutoff value. The use of the combination of three distinct monitoring assays for this patient allowed the surgical team an added level of confidence that appropriate anticoagulation had been maintained.     

Heparinase in the activated clotting time assay: monitoring heparin-independent alterations in coagulation function.

The activated clotting time (ACT) is routinely used to monitor heparin during cardiopulmonary bypass surgery. Activated clotting times may be influenced by a number of factors other than heparin. The presence of heparin in blood samples disguises the occurrence of non-heparin-related changes in coagulation function. During cardiopulmonary bypass, it is difficult to ascertain baseline clotting time fluctuations with ACT alone. Previous attempts to establish accurate baseline data were imprecise and involved extensive sample handling. In this study, we present data obtained using a modified (ACT) assay that incorporates heparinase. The heparinase test cartridge (HTC) instantaneously, specifically, and completely removes heparin in the blood sample at the initiation of the test. In conjunction with standard ACT techniques, the clinician is provided with heparin-independent (baseline) and functional clotting data. The HTC/ACT assay was used in a case study involving 19 patients undergoing cardiopulmonary bypass surgery. The data gathered indicate the usefulness of this assay in monitoring incidents of baseline drift, hemodilution, and hypercoagulation and the efficacy of protamine reversal.     

Comparison of point-of-care activated clotting time systems utilized in a single pediatric institution

This study compares four different activated clotting time (ACT) point-of-care (POC) testing systems used at our institution for the management of patients undergoing heparin therapy. We evaluated these systems under identical conditions to determine their accuracy, reproducibility, ease of use, and cost. Two separate testing stations containing four ACT systems were used. The testing order was randomized for every sample and performed by two trained individuals. Samples of fresh heparinized whole blood were taken at regular intervals and distributed to each station. Each operator tested 50 samples, totaling 400 ACT tests. The ACT value was significantly affected by the type of machine used at both stations 1 and 2 (p < .001). Compared with all systems, the Medtronic ACT Plus Automated Coagulation Timer System (ACT Plus) resulted in the most consistent ACT values (median = 171, Interquartile Range (IQR): 169-175) and least variability (172.17 +/- 5.24). The Hemochron Signature Elite Whole Blood Microcoagulation System had the most variability (221.10 +/- 14.78) and yielded consistently higher ACT values (median = 220, IQR: 210-229.5) compared with other systems. The ACT values reported by the i-STAT Handheld and Test Cartridge Blood Analysis System (153.30 +/- 7.87) were consistently lower (median = 154, IQR: 147-161) in comparison to the ACT Plus and Medtronic HMS Plus Hemostasis Management System (180.60 +/- 7.60, median = 181, IQR: 175-186). There was no statistical difference in results between the two testing sites (p > .05) or the operators (p > .05). The significant finding of this study was the affect each system has on the ACT value. This investigation demonstrates the variability that exists among different ACT monitoring systems at our institution. The discrepant variation in ACT values that exists with the Hemochron system questions the reliability of its use in the management of patients undergoing heparin therapy.     

Measurement of activated clotting time in children--comparison of the Celite i-STAT ACT with the Medtronic ACT II

BACKGROUND: To evaluate a recently introduced blood-saving method for the measurement of activated clotting time (ACT), the Celite i-STAT ACT, by comparing the values obtained with those from the widely used Medtronic ACT II device. METHODS: In a prospective clinical study, we compared ACT values from the i-STAT device with the Medtronic ACT II device in 60 paediatric, interventional, cardiac catheterization procedures necessitating prophylactic heparinization. Blood samples were pair-analyzed using two i-STAT analyzers and one Medtronic ACT II device with double-tube-cartridges before and after heparinization. Data were compared using Bland-Altman bias analysis, Student's t-test and simple regression analysis. RESULTS: Bias and precision between the Medtronic ACT II and the i-STAT ACT values was -5.4 +/- 26.3. The i-STAT and Medtronic ACT II values were similar before heparinization (P = 0.22), but i-STAT ACT values became significantly longer than Medtronic ACT II values after heparinization (P = 0.021). The increase of ACT after heparinization was greater (median 86.3; range 40-187 s) in the i-STAT analyzer than in the Medtronic ACT II analyzer (median 73.0; range 19-235.5 s). Increase in ACT values was inversely affected by intraoperative haemoglobin concentration in the Medtronic ACT II analyzer (P = 0.001) but not in the i-STAT analyzer. CONCLUSION: Activated clotting times obtained from the Celite i-STAT ACT and the Medtronic ACT II demonstrated poor agreement. The technical principles are quite different and the two methods showed diverse susceptibility to intraoperative haemoglobin concentration. Users have to be aware of technique-specific ACT target ranges and their confounders, which need to be provided by the manufacturers.     

Measurement of patients' bivalirudin plasma levels by a thrombelastograph ecarin clotting time assay: a comparison to a standard activated clotting time

Standard activated clotting time (ACT) tests have a poor correlation to bivalirudin levels, leading to uncertainty regarding adequate anticoagulation in percutaneous coronary intervention patients. We tested a Thrombelastograph (TEG) ecarin clotting time (ECT) assay for sensitivity to bivalirudin using blood from 80 patients undergoing interventional cardiology procedures with bivalirudin anticoagulation. This was compared to a standard Hemochron ACT assay using diatomaceous earth. With the TEG assay, the direct thrombin activator, ecarin, was used to initiate coagulation and measured as the reaction time. Plasma samples were evaluated for bivalirudin by a chromogenic assay at an independent hematological laboratory. Linear regression of the standard ACT versus bivalirudin level gave an r = 0.306 whereas the TEG ECT gave a much higher r2 = 0.746 (both P < 0.0001). The TEG ECT should prove more useful than the standard ACT for monitoring bivalirudin anticoagulation across the clinically therapeutic range.     

Intraoperative monitoring of danaparoid sodium anticoagulation during cardiovascular operations

Purpose: Patients with cardiovascular disorders frequently need anticoagulation for diagnostic studies, surgical procedures, and therapy. Heparin-induced thrombocytopenia is a relatively common complication of heparin therapy that can result in thrombosis and subsequent limb loss or death, necessitating use of alternative anticoagulants. Methods: Two patients who needed cardiac surgery had thrombocytopenia induced by exposure to heparin and heparin-coated tubing. Several assays were examined for their ability to monitor intraoperative anticoagulation of a factor Xa inhibitor, danaparoid sodium. Results: In vitro, celite and kaolin activated clotting times and activated partial thromboplastin time were prolonged linearly in the presence of increasing concentrations of danaparoid sodium. Aprotinin did not alter the linearity of the response but did alter its slope. In vivo, activated clotting times and activated partial thromboplastin time were insensitive to clinically significant changes in danaparoid sodium plasma levels during cardiopulmonary bypass. Correction in activated partial thromboplastin time lagged 2 hours behind clinically important changes in anti-factor Xa levels. Only anti-factor Xa levels were adequate to monitor intraoperative danaparoid sodium levels. Conclusion: Anticoagulation for cardiopulmonary bypass can be successfully performed with danaparoid sodium and intraoperative anti-factor Xa monitoring. (J Vasc Surg 1998;27:568-75.)