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

Can We Rely on the Activated Clotting Time to Measure Heparin Anticoagulation? A Clinical Evaluation of Two ACT Monitors

The sensitivity to heparin during cardiopulmonary bypass (CPB) is determined by patient-specific characteristics and is assessed by the whole blood activated clotting time (ACT). We aimed to examine reliability measures between two different ACT monitors using Bland-Altman analysis: bias should not exceed 50 ± 50 seconds for measurements performed during CPB or 10 ± 10 seconds before and after CPB. The ACT response should be linear in relation to the concentration of heparin in plasma. Twenty patients (n = 20) aged 20-80 years and admitted for coronary artery bypass surgery were enrolled to this clinical observational study. ACT values and antifactor Xa were sampled: 1) before induction of anesthesia, 2) after heparin bolus, 3) during CPB at the start of rewarming, 4) at weaning from CPB, and 5) after heparin reversal. The evaluation comprised the Hemostasis Management System Plus™ (HMS, Medtronic Inc., Minneapolis, MN) and i-STAT™ (Abbott, Point of Care Inc., Princeton, NJ). Bias for the HMS Plus™ vs. i-STAT™ was +105 ± 119 seconds for measurements during CPB and +2.8 ± 11.7 seconds before and after CPB. Associated limits of agreement for the observed bias were ±235 and ±23 seconds, respectively. Inter-device correlation of ACT values was .46 (p < .001) during CPB; otherwise .48 (p = .02). Both devices produced ACT values unrelated (<10%) to the measured heparin concentration. The use of multivariable regression analysis demonstrated an independent association between the ACT measurement and hematocrit, however, not with the plasma concentration of heparin. ACT monitors demonstrate unacceptable bias differences, combined with wide limits of agreement. The ACT response correlated with hematocrit, but not with the actual heparin concentration.

Comparison of Point-of-Care Activated Clotting Time Methods in Different Clinical Settings in a Large Academic Medical Center

OBJECTIVES

This study is a comparative analysis of measured activated clotting time (ACT) values by use of 5 different point-of-care (POC) ACT methods spanning the range detected during different clinical procedures at our institution.

METHODS

We determined the correlation, imprecision, and differences in measured ACT values with use of 4 POC ACT methods compared with a reference ACT method in 41 venous whole blood samples collected from 25 adult patients undergoing interventional procedures. The POC ACT methods evaluated included the i-STAT with kaolin activator in prewarm mode, i-STAT with Celite activator in prewarm and nonprewarm modes, ACTPlus, and HMSPlus, which was designated the reference method. Each venous whole blood patient sample was tested in duplicate on each POC ACT test system (total n = 410 ACT measurements). Analyses of imprecision and differences in measured ACT values were stratified by moderate (100-299 s) and high (≥300 s) ACT ranges.

RESULTS

In this study population, measured ACT values ranged from 100-835 s with use of the HMSPlus. All methods demonstrated good correlation (r ≥ 0.95) in ACT values compared to the reference method. Imprecision varied by method with ranges of 1.7%-2.7% CV in the moderate ACT range and 2.5%-4.8% CV in the high ACT range. ACTPlus and i-STAT-Celite-prewarm methods exhibited proportional differences in measured ACT values whereas the i-STAT-Celite-nonprewarm and i-STAT-kaolin-prewarm demonstrated constant differences in measured ACT values compared to HMSPlus.

CONCLUSIONS

ACT values correlate well between POC methods. Imprecision and difference profiles vary by method; notably, imprecision exceeds systematic differences in the high ACT range and contributes to intermethod differences that are limitations worthy of consideration when contemplating a change in ACT methods.

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.

Heparin-based nanocapsules as potential drug delivery systems

Herein, the synthesis and characterization of heparin-based nanocapsules (NCs) as potential drug delivery systems is described. For the synthesis of the heparin-based NCs, the versatile method of miniemulsion polymerization at the droplets interface was achieved resulting in narrowly distributed NCs with 180 nm in diameter. Scanning and transmission electron microscopy images showed clearly NC morphology. A highly negative charge density for the heparin-based NCs was determined by measuring the electro-kinetic potential. Measuring the activated clotting time demonstrated the biological intactness of the polymeric shell. The ability of heparin-based NCs to bind to antithrombin (AT III) was investigated using isothermal titration calorimetry and dynamic light scattering experiments. The chemical stability of the NCs was studied in physiological protein-containing solutions and also in medically interesting fluids such as sodium chloride 0.9%, Ringer's solution, and phosphate buffer saline using dynamic light scattering and measuring the fluorescence intensity. The impressive uptake of NCs in different cells was confirmed by fluorescence-activated cell sorting, confocal laser scanning microscopy, and transmission electron microscopy. The low toxicity of all types of NCs was demonstrated.

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.

Clinical evaluation of the i-STAT kaolin activated clotting time (ACT) test in different clinical settings in a large academic urban medical center: comparison with the Medtronic ACT Plus

Historically, it has been difficult for hospitals to change methods for activated clotting time (ACT) testing because of differences in ACT values obtained with different instruments, wide differences in target ranges used in different procedures, and the difficulty of performing crossover studies at the bedside in critical care situations. There are limited published data comparing the i-STAT (Abbott Point of Care, Princeton, NJ) kaolin ACT with the Medtronic ACT Plus (Medtronic, Minneapolis, MN). The i-STAT system can perform ACT testing in addition to testing of a number of critical care analytes and may offer potential advantages over other ACT analyzers. Comparison of ACT values on 121 simultaneous split-sample tests yielded an R(2) of 0.88 with i-STAT = 0.79 Medtronic + 72.0. The Pearson correlation was R = 0.94, indicating statistically significant correlation between the 2 methods. Based on this comparison, we were able to implement the i-STAT ACT throughout our institution without changing target ranges for any individual procedure.

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

OBJECTIVE

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

DESIGN

A prospective, observational single-center study.

PARTICIPANTS

Forty-four pediatric cardiac surgery patients.

INTERVENTION

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

METHODS AND MAIN RESULTS

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

CONCLUSION

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

Measurement of the activated clotting time during cardiopulmonary bypass: differences between Hemotec ACT and Hemochron Jr apparatus

BACKGROUND

Measurement of the activated clotting time (ACT) represents a standard method for coagulatory assessments. The test employs specific agents to trigger the coagulation process. The present study aimed to compare kaolin (Hemotec) versus a combination of silica, kaolin and phospholipid (Hemochron Jr) ACTs.

METHODS

Hemotec and Hemochron Jr ACT monitors were compared by simultaneous measurement of paired arterial blood samples (n = 114) with respect to precision and bias during clinical conditions of cardiopulmonary bypass (CPB). The influence of haemodilution on the ACT was tested in an ex-vivo model.

RESULTS

The precision of Hemotec and Hemochron Jr ACT measurements attained 21 +/- 2.6 s versus 27.0 +/- 2.6 s (p = 0.126) during CPB and 2.5 +/- 2.2 s versus 9.4 +/- 6.9 s (p = 0.000) after protamine administration, respectively. The Hemochron Jr monitor was associated with a bias of -102 +/- 13.7 s compared to the Hemotec ACT monitor (p = 0.000) during CPB and -6.9 +/- 2.9 s after protamine (p = 0.025). Linear regression analysis of ACT readings between monitors reached r = 0.526 (p = 0.000). Hemochron Jr ACT values correlated with the erythrocyte volume fraction r = 0.379 (p = 0.000). Ex-vivo data indicated that the Hemotec ACT monitor was associated with relatively higher ACT readings after haemodilution.

CONCLUSION

The ACT is not a standardized measure. Test results are strongly associated with the specific compounds used to initiate the coagulation process.