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

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.

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 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.

Bivalirudin Provides Rapid, Effective, and Reliable Anticoagulation During Off-Pump Coronary Revascularization: Results of the ???EVOLUTION OFF??? Trial

In the EVOLUTION OFF trial, we evaluated the safety and efficacy of bivalirudin during off-pump coronary artery bypass grafting as compared with heparin-protamine. In this subanalysis of EVOLUTION OFF data of bivalirudin-treated patients, we assessed the pharmacokinetics (PK) and effectiveness of bivalirudin anticoagulation to achieve target activated clotting time (ACT)+ values. Data from 101 patients were assessed. A bolus of 0.75 mg/kg of bivalirudin was followed by a continuous infusion of 1.75 mg x kg(-1) x h(-1) during the grafting procedure. An ACT+ value of >300 s was the target. In four patients, PK data for bivalirudin were obtained. Only in exceptional cases were repeat fractional boluses or an increase of the infusion rate required. Assessment of the PK data showed a mean concentration of bivalirudin after the initial bolus of 11.0 +/- 0.53 microg/mL and a mean concentration during infusion of 11.2 +/- 2.32 microg/mL. Pearson's correlation between bivalirudin concentrations and ACT+ values was 0.92. Bivalirudin PK data consistently exceeded concentrations of 6.5 microg/mL, which have been evaluated as effective during percutaneous coronary intervention. The correlation between bivalirudin levels and ACT+ values was good, and the target ACT+ values were almost always achieved. These results suggest that bivalirudin, given according to the current protocol, provides reliable and effective anticoagulation during off-pump coronary artery bypass graft surgery.

Point-of-care testing in the cardiovascular operating theatre

Point-of-care testing (POCT) remains under scrutiny by healthcare professionals because of its ill-tried, young history. POCT methods are being developed by a few major equipment companies based on rapid progress in informatics and nanotechnology. Issues as POCT quality control, comparability with standard laboratory procedures, standardisation, traceability and round robin testing are being left to hospitals. As a result, the clinical and operational benefits of POCT were first evident for patients on the operating table. For the management of cardiovascular surgery patients, POCT technology is an indispensable aid. Improvement of the technology has meant that clinical laboratory pathologists now recognise the need for POCT beyond their high-throughput areas.

Clin Chem Lab Med 2006;44:1060–5.