A-149 Comparison of Activated Clotting Time (ACT) Measurements Using GEM Hemochron 100 and Medtronic HMS Plus During Cardiopulmonary Bypass: Establishing New Target Ranges at Medstar Washington Hospital Center

Abstract Background Activated Clotting Time (ACT) is a critical parameter in managing anticoagulation during cardiopulmonary bypass (CPB). At MedStar Washington Hospital Center (MWHC), the Medtronic HMS Plus (HMS+) system has traditionally been used to determine heparinization levels through Heparin Dose Response (HDR), Heparin Assay (HPT), and High-Range ACT (HR-ACT). To ensure safe CPB, ACT values must exceed 400 seconds for cannulation and 480 seconds for bypass initiation. The GEM Hemochron 100 (GH100) offers a streamlined approach, requiring less blood volume, providing faster results, and improving operational efficiency. This study compares ACT measurements between the HMS+ and GH100 to establish new target ACT ranges for CPB procedures. Methods A comparative analysis was conducted using 215 paired ACT tests from cardiac surgery patients post-heparinization. ACT measurements were obtained at key clinical decision points: baseline, pre-cannulation, during bypass, and post-protamine neutralization, using both HMS+ and GH100 devices. Split samples were analyzed to determine the correlation between the two instruments. Regression modeling via Microsoft Excel’s FORECAST.LINEAR function was used to predict GH100 ACT values based on HMS+ reference measurements, focusing on three key medical decision thresholds: 120 seconds (baseline/post-protamine), 400 seconds (cannulation), and 480 seconds (bypass initiation). Results ACT measurements from the GH100 showed a strong correlation with HMS+ results, with a correlation coefficient (R = 0.91). What we have confirmed is that ACT values differ between the GH100 and HMS+, necessitating adjusted target ranges for safe anticoagulation management (at least 40 additional patients per procedure is recommended). Regression modeling established the following new target ACT values for GH100:Cannulation ACT: 389 seconds (GH100) vs. 400 seconds (HMS+)Bypass ACT: 426 seconds (GH100) vs. 480 seconds (HMS+) Additionally, the GH100 demonstrated several operational advantages:Faster results: ∼4 minutes vs. ∼8 minutes for HMS+Lower blood volume requirement: 35 µL (1 drop of blood) vs. 3,000 µL per testReduced complexity: GH100 uses a single test (ACT+) throughout the procedure, eliminating the need for multiple cartridgesRemote instrument management through the GEMweb Plus 500 middlewareLower costs compared to MedtronicNo change in patient management despite eliminating heparin dosing and protamine dosing tests from HMS+ Conclusion The GH100 provides reliable ACT measurements with a strong correlation to HMS+, while offering significant workflow improvements. New ACT target values have been established to maintain optimal heparinization during CPB. Given the advantages of reduced complexity, enhanced connectivity, faster turnaround time, and lower costs compared to Medtronic, MWHC has decided to transition to GH100 for ACT monitoring in cardiac surgery. Importantly, this transition does not alter patient management, despite eliminating heparin dosing and protamine dosing tests from HMS+.