Blood Coagulation Analysis in Pediatric Extracorporeal Membrane Oxygenation Patients with Small-Volume Acoustic Tweezing Thromboelastometry

Introduction: In critical care patients and those with coagulation abnormalities, blood coagulation analysis is vital for determining bleeding and clotting risks. Patients undergoing Extracorporeal Membrane Oxygenation (ECMO) are treated with anticoagulants to prevent blood clotting in the ECMO circuit, and thus they need regular coagulation monitoring to ensure the therapy is effective and safe. Traditional coagulation analyzers can be unreliable due to contact between the blood sample and container walls and require relatively large volumes of blood which may cause additional complications, such as iatrogenic anemia, in pediatric patients. Using integrated quasi-static acoustic tweezing thromboelastometry (i-QATT), a non-contact drop-of-blood technique, comprehensive information about blood coagulation can be obtained without these limitations. The objectives of this study were to establish the validity of the i-QATT technique through correlation analysis with gold-standard tests and apply this technique to examine the effects of anticoagulants (heparin, bivalirudin) and reversal agents (heparinase) on blood plasma coagulation in pediatric ECMO patients.

Materials and

Methods: Blood samples used in this study include (1) Factor Assay Control Plasma (George-King Biomedical, Overland Park, KS) and (2) plasma samples collected from pediatric ECMO patients on heparin or bivalirudin treatment in Texas Children’s Hospital (Houston, TX). Plasma samples from heparin-treated patients were exposed to heparinase (Dade Hepzyme, Siemens Scientific) to test the reversal of anticoagulation. To trigger coagulation, the samples were exposed to either intrinsic (aPTT-XL) and extrinsic (Thromboplastin-D) pathway activators mixed with calcium chloride. Each i-QATT test was performed using a 4-6 uL drop of the final solution. The test produced mechanical (sample firmness vs. time) and photo-optical (sample darkness vs. time) tweezographs. From this graphical output, the following i-QATT coagulation parameters were extracted and analyzed: reaction time (RT), clot initiation time (CIT), time to firm clot formation (TFCF), clotting time (CT), clotting rate (CR), and maximum clot firmness (MCF). The values of these parameters were compared with PT/aPTT, INR, fibrinogen concentration, and hematocrit values as well as ROTEM data collected from the same patients by Texas Children’s Hospital.

Results, Conclusions, and Discussions: Fig. 1a shows representative mechanical tweezographs for normal FACT plasma and anticoagulated and Hepzyme-corrected plasma samples from pediatric ECMO patients. As seen in Fig. 1b, i-QATT parameters TFCF and CT were strongly correlated with aPTT values, and i-QATT MCF values were strongly correlated with fibrinogen (FGN) values. Statistically significant differences in TFCF and CT parameters were observed between normal FACT plasma, Hepzyme-treated FACT plasma, heparin-treated patient plasma, and Hepzyme-corrected patient plasma (Fig. 1c). Statistically significant differences were also observed in TFCF and CT between normal FACT plasma and bivalirudin-treated patient plasma (Fig. 1c).
The i-QATT technique provides comprehensive analysis of blood plasma coagulation and accurately identifies anticoagulant effects and their reversal in pediatric ECMO patients. This study demonstrates the clinical potential of acoustic tweezing technology in monitoring anticoagulant therapy in pediatric patients using small-volume samples.

Acknowledgements (Optional): This study has been supported by grants from the National Science Foundation (2134020) and the National Institutes of Health (R21EB031401, R43EB031013).