‘Point-of-Care’ Coagulation Monitors

1. ‘Point-of-Care’ Coagulation Monitors Evan Pivalizza, M.D. October, 2005

2. A. Anticoagulation (heparin) management • Function – whole blood clotting • Quantitative- heparin level

3. ACT (Activated clotting time) • Hemachron • 2 ml blood + activator (celite → kaolin) • Magnet in rotating test tube (dependent) • Blood clots → magnet moves/breaks contact → time • Normal 80-120 secs • Aim > 480 secs (animal, ltd human data)

4. B. Hemotec • Cartridge kaolin • Blood automatically added → plunger • Clot impedes speed plunger → time

5. Advantages • Easy, inexpensive • Sizable body data

6. Disadvantages • 4% coefficient variability normal • Exaggerated hypothermia, hemodilutiuon • Affected thrombocytopenia, antiplatelet drugs • NOT reflect heparin level/concentration, e.g., ‘Heparin resistance’ • ↓ AT III

7. 2. Heparin concentration A. Hepcon (Heparin management system – HMS) • Automated protamine titration (multiple channels) • < protamine = not antagonize heparin • > protamine = inhibits clot formation • √ protamine = fastest clot → heparin []

8. Advantages • Not affected temperature, dilution • Disadvantages • NOT measure function (heparin resistance)

9. B. High dose Thrombin Time (HiTT) • TT = time fibrinogen → fibrin by thrombin • Sensitive to low levels heparin • High dose thrombin added, bind heparin-ATIII complexes • Remaining unbound heparin ↑ time fibrin formation (measured)

10. Advantages • Not affected temp, dilution, aprotinin • Disadvantages • Variable

11. B. Platelet Function • Point-of care monitors • Rapid results • Help predict bleeding/cause • NOT always correlate laboratory analyses • NOT exclusive, ideally incorporated into transfusion algorithm • Clinical • Point of care • Laboratory

12. Dynamic tests platelet function • Thrombelastograph (TEGTM), Haemoscope, IL

13. Viscoelastic test of fibrin formation → fibrinolysis • Incorporation ↓ bleeding/ transfusion/ re-exploration • Cardiac surgery (esp complex) • Pedi cardiac surgery • Liver transplantation

16. R: Time initial fibrin formation • K: Subsequent fibrin- plt interaction • Angle: Ditto • MA: 60% plt function (40% fibrinogen) • G: Manipulation MA - > plt function • Index: Summary first 4 measures • Lysis: At 30 minutes

17. Modifications • Heparinase • Undercover defect during CPB • Is heparin reversed? • Tissue factor • ++ acceleration thrombin formation → MA (plt function) • Abciximab • GpIIb/IIIa antagonist • Differentiate platelet/ fibrinogen effect

18. 2. Sonoclot (Sienco, CO)

19. Changing impedance ultrasonic probe immersed sample • Start fibrin formation (ACT) • Fibrin cross-linkage (Rate = slope curve) • Platelet-mediated clot strength (Peak impedance and time to peak) • Data primarily cardiac

20. B. Tests platelet response to activator • Platelet function analyzer (PFA – Dade Behring)

21. Plt adhesive activity whole blood • Perfused across aperture in membrane coated agonist (epinephrine, ADP) • Plt adhesion seals aperture → closure time • High negative predictive value bleeding

22. 2. Ultegra (Accumetrics, CA)

23. Measure platelet response to TRAP (thrombin receptor agonist peptide) • Platelet-agglutination of fibrinogen-coated beads – optical detection • Sensitive GpIIb/IIIa – cath lab

24. 3. Platelet aggregometry (lab gold std) • Photo-optical measure light transmittance through plt-rich plasma • Exposed agonist (ADP, collagen, epinephrine) → aggregation → ↓ turbidity → ↑ transmittance

25. References • Shore-Lesserson, Anesthesiology Clinics N America 2003:21;511-26 • Shore-Lesserson, J Cardiothoracic and Vascular Anesthesia 2002:16;99-106