From Lesa Nelson, who was a graduate student in George’s fall, 2015 Michigan State University Hemostasis and Thrombosis and Resource Management online graduate course.
Our cardiac catheterization laboratory performed an ACT using the Hemochron ACT+ cuvette, designed to measure the effects of 1–6 U/mL (high dose) heparin. They were getting ACT results of 149–190 seconds on measurements made 10 minutes post heparin administration. They then dosed the patient with more heparin and ran a Hemochron ACTLR cuvette and obtained the result they were expecting. The 90 kg patient received a total dose of 11,000 units of heparin. The cath lab staff felt this was a high dose.
Here is what I discovered. The staff’s impression of “high dose” is actually not high when calculated mathematically and compared to the units measured by the cuvettes. The ACTLR measures the effects of heparin doses up to 2.5 U/mL, the ACT+ measures effects of 1–6 U/mL.
I calculated (estimated) using Gilcher’s Rule of Five, which closely correlated with the Nadler Equation for total blood volume: 90kg x the factor of 70 = blood volume of approximately 6300 mL. 11000 units heparin/6300mL = 1.7 U/mL, which is the calculation the cath lab should be using to determine which cuvette to use. They should have used the ACTLR cuvette initially.
The ACTLR and ACT+ cuvettes have different, but similar linear slopes and should not be compared with each other. They perform well when utilized appropriately. The cath lab was also expecting the two cuvette results to correlate more closely. The cath lab staff doses heparin based on units per kilogram, which does not compare to the procedural instructions.
My solution is attached below. I did the math for them and created a quick reference table to put into perspective how much heparin is being given in U/mL blood. I used the Gilcher Rule of Five and made a chart for each factor. Now, it is overkill, but it makes the staff better understand which cuvette to use to obtain the most accurate result in an imprecise and difficult to reproduce testing system…aaaahhh…coagulation at it’s finest.
Let me know what you think. I would love to have more input from others to see if I am totally off base. I am interested in what information leads to the determination of which cuvette to use. Calculation? Specific cath procedure? Amount of Heparin given? Thank you, Lesa
Here is Lesa’s table:/sites/default/files/heparin_v_tbv_table_70-65.pdf
Here is the Glicher rule of five and the Nadler equation: /sites/default/files/tbv_calculation.pdf
Thank you, Lesa, your table will hellp anyone who monitors heparin therapy with the Hemochron ACT during cardiac catheterization and coronary bypass surgery. Your discussion is sure to attract responses.
Posted for Tom Exner,
Posted for Tom Exner, Haemonetics, Sydney, Australia. Thanks for posting this interesting topic. There’s bit of a gulf between expert ACT users in emergency clinical situations and heparin testing in coag labs but some conditions are common to both. Patients may display a wide range in heparin response depending on how big any particular thrombus may be. Usually the bigger the thrombotic episode, the more heparin resistance occurs due to PF4 release and presence of activated factors including microparticles. ATIII is also a complication. It’s probably a matter of clinical judgement as to what level to heparin to administer and then testing for a potentially highly variable result.
Good to see someone taking time to provide more reliable results.
Best wishes from Tom Exner.