Activated clotting time

They're going to do clotting tests like PT, APTT.

and possibly activated clotting time, that's ACT, to see if you're showing any clotting coagulopathies from the venom because venom tends to act like an anticoagulant.

It makes your blood thinner.

It neutralizes your blood because venom is hemotoxic.

And the dose for bypass is about 400 units per kilo.

You're going to check the ACT about three to five minutes later, and a normal ACT is about 80 to 120 seconds.

But your target to go on bypass has to be greater than 480 seconds.

And then after that, the ACT is going to get rechecked every about 20 to 30 minutes during the run.

If the ACT won't come up, even with massive doses of heparin, you're going to think about heparin resistance.

So the classic cause of that is antithrombin deficiency.

And the fix is to give more antithrombin, either through an antithrombin concentrate or as fresh frozen plasma.

What is the enemy of coronary disease? Tachycardia, because it raises demand and it's going to cut your supply.

So that's gonna measure the extrinsic and common pathways, and then the aPTT measures the intrinsic and the common pathways.

And the ACT is a whole blood test of the intrinsic and common pathways that we use when the heparin levels are too high for the PTT to read accurately, such as during cardiopulmonary bypass.

Now, the two most important targets in this entire episode are factor Xa and thrombin, which is also activated factor two a.

Almost every anticoagulant that we're gonna talk about today hits one or both of these targets, so keep these two targets in your mind.

Now, unfractionated heparin has roughly equal activity against thrombin and Xa, about a one-to-one ratio.

Because heparin depends on antithrombin, a patient with low antithrombin levels are not going to respond to heparin, and we call this heparin resistance.

So if you picture a cardiac surgery patient who's receiving that full heparin dose, but the ACT won't come up, one classic cause is antithrombin deficiency, and the treatment is usually to replace that antithrombin with antithrombin concentrate or FFP, which contains that antithrombin.

For a typical heparin infusion, you monitor the aPTT, usually aiming for about one and a half to two and a half times normal or an anti-Xa level.

When a glycoprotein 2b3a inhibitor is also used, a lower target is appropriate.

Check the ACT regularly in long procedures.

Flush catheters meticulously.

If thrombus forms, glycoprotein 2b3a inhibitors can be used as bailout.

For elective procedures in patients on oral anticoagulants, decide in advance whether to interrupt.

Many operators perform radial procedures on uninterrupted warfarin with a therapeutic INR, while direct oral anticoagulants are often held for a short period, depending on kidney function.

During PCI, use weight, adjusted heparin, and monitor the ACT.

After PCI, choose the antithrombotic regimen deliberately.