Systemic heparin vs heparin through CVVHD machine

[CardiacIntensivist]

Hi all, I rotate in a CTICU with a heavy load on VAD and ECMO patients. One thing that has puzzled me is the insistence of attendings on running heparin only through the CVVHD machine instead of systemically.

So what I gathered so far is that:
-They keep heparin at 300U/hr and do not titrate to any PTT (as UTD would recommend 45-60)
-Only when the bleeding risk is over will they change over to systemic heparin (systemic heparin is needed for the ECMO or VAD)
-We are definitely NOT doing regional heparinization of the CVVHD machine (i.e. running heparin on the inflow with protamine to neutralize it at the outflow)

Is there even a difference between heparin @300 U/hr systemically vs heparin @300U/hr via the CVVHD machine? It seems like heparin would be too large to be dialyzed and whatever heparin goes into the machine will be the same amount coming out.

I've tried googling and reviewing all the articles on UpToDate on CRRT and nothing touches on that point. Perhaps it is too simple a question?

Thanks!

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[Stitch]

They don't monitor anticoagulation at all? That seems odd given the bleeding risks with ECMO and the clotting risks with VADs. I'm peds and do a lot of ECMO stuff (with concurrent CVVHD), so I can't comment on the adult protocols. But we run heparin straight into the ECMO circuit, then follow Xa levels every six hours, adjusting the drip to maintain normal range (0.3-0.7). We also trend ACTS in between, and get a TEG twice daily. We usually run it straight into the circuit just out of convenience; it's basically a giant IV and frees up the patient's IV access for other things. Otherwise, aside from the volume of distribution difference (which may not be an issue in adults), I don't see a lot of difference between giving it to the circuit, though some might say that tubing and oxygenator would 'eat' it.

If we're doing only CVVHD/F then we regionally anticoagulate with citrate, not heparin.

 

[CardiacIntensivist]

We follow PTT but it is because we essentially we do BID labs on everyone. Yes, we don't titrate to goal when we first start. When we do titrate to goal, it is relative for the ECMO or VAD, we never titrate PTT for the sake of the CVVH machine (or at least, I've never seen it). And we don't have a citrate protocol for CVVHD in my ICUs.

We only follow heparin assays or anti-Xa for VAD pts who do not seem to be responding to the heparin (i.e. clotting despite adequate PTT or PTT that isn't rising appropriately).

So it seems like your statement agrees with what I thought in regards to not being very different. It may be a state of mind thing? The surgeons want to believe CVVHD heparin does not equate to systemic heparin? *shrug*

 

[Hernandez]

In the grand scheme of things, 300U heparin/hour is a small dose and less than SubQ DVT prophylaxis dosing. How much affect on PTT would you expect?

 

[CardiacIntensivist]

In the grand scheme of things, 300U heparin/hour is a small dose and less than SubQ DVT prophylaxis dosing. How much affect on PTT would you expect?

Oh you misunderstand. I don't care about any effect on the PTT. My question was just if there is ANY difference between running systemically through an IV or first going through the CVVH machine.

 

[dienekes88]

They don't monitor anticoagulation at all? That seems odd given the bleeding risks with ECMO and the clotting risks with VADs. I'm peds and do a lot of ECMO stuff (with concurrent CVVHD), so I can't comment on the adult protocols. But we run heparin straight into the ECMO circuit, then follow Xa levels every six hours, adjusting the drip to maintain normal range (0.3-0.7). We also trend ACTS in between, and get a TEG twice daily. We usually run it straight into the circuit just out of convenience; it's basically a giant IV and frees up the patient's IV access for other things. Otherwise, aside from the volume of distribution difference (which may not be an issue in adults), I don't see a lot of difference between giving it to the circuit, though some might say that tubing and oxygenator would 'eat' it.

If we're doing only CVVHD/F then we regionally anticoagulate with citrate, not heparin.

Interesting. We try to avoid Xa levels given the high frequency of discordant Xa and PTTs. Reasonable evidence that following Xa levels in discordant patients increases risk for mortality and clinically significant bleeding.

As for anticoagulation, it's always ACT for ECMO and PTT for VAD.

For CVVH, pretty sure we use citrate too.

Oh you misunderstand. I don't care about any effect on the PTT. My question was just if there is ANY difference between running systemically through an IV or first going through the CVVH machine.

Probably the surgeons just want to make sure that you get the maximum effect (the actual 300u/h) going through the CVVH machine and the area immediately surrounding the CVVH line. Otherwise, if you gave it systemically first, there would be some metabolism and distribution, so you wouldn't get the concentrated effect. Indeed, the minimal anticoagulation of the patient would be the minimal anticoagulation of the actual machine, which would then clot. By doing it this way, you're anticoagulated enough to stop the machine from clotting off but not enough to actually cause the patient to bleed. The heparin running into the machine is the same as the heparin coming out, but then it's distributed in the systemic circulation and diluted out. As compared to anticoagulating the entire patient enough to prevent clotting of the CVVH machine. That would require more.

It's kinda like when you're running an overnight tpa gtt for thrombolysis before going back for a second look the next day. Non-titrated heparin at 500/h through the sheath that is running the TPA, because you just want to make sure the sheath and the area around the sheath doesn't clot. If the patient's actual systemic PTT is low, it doesn't matter.

I'm more accustomed to citrate, though.