Heparin Resistance Before Bypass: Concentrate, Plasma, or Simply More Heparin
A 70-year-old man on a preoperative heparin infusion bridge won't clot down after a standard heparin dose. Three ways exist to fix the same antithrombin problem, and each one trades a different risk for the others.
Frank D., a 70-year-old man, spent his career as a long-haul truck driver and has been living at his daughter's house for the past nine days, since a pulmonary embolism diagnosed during workup for his upcoming aortic valve replacement put him on a continuous unfractionated heparin infusion as a bridge — his valve disease had already been scheduled for surgery before the PE was found, and his care team elected to bridge rather than delay the operation further. Nine days is longer than most patients spend on a preoperative heparin bridge, and it matters directly to what is happening on the table now: prolonged heparin exposure is a recognized cause of acquired antithrombin depletion, since heparin's own mechanism of action consumes the cofactor it depends on over sustained exposure.
This morning, after a standard weight-based heparin dose for cardiopulmonary bypass, his activated clotting time came back at 340 seconds — well short of the 480-second target the perfusionist needs before bypass can safely begin. A second, smaller dose brought him only to 365. The ISTH's perioperative subcommittee defines heparin resistance in this setting as the failure of 500 units per kilogram to produce an ACT of at least 480 seconds, and he is tracking toward meeting that definition rather than merely responding slowly. What the numbers also show, though, is that he is not refractory: 340 to 365 is a real if inadequate response, not the flat non-response a profound antithrombin deficit would produce, and that distinction is the one the room actually has to act on. His platelet count and fibrinogen were normal preoperatively, so this is not a broader coagulopathy presenting as resistance. The working assumption — consistent with nine days on infusion — is that his own antithrombin reserves have been drawn down by the bridge itself, leaving standard heparin dosing unable to reach the anticoagulation bypass requires no matter how carefully it is calculated.
Two heparin doses in, still short of target
I want antithrombin concentrate before we give a third heparin dose. Nine days on a heparin infusion is a real, recognized setup for acquired antithrombin depletion, and heparin can't do its job without enough AT to potentiate — giving him more heparin without addressing that is asking the same broken mechanism to work harder.
I don't disagree with the mechanism, but AT concentrate has to come from pharmacy and it's going to add real time we don't have if his surgeon wants to start soon. FFP is sitting in the blood bank fridge right now and replaces AT along with whatever else nine days of heparin infusion may have drawn down.
The dosing predictability argument for concentrate is real, but in practice a couple of units of FFP has worked for heparin resistance plenty of times at this institution — I don't think the theoretical precision advantage is worth the delay here.
Before either blood product, I'd try one more heparin dose. His resistance so far is partial, not absolute — he moved from 340 to 365 with the second dose, which tells me some additional heparin is still finding receptor. That's not what I'd expect if his AT were profoundly depleted; it's more consistent with a milder deficit that more heparin, by mass action, might still close.
I take the delay point seriously, but escalating heparin avoids any blood product exposure entirely, which matters for a patient already carrying a fresh PE diagnosis. If a third dose still leaves him short, I'd move straight to AT concentrate rather than FFP — not because the delay concern is wrong, but because I think we owe him the cleanest option once we do commit to a product.
Agreed: one additional heparin dose was given first, consistent with the partial-resistance pattern; when ACT still fell short at 410 seconds, antithrombin concentrate was administered and brought him to target on the next check, allowing bypass to proceed.
Not agreed as a general rule: whether future heparin-resistant patients on a similarly prolonged preoperative bridge should go straight to AT concentrate rather than trialing another heparin dose first, given the time cost of a sequential approach. The perfusionist's preference for FFP as the faster product was not adopted this time, but was noted as a reasonable fallback if concentrate isn't readily available at a future case's own hospital.