Protamine: The Most Dangerous Drug We Give Every Day

You will have noticed that consultants tend to give the protamine themselves, and if you're an ST3 who hasn't done much cardiac, nobody asks you to do it. Most people assume that's habit. It isn't. This is the theatre half of the bleeding week — the drugs, the traps in the tests, and a salvage case at the far end of what's possible. Last episode was the unit. Please note: the doses and drug choices are Wythenshawe-specific local practice. Take the principles, and check your own guidelines. The scale first: cardiac surgery consumes around ten per cent of the entire NHS blood supply, and ninety per cent of those products go into ten per cent of patients. Which makes anticipating who that will be most of the job. Bypass is hostile to clotting in five ways at once — a large heparin dose, haemodilution, cooling, platelet activation and consumption, and contact with the circuit — so know the cases where you will predictably need products (deep hypothermic circulatory arrest, redos, long pump runs, transplants and VAD explants, endocarditis, and anyone arriving anticoagulated) and act on it while they're still on bypass. Order them, get them thawed, get them physically in the room. The worst position is realising you need four units of something that's still in a freezer twenty minutes away. Then the antifibrinolytics. Tranexamic acid at three to four grams is the modern default; aprotinin — Trasylol — was withdrawn in 2008, reintroduced in 2012 with very narrow licensing, and is now used off-license for high bleeding risk, with the honest admission that there is very little evidence directly comparing the two. And a trap the crib sheet asks about directly: aprotinin artificially prolongs the R time on your TEG, so the trace suggests a coagulopathy that isn't there and you can go chasing it with products the patient doesn't need. We do the acquired von Willebrand story properly, because it's lovely physiology: turbulent flow across a tight aortic valve shears platelets and cleaves the large von Willebrand multimers, so the valve lesion itself causes a bleeding disorder — and explains the patient who oozes at the end of an aortic valve replacement for no other obvious reason. DDAVP, twenty micrograms in a hundred millilitres, given slowly, because giving it fast to a marginal patient at the end of a case will drop their pressure. The centrepiece is protamine. What it actually does (electrostatic neutralisation, not a receptor effect), the three types of reaction, and why type three — profound pulmonary vasoconstriction, pulmonary hypertension and right ventricular failure — is the one that empties the ventricle and stops the heart. Then the technique that follows from the principle that when you decide to stop, no more protamine must reach the patient: not through a running flush with a column of drug behind it, but through the central line with the tap turned between patient and syringe. And the counterintuitive part — protamine in excess is itself an anticoagulant, so the generous dose given "to be sure" makes the patient oozier, not drier. Heparin rebound gets its own section, because it's the four-in-the-morning diagnosis that saves a patient a lot of unnecessary products: protein-bound and extravascular heparin redistributing into a circulation whose protamine has already been cleared. Unexplained oozing in a patient who left theatre dry needs a small further dose of protamine, not factors. We also cover heparin resistance as an antithrombin problem, and recombinant factor seven — including a real case where it arrived from another hospital by ambulance and stopped the bleeding immediately, with proper caveats about cost, availability, thrombosis and haematology authorisation. We finish at the salvage end: a patient with acute HIT and thrombotic complications who needs an emergency BiVAD, with no time for plasma exchange or immunoglobulin. Heparin is out, argatroban is a unit drug rather than a theatre one, and almost nobody is comfortable with bivalirudin. The answer starts with getting the right surgeon — because some will go onto cardiopulmonary bypass first, and a bypass circuit demands full anticoagulation. Instead: VA-ECMO first as a heparin-free run, then the BiVAD from there, decided at a full MDT that is honest about what this is. And for the patient with HIT who needs surgery but isn't an emergency, the first and best intervention is simply time. Chapters (00:00) Cold open — the most dangerous drug we give (00:50) The scale: ten per cent of the blood supply (01:40) Why bypass is hostile to clotting (02:30) Who predictably needs products — and acting while still on bypass (03:40) Tranexamic acid, and aprotinin (05:20) Aprotinin prolongs the R time — don't chase it (06:10) Acquired von Willebrand disorder in aortic stenosis (07:40) DDAVP, and why you give it slowly (08:50) Protamine — what it does and why it's dangerous (10:00) The three types of reaction (11:00) Giving it so that stopping means stopping (12:20) Too much protamine is an anticoagulant (13:00) Heparin rebound — the 4am diagnosis (14:40) Heparin resistance and antithrombin (15:40) Recombinant factor seven, and the ambulance (17:20) Acute HIT needing an emergency BiVAD (19:40) After the salvage: no platelets, and buying time (20:30) Elective HIT: delay is the treatment (21:40) Bivalirudin, if you had to (22:40) Wrap-up Key takeaways Cardiac surgery uses around 10% of the NHS blood supply, and 90% of those products go to 10% of patients — anticipate, and get products thawed and in the room while the patient is still on bypass Bypass impairs clotting five ways: heparin, haemodilution, cooling, platelet activation and consumption, and circuit contact Tranexamic acid 3–4 g is the default; aprotinin is off-license for redos and high bleeding risk, with little comparative evidence Aprotinin prolongs the R time on the TEG — don't chase a coagulopathy that isn't there Severe aortic stenosis causes acquired von Willebrand disorder through shear; DDAVP 20 micrograms in 100 mL, given slowly, and cryoprecipitate is a rational choice Protamine neutralises heparin by charge, and can cause pulmonary hypertension, RV failure and cardiac arrest Type 1 is rate-related hypotension, type 2 anaphylactoid, type 3 the catastrophic pulmonary vasoconstriction — type 3 is what kills Give protamine so that stopping means stopping: no flush behind it, tap turned between patient and syringe Excess protamine is itself an anticoagulant — titrate it, don't pour it in Unexplained oozing hours later on the unit is heparin rebound: give more protamine, not more products Heparin resistance is an antithrombin problem — antithrombin III around 500 units, not more heparin Recombinant factor seven works but is expensive, hard to locate, prothrombotic and needs haematology sign-off For emergency surgery in acute HIT: the right surgeon, VA-ECMO before the BiVAD, a heparin-free run, no platelets, and an MDT honest about it being salvage Where there is time, time is the treatment — delay towards remote HIT, plasma exchange, IVIG, and a single intra-operative heparin exposure only References / further reading Boer C et al. 2017 EACTS/EACTA Guidelines on patient blood management for adult cardiac surgery. J Cardiothorac Vasc Anesth 2018 Task Force et al. 2024 EACTS/EACTAIC Guidelines on patient blood management in adult cardiac surgery Myles PS et al. Tranexamic acid in patients undergoing coronary-artery surgery (ATACAS). N Engl J Med 2017 Fergusson DA et al. A comparison of aprotinin and lysine analogues in high-risk cardiac surgery (BART). N Engl J Med 2008 Nybo M, Madsen JS. Serious anaphylactic reactions due to protamine sulfate: a systematic literature review. Basic Clin Pharmacol Toxicol 2008 Vincentelli A et al. Acquired von Willebrand syndrome in aortic stenosis. N Engl J Med 2003 Cuker A et al. American Society of Hematology 2018 guidelines: heparin-induced thrombocytopenia. Blood Adv2018 Koster A et al. Anticoagulation during cardiopulmonary bypass in patients with heparin-induced thrombocytopenia. Ann Thorac Surg Follow the podcast Bluesky: @cardiacoutput.bsky.social X: @CardiacOutputMC If you've found this useful, a follow or a share genuinely helps other trainees find it — and do get in touch if there's a topic you'd like covered. This podcast is for medical education for healthcare professionals. It is not clinical advice. All drugs and doses discussed reflect local Wythenshawe practice at the time of recording — always follow your own centre's guidelines.