Why we use it
Protamine is a small, strongly positively-charged peptide that binds heparin’s negatively-charged molecule directly, forming an inactive complex. The result is rapid neutralization of heparin’s anticoagulant effect. We reach for it when we need to shorten time to sheath pull, manage bleeding, or rescue from a complication like tamponade.
Indication in the lab
- Selective reversal at end of left-heart cases (often only partial reversal — many operators target ACT ~180 s for sheath pull)
- Active bleeding (groin, pericardial, retroperitoneal)
- Tamponade requiring pericardiocentesis
- Operator preference for faster turnaround between cases
We do not routinely reverse every heparinized case. Many AF ablation patients are simply allowed to drift down naturally before sheath pull.
Dose and route
- Rule of thumb: 1 mg protamine per 100 U heparin given in the last 2–3 hours.
- Cap any single push at ~50 mg. Larger needs are given in divided doses.
- Often we give a partial reversal — e.g., 25–30 mg — to bring ACT to a safe sheath-pull window rather than fully neutralize.
- Confirm dose verbally with the attending before pushing.
Administration
- Slow IV push over 10 minutes. Fast pushes are the number-one cause of complications.
- Best given through a peripheral or central line — never directly down a sheath into the LA.
- Recheck ACT 5–10 minutes after the dose to confirm effect.
Onset and duration
- Onset: within 5 minutes.
- Effect lasts ~2 hours — long enough to safely close access and get the patient to recovery.
- If heparin was given as a long infusion, rebound anticoagulation can occur; watch for late oozing.
Side effects to watch for
- Hypotension is by far the most common — almost always from pushing too fast.
- Pulmonary vasoconstriction with sudden rise in PA pressure and right-heart strain. Rare but dangerous.
- Anaphylactoid reactions — bronchospasm, flushing, rash. More likely in:
- Patients on NPH insulin (which contains protamine)
- Patients with documented fish allergy
- Patients with prior protamine exposure (previous cardiac surgery, prior cath)
- Flag any of the above on the pre-case timeout.
What we monitor
- Continuous BP and HR — call out any drop the moment the syringe starts.
- SpO2 and end-tidal CO2 if available.
- Post-reversal ACT to confirm we got where we wanted to be.
- Visual check of access sites once we’re back in window.
Common pitfalls
- Pushing fast because the case is running long. Don’t.
- Calculating dose off total heparin instead of recent heparin — leads to over-dosing.
- Forgetting to flag fish allergy or NPH insulin on the preop checklist.
- Pulling sheaths immediately after the push without rechecking the ACT.