Heparin-Free Dialysis
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Direct answer
Heparin-free (anticoagulation-free) dialysis runs the extracorporeal circuit on mechanics instead of pharmacology: blood flow pushed to the highest tolerated rate — commonly 250-300 mL/min — saline flushes of 50-100 mL every 15-30 minutes into the arterial limb (with the added volume programmed into the ultrafiltration goal), minimal flow interruptions, and disciplined visual surveillance of the dialyser and venous chamber for clot strands. It is indicated when systemic anticoagulation is unsafe: active bleeding, major surgery or trauma within roughly the past 24-48 hours, intracranial haemorrhage, severe thrombocytopenia, coagulopathy and liver failure, and heparin-induced thrombocytopenia where even LMWH is barred. Some clotting risk is accepted by design; when it threatens adequacy, the fallbacks are regional citrate anticoagulation or a planned circuit change.
What you must remember
- Indications to list: active bleeding, recent major surgery (commonly within about 24-48 hours, per surgical team), intracranial bleed, severe thrombocytopenia or coagulopathy, advanced liver disease, obstetric complications, and heparin-induced thrombocytopenia with its LMWH cross-reactivity.
- Technique pillars: blood flow 250-300 mL/min or the highest tolerated, saline flushes of 50-100 mL every 15-30 minutes, uninterrupted flow, priming done so the circuit is fully wetted and saline-washed before connection.
- The volume arithmetic trap: every flush is extra volume — 100 mL every 30 minutes over four hours adds 800 mL — which must be added to the ultrafiltration goal or the session ends with the patient volume-overloaded.
- Surveillance ritual: every 15-30 minutes inspect the arterial drip chamber for strands, the dialyser header for fibre darkening, and watch transmembrane and venous pressures creeping upward — the signature of a dying circuit.
- When to abandon: visible clotting, transmembrane pressure climbing toward the alarm limit, or a darkened dialyser — return blood early and, if the dose target stands, continue with a fresh circuit.
- Alternatives when heparin-free fails or is unsuitable: regional citrate anticoagulation (circuit-only, with calcium reinfusion and ionised calcium monitoring), and argatroban or danaparoid in HIT settings per physician direction.
- Circuit-friendly choices: a well-running access at high flow, a venous chamber never allowed to run dry, no mid-session stops, interruptions scheduled outside the run.
Four heparin-free hours
A patient reaches the unit 24 hours after a craniotomy for a ruptured aneurysm — uraemic, potassium 6.2, and absolutely not a candidate for systemic heparin. The plan is built before connection: blood flow 280 mL/min from a well-functioning tunnelled catheter, flushes of 100 mL every 30 minutes with 800 mL budgeted into the ultrafiltration goal, the transmembrane pressure and chamber appearance checked at each flush, and the team briefed that any interruption of flow starts the clot clock. The circuit is primed slowly and fully wetted; connection is smooth; the first hour passes with clear chambers and a pale, uniform dialyser.
Hour three tests the plan: the arterial chamber shows a fine strand and the transmembrane pressure has climbed 30 mmHg. The response is graduated — flush, note the trend, prepare a spare circuit, inform the physician. The strand does not progress; the run completes four hours with a potassium of 4.8 and the intended fluid off. The log records flushes, volumes, pressure trends and the near-miss; tomorrow's surgical review decides when heparin returns. What made it work was not luck but the three habits: keep it fast, keep it wet, keep watching.
Where students slip
The forgotten flush-volume is the exam's favourite error: candidates prescribe saline flushes and omit the ultrafiltration adjustment, drowning the fluid-restricted patient they meant to protect. The second slip is technique half-measures — flow of 200 with frequent interruptions is a clotted circuit by hour two; heparin-free dialysis is a commitment to high flow and continuity. The third is scope confusion with alternatives: citrate is regional anticoagulation (the circuit is anticoagulated, the patient is not) and belongs in the same high-bleeding-risk family, whereas argatroban answers the HIT scenario specifically. And the honest limitation: heparin-free dialysis accepts a small risk of circuit and blood loss — a planned, monitored strategy, not a casual default.
Frequently asked questions
When is heparin-free dialysis chosen over standard anticoagulation?
For active bleeding, recent major surgery or intracranial haemorrhage, significant coagulopathy or thrombocytopenia, and heparin-induced thrombocytopenia where LMWH also cross-reacts.
Describe the core technique of a heparin-free session.
High blood flow of 250-300 mL/min, 50-100 mL saline flushes every 15-30 minutes, continuous flow without interruptions, and regular inspection of chamber and dialyser for clot.
Why must flush volumes be added to the ultrafiltration goal?
The flushes add roughly 100 mL every 15-30 minutes — several hundred millilitres per session — which otherwise accumulates and volume-overloads the patient.
What signs indicate the circuit is clotting during heparin-free dialysis?
Strands in the drip chamber, darkening dialyser fibres, and rising transmembrane and venous pressures — prompting early blood return and, if needed, a fresh circuit.
What is the alternative when heparin-free dialysis repeatedly fails?
Regional citrate anticoagulation with calcium reinfusion and ionised calcium monitoring, or argatroban-based anticoagulation in heparin-induced thrombocytopenia per physician plan.