Anticoagulation in Hemodialysis | Heparin Protocols & Alternatives

💉 Anticoagulation in Hemodialysis UFH · LMWH · Heparin-Free · Citrate

Preventing extracorporeal circuit clotting while minimizing bleeding risk — protocols, dosing, and monitoring

Anticoagulation is essential during hemodialysis to prevent clotting of the extracorporeal circuit (dialyzer, bloodlines, venous air trap). The choice of anticoagulant depends on patient bleeding risk, comorbidities, and institutional protocols. Unfractionated heparin (UFH) remains the most common agent, but low-molecular-weight heparin (LMWH), heparin-free strategies, and regional citrate anticoagulation (RCA) are alternatives for high-risk patients.

💊 Unfractionated Heparin (UFH) — Standard Protocol

Mechanism: Activates antithrombin III → inhibits thrombin (Factor IIa) and Factor Xa.

Standard dosing (weight-based):

Initial bolus: 50–80 units/kg (max 5,000 units) IV at start
Maintenance infusion: 1,000–2,000 units/hour (500–1,500 units/hour for low bleeding risk patients)
Stop infusion: 30–60 minutes before end of treatment

Alternative (fixed-dose):

Bolus: 2,000–4,000 units, then infusion 500–1,500 units/hour

📋 Monitoring: ACT target 120–180% of baseline (or 180–220 seconds) or aPTT 1.5–2.5x baseline. Check ACT 30–60 min after bolus.

🩸 UFH: Low-Dose Protocol (Bleeding Risk)

For patients with mild to moderate bleeding risk:

Bolus: 15–30 units/kg (max 2,000 units)
Infusion: 5–10 units/kg/hour (approx 300–600 units/hour)

No bolus protocol (very high risk):

Infusion only: Start at 500 units/hour, titrate based on circuit checks
Inspect venous air trap and dialyzer every 30 minutes

⚠️ Heparin-Induced Thrombocytopenia (HIT): Sudden platelet drop >50% or thrombosis 5–10 days after heparin exposure. Discontinue all heparin, start direct thrombin inhibitor (argatroban, bivalirudin) or danaparoid.

📦 Low-Molecular-Weight Heparin (LMWH)

Advantages: Predictable pharmacokinetics, less monitoring, lower HIT risk.

Enoxaparin (Lovenox) dosing:

Single IV bolus at start: 0.5–0.75 mg/kg (typical 40–60 mg for 70 kg patient)
Alternative: 40 mg for low risk, 60 mg for high clotting risk
No additional infusion needed (duration 3–4 hours)

Tinzaparin (Innohep): 2,500–5,000 IU IV bolus

Nadroparin (Fraxiparine): 0.3–0.6 ml (3,075–6,150 IU) bolus

💡 Note: LMWH is NOT reversed by protamine completely (only 60%). Contraindicated in patients at high bleeding risk.

🚫 Heparin-Free Dialysis Protocols

Indications: Active bleeding, high bleeding risk (post-surgery, trauma, coagulopathy), HIT, recent intracranial hemorrhage.

Protocols:

Saline flushes: 100–200 ml normal saline every 15–30 minutes through arterial port (prevents stagnation) — dialyzer and lines flushed
Heparin-coated dialyzers: Surface-bound heparin (e.g., AN69ST, Evodial) — minimal systemic effect
High blood flow (Qb ≥ 300–350 ml/min): Reduces stasis and clotting tendency
Shorter treatment duration: 2–3 hours if possible

⚠️ Monitor closely: Inspect venous air trap and dialyzer fibers every 15–30 minutes. Prepare for circuit change if clotting occurs.

🧪 Regional Citrate Anticoagulation (RCA)

Mechanism: Citrate chelates ionized calcium in the extracorporeal circuit → prevents coagulation. Calcium is reinfused post-filter.

Protocol (simplified):

Citrate infusion (4% trisodium citrate): 200–300 ml/hour into arterial line
Calcium chloride or gluconate infusion: Into venous return to normalize systemic ionized calcium
Target post-filter ionized calcium: 0.25–0.35 mmol/L
Target systemic ionized calcium: 1.0–1.2 mmol/L

✅ Advantages: Minimal systemic anticoagulation, no bleeding risk, prolonged filter life. Ideal for high bleeding risk patients.

Monitoring: Ionized calcium (q1h for first 2 hours, then q2h), acid-base status (citrate accumulation → metabolic acidosis), total calcium.

⚖️ RCA: Troubleshooting & Complications

Common issues:

Citrate accumulation: Increased anion gap metabolic acidosis, low total Ca/high ionized Ca ratio (total Ca / iCa >2.5). Reduce citrate or stop.
Hypocalcemia: Tetany, paresthesia, hypotension → increase calcium infusion.
Hypercalcemia: Increase citrate or decrease calcium.
Metabolic alkalosis: Citrate metabolized to bicarbonate. Adjust dialysate bicarbonate.

⚠️ Contraindications to RCA: Severe liver failure (impaired citrate metabolism), severe lactic acidosis, hypoxemia, shock.

📊 Monitoring Anticoagulation: ACT, aPTT, Circuit Inspection

Parameter	Target Range	Frequency	Action if abnormal
ACT (activated clotting time)	180–220 seconds (or 120–180% of baseline)	Baseline, 30–60 min after bolus, then q1-2h	<160 → increase heparin; >250 → reduce/decrease heparin
aPTT	1.5–2.5 × baseline (45–70 seconds typical)	Baseline, 1h, PRN	Subtherapeutic → increase heparin; supratherapeutic → reduce
Platelet count	>150,000 /μL	Baseline, weekly, or if HIT suspected	Drop >50% → SUSPECT HIT, stop heparin
Circuit visual inspection	No visible clots in dialyzer fibers or venous air trap	Every 15–30 minutes	Clots → increase anticoagulation or change protocol

ACT = activated clotting time; aPTT = activated partial thromboplastin time; HIT = heparin-induced thrombocytopenia

📋 Post-dialysis Assessment: Visually inspect dialyzer for residual blood/clots. Grade 0 (no clots) to 3 (complete clotting). Document in patient record.

⚠️ Anticoagulation Complications & Management

🩸 Bleeding (most common):

Access site bleeding, prolonged post-dialysis puncture site oozing
Serious: GI bleed, intracranial hemorrhage, retroperitoneal bleed
Management: Reduce/stop heparin, protamine sulfate 1 mg per 100 units UFH (max 50 mg IV slow), apply pressure, transfuse if needed

🧬 Heparin-Induced Thrombocytopenia (HIT):

Type II HIT: Immune-mediated platelet activation → thrombosis (70% risk)
Diagnosis: 4Ts score, PF4 ELISA, serotonin release assay (SRA)
Management: Stop ALL heparin (including flushes, line locks), start direct thrombin inhibitor (argatroban, bivalirudin). DO NOT use warfarin until platelets normalize.

🩺 4Ts Score for HIT (pretest probability): Thrombocytopenia (2), Timing (2), Thrombosis (2), Other causes (2). Score ≥4 → high probability, send confirmatory testing.

📋 Anticoagulation Options Comparison

Agent	Dosing	Monitoring	Reversal	Bleeding Risk	Cost
UFH	Bolus + infusion	ACT, aPTT	Protamine (1:100)	Moderate-High	Low
LMWH (Enoxaparin)	Single bolus	Anti-Xa (rare)	Partial (protamine 1 mg/1 mg enoxaparin)	Moderate	Moderate
Heparin-free (saline flushes)	Q15-30 min flushes	Circuit inspection	Not applicable	Very Low	Low
Regional Citrate (RCA)	Citrate + Ca infusion	iCa post-filter, iCa systemic, pH	Calcium, discontinue citrate	Very Low	High (requires machine)
Argatroban (HIT)	Infusion 0.5–2 μg/kg/min	aPTT (1.5–3x baseline)	None (short half-life)	High	Very High

🧠 Key Takeaways:

UFH is first-line for most patients — monitor ACT or aPTT, adjust to clotting risk.
For high bleeding risk: Heparin-free with saline flushes, heparin-coated dialyzer, or regional citrate anticoagulation.
LMWH offers convenience (single bolus) but is costlier and incompletely reversible.
HIT is a medical emergency — suspect with platelet drop >50%, stop all heparin, start direct thrombin inhibitor.
Individualize anticoagulation based on bleeding risk, thrombosis history, access type, and previous reactions.