What is the recommended protocol for a heparin bridge to warfarin (International Normalized Ratio (INR) anticoagulant)?

Heparin Bridge to Warfarin Protocol

The recommended protocol for heparin bridging to warfarin involves stopping warfarin 5 days before procedures, initiating therapeutic-dose LMWH 3 days before the procedure, administering the last dose 24 hours pre-procedure, and resuming LMWH 12-24 hours post-procedure for low bleeding risk or 48-72 hours for high bleeding risk procedures until the INR returns to therapeutic range. 1, 2

Patient Selection for Bridging

Bridging anticoagulation should only be used in patients at high risk for thromboembolism:

• High thromboembolism risk (requires bridging):

  • Mechanical heart valves, especially mitral position
  • Recent venous thromboembolism (<3 months)
  • Atrial fibrillation with CHADS₂ score ≥5
  • Antiphospholipid syndrome
  • Thrombophilia syndromes (protein C/S deficiency, antithrombin deficiency) 1, 2

• Low thromboembolism risk (bridging not required):

  • Most patients with atrial fibrillation
  • Venous thromboembolism >3 months ago 2

Standard Bridging Protocol

Pre-procedure Management:

1. Stop warfarin 5 days before procedure (allows INR to decrease to <1.5) 1, 2
2. Check INR day before procedure (target <1.5)
   • If INR 1.5-1.8, consider low-dose oral vitamin K (1-2.5 mg) 1
3. Start LMWH 3 days before procedure (36-48 hours after last warfarin dose) 1
4. Last LMWH dose should be given 24 hours before procedure at half the normal daily dose 1

LMWH Dosing Options:

• Therapeutic dose (for high-risk patients):
  • Enoxaparin: 1 mg/kg twice daily or 1.5 mg/kg once daily
  • Dalteparin: 100 IU/kg twice daily or 200 IU/kg once daily 2
• Prophylactic dose (for lower-risk patients):
  • Enoxaparin: 40 mg once daily
  • Nadroparin: weight-based dosing (see table in guidelines) 1

Post-procedure Management:

1. Resume warfarin within 24 hours post-procedure at maintenance dose or twice maintenance dose for 2 days 1
2. Resume LMWH based on bleeding risk:
   • Low bleeding risk procedures: Resume 12-24 hours after procedure at full therapeutic dose
   • High bleeding risk procedures: Delay LMWH for 48-72 hours, consider prophylactic dose initially 1, 2
3. Continue LMWH until INR returns to therapeutic range (typically 2.0-3.0) on two consecutive measurements 1, 3

Special Considerations

Renal Impairment

• For patients with severe renal impairment (CrCl <30 ml/min), consider unfractionated heparin (UFH) instead of LMWH 1
• UFH dosing: IV infusion to achieve aPTT 1.5-2.0 times control 2

High Bleeding Risk Procedures

• For procedures with high bleeding risk (e.g., neuraxial anesthesia, spinal procedures), consider:
  • More careful monitoring of post-procedure hemostasis
  • Longer delay before restarting anticoagulation
  • Using prophylactic rather than therapeutic LMWH doses initially 1

Mechanical Heart Valves

• Some centers hospitalize patients with mechanical heart valves and use IV UFH up until 4 hours prior to surgery, resuming after surgery until INR is therapeutic 1
• This approach may provide more solid protection for highest-risk patients 1

Common Pitfalls and Caveats

1. Premature LMWH resumption can significantly increase bleeding risk (reported 20% vs 0.7% for minor procedures) 2

2. Residual anticoagulation can occur in over 90% of patients who receive LMWH 12 hours before surgery, with 34% having therapeutic levels at surgery 2

3. Unnecessary bridging in low-risk patients increases bleeding complications without reducing thrombotic events 2

4. When transitioning from heparin to warfarin, continue heparin until INR is therapeutic to prevent potential hypercoagulable state during warfarin initiation 1, 3

5. For INR monitoring during transition, draw blood for PT/INR determination at least:

   • 5 hours after last IV bolus dose of heparin
   • 4 hours after cessation of continuous IV heparin infusion
   • 24 hours after last subcutaneous heparin injection 3

By following this evidence-based protocol, clinicians can effectively manage the transition between warfarin and heparin while minimizing both thrombotic and bleeding risks.