How is a heparin (unfractionated heparin) drip used to bridge anticoagulation in patients on warfarin (coumarin)?

Heparin Bridging for Warfarin Interruption

Critical First Principle: Most Patients Should NOT Be Bridged

The majority of patients on warfarin—including those with atrial fibrillation and most venous thromboembolism cases—should NOT receive heparin bridging due to 2-3 fold increased bleeding risk without proven thrombotic benefit. 1

When Bridging IS Indicated (High Thromboembolic Risk Only)

Bridge with therapeutic-dose unfractionated heparin (UFH) or LMWH only in these specific situations:

• Mechanical mitral valve or any mechanical valve with prior stroke/TIA 2, 1
• Atrial fibrillation WITH mitral stenosis 1
• Recent VTE within 3 months of the procedure 1
• Severe thrombophilia with active thrombotic complications 1

When Bridging Is NOT Indicated

Do NOT bridge these patients despite anticoagulation:

• Non-valvular atrial fibrillation (even with high CHADS₂ scores) 1
• Bileaflet mechanical aortic valve without additional risk factors 3
• VTE beyond 3 months from the procedure 1
• Bioprosthetic valves 3
• Thrombophilia without active thrombosis (Factor V Leiden, prothrombin mutations, protein C/S deficiency) 1

Pre-Procedure Bridging Protocol

Warfarin Discontinuation

• Stop warfarin 5 days before the procedure to allow INR to decrease to ≤1.5 2, 1

Heparin Initiation Timing

• Start therapeutic-dose heparin 3-4 days before the procedure when INR falls below 2.0 3, 4

UFH Dosing Options

Continuous IV infusion (preferred for inpatient bridging):

• Initial bolus: 5,000 units IV 5
• Continuous infusion: 20,000-40,000 units/24 hours (approximately 1,000-1,500 units/hour) 5
• Target aPTT: 1.5-2 times control (approximately 60-85 seconds) or anti-Factor Xa level 0.35-0.70 IU/mL 2, 5

Subcutaneous UFH (alternative for outpatient bridging):

• Initial dose: 5,000 units IV, followed by 10,000-20,000 units subcutaneously every 8-12 hours 5
• Administer deep subcutaneously (above iliac crest or abdominal fat layer) with 25-26 gauge needle 5

LMWH as Alternative to UFH

Therapeutic-dose LMWH regimens (more commonly used than UFH for bridging):

• Enoxaparin: 1 mg/kg subcutaneously twice daily OR 1.5 mg/kg once daily 2, 4
• Dalteparin: 100 IU/kg twice daily OR 200 IU/kg once daily 2, 4
• Tinzaparin: 175 IU/kg once daily 4

LMWH offers practical advantages: predictable anticoagulation without monitoring, subcutaneous administration, and outpatient feasibility 6

Pre-Procedure Heparin Discontinuation

• Last LMWH dose: 24 hours before the procedure 2, 1
• Stop IV UFH: 4-6 hours before the procedure 5

Post-Procedure Resumption Protocol

Warfarin Resumption

• Resume warfarin the evening of surgery or morning after at usual maintenance dose 1, 4
• Alternative: Give 1.5x maintenance dose for first 2 days 1

Heparin Resumption: Critical Timing Based on Bleeding Risk

High-bleeding-risk procedures (cardiac surgery, intracranial surgery, spinal surgery, major vascular surgery):

• Wait 48-72 hours before starting therapeutic-dose heparin 1, 4
• Consider prophylactic-dose LMWH (enoxaparin 40 mg daily) for first 24-48 hours, then escalate to therapeutic dose once hemostasis confirmed 1, 4

Low-to-moderate-bleeding-risk procedures:

• Resume therapeutic-dose heparin 24 hours post-procedure if adequate hemostasis achieved 1, 4

Duration of Bridging

• Continue therapeutic-dose heparin for minimum 7-10 days postoperatively until INR reaches ≥2.0 on two consecutive measurements 4
• Check INR on postoperative days 4 and 7-10 4

Special Populations

Renal Insufficiency (CrCl <30 mL/min)

• Use IV UFH instead of LMWH due to unpredictable LMWH clearance 1, 4
• Target aPTT 1.5-2 times control 4
• If subcutaneous UFH used: adjust to once-daily dosing 4

Mechanical Heart Valves

• UFH remains the only FDA-approved heparin for mechanical prostheses 2
• IV administration preferred over subcutaneous route for mechanical valves 2
• If LMWH used (off-label): administer twice daily at therapeutic doses with anti-Xa monitoring targeting 0.5-1.0 U/mL 2

Critical Pitfalls to Avoid

Pitfall #1: Over-Bridging Low-Risk Patients

• Do not bridge based solely on anticoagulation indication—the BRIDGE trial demonstrated that bridging in atrial fibrillation causes more harm than benefit 1, 3

Pitfall #2: Premature Postoperative Heparin

• Resuming therapeutic-dose heparin too early is the primary driver of major bleeding complications (up to 20% bleeding rate when given without adequate hemostasis assessment) 1, 4
• Always assess surgical hemostasis before any postoperative therapeutic heparin—examine wound drainage amount, type, and progression 1

Pitfall #3: Inadequate UFH Dosing

• Low-intensity UFH regimens may reduce bleeding but recent data show only 29% of patients achieve therapeutic aPTT within first 24 hours with protocol-driven UFH 7
• High-intensity UFH regimens increase bleeding without reducing thrombotic events in atrial fibrillation patients 8

Pitfall #4: Using Bridging for DOACs

• Heparin bridging is NOT indicated for direct oral anticoagulants (apixaban, rivaroxaban, dabigatran, edoxaban) due to their short half-lives and rapid onset 1
• Simply interrupt DOACs 2-5 half-lives pre-procedure based on renal function 1

Monitoring Parameters

For IV UFH

• aPTT every 6 hours until therapeutic, then daily 5
• Target aPTT: 1.5-2 times control (approximately 60-85 seconds) 2, 5
• Alternative: anti-Factor Xa level 0.35-0.70 IU/mL 2

For LMWH

• No routine monitoring required for standard patients 2
• Consider anti-Xa monitoring (target 0.5-1.0 U/mL) in mechanical valve patients, renal insufficiency, or extremes of body weight 2

For Warfarin Overlap

• Check INR on postoperative days 4 and 7-10 4
• Discontinue heparin only when INR ≥2.0 on two consecutive measurements 4