How to Give Heparin Infusion in DVT and PTE Cases
For patients with acute DVT or pulmonary embolism, administer unfractionated heparin as an intravenous bolus of 80 units/kg followed by continuous infusion at 18 units/kg per hour, with dose adjustments based on aPTT monitoring to maintain a therapeutic ratio of 1.5-2.5 times control (corresponding to anti-Xa levels of 0.3-0.7 IU/mL). 1
Initial Dosing Protocol
Weight-based dosing is critical for efficacy. Studies demonstrate that patients receiving inadequate initial heparin doses have significantly higher recurrence rates—up to 25% when therapeutic aPTT is not achieved within 24 hours 2. The standard regimen is:
An alternative subcutaneous regimen exists (333 units/kg initial dose, then 250 units/kg twice daily), though IV administration is preferred for PE or when immediate anticoagulation is required 1.
Monitoring and Dose Adjustment
Check aPTT approximately every 4 hours initially until therapeutic range is achieved, then at appropriate intervals 3. The therapeutic target is:
Critical pitfall: aPTT reagents vary significantly between institutions. Your hospital's therapeutic aPTT range must be validated against anti-Xa assays to ensure it corresponds to heparin levels of 0.3-0.7 units/mL 2. A standardized dose-adjustment nomogram should be used and validated at your institution 1, 2.
Example Dose Adjustment Nomogram 2:
| aPTT Result | Action |
|---|---|
| <35 seconds | 80 units/kg bolus, increase infusion by 4 units/kg/h |
| 35-45 seconds | 40 units/kg bolus, increase infusion by 2 units/kg/h |
| 46-70 seconds (therapeutic) | No change |
| 71-90 seconds | Decrease infusion by 2 units/kg/h |
| >90 seconds | Hold infusion 1 hour, decrease by 3 units/kg/h |
Additional Monitoring Requirements
Beyond aPTT monitoring, perform:
- Platelet counts every 2-3 days from day 4 to day 14 to screen for heparin-induced thrombocytopenia (HIT), which occurs in up to 5% of patients receiving UFH 1
- Hemoglobin and hematocrit at baseline and periodically
- Occult blood in stool during therapy 3
HIT warning: Immune-mediated HIT typically presents with ≥50% platelet decline 5-10 days after starting heparin (earlier with previous exposure) and paradoxically increases thrombosis risk 1.
Duration and Transition to Oral Anticoagulation
Overlap heparin with warfarin for minimum 5 days and continue until INR is ≥2.0 for at least 24 hours on two consecutive measurements 1, 2. Start warfarin on day 1 or 2 of heparin therapy 2.
For transition to DOACs other than warfarin: Stop IV heparin immediately after administering the first DOAC dose, or for intermittent IV dosing, start the DOAC 0-2 hours before the next scheduled heparin dose 3.
Special Considerations
Renal impairment (CrCl <30 mL/min): UFH is preferred over LMWH as it does not accumulate with renal dysfunction 4, 1. No dose adjustment needed for UFH.
Heparin resistance (requiring >35,000 units/day): Consider switching to anti-Xa level monitoring (target 0.35-0.7 units/mL) rather than aPTT-based dosing 2.
Pregnancy: UFH is safe; does not cross the placenta 4.
Important Clinical Context
While LMWH or fondaparinux is preferred over UFH for most DVT/PE cases (grade 2C) 1, UFH remains appropriate when:
- Immediate anticoagulation effect is required
- Concern exists about subcutaneous absorption (massive PE, shock)
- Thrombolytic therapy is being considered
- Severe renal impairment is present (CrCl <30 mL/min)
- Rapid reversibility may be needed (protamine available) 2, 5
Reversal: If bleeding occurs, protamine sulfate 1% solution neutralizes heparin (1 mg protamine per ~100 units heparin), administered slowly—no more than 50 mg in any 10-minute period 3.