Recommended Dosing for PE Prophylaxis Until CT Scan
For patients with intermediate or high clinical probability of pulmonary embolism (PE), heparin should be given before imaging, with low molecular weight heparin (LMWH) preferred over unfractionated heparin (UFH) in hemodynamically stable patients. 1
Initial Assessment and Risk Stratification
Before initiating prophylactic anticoagulation, assess:
- Clinical probability of PE using validated scoring systems
- Hemodynamic stability (systolic BP <90 mmHg indicates high-risk PE)
- Bleeding risk factors
- Renal function
Anticoagulation Options and Dosing
For Hemodynamically Stable Patients:
LMWH (Preferred Option):
- Enoxaparin: 1 mg/kg subcutaneously twice daily or 1.5 mg/kg once daily 2
- Dalteparin: 5,000 IU subcutaneously once daily 3
- Fondaparinux:
- 5 mg SC daily (body weight <50 kg)
- 7.5 mg SC daily (body weight 50-100 kg)
- 10 mg SC daily (body weight >100 kg) 3
For Hemodynamically Unstable Patients or Those Requiring Rapid Reversal:
Unfractionated Heparin (UFH):
- Initial bolus: 80 IU/kg (or 5,000-10,000 IU fixed dose)
- Maintenance: 18 IU/kg/hour (or approximately 1,300 IU/hour) 4
- Adjust dose to maintain aPTT at 1.5-2.5 times control value (45-75 seconds) 1
- First aPTT should be checked 4-6 hours after starting therapy 4
Timing Considerations
- Imaging should be performed within 1 hour in massive PE and ideally within 24 hours in non-massive PE 1
- Continue anticoagulation until CT scan confirms or excludes PE
- If CT confirms PE, continue therapeutic anticoagulation for at least 3 months 1
Special Populations
Pregnancy:
- LMWH is the preferred agent based on early pregnancy weight 1
- Avoid DOACs during pregnancy and lactation 1
- Consider V/Q scan over CT pulmonary angiography 1
Renal Impairment:
- For severe renal impairment, UFH is preferred over LMWH or fondaparinux
- Adjust dosing based on aPTT monitoring
Monitoring
- For UFH: Monitor aPTT 4-6 hours after initial bolus, 6-10 hours after any dose change, and daily when in therapeutic range 1
- For LMWH: Routine monitoring of anti-Xa levels is not required except in pregnancy, renal impairment, or extreme body weights
Common Pitfalls to Avoid
- Delaying anticoagulation: Do not wait for imaging confirmation in patients with intermediate or high clinical probability of PE 4
- Inadequate initial dosing: Underdosing can lead to treatment failure and recurrent thromboembolism
- Overlooking contraindications: Assess for active bleeding, recent surgery, or other contraindications before initiating anticoagulation
- Forgetting to transition: If PE is confirmed, have a clear plan to transition to long-term anticoagulation
Remember that prompt initiation of appropriate anticoagulation while awaiting definitive diagnosis can be lifesaving in patients with suspected PE, as mortality is highest in the first hours after presentation.