What are the indications for a heparin (unfractionated heparin) drip in a patient with pulmonary embolism, particularly those who are hemodynamically unstable or at high risk of recurrence?

Indications for Unfractionated Heparin Drip in Pulmonary Embolism

Unfractionated heparin (UFH) drip is specifically indicated for high-risk pulmonary embolism with hemodynamic instability (shock or systolic blood pressure <90 mmHg), severe renal dysfunction (creatinine clearance <20-30 mL/min), extreme obesity, or high bleeding risk where rapid reversibility is needed. 1

High-Risk (Massive) Pulmonary Embolism

Hemodynamic instability is the primary indication for UFH drip over other anticoagulants:

• Patients presenting with shock, persistent hypotension (systolic BP <90 mmHg), or cardiogenic shock require immediate intravenous UFH 1
• UFH should be initiated without delay in high-risk PE, as LMWH and fondaparinux have not been adequately tested in hemodynamically unstable patients 1, 2
• The FDA approves UFH for both prophylaxis and treatment of pulmonary embolism 3

Dosing protocol for UFH in high-risk PE:

• Initial bolus: 5,000-10,000 units IV, followed by continuous infusion of 400-600 units/kg/day (approximately 30,000-40,000 units per 24 hours) 4, 3, 5
• Target aPTT: 1.5-2.5 times control value 1, 3
• Monitor aPTT every 4 hours initially, then at appropriate intervals 3

Severe Renal Dysfunction

• UFH is preferred when creatinine clearance is <20-30 mL/min, as LMWH and fondaparinux are contraindicated or require significant dose adjustment 1, 6
• UFH does not accumulate in renal failure and can be safely titrated to effect 1

High Bleeding Risk Requiring Rapid Reversibility

• UFH has a short half-life (60-90 minutes) and can be rapidly reversed with protamine sulfate 1
• Patients at elevated bleeding risk include those with recent surgery, recent hemorrhage, or active peptic ulcer disease 4, 7
• The ability to quickly discontinue and reverse UFH makes it preferable when bleeding risk is substantial 1

Extreme Obesity

• UFH is recommended over LMWH in patients with extreme obesity due to unpredictable pharmacokinetics of weight-based LMWH dosing 7

Initiation Before Diagnostic Confirmation

A critical indication is high or intermediate clinical probability of PE while awaiting diagnostic workup:

• Anticoagulation with heparin should be started immediately based on clinical suspicion before imaging confirmation 1, 4, 7
• The risk of delayed treatment outweighs the risk of unnecessary anticoagulation in patients with reasonable clinical suspicion 7
• This applies when diagnostic testing cannot be performed within 24 hours 1

When UFH is NOT Preferred (Use LMWH Instead)

For non-high-risk (hemodynamically stable) PE, LMWH or fondaparinux is preferred over UFH:

• LMWH is the recommended initial treatment for most hemodynamically stable patients with PE 1, 7, 2
• LMWH has equal or superior efficacy with lower bleeding risk compared to UFH 2, 6
• LMWH allows for fixed-dose subcutaneous administration without monitoring and potential outpatient management 8, 6

Absolute Contraindications to Heparin

Do not use UFH in the following situations:

• Active bleeding or recent hemorrhage 4, 7
• Acute stroke 7
• Current gastrointestinal bleeding 7
• Recent neurosurgery or ophthalmologic surgery 7

Monitoring Requirements

• Platelet count monitoring is mandatory due to risk of heparin-induced thrombocytopenia (HIT), especially if continued beyond 5 days 4
• Monitor hematocrit and occult blood in stool throughout therapy 3
• Weight-based dosing achieves therapeutic levels more quickly than fixed dosing 4

Duration and Transition

• Continue UFH for at least 5 days and until adequate oral anticoagulation (INR 2.0-3.0 for at least 2 consecutive days) is achieved 1, 4
• Warfarin can be started on the same day as heparin once PE is confirmed 1, 7