What is the recommended dose and frequency of heparin (Heparin) subcutaneously for prevention of blood clots in a patient with a history of ischemic Cerebrovascular Accident (CVA)?

Heparin Dosing for Prevention of Blood Clots in Patients with History of Ischemic CVA

For prevention of blood clots in patients with a history of ischemic CVA, unfractionated heparin should be administered at a dose of 5,000 units subcutaneously every 8 hours. 1, 2

Dosing Recommendations

The recommended prophylactic anticoagulation regimen for patients with a history of ischemic stroke is:

• Unfractionated heparin (UFH): 5,000 units subcutaneously every 8 hours 1, 2

Alternative options include:

• Low-molecular-weight heparin (LMWH) such as:
  • Enoxaparin: 40 mg subcutaneously daily
  • Dalteparin: 5,000 units subcutaneously daily
  • Tinzaparin: 4,500 units (fixed dose) subcutaneously daily or 75 units/kg subcutaneously daily 1

Rationale and Evidence

The American College of Chest Physicians (ACCP) guidelines recommend prophylactic-dose subcutaneous heparin for patients with acute ischemic stroke and restricted mobility 1. Studies have demonstrated that subcutaneous unfractionated heparin at 5,000 units every 8 hours significantly reduces the risk of deep vein thrombosis (from 73% to 22%) and pulmonary embolism (from 20% to 5%) 1, 2.

The FDA-approved dosing for prophylaxis of postoperative thromboembolism with unfractionated heparin is 5,000 units subcutaneously 2 hours before surgery and then 5,000 units every 8 to 12 hours thereafter 3. However, for patients with higher risk factors such as a history of ischemic stroke, the more frequent dosing schedule (every 8 hours) is preferred 1, 2.

Monitoring Requirements

When using prophylactic doses of unfractionated heparin:

• Monitor hemoglobin, hematocrit, and platelet count every 2-3 days up to at least day 14 and every 2 weeks thereafter 1
• Watch for signs of heparin-induced thrombocytopenia (HIT), which may occur in up to 5% of patients receiving UFH 1
• A significant drop in platelet count (≥40%) has been associated with poor outcomes in patients with cerebrovascular ischemic disease treated with heparin 4

Contraindications and Precautions

Absolute contraindications:

• Recent central nervous system bleeding
• Active major bleeding (>2 units transfused in 24 hours)
• Spinal anesthesia/lumbar puncture 1

Relative contraindications:

• Chronic, clinically significant bleeding >48 hours
• Thrombocytopenia (platelets <50,000/mcL)
• Severe platelet dysfunction
• Recent major operation at high risk for bleeding
• Underlying hemorrhagic coagulopathy
• High risk for falls with potential head trauma 1

Special Considerations

1. Risk-benefit assessment: A systematic review and meta-analysis found that prophylactic/low-dose heparin increased symptomatic intracerebral hemorrhage more than they reduced symptomatic pulmonary embolism in patients with recent ischemic stroke 5. Therefore, careful patient selection is critical.

2. Timing: Consider delaying initiation of prophylactic anticoagulation for 3-4 days after the onset of stroke in patients with larger infarcts or other risk factors for hemorrhagic transformation 1.

3. Renal function: Unfractionated heparin is preferred over LMWH in patients with severe renal insufficiency (creatinine clearance <30 mL/min) 1, 2.

4. Duration: Continue prophylaxis for 7-10 days or until the patient is fully ambulatory, whichever is longer 3.

5. Alternative options: In patients where heparin is contraindicated, consider mechanical prophylaxis with intermittent pneumatic compression devices 1.

By following these recommendations, the risk of recurrent venous thromboembolism can be minimized while maintaining an acceptable safety profile in patients with a history of ischemic CVA.