When do you start anticoagulation for Deep Vein Thrombosis (DVT) prophylaxis in a patient with Subarachnoid Hemorrhage (SAH)?

Timing of DVT Prophylaxis After Subarachnoid Hemorrhage

For patients with aneurysmal subarachnoid hemorrhage (aSAH), pharmacological DVT prophylaxis with subcutaneous heparin or low-molecular-weight heparin (LMWH) should be initiated once the aneurysm is secured, typically starting 24-48 hours after aneurysm treatment (coiling or clipping), with mechanical prophylaxis (intermittent pneumatic compression devices) used immediately upon admission until pharmacological prophylaxis can be safely started. 1, 2

Initial Management Strategy

Immediate Measures (Day 0-1)

• Begin mechanical prophylaxis with intermittent pneumatic compression (IPC) devices immediately upon admission, as these do not increase bleeding risk and provide some VTE protection while awaiting aneurysm securing 1
• Graduated compression stockings alone are less effective than IPC devices and should not be relied upon as sole prophylaxis 1
• Prioritize urgent aneurysm securing (ideally within 24-48 hours) to reduce rebleeding risk and facilitate early DVT prophylaxis 1

Pharmacological Prophylaxis Timing

After aneurysm is secured:

• Start subcutaneous heparin (5,000 units twice or three times daily) or LMWH (enoxaparin 40 mg daily) at 24-48 hours post-aneurysm treatment 2, 3
• The earliest safe initiation in research studies was 25 hours after admission, with most evidence supporting a 24-48 hour window 1
• Delayed initiation beyond 48 hours significantly increases VTE risk without reducing hemorrhagic complications 3, 4

Special Considerations

Patients with External Ventricular Drains (EVD)

• Do NOT withhold prophylactic anticoagulation in patients with EVDs in place 2, 4
• Evidence demonstrates that prophylactic anticoagulation with EVDs is safe, with only minor hemorrhages occurring rarely (3 of 53 patients in one series) 2
• For EVD removal or replacement, withhold no more than 1 dose of anticoagulant 4
• Withholding >1 dose increases DVT/PE risk nearly 5-fold (OR 4.8) without reducing catheter-related hemorrhage 4
• Resume prophylaxis immediately after EVD removal or replacement 4

High-Risk Patients Requiring Earlier Initiation

Patients with the following characteristics may benefit from earlier prophylaxis (closer to 24 hours):

• Mechanical ventilation requirement 3
• Poor neurological grade (Hunt-Hess 4-5) 3
• Prolonged immobilization expected 3
• History of prior VTE 2

Contraindications to Early Pharmacological Prophylaxis

Delay pharmacological prophylaxis beyond 48 hours if:

• Aneurysm remains unsecured 1
• Evidence of ongoing hemorrhage or hematoma expansion on repeat imaging 1
• Coagulopathy (INR >1.4, platelets <50,000) 2
• Large intraparenchymal hematoma with mass effect 1

Monitoring and Documentation

• Obtain repeat CT imaging at 24 hours post-aneurysm treatment to document hemorrhage stability before initiating pharmacological prophylaxis 1, 5
• Monitor for signs of VTE (leg swelling, chest pain, dyspnea) throughout hospitalization 3
• Document timing of aneurysm securing, EVD placement/removal, and anticoagulation initiation 4

Critical Pitfalls to Avoid

Do not delay prophylaxis unnecessarily: Delayed heparin initiation significantly increases symptomatic VTE risk (p=0.02 on univariate analysis), leading to longer hospital stays and worse functional outcomes 3

Do not withhold multiple doses for EVD procedures: This practice increases thromboembolic complications without reducing hemorrhagic risk 4

Do not rely on compression stockings alone: They are significantly less effective than pharmacological prophylaxis for PE prevention 1

Do not use therapeutic anticoagulation for prophylaxis: One patient on therapeutic anticoagulation experienced a major fatal hemorrhage in a cohort study, emphasizing the importance of prophylactic dosing only 2

Outcome Impact

VTE occurs in approximately 6-17% of aSAH patients without adequate prophylaxis and is independently associated with worse modified Rankin Scale scores at discharge and 3-month follow-up 1, 3. Early, appropriate prophylaxis reduces VTE risk by more than 50% (7.5% vs 18% in one series) while maintaining safety 2.