What is the recommended dose of heparin (unfractionated heparin) or low molecular weight heparin (LMWH) for deep venous thrombosis (DVT) prophylaxis post-operatively?

Postoperative DVT Prophylaxis Dosing Recommendations

For postoperative deep venous thrombosis prophylaxis, unfractionated heparin should be administered at a dose of 5,000 units subcutaneously every 8 hours, while low molecular weight heparin (LMWH) should be given at standard prophylactic doses (e.g., enoxaparin 40 mg once daily or dalteparin 5,000 units once daily) for at least 7-10 days post-surgery.

Unfractionated Heparin (UFH) Dosing

UFH is administered according to the following regimen:

• Dosage: 5,000 units subcutaneously every 8 hours 1, 2, 3
• Timing: Start 2-12 hours preoperatively and continue for at least 7-10 days 1
• Duration: Until the patient is fully ambulatory or at least 7-10 days postoperatively 2, 3

The three-times-daily regimen (every 8 hours) is preferred over twice-daily dosing, as it provides more consistent anticoagulation and better efficacy 2.

Low Molecular Weight Heparin (LMWH) Dosing

LMWH options include:

• Enoxaparin: 40 mg subcutaneously once daily 1
• Dalteparin: 5,000 units subcutaneously once daily 1
• Timing: Start 2-12 hours preoperatively and continue for at least 7-10 days 1

LMWH offers advantages over UFH including:

• Once-daily administration
• More predictable pharmacokinetics
• Lower risk of heparin-induced thrombocytopenia 1

Special Considerations

Renal Function

• For patients with severe renal impairment (CrCl <30 mL/min), UFH is preferred over LMWH 2

Extended Prophylaxis

• Extended prophylaxis (4 weeks) with LMWH is recommended after major abdominal or pelvic cancer surgery in patients without high bleeding risk 1, 2
• This extended regimen has been shown to significantly reduce postoperative VTE risk 1

Surgical Patients

• The highest prophylactic dose of LMWH is recommended for surgical patients 1
• For high-risk surgical patients, consider combining pharmacological prophylaxis with mechanical methods 1

Timing of Initiation

• Pharmacological prophylaxis should be started 2-12 hours preoperatively and continued for at least 7-10 days 1
• If neuraxial anesthesia is planned, timing should be adjusted to avoid increased bleeding risk 1

Common Pitfalls and Caveats

1. Inadequate dosing: Using UFH every 12 hours instead of every 8 hours appears to be less effective 1

2. Insufficient duration: Prophylaxis should continue until the patient is fully ambulatory or for at least 7-10 days 2, 3

3. Renal impairment: LMWH should be avoided or dose-adjusted in patients with severe renal impairment (CrCl <30 mL/min) 2

4. Mechanical prophylaxis alone: Mechanical methods (compression stockings, intermittent pneumatic compression) should not be used as monotherapy except when pharmacological methods are contraindicated 1

5. Overlooking extended prophylaxis: High-risk patients, particularly those undergoing major cancer surgery, benefit from extended prophylaxis (4 weeks) 1, 2

6. Contraindications: Pharmacological prophylaxis is contraindicated in patients with active bleeding, high bleeding risk, severe thrombocytopenia, history of heparin-induced thrombocytopenia, or recent intracranial hemorrhage 2

In summary, the evidence strongly supports using UFH 5,000 units subcutaneously every 8 hours or LMWH at standard prophylactic doses for postoperative DVT prophylaxis, with consideration for extended prophylaxis in high-risk patients, particularly those undergoing cancer surgery.