When should deep vein thrombosis (DVT) prophylaxis be started in high-risk patients, such as those undergoing major surgery, trauma patients, or individuals with limited mobility and impaired renal function?

When to Start DVT Prophylaxis

DVT prophylaxis should be initiated immediately upon hospital admission for high-risk patients, with pharmacological agents started preoperatively (2 hours before surgery) for surgical patients, or within the first 24 hours of admission for medical and trauma patients once bleeding risk is controlled. 1, 2

Timing by Patient Population

Surgical Patients

• Commence pharmacological prophylaxis 2 hours preoperatively with low-dose subcutaneous heparin 5,000 IU or LMWH, continuing every 12 hours until full mobilization 3
• For cancer surgery patients, prophylaxis must be started preoperatively and continued for at least 7-10 days, with extended duration up to 4 weeks for major abdominal/pelvic procedures 4, 2
• Never administer fondaparinux earlier than 6 hours post-surgery, as this significantly increases major bleeding risk 1
• The optimal window is between 2 hours before and 10 hours after surgery 5

Stroke Patients

• Start prophylaxis immediately upon admission if the patient is at high risk (unable to move lower limbs, unable to mobilize independently, previous VTE history, dehydration, or comorbidities like cancer) 4
• If intermittent pneumatic compression (IPC) is selected, apply as soon as possible and within the first 24 hours after admission 4
• For ischemic stroke patients, low-molecular-weight heparin should be considered immediately if no contraindication exists; use unfractionated heparin for patients with renal failure 4

Trauma Patients

• Initiate pharmacological prophylaxis once bleeding risk is controlled, typically within 24-48 hours of admission 1, 6
• High-risk trauma patients (traumatic brain injury, chest injury with AIS >3, mechanical ventilation, major surgery, prior VTE) require immediate assessment and prophylaxis initiation 1
• Standard use of DVT prophylaxis in high-risk trauma populations should begin early to achieve low DVT incidence 5

Medical Patients

• Begin prophylaxis throughout hospitalization for acutely ill patients with reduced mobility, active malignancy, or prior VTE history 2
• Enoxaparin 40 mg subcutaneously once daily, dalteparin 5000 IU once daily, fondaparinux 2.5 mg once daily, or unfractionated heparin 5000 units twice or thrice daily should be started immediately upon risk identification 1, 2

Critical Timing Considerations

Renal Impairment

• For creatinine clearance 30-50 mL/min: reduce fondaparinux to 1.5 mg once daily 1, 2
• For creatinine clearance <30 mL/min: reduce enoxaparin to 30 mg once daily or use unfractionated heparin 4, 1, 2

When Pharmacological Prophylaxis is Contraindicated

• Immediately apply mechanical prophylaxis (IPC devices or graduated compression stockings) if active bleeding, severe thrombocytopenia (platelets <50,000/μL), or recent neurosurgery exists 4, 1, 2
• For stroke patients, if IPC is considered after the first 24 hours of admission, perform venous leg Doppler studies first 4

Extended Duration Prophylaxis

• For patients remaining immobile longer than 30 days, continue ongoing pharmacological prophylaxis beyond the initial period 4
• Major cancer surgery requires extended prophylaxis for up to 4 weeks postoperatively 4, 2
• Hip fracture surgery requires total duration up to 32 days 1

Common Pitfalls to Avoid

• Do not delay prophylaxis initiation while waiting for "perfect" conditions—the risk of VTE increases exponentially with each day of delay 1
• Do not withhold prophylaxis in trauma patients indefinitely due to bleeding concerns; reassess bleeding risk daily and initiate as soon as feasible 6
• Do not use anti-embolism stockings alone for post-stroke VTE prophylaxis—they are ineffective as monotherapy 4
• Do not overlook the need for extended prophylaxis in major cancer surgery or hip fracture patients, as VTE risk remains elevated for weeks postoperatively 4, 1
• Despite high-quality evidence, only 58.5% of at-risk surgical patients and 39.5% of at-risk medical patients receive appropriate VTE prophylaxis—ensure systematic implementation 1