Peri-op Care: DVT Prophylaxis

Question 1

What is the most common cause of preventable deaths in surgical patients?

Answer 1

Fatal post-op PE (25,000 deaths/yr UK)

Question 2

Describe how venous blood from the lower limbs returns to the heart.

Answer 2

Soleus and gastrocnemius muscles contain venous sinuses. When calf muscles contract, blood pumped into lower limb veins. These veins contain valves which are closed by muscle contraction, preventing retrograde flow of blood.

Nearly all surgical DVTs originate in the calf veins.

Question 3

When does post-op PE classically occur?

Answer 3

10-12 days post-op when the patient is straining at stool (because the venous pressure waves during straining cause the thrombus to fracture and embolise to the pulmonary circulation)

Question 4

Suggest patient factors that increase risk of post-op DVT.

Answer 4

• smoking
• diabetes
• coagulopathies
• immobility
• increasing age
• lower limb fractures
• malignancy
• heart failure
• pregnancy
• Hx of DVT
• HRT

Question 5

Suggest methods to reduce risk of post-op DVT.

Answer 5

1. Pre- and post-op mobilisation
2. Anti-embolism stockings
3. Intra-operative intermittent calf compression
4. Maintain hydration
5. Stop pro-thrombotic drugs, e.g. COCP
6. LMWH prophylaxis

Question 6

Name the most commonly used LMWH for DVT prophylaxis in surgical patients. How does dose differ according to whether patient is high or low risk?

Answer 6

Dalteparin

2,500 units for low-risk
5,000 units for high-risk

Question 7

If an epidural is used, how much time must have elapsed since its insertion before administration of LMWH?

Answer 7

4 hrs as risk of spinal epidural haematoma

Question 8

Does prophylactic dalteparin dosage need to be reduced in a patient with significant renal impairment (eGFR <30 ml/min)?

Answer 8

LMWHs are primarily cleared via renal excretion so use with caution in patients with renal impairment as drug can accumulate and increase risk of bleeding

Reducing dose to 2500u OD may be considered in renal impairment patients if weight <50kg or evidence of minor bleeding.

Question 9

What group of patients should receive prophylactic dalteparin for up to 35 days after surgery?

Answer 9

Chemotherapy patients

Question 10

What is the mechanism of heparin?

Answer 10

Binds to antithrombin III (AT), that results in its activation = inactivates thrombin, factor Xa and other proteases