Venous Thromboembolism

Question 1

Risk Factors

Answer 1

Virchow’s Triad

• 1- Hypercoagulability
  
  • Primary Causes
  • Secondary
• 2- Stasis of Blood Flow
  
  • Surgery (esp knee or hip), lower extremity paralysis (SC injury), immobilization (long car or plane rides, bed rest or cast)
• 3- Vessel Injury
  
  • Crush injuries, ortho or vascular surgeries
• OTHERS
  
  • Age
  • Women > men
  • Prior thromboembolism

Question 2

Primary Causes of Hypercoagulation (6)

Answer 2

• Protein C def, protein S def, antithrombin III def, plasminogen deficiency
• Most common = Factor V or activate protein C resistance (factor V is resistant to normal inactivation by protein C)
• Also common = inc plasma pro-thrombin conc

Question 3

Secondary Causes of Hypercoagulation (4)

Answer 3

• Malignancy (malignant cells release pro-coag material)
• Estrogen (birth controls and prostate cancer therapy)
• Pregnancy and Post-Partum
• Anti-phospholipid Antibodies (lupus anti-coagulant

Question 4

How does PE affect gas exchange and hemodynamics?

Answer 4

• If mild/moderate - may not actually see hypoxemia; instead - dec perfusion –> high V/Q areas –> inc dead space –> inc RR/minute ventilation to maintain PaCO2 –> resp alkalosis
• If large PE –> V/Q inequality –> dec PaO2 and inc A-a gradient
• Less capillary surface area –> inc pulmonary circulation resistance –> high RV afterload –> RV dilation
• RV dilation –> LV dysfunction b/c less LV preload and RV dilation pushes septum which dec LV size and LV compliance –> dec CO (shock, hypotension, dec coronary perfusion)

Question 5

Source of DVTs

Answer 5

usually proximal deep veins of leg (popliteal and femoral)

OR pelvic, calf veins

OR internal jugular/subclavian if central line

Question 6

3 Diagnostic Techniques

Answer 6

1- D-dimer (sensitive but not specific)
- Clot breakdown product (when plasmin degrades fibrin crosslinks it yields bonded D-domains of 2 fibrin molecules that were crosslinked)

2- CT w/ angiography
- Give iodine contrast - intraluminal filling defect (part of lumen) or complete vessel cut off (whole lumen)

3- Venous Ultrasound (very sensitive and specific for dx DVT but not as helpful for PE - may have embolized)
- Look for lack of venous compressability (normally pressing down w/ probe causes vein lumen o totally collapse)

Question 7

Anti-Coag Meds (3)

Answer 7

• Warfarin - inhibits synthesis of Vit K dep factors (II, VII, IX, X); given orally
• Heparin - enhances anti-thrombin III (heparin drip - IV)
• Xa Inhibitors (apixaban, rivaroxaban)

Question 8

Thrombolytic Meds

Answer 8

• Can give IV or cath right into blood clot
• Usually seen in bad cases; shock
• Mainly tPA (dissolves clots by converting plasminogen to plasmin)

Question 9

3 Indications for IVC Filter

Answer 9

• Contra-indication to anti-coagulation meds
• High risk for recurrent PE
• Recurrent PEs despite anticoag therapy