Thrombotic Disorders - DVT/PE Flashcards Preview

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Flashcards in Thrombotic Disorders - DVT/PE Deck (12):
1

How does the body prevent thrombus at the venous valves?

  • In the erect position, blood is propelled proximally from the calf veins by muscular action
  • Back flow is prevented by an extensive system of valves, located all along the veins from the lower leg to the pelvis
    • While the valves prevent blood pooling distally, there is increased turbidity within the valve sinus potentially stimulating thrombus formation
  • To prevent thrombus formation, the levels of the anticoagulant factors, endothelial cell protein C receptor and thrombomodulin are higher in the valvular sinus endothelium (D and E) than in the luminal endothelium (A and B)
    • The levels of the procoagulant, von Willebrand factor, are lower in the valvular sinus endothelium than in the luminal endothelium (F versus C)

2

What are the possible causes of venous thrombosis?

  • The precise cause of venous thrombosis is unknown, but tears in the vein wall or pressure necrosis of the delicate endothelium are likely
    • Platelets and neutrophils adhere at the site of injury and activate procoagulants
    • Thrombin is generated, fibrin formed, and red cells are trapped within the growing thrombus
  • Proximal thrombi are located in the iliac, femoral, and popliteal veins
    • Distal thrombi are in the tibial and peroneal veins
    • Embolization occurs when the adherent thrombus becomes dislodged, either spontaneously or by increased muscular activity
  • Venous thrombosis also occurs with direct injury or prolonged compression of the veins
    • For example, when you fall asleep during a long trip with your legs crossed, or you assist during surgery and inadvertently lean on the leg of the anesthetized patient!
    • Other examples are compression of the left iliac vein by the right iliac artery in pregnancy
    • Compression of the retinal vein by the retinal artery in hypertensive patients

3

What is the incidence of DVT and PE?

  • Deep vein thrombosis (DVT) is a major cause of death and morbidity. It is estimated that DVT occurs in approximately 2 million Americans each year
  • Pulmonary embolism (PE), the most serious sequela to DVT, occurs in up to 600,000 patients each year and an estimated 60,000 die of this complication
    • The incidence of DVT/PE rises with age

4

What are some of the major risk factors of DVT?

  • DVT are unprovoked or provoked by specific risk factors:
    • Immobility in medical patients after a stroke, and in surgical patients during the post-operative period, is a common triggering event
    • DVT/PE is a major complication of total hip arthroplasty, and the risk persists for up to 4 weeks post-operatively
    • Patients with lower extremity fractures and plaster casts are also vulnerable
    • The risk of DVT/PE with air travel is 27/million/travelers, and increases with the duration of flight
  • Other risk factors are:
    • Genetic thrombophilia
    • Obesity, usually in combination with other risk factors
    • Pregnancy, oral contraceptives, estrogens, anti-estrogens
    • Cancer - Most frequent with adenocarcinomas and metastatic disease
      • Migratory thrombophlebitis is sequential inflammation of several superficial veins, very characteristic of high-grade tumors
      • DVT in cancer patients is often resistant to antithrombotic agents and recurrences are common
      • Thrombi also occur in unusual locations, such as axillary, mesenteric, and portal veins

5

What are the common sites of involvement of DVTs?

  • Superficial and deep veins of the arms are the brachiocephalic and subclavian
    • Thrombi in these veins are usually associated with intravenous catheters
  • Superficial veins of the legs are the greater & lesser saphenous
    • Involvement of these veins is called superficial thrombophlebitis, and the veins are usually tender, red, and palpable
  • Deep veins of the legs: iliac, superficial femoral, popliteal, gastrocnemius, tibial - these are the traditional “DVT”
    • Note: although called “superficial” femoral, this is the major deep vein of the thigh
    • The deep femoral vein is short and rarely the site of thrombi
  • Pulmonary artery emboli (“PE”) usually arise from DVT
  • Thrombi in mesenteric, portal, ovarian, axillary, cerebral, and retinal, veins are uncommon

6

Describe the clinical diagnosis of DVT.

  • Suspect DVT in patient with unilateral leg swelling, pain, and calf tenderness
    • These findings are simulated by a ruptured Baker’s cyst, usually located in the patella fossa
    • Other differential diagnoses are muscle cramps, cellulitis, and heterotopic bone formation (in paralyzed patients)
  • PE is suspected in patients with cough, shortness of breath, tachycardia or other arrhythmias, and fever
    • If the lung is infracted, there is pleuritic chest pain and hemoptysis, and with massive PE, syncope
    • Differential diagnosis includes pneumonia, heart failure, sepsis, and cancer
    • Pre-test probability indicates likelihood of disease (Wells Criteria)

7

Describe the Well's Criteria for DVTs.

  • Major surgery within 4wks - 1pt
  • Paralysis, recent casts - 1pt
  • Cancer in past 6 months - 1pt
  • Tenderness along veins - 1pt
  • Leg swelling 3 cm > nl leg - 1pt
  • Edema of symptomatic leg - 1pt
  • Collateral veins - 1pt
  • Alternative diagnosis more likely - subtract 2pts
  • Intermediate 1-2; High ≥ 3

8

What are the Well's Criteria for pulmonary embolism?

  • Major surgery within 4wks - 1.5pts
  • Previous venous thromboembolism - 1.5pts
  • Cancer in past 6 months - 1.0pts
  • DVT signs/symptoms - 3.0pts
  • Heart rate >100 - 1.5pts
  • Alternative diagnosis less likely - 1.0pts
  • Intermediate 2-6; High >6

9

What are the lab tests for DVT and PE?

  • D-dimer is a cross-linked fibrin degradation product
    • Elevated levels occur in thrombotic disorders but also in cancer, pregnancy, renal failure, and rise with age
    • Therefore, it is necessary to use the d-dimer test in conjunction with the pre-test probability:
      • If pre-test probability is intermediate or low and age-adjusted d-dimer is normal, DVT/PE is unlikely and no further testing is indicated
      • If pre-test probability and d-dimer are both high, DVT/PE is likely and venous ultrasound or CT pulmonary angiogram will show the location & extent of the thrombus
      • If there are discrepancies between the pre-test probability and d-dimer, do venous ultrasound for DVT or CT pulmonary angiogram for PE.
      • If diagnosis is still uncertain, do venography for DVT or pulmonary angiography for PE

10

What is the main complication of DVTs and what is the occurrence rate?

  • The main complication of DVT is PE, which might be fatal
  • Other complications are recurrent DVTs and the post-thrombotic syndrome
  • Recurrences usually occur after anticoagulants are discontinued, even after 2 or more years of treatment
  • The recurrence rate in men is 30%, but only 10% in women
    • This difference might be due to transient risk factors, such as pregnancy, oral contraceptives, and estrogens, for DVT
    • Avoidance of these risk factors leads to fewer recurrences

11

What is postphlebitic syndrome?

  • The postphlebitic syndrome is characterized by:
    • pain
    • muscle cramps
    • pruritus
    • paresthesias
    • a feeling that the involved leg is heavy
  • The skin is:
    • indurated
    • pigmented
    • becomes ulcerated
    • the entire leg is edematous
  • Repeated attacks of pain and swelling occur, and it becomes difficult to distinguish between new onset thrombi or extension of existing thrombi
  • Frequent hospitalizations for medical and surgical procedures, including plastic surgery to manage the ulcers, are common, and patients experience major disability

12

What is chronic thromboembolic pulmonary hypertension?

  • Chronic thromboembolic pulmonary hypertension occurs in about 4% of patients following repeated clinical and subclinical (inapparent) pulmonary emboli
  • The pulmonary vasculature becomes attenuated due to vessel wall thickening and luminal narrowing
  • The resulting pulmonary hypertension is associated with symptoms such as:
    • dyspnea
    • fatigue
    • anorexia
    • hemoptysis
  • This complication occurs in about 4% of patients with recurrent PE