College Answer

(e) The caval filter:

The caval filter is effective in preventing pulmonary embolism from the lower limbs, but is not without problems.  ·

PROS: Prevents PE and is particularly indicated in patients with:

•  Contraindications to anticoagulation (HITTS, haemorrhage)

•   Recurrent embolism despite anticoagulation

•  Free floating IVC thrombus

•  Immediately after embolectomy when heparin is contraindicated

CONS:        •  Requires expertise and equipment

•  IVC obstruction and long term venous stasis of the lower limbs may result

•  Technical problems:

misplacement obstructing renal veins caval perforation

fracture end embolisation

•  In one study of patients with DVT the two year mortality was not reduced and venous stasis of limbs was common

Technique: Commonly the filters are  placed by  interventional radiologists using sterile technique under II control. There are various types including removable filters. The umbrella type is outdated. Greenfield and the birdnest filter are still used in many parts of the world.

If there is extensive clot in the iliofemoral veins, upper extremity access (IJ or SV or axillary) is indicated via a Seldinger technique. The delivery system is advanced through an introducer after localisation of renal veins by contrast venography and the filter is placed below the renal veins

Thrombolytic Therapy of Pulmonary Embolism. Chest 115(6): 1999; p169-1707. Medical Progress: Pulmonary·Embolism. NEJM 339(2); 1998  p93·104

Recommended  reporting standards for vena caval filter  placement and patient follow-up. Journal ofVascular Surgery 30(3), 1999: p573-579

Discussion

LITFL have an excellent page on IVC filter placement.

For the time-rich exam candidate, this issue of CHEST published all of the most recent (9th edition) ACCP guidelines. Whereas previously they had a specific set of guidelines for IVC filters, they have now split them all up between different indications, and one needs to hunt though the articles for the recommendations. The British, however, have a set of discrete recommendations available (from 2006).

Contrary to the college answer, free-floating IVC thrombus is no longer considered an indication.

Rationale of IVC filter insertion

• Pulmonary embolis is common, and carries with it a substantial mortality and morbidity.
• Preventative measures such as mechanical thromboprophylaxis and prophylactic anticoagulation are not uniformly effective, and not always appropriate.
• Certain at-risk groups will therefore be at increased risk of fatal pulmonary embolism.
• A mechanical filter may prevent such fatal embolism at the cost of some filter-related complications
• Therefore, there are certain groups in whom the risk of filter-related complications weighs favourably against the risk of massive PE.

Indications for insertion

• Absolute contraindication to anticoagulation in a patient with high risk of DVT/PE
  • These might include unsecured aneurysm after SAH,  or recent major gastrointestinal haemorrhage eg. from varices.
• Complication of anticoagulation which requires it to be reversed
  • eg. significant bleeding while anticoagulated, or HITTS
• Inability to achieve full anticoagulation for whatever reason
• Pulmonary emboli while fully anticoagulated
• Previously, the indications also included pulmonary embolectomy and large free-floating iliofemoral venous thrombus.
• "Extended indications" for placement:
  • Major trauma
  • Burns
  • cancer patients
  • Patients with clot-induced pulmonary hypertension
  • Patients with predictably poor compliance with anticoagulation

Advantages of the IVC filter

• Can be inserted in patients with a contraindication to anticoagulation
• May decrease the risk of fatal PE
• Is retrievable, supposedly

Disadvantages of the IVC filter

• These things do not prevent or treat DVT; they are not a replacement for anticoagulation
• Venous stasis of lower limbs will occur
• Though retrievable, in practice fewer than 60% are ever retrieved.
• Filter related complications, eg malposition,  IVC damage, perforation, IVC thrombosis, and embolism of filter fragments. The filter may even migrate into the pulmonary artery.
• It may offer no mortality benefit whatsoever.

Insertion of the IVC filter:

• Interventional radiology procedure
• Access via the femoral or IJ
• venogram is performed to define the anatomy
• Seldinger technique of insertion, with fluoroscopic guidance
• Desired position is infrarenal

Evidence to support or refute the use of these devices

• PREPIC trial (2005):  IVC filter reduced the rate of PE from 15% to 6%., but no mortality benefit was seen at 8-year follow-up. Also, all the patients were anticoagulated, and so did not meet the major indication for IVC filter insertion (i.e. contraindication to anticoagulation).
• White et al (2000):  observational study: no difference in hospitalisation for PE recurrence in a large group of patients from California.
• Hemmila et al, (2015): retrosepctive study of trauma patients;  also did not demonstrate any mortality benefit.