Bedside Placement of IVC Filters
This new IVUS-directed technique of filter placement significantly reduces risk in some patients.
The incidence of pulmonary embolism (PE) has been reported in approximately 355,000 patients per year, with an estimated annual mortality rate of 240,000.1 The search for safe and effective means of preventing or reducing PE in postoperative and critically ill patients led to the invention of devices for vena cava interruption and filtration. Prophylactic vena cava filter placement offers a protection rate of almost 99% against fatal PE.2-4 Vena cava filters are most strongly indicated for patients with PE who have contraindications for anticoagulation. For these specific patients, a 4% incidence of recurrent PE has been reported after vena cava filter placement.5
INDICATIONS FOR FILTER PLACEMENT
Anticoagulation, if tolerated, is the first-line therapy for patients with acute deep venous thrombosis (DVT) and PE. The following are frequent indications for vena cava filter placement:
(1) Documented DVT or PE with a contraindication to anticoagulation: Hemorrhage or recent or impending major surgery frequently are contraindications to anticoagulant administration. Patients with central nervous system or intracranial hemorrhage, massive hemoptysis, gross gastrointestinal bleeding, or retroperitoneal hemorrhage are typical examples of contraindications for anticoagulation.
(2) PE despite therapeutic anticoagulation.
(3) Prophylaxis for proximal free-floating thrombus: A 60% incidence of PE has been reported when free-floating thrombus in an iliofemoral vein exist, even in the presence of therapeutic anticoagulation.6 Iliofemoral thrombosis with a 5 cm or longer free-floating tail may have a higher risk of emboli and could undergo prophylactic vena cava filter placement through a pathway that avoids the involved vessel for filter placement.7 However, this indication is not universally accepted, and many experts do not recommend filters for these patients.
(4) High-risk patient populations: Patients with pre-existing pulmonary hypertension and reduced cardiac reserve who are undergoing surgery for morbid obesity or prolonged spinal procedures have been considered for this category. Near-fatal PE is sometimes an indication for filter placement.
Because of the increased incidence of PE in trauma patients, the use of prophylactic filter placement in this patient population has been considered.8 Many experts recommend chemoprophylaxis and mechanical compression for trauma patients who have sustained severe head injury, spinal cord trauma, multiple long-bone fractures, pelvic fracture, or direct venous trauma. One single-institution study found that prophylactic vena cava filters offered a 99.5% protection rate, with only one of 187 patients having a nonfatal PE.2
BEDSIDE FILTER PLACEMENT TECHNIQUES
Vena cava filters have been placed at the bedside because of increased patient safety, convenience, and cost savings. By removing the risk of patient transport, this technique appears particularly useful for critically ill patients who require ongoing intensive care. Portable fluoroscopy, duplex ultrasound, and intravascular ultrasound (IVUS; Boston Scientific Corporation, Natick, MA) have all been used to assist with bedside filter placement.9,10
At Northwestern University, we developed a technique for inferior vena cava (IVC) filter insertion using IVUS guidance. In our protocol, patients underwent lower-extremity, venous duplex imaging to examine the common femoral and external iliac veins on the side of the proposed insertion to ensure that no thrombus would be encountered in the passage of the IVUS probe and during filter deployment. After appropriate preparation and draping of the groin, we performed “premeasurement” of the monorail-configuration IVUS catheter to the precise length of the over-the-wire percutaneous femoral Greenfield deployment device (Boston Scientific Corporation). Premeasurement allows placement of external markers during IVUS pullback assessment, which will directly correlate with the subsequent IVC filter deployment device length and position.
After access to the femoral vein is achieved, a J-tipped guidewire is passed into the central venous circulation and exchanged for a floppy-tipped, super-stiff wire. The IVUS catheter is passed over the super-stiff wire to the level of the right atrium. Venous anatomy is documented during pullback (Figure 1), and the landing zone between the renal veins and iliac vein confluence is marked on the immobilized external sterile drape. The right renal artery is a key landmark for placement of the apex of the filter. This is confirmed with a second pullback run. The 8-F sheath is removed and the deployment sheath is inserted after serially dilating the tract. The vena cava filter is then deployed in the cephalad end of the landing zone after removal of the guidewire. The guidewire is removed before deployment to avoid entrapment of the wire in the limbs of the filter. After deployment, an abdominal x-ray is obtained to assess filter location, tilt, and limb deployment.
A study done by Conners et al examined the efficacy of duplex ultrasound-directed IVC filter placement, and found it to be safe, cost-effective, and convenient for patients who require IVC filters.11 Both IVUS and transabdominal ultrasound methods avoid radiation exposure, use of nephrotoxic intravenous contrast, and transportation from an intensive care unit to the operating room or angiography suite.9,11
Vena cava visualization using duplex ultrasound can be limited by a patient's body habitus, overlying abdominal wounds, bowel distention, and abdominal packing. IVUS can overcome these limitations. A 92% successful placement rate has been achieved in previous studies and the procedure can take less than 15 minutes after obtaining venous access. In the last 5 years, we have placed more than 50 Greenfield filters by an IVUS-directed technique. Compared to duplex ultrasound and fluoroscopy, IVUS requires a single operator, and caval visualization is not hindered by obesity, open abdominal wounds, bowel gas, and abdominal packing. Immediate confirmation of filter placement with a portable abdominal radiograph showed only one patient to have had filter tilt greater than 13º, and there was no significant limb asymmetry. One filter was placed in the common iliac vein before the current premeasurement technique was adopted. In follow-up, there was one episode of insertion site thrombosis that resolved after 29 days, and one filter thrombosis that resolved after 5 months of anticoagulation. No clinical pulmonary emboli have occurred. It is also cost-effective compared to the angiography suite and operating room.12
Vena cava filters can be effective in reducing the mortality rates associated with PE, particularly for patients who cannot be treated with anticoagulation. New techniques are available for bedside placement of filters that eliminate the risk of transporting critically ill patients. We have found IVUS is our preferred imaging technique to guide bedside filter placement and is safe and cost-effective.
Andy C. Chiou, MD, MPH, FACS, is Assistant Professor of Surgery and Radiology Endovascular Surgery Section, Department of Surgery, University of Illinois College of Medicine at Peoria, Illinois. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Chiou may be reached at (309) 655-2383; email@example.com.
Jon S. Matsumura, MD, FACS, is from the Division of Vascular Surgery, Department of Surgery, Northwestern University Medical School, Chicago, Illinois. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Matsumura may be reached at JMatsumu@nmh.org.
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