Inferior Vena Cava Filters

Inferior Vena Cava Filters

In f erior Ven a C ava F i l t e rs Types, Indications, and Removal Mary A. Medeiros, MD, MPH a, *, Donald T. Baril, MD b KEYWORDS  IVC filter ...

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In f erior Ven a C ava F i l t e rs Types, Indications, and Removal Mary A. Medeiros,

MD, MPH

a,

*, Donald T. Baril,

MD

b

KEYWORDS  IVC filter  Inferior vena cava filter  Pulmonary embolism  Venous thromboembolism  Retrievable IVC filter  Permanent IVC filter

HOSPITAL MEDICINE CLINICS CHECKLIST

1. Inferior vena cava (IVC) filters are used to prevent acute pulmonary embolism (PE), a common and preventable entity with significant clinical consequences. 2. IVC filter placement is generally considered a second-line intervention to anticoagulant therapy, whether in the acute setting of a venous thromboembolism or as primary prophylaxis in surgical or trauma patients. 3. Although placing an IVC filter may decrease the incidence of PE in patients with proximal lower extremity deep vein thrombosis (DVT) compared with anticoagulation alone, doing so does not offer any long-term mortality benefit, and may increase the risk of developing a new or recurrent DVT within 2 years. 4. The development of retrievable IVC filters has contributed to an increase in usage over the past 10 to 20 years, although actual retrieval rates remain low. 5. Several types of permanent and retrievable filters are available for implantation in the United States. Filter choice is often dependent on market availability and physician preference. 6. Because the risk of PE is often time limited, retrieval after a certain period postplacement is believed to ameliorate the risks and complications associated with an indwelling vena cava filter. This period is not well defined, and patients are frequently lost to follow-up before retrieval can occur.

a

Division of Hospital Medicine, UMass Memorial Medical Center, 55 Lake Avenue North, Worcester, MA 01655, USA; b Division of Vascular and Endovascular Surgery, UMass Memorial Medical Center, 55 Lake Avenue North, Worcester, MA 01655, USA * Corresponding author. E-mail address: [email protected] Hosp Med Clin 2 (2013) e561–e573 http://dx.doi.org/10.1016/j.ehmc.2013.04.009 2211-5943/13/$ – see front matter Ó 2013 Elsevier Inc. All rights reserved.

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DEFINITIONS

1. What is an IVC filter and what is it used for? An inferior vena cava (IVC) filter is a device that is deployed into the IVC with the intention of disrupting the flow of embolic material from a distal venous site in the lower extremities to the central cardiopulmonary venous system. IVC filters are placed to prevent the acute onset of pulmonary embolism. 2. What is the definition of a pulmonary embolism and how dangerous is it? Acute pulmonary embolism (PE) is a fairly common condition, which, if left untreated, is associated with a 30% mortality rate1 and is 1 of the leading causes of preventable hospital deaths.2 Any free-floating foreign material contained in the venous circulation may travel to the pulmonary vascular bed and become trapped in a vessel, impeding blood flow distally. The affected lung parenchyma becomes physiologic dead space (ventilated but not perfused), leading to hypoxemia. Although substances such as air or fat may cause a PE, thromboembolism arising from the proximal lower extremity deep veins or pelvis is by far the most common source of clinically significant PEs. Deep venous thrombosis (DVT) and PE are often collectively referenced under the umbrella term venous thromboembolism (VTE). EPIDEMIOLOGY

1. How frequently are IVC filters used? The number of IVC filters placed per year in the United States increased nearly 25-fold between 1979 and 1999, from 2000 to 49,000.3 The trend has continued with approximately 167,000 filters placed in the United States in 2007, and annual use is expected to top 259,000 in 2012.4 This increase is attributable to advancing technology with the development of optional filters5 and improved ease of placement,6 as well as the broadening of indications to include VTE prophylaxis in surgical patients.7 2. How effective are IVC filters at preventing PE? Compared with anticoagulation alone, permanent IVC filters have been found to provide additional protection against symptomatic and asymptomatic PE for up to 8 years after placement. However, this benefit is countermanded by an increased risk of recurrent DVT among patients with filters; having an IVC filter offers no improvement in mortality.8 VTE recurrence is not well studied in patients with filters who are not receiving anticoagulation. IVC filters have also been used increasingly as primary prevention against PE among surgical patients. The incidence of PE is significantly reduced in comparison with controls, as demonstrated in several studies of trauma patients, but it is notable that none of these are class I studies. Prophylactic vena cava filters are believed to provide good protection against fatal PE, and they are associated with a low incidence for adverse outcomes.9 CLINICAL GUIDELINES

Evidence-based guidelines have been developed by the American College of Chest Physicians (ACCP),10 the Society of Interventional Radiology (SIR),11 and the Eastern

Inferior Vena Cava Filters

Association for the Surgery of Trauma (EAST)9; various indications for filter placement have been discussed (Box 1). Physician compliance with these guidelines has been suboptimal at best,12 although because evidence supporting the benefits and risks of IVC filter usage remains generally weak, many practitioners are left to render indications for placement subject to interpretation. INDICATIONS

1. What are the indications for placing an IVC filter? First-line therapy for the treatment of VTE is therapeutic anticoagulation. In the acute setting, heparin products are recommended initially, with early initiation of oral vitamin K antagonists.10 When anticoagulation has failed or is contraindicated, IVC filters are used as a means of mechanical thromboprophylaxis to prevent PE. Although this has been well supported by evidence and is broadly accepted, filters are placed with increasing frequency for indications where the evidence basis remains marginal.13 2. What are the indications for choosing a permanent versus retrievable filter? Retrievable IVC filters were developed in answer to known complications associated with long-term implantation of permanent devices, specifically the development of iliocaval thrombosis and filter migration. The indications for placing retrievable filters are similar to those used for permanent filtration, given that the need for protection against PE is anticipated to be of short duration. Because retrievable filters are relatively new to the market, their use and actual rates of retrieval remain conservative.5,14,15 The selection of filter type is often related to availability and physician preference. Retrospective reviews demonstrate that clinical outcomes are comparable between permanent and retrievable filters.5,16 Management of retrievable filters is discussed later (see section entitled Under what conditions might an IVC filter be removed, and after how long?). CONTRAINDICATIONS

Under what conditions should placement of an IVC filter be avoided? Absolute contraindications to filter placement are not often discussed, but are generally anatomic in nature, such as lack of an access route to the vena cava or unavailability of a location within the vena cava to place the filter. In addition, filter placement is contraindicated in the setting of a markedly enlarged IVC. TYPES

What types of IVC filters are currently in use and what are the differences between them? Current filter designs are a product of more than 100 years of evolution in the procedure of vena caval interruption for the prevention of PE, which was first performed by ligation in 1893.17 The endovascular approach was introduced in 1967 with the MobinUddin filter placed via right internal jugular vein cutdown.18 The original stainless steel Greenfield filter became available for clinical use in 1973, and since then many designs have been developed to optimize ease of placement and efficacy at trapping clots while minimizing complications.

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Box 1 Evidence-based guidelines for IVC filter placement published by professional societies ACCP: Evidence-based clinical practice guidelines A. Vena caval filters for the initial treatment of DVT: for patients with acute proximal DVT, if anticoagulant therapy is not possible because of the risk of bleeding, placement of an IVC filter is recommended (grade 1C). B. In children >10 kg body weight with lower extremity DVT and a contraindication to anticoagulation, placement of a temporary IVC filter is suggested (grade 2C). C. Vena caval filters for the initial treatment of PE: in patients with acute PE, if anticoagulant therapy is not possible because of risk of bleeding, placement of an IVC filter is recommended (grade 1C). D. For patients with chronic thromboembolic pulmonary hypertension undergoing pulmonary thromboendarterectomy, placement of a permanent vena caval filter before or at the time of the procedure is suggested (grade 2C). SIR: Indications and contraindications for all vena cava Absolute indications (proven VTE):  Recurrent VTE (acute or chronic) despite adequate anticoagulation  Contraindication to anticoagulation, complication of anticoagulation  Inability to achieve/maintain therapeutic anticoagulation Relative indications (proven VTE):  Iliocaval DVT, large, free-floating proximal DVT  Difficulty establishing therapeutic anticoagulation  Massive PE treated with thrombolysis/thrombectomy  Chronic PE treated with thromboendarterectomy  Thrombolysis for iliocaval DVT  VTE with limited cardiopulmonary reserve  Recurrent PE with filter in place  Poor compliance with anticoagulant medications  High risk of complication of anticoagulation (eg, ataxia, frequent falls) Prophylactic indications (no VTE, primary prophylaxis not feasible as a result of high bleeding risk, inability to monitor the patient for VTE):  Trauma patient with high risk of VTE  Surgical procedure in patient at high risk of VTE  Medical condition with high risk of VTE Contraindications to filter placement:  No access route to the vena cava  No location available in vena cava for placement of filter EAST: Practice management guidelines for the prevention of venous thromboembolism in trauma patients (2002) Level I and II recommendations on this topic cannot be supported because of insufficient data. Level III: Insertion of a prophylactic vena cava filter should be considered in very-high-risk trauma patients: 1. Who cannot receive anticoagulation because of increased bleeding risk, and

Inferior Vena Cava Filters

2. Have an injury pattern rendering them immobilized for a prolonged period of time, including the following: a. Severe closed head injury (Glasgow Coma Score <8) b. Incomplete spinal cord injury with paraplegia or quadriplegia c. Complex pelvic fractures with associated long-bone fractures d. Multiple long-bone fractures Data from Refs.9–11

More recent advancements have introduced compatibility with magnetic resonance imaging (MRI) by using newer materials, as well as the option of retrieval. Two types of optional filters have been developed: (1) temporary filters that are tethered by a guidewire or catheter to the subcutaneous tissue at the site of insertion, and must be removed within a few days of insertion because of infection risk; although available for use in Europe, none are currently approved by the US Food and Drug Administration (FDA); and (2) retrievable filters that are anchored by hooks or barbs that may become incorporated into the walls of the IVC after a certain amount of time, leading to more permanent implantation. Table 1 provides a list of permanent and retrievable filters currently approved by the FDA, as well as graphic representations of the models. DESCRIPTION OF PROCEDURE

1. How is an IVC filter placed? Basic procedural techniques are delineated in Fig. 1. Perhaps the 2 most significant facets of technique when placing an IVC filter are adequate visualization of the location where the filter will be deployed and the ability to release the filter accurately at that location.19,20 In most instances, an IVC gram is performed (intravenous contrast under fluoroscopy) at the time of the filter placement procedure to evaluate the anatomy and ensure an appropriate deployment location. Less commonly, IVC filter placement has been performed using intravascular ultrasonography (IVUS) or conventional transabdominal duplex ultrasonography for guidance. The use of ultrasonography, either via IVUS or conventional duplex ultrasonography, has made filter placement at the bedside an option as well. Because 90% of clinically significant PEs originate from the lower extremity or pelvic veins, most filters are placed infrarenally. The right internal jugular or right common femoral veins are the most common sites of access for placement of IVC filters. The filter is most commonly placed well above the confluence of the iliac veins, just inferior to the lowest renal vein. 2. Are there special circumstances that might affect the procedure of filter placement? Currently available IVC filters may be safely deployed in an IVC that is between 28 to 32 mm in diameter. An IVC greater than this size is known as a megacava, and only certain filters may be used in the case of this anatomic phenomenon.21 Approximately 0.2% to 3% of the population has a duplicated IVC. In most instances of duplicated IVC, the left IVC drains into the left renal vein. When this is found

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Manufacturer (Location)

Material [MRI Compatibility]

Year of FDA Approval

Greenfield

Boston-Scientific (Natick, MA)

Stainless steel [no]

1973

Cone shaped with the apical hub pointing cranially and 6 stainless steel legs radiating caudally

Greenfield titanium

Boston-Scientific (Natick, MA)

Titanium alloy [yes]

1989

Same physical design as original Greenfield

Vena Tech-LGM

B. Braun Medical (Bethlehem, PA)

Phynox [yes]

1989

Conical design with 6 limbs radiating from the apex Obliquely angled side rails attached to each limb for added stability

Vena Tech-LP

B. Braun Medical (Bethlehem, PA)

Phynox [yes]

2001

Made of 8 wires attached to 4 sets of inverted V-shaped adhering limbs 9-Fr introducer sheath; thus, it is small enough to be placed via the antecubital approach in addition to internal jugular and femoral venous approaches

Simon Nitinol

Bard Peripheral Vascular (Tempe, AZ)

Nitinol [yes]

1970

Has 2 components:  Top umbrella-shaped filter mesh is attached to an anchoring basal component  Basal component has small hooks that allow for attachment to the wall of the cava

Filter Type

Description/Distinguishing Features

Graphic

Permanent

See Greenfield

See Vena Tech-LGM

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Table 1 Types of IVC filters available

Bird’s Nest

Cook Medical (Bloomington, IN)

Stainless steel [no]

1982a

Composed of 4 long stainless steel wires, each preshaped with many nonmatching bends of short radius Wires then attached to v-shaped struts, which anchor the filter to the cava wall Later revised version allowed for a larger filter size (from an 8-Fr to a 12-Fr catheter system), permitting placement into IVCs up to 40 mm in diameter

TrapEase

Cordis Corp. (New Brunswick, NJ)

Nitinol [yes]

2000

Trapezoid-shaped and made up of 2 baskets that are attached to 6 side struts Distal hooks at each end of the side struts allow for filter anchoring

Cook Medical (Bloomington, IN)

Conichrome [yes]

2003b

Uses 4 struts configured as a cross that form a half basket with hooks at each end of each strut Hooks attach the filter to the caval wall. There is a hook at the caudal aspect of the filter, which facilitates retrieval Generally introduced via the right internal jugular approach

Retrievable Gunther Tulip

Inferior Vena Cava Filters

(continued on next page)

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Manufacturer (Location)

Material [MRI Compatibility]

Year of FDA Approval

G2

Bard Peripheral Vascular (Tempe, AZ)

Nitinol [yes]

2008c

Composed of 12 nitinol wires joined at the apical end Six short upper wires act as stabilizing arms that contact the wall of the IVC, and the remaining 6 have longer wires with hooks at their tips for further anchoring of the filter

OptEase

Cordis Corp. (New Brunswick, NJ)

Nitinol [yes]

2002

Similar design to the TrapEase (permanent) filter Made up of a single nitinol metal tube with a double basket design Unidirectional barbs at the superior aspect of the 6 struts aid in anchoring the filter in the IVC Once deployed, the filter imparts an outward radial force on the luminal surface of the cava to ensure appropriate positioning and stability Option for femoral retrievability is unique to this filter, facilitated by the unidirectional barbs and a hook at the caudal end of the filter

See TrapEase

Celect

Cook Medical (Bloomington, IN)

Conichrome [yes]

2008

Similar design to the Gunther Tulip filter Four primary struts serve as anchoring legs along with 8 independent secondary struts Design serves to center the filter and prevent tilt and allows improved filter removal if any of the struts become incorporated into the IVC wall

See Gunther Tulip

Filter Type

a

Description/Distinguishing Features

Graphic

Revised in 1986. Initially approved as a permanent filter in 2001. c Initially approved as a permanent filter in 2005. Data from Princewill K, Awan OA, Ali MM, et al. Inferior vena cava filters: a contemporary review. Appl Radiol 2011;40(3). Available at: http://www. appliedradiology.com/. Accessed November 25, 2012. b

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Table 1 (continued )

Inferior Vena Cava Filters

Fig. 1. CT scan demonstrating IVC filter struts outside the caval walls extending into the aorta and gallbladder (red arrow).

to be the case, either 2 IVC filters may be placed, or a single filter may be deployed in a suprarenal location.22 COMPLICATIONS

What complications might arise from the procedure of IVC filter placement? Most documented complications associated with vena cava filters occur in the setting of long-term placement. In 2010, the FDA issued a notice in response to a high volume of adverse event reporting involving IVC filters, nearly two-thirds of which were device related and believed to be associated with retention of the filter beyond the duration of need for PE protection, explicitly advising removal of a retrievable filter “as soon as protection from PE is no longer needed.”23 Adverse events associated with insertion or retrieval have been documented but are rare. Complications associated with IVC filters are outlined in Table 2. Radiographic depictions of certain complications are provided in Fig. 1 and Fig. 2. FOLLOW-UP

1. Under what conditions might an IVC filter be removed, and after how long? Time limits for filter retrieval have not been precisely defined. Data have indicated that retrieval may be performed safely for up to 17 months after placement.24 However, the benefits of performing retrieval have been poorly supported in the literature. In response, the SIR developed recommendations regarding patient conditions to be met before considering filter retrieval (Box 2).12 2. What is the course of short-term and long-term follow-up after placement of an IVC filter? Follow-up is often poorly defined and loss to follow-up can be in the range of 60% to 65%,25,26 which is primarily significant in the instance of retrievable filters when there is an explicit intention to remove the filter after a certain period of time. One study of military trauma patients showed that follow-up improved dramatically with the implementation of a registry to facilitate dedicated tracking, leading to significantly

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Table 2 Complications of vena cava filters % Incidence Associated With Insertion Improper anatomic placement

7

Migration

2–3

Angulation of the filter

2

Air embolism

1

Penetration of the caval wall

1

Pneumothorax (if filter placed via jugular vein)

*

Iodine contrast–induced nephropathy

*

Infection

*

Device-Related Complications Insufficient opening of the filter



Change in filter diameter 7 mm

1.4–5.8

Filter fracture



Failure of filter to deploy properly



Long-Term Complications Caval stenosis or filter narrowing

2

Caval occlusion

2–9

Lower extremity edema Sequelae of venous stasis Erosion of the caval wall Arteriovenous fistula formation

13–26 27 — —

VTE After Placement Insertion site thrombosis

2–5.8

New PE on follow-up

1.5–2.6

New DVT on follow-up

1.1–20

* Data not available. Data from Refs.3,34,35

improved retrieval rates. However, the study does not clearly demonstrate an increased risk of complications among patients whose filters remained in situ beyond the expected time period.25 PERFORMANCE IMPROVEMENT

In light of low retrieval rates27–29 and the FDA notice to focus on removal of filters as soon as possible, heightened efforts are being made to improve follow-up of retrievable filter insertion.30,31 These generally involve the use of electronic tracking methods, which may or may not be directly linked to a facility’s electronic medical record system. Studies examining the success of such efforts are still in their early stages. UNRESOLVED AREAS OF CONTROVERSY

Although several clinical disciplines have developed guidelines regarding the use of IVC filters, randomized studies demonstrating efficacy are lacking, and yet filter

Inferior Vena Cava Filters

Fig. 2. Cavagram at the time of attempted retrieval showing migration of the filter hook outside the caval walls (red arrow).

Box 2 Society of Interventional Radiology (SIR) patient conditions to be met before considering IVC filter retrieval  No current indication for implanting a permanent filter  Acceptably low risk of clinically significant PE because of continued anticoagulation therapy or change in clinical status  No expected near-term, recurrent high risk of PE (eg, stopping anticoagulation therapy for a planned surgery)  Life expectancy of more than 6 months after implantation to appreciate the potential benefits of filter retrieval  Ability to retrieve the filter without causing unacceptable injury to the patient  Patient or consenting guardian agrees to filter removal Data from Kaufman JA, Kinney TB, Streiff MB, et al. Guidelines for the use of retrievable and convertible vena cava filters: report from the Society of Interventional Radiology multidisciplinary consensus conference. J Vasc Interv Radiol 2006;17:449–59.

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placement has increased significantly in recent years. For this reason, questions are being raised about the true risk-benefit ratio of these devices, and it is believed that the best way to find an answer is to increase the number of randomized controlled trials looking at efficacy.32,33 REFERENCES

1. Horlander KT, Mannino DM, Leeper KV. Pulmonary embolism mortality in the United States, 1979-1998: an analysis using multiple-cause mortality data. Arch Intern Med 2003;163:1711. 2. Anderson FA Jr, Wheeler HB, Goldberg RJ, et al. A population-based perspective of the hospital incidence and case-fatality rates of deep vein thrombosis and pulmonary embolism. The Worcester DVT Study. Arch Intern Med 1991; 151:933–8. 3. Stein PD, Kayali F, Olson RE. Twenty-one-year trends in the use of inferior vena cava filters. Arch Intern Med 2004;164(14):1541. 4. Smouse B, Johar A. Is market growth of vena cava filters justified? Endovascular Today 2010;2:74–7. 5. Van Ha TG, Chien AS, Funaki BS, et al. Use of retrievable compared to permanent inferior vena cava filters: a single-institution experience. Cardiovasc Intervent Radiol 2008;31:308–15. 6. Rutherford R. Prophylactic indications for vena cava filters: critical appraisal. Semin Vasc Surg 2005;18:158–65. 7. Moore P, Andrews JS, Craven TE, et al. Trends in vena caval interruption. J Vasc Surg 2010;52(1):118–25. 8. The PREPIC Study Group. Eight-year follow-up of patients with permanent vena cava filters in the prevention of pulmonary embolism: the PREPIC (Prevention du Risque d’Embolie Pulmonaire par Interruption Cave) randomized study. Circulation 2005;112:416–22. 9. Rogers FB, Cipolle MD, Velmahos G, et al. Practice management guidelines for the prevention of venous thromboembolism in trauma patients: the EAST practice management guidelines work group. J Trauma 2002;53:142–64. 10. Guyatt GH, Akl EA, Crowther M, et al. Antithrombotic therapy and prevention of thrombosis, 9th ed: ACCP Guidelines Executive Summary. Chest 2012;141: 7S–47S. 11. Kaufman JA, Kinney TB, Streiff MB, et al. Guidelines for the use of retrievable and convertible vena cava filters: report from the Society of Interventional Radiology multidisciplinary consensus conference. J Vasc Interv Radiol 2006;17:449–59. 12. Baadh A, Zikria JF, Rivoli S, et al. Indications for inferior vena cava placement: do physicians comply with guidelines? J Vasc Interv Radiol 2012;23:989–95. 13. Streiff MB, Kim K, Hong K. Vena cava filters: a call to action. CHEST Physician 2011;6(2):18. Available at: http://www.chestnet.org/accp/article/chest-physician/ vena-cava-filters-call-action. Accessed October 18, 2012. 14. Meisner RJ, Labropoulos N, Gasparis AP, et al. Review of indications and practices of vena caval filters at a large university hospital. Vasc Endovascular Surg 2012;46(1):21–5. 15. Friedell ML, Nelson PR, Cheatham ML. Vena cava filter practices of a regional vascular surgery society. Ann Vasc Surg 2012;26:630–5. 16. Kim HS, Young MJ, Narayan AK, et al. A comparison of clinical outcomes with retrievable and permanent inferior vena cava filters. J Vasc Interv Radiol 2008; 19(3):393–9.

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17. Silver D, Sabiston DC. The role of vena cava interruption in management of pulmonary embolism. Surgery 1975;77:1–10. 18. Greenfield L. Evolution of venous interruption for pulmonary thromboembolism. Arch Surg 1992;127:622–6. 19. Burket MW. Obtaining optimal filter placement. Endovascular Today 2010;2: 42–50. 20. Puppala S, Windle ML, Siegal JA, et al. Inferior vena cava vascular filter placement. 2011. Available at: http://emedicine.medscape.com/article/1377859overview. Accessed November 17, 2012. 21. Turba UC, Sabri SS, Saad WE, et al. Before you place that filter: a guide to IVC filter placement and troubleshooting procedural challenges. Endovascular Today 2010;2:59–68. 22. Sartori MT, Zampieri P, Andres AL, et al. Double vena cava filter insertion in congenital duplicated inferior vena cava: a case report and literature review. Haematologica 2006;91(Suppl):ECR30. 23. US Food and Drug Administration. Removing retrievable inferior vena cava filters: initial communication. 2010. Available at: http://www.fda.gov/medicaldevices/ safety/alertsandnotices/ucm221676.htm. Accessed November 14, 2012. 24. Smouse HB, Rosenthal D, Thuong VH, et al. Long-term retrieval success rate profile for the Gu¨nther Tulip vena cava filter. J Vasc Interv Radiol 2009;20:871–7. 25. Lucas DJ, Dunne JR, Rodriguez CJ, et al. Dedicated tracking of patients with retrievable inferior vena cava filters improves retrieval rates. Am Surg 2012;78: 870–4. 26. Tan XL, Tam C, McKellar R, et al. Out of sight, out of mind: an audit of inferior vena cava filter insertion and clinical follow up in an Australian institution and literature review. Intern Med J 2012. http://dx.doi.org/10.1111/j.1445-5994.2012.02869. 27. Karmy-Jones R, Jurkovich GJ, Velmahos GC, et al. Practice patterns and outcomes of retrievable vena cava filters in trauma patients: an AAST multicenter study. J Vasc Surg 2009;49:410–6. 28. Smoot RL, Koch CA, Heller SF, et al. Inferior vena cava filters in trauma patients: efficacy, morbidity, and retrievability. J Trauma 2010;68:899–903. 29. Rosenthal D, Wellons ED, Lai KM, et al. Retrievable inferior vena cava filters: early clinical experience. J Cardiovasc Surg (Torino) 2004;46:163–9. 30. Lynch FC. A method for following patients with retrievable inferior vena cava filters: results and lessons learned from the first 1,100 patients. J Vasc Interv Radiol 2011;22:1507–12. 31. El-Amm J, Mobarek DA, Furmark L, et al. The infrequent removal of retrievable IVC filters. Thromb Res 2013;131:277–8. 32. Wehrenberg-Klee E, Stavropoulos SW. Inferior vena cava filters for primary prophylaxis: when are they indicated? Semin Intervent Radiol 2012;29:29–35. 33. Prasad V, Rho J, Cifu A. The inferior vena cava filter: how could a medical device be so well accepted without evidence of efficacy? JAMA Intern Med 2013;173: 493–5. 34. Tschoe M, Kim HS, Brotman DJ, et al. Retrievable vena cava filters: a clinical review. J Hosp Med 2009;4:441–8. 35. Greenfield LJ, Proctor MC, Michaels AJ, et al. Prophylactic vena caval filters in trauma: the rest of the story. J Vasc Surg 2000;32:490–7.

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