Vena Cava Filters: Too Often, Too Many, or Just Right?

VASCULAR DISEASE MANAGEMENT 2014;11(5):E114-E125

Abstract

Venous thromboembolism (VTE) comprising both deep vein thrombosis (DVT) and pulmonary embolism (PE) is a common disease in the general population. The mainstay of the treatment for the most patients is anticoagulation. However, for patients who fail anticoagulation or are unable to receive anticoagulation because of a contraindication or increased risk of bleeding, inferior vena cava filters (IVCF) offer an attractive alternative for prevention of PE. Although beneficial in some patients, the utilization of IVCF has skyrocketed despite limited level I evidence. Much of this increase occurred after the introduction of optional (or retrievable) IVCF. Owing to low retrieval rates, so-called “optional” filters frequently become permanent, which may add to the morbidity associated with their routine use. In this review, we discuss various types of filters, their main indications, evidence behind their use, and the patterns of utilization.

Venous thromboembolism (VTE) comprising both deep vein thrombosis (DVT) and pulmonary embolism (PE) is a common disease with an estimated 2-3 cases per 1,000 in the general population.¹ Every year approximately 330,000 patients are admitted to the hospital with the diagnosis of VTE.² The mainstay of the treatment for most patients is anticoagulation. However, some patients fail anticoagulation or are unable to receive anticoagulation because of a contraindication or increased risk of bleeding. 

Inferior vena cava filters (IVCF) offer an attractive alternative for prevention of PE in patients who cannot receive anticoagulation. Dr. Mobin-Uddin introduced IVCF in 1967 with the umbrella filter.³ Since then, many filters have become commercially available and their use has increased at an explosive rate, especially after the introduction of the optional (or “retrievable”) IVCF.⁴ Stein et al reported a 25-fold increase in the use of IVCF from 1979 to 1999 (Figure 1).^4,5 This trend continues. In 2006, optional filters represented approximately 50% of the total filters placed and it was estimated that in 2012 optional filters would constitute approximately 75% of the total filters placed.⁶ The annual cost associated with insertion and follow-up of IVCF in patients was $190 million in 2007 and was expected to reach $300 million in 2012.⁶ The cost associated with complications of IVCF and associated malpractice issues further adds to the financial burden on the health care system. 

Despite the marked increase in the use of IVCF, there appears to be little level-1 data supporting their widespread use. IVCF are associated with multiple complications including recurrent DVT, filter migration, embolization, fracture, and IVC occlusion. Moreover, owing to low retrieval rates, optional filters frequently become permanent, which adds to the morbidity associated with their routine use. In this review, we discuss indications for filter placement, evidence behind their use and the patterns of utilization.

Indications for IVCF Placement 

According to the guidelines, absolute indications for IVCF placement include a contraindication or failure of anticoagulation in patients with VTE and in patients who experience a complication of anticoagulation (Table 1). However, there are many “relative” indications for their placement and no clear consensus between the different guidelines. ^7-9 For example, the Society of Interventional Radiology (SIR) has more relative indications compared to American College of Chest Physician (ACCP) guidelines.^7,8 This difference could be explained partly by the fact that there is a lack of quality data from randomized control trials (RCTs) on the use of IVC filters and results from case series may conflict. The most common indications for insertion of IVC filters are contraindications to anticoagulation (48%), prophylactic filter placement in the absence of documented PE/DVT (17%), and anticoagulation failure (8%).¹⁰ 

Evidence Behind IVCF Placement

Although many case series and retrospective studies have evaluated the effectiveness of IVCF, there remains only one RCT that has evaluated their effectiveness in preventing PE. The Prévention du Risque d’Embolie Pulmonaire par Interruption Cave (PREPIC) study randomized 400 patients with proximal DVT to receive either anticoagulation alone or a combination of anticoagulation and an IVC filter.¹¹ The primary outcome was occurrence of PE in the first 12 days after randomization. Secondary outcomes were occurrence of symptomatic PE, recurrent DVT, death, filter complication, and major bleeding in a 2-year follow-up period. The authors found that at 12 days, fewer patients developed PE among those who received the IVC filter (1.1% vs 4.8%, OR 0.22; 95% confidence interval, 0.05-0.90, P=.03). At 2-year follow-up, more patients developed recurrent symptomatic DVT in the IVC filter group (20.8% vs 11.6%, OR 1.87; 95% confidence interval, 1.10-3.20, P=.02). There was no significant difference in mortality between the groups. The data from the PREPIC trial show that IVC filters could be beneficial in prevention of PE in the short term when used in combination with anticoagulation. On the other hand, their long-term use is associated with increased risk of DVT. Another study looked at 8-year follow-up outcomes of these patients.¹² The authors found fewer PEs in patients who received the IVC filter (6.2% vs 15.1%, P=.008); however, patients with IVC filters had a higher incidence of recurrent DVT (35.7% vs 27.5%, P=.042). There was no significant difference in the mortality between the groups.

Evidence Underlying Other Indications

According to the guidelines there are several relative indications for the use of IVCF. Some of those are discussed in this section. Evidence for the use of IVCF in these patients primarily comes from case series and retrospective studies.

1) Patients With Poor Cardiopulmonary Reserve: A study conducted on the US DVT prospective registry found a higher rate of IVCF implantation in patients with COPD and DVT.¹³ Patients with COPD and DVT (668/4,575) had a greater rate of ICU admissions and required mechanical ventilation more frequently than patients who did not have COPD. The rate of IVCF insertion was higher in patients with COPD and DVT (19% vs 15%, P=.009). COPD patients also had more incidental PE (22.8% vs 17.8%, P=.005) and heart failure (29.5% vs 12.5%, P<.0001). However, because this was a prevalence study, the authors did not report data on clinical outcomes or mortality after IVCF insertion. In another study, 23 patients with chronic pulmonary hypertension were retrospectively studied. All of the patients were severely symptomatic; 8/23 (35%) and 10/23 (43%) had a history of venous thrombosis and thromboembolism, respectively. Inferior vena cava filters were inserted in 18 patients. At 18-month follow-up, all patients (n=5) who did not receive filters died and 3 of those patients had documented evidence of thromboembolism during the follow-up period or at the time of autopsy. Among patients who received filters (n=18), 4 died (2 within 24 hours of presentation with shock and 1 each at 8 months and 1 year follow-up). Due to this observed benefit of IVCF in pulmonary hypertension patients, the authors recommended the use of IVC filters in patients with chronic pulmonary hypertension.¹⁴  

2) Large Free-Floating Proximal DVT: There may be a high risk of PE with floating proximal DVT.^15,16 Radomski et al reviewed records of 39 patients with documented IVC thrombosis, 26 of whom had free-floating thrombi and 13 patients had thrombi with no evidence of a free-floating component. The rate of ventilation-perfusion or pulmonary angiogram confirmed PE was significantly higher in patients who had free-floating thrombi (50% vs 15%, P<.05). Rate of recurrent PE on anticoagulation was also higher in patients with free-floating thrombi (27% vs 17%, P>.05). In contrast, another study observed no significant difference in the incidence of recurrent PE.¹⁷ In this prospective study, authors assessed outcomes in 62 patients with free-floating thrombi and 28 with occlusive thrombi. Patients were assessed in the hospital at day 1 and 3 with color venous duplex scanning. There was no difference in the incidence of recurrent PE between the free-floating thrombi and occlusive thrombi groups (3.3% vs 3.7%, P=.92). Moreover, at 3-month follow-up none of the patients developed symptomatic recurrent PE. It appears uncertain that patients with free-floating thrombi benefit from insertion of IVCF.¹⁸

3) Inferior Vena Cava Filter Use in High-Risk Patients: IVC filters are also placed in some patients considered to be at high risk for VTE. These include patients who have had major trauma or who are undergoing spinal or bariatric surgery. The rate of PE ranges from 1.5% to 20% or more in trauma patients.¹⁹ In morbidly obese (BMI>55 kg/m²) patients undergoing bariatric surgery, the PE rate was up to 2% despite prophylaxis that included sequential compression stockings and subcutaneous heparin.²⁰ The placement of IVC filters in these patients is increasingly considered, especially after the introduction of optional filters. ^6,19,21 The data behind their use come from small studies with short follow-up duration.

Patients with major trauma may have transient contraindications to receiving VTE prophylaxis, and some studies suggest that IVCF may be useful in these patients.^21-23 In a retrospective analysis of 226 trauma patients who received IVC filters (62% received an optional filter); 6 patients (3%) developed PE while the filter was in place and 2 patients (1%) developed PE after the filter was removed.²¹ Thrombosis within or below the filter was the most common complication associated with filters (12%). Clinically significant thrombosis (i.e., requiring thrombolysis, ileofemoral DVT, or complete occlusion of IVC) was observed in 7% of the patients. The increased thrombosis risk was not associated with any particular filter type or brand. In another study, the authors compared the outcome in 40 trauma patients who received IVCF and were high risk for VTE to 80 matched patients who did not receive a filter. Patients with IVCF were continued on anticoagulation after IVCF placement. Patients who received an IVCF enjoyed a significant reduction in the incidence of PE (2% vs 17%, P=.02) and nonsignificant reduction of PE-related and overall mortality compared with patients who did not receive an IVCF. There was no significant difference in the rate of DVT between these groups. In light of the above evidence, the use of IVC filters in trauma patients seems controversial.

The role of IVCF in patients after neurosurgical procedures remains unclear. A study evaluated the effects of prophylactic IVCF in 74 patients after undergoing spine surgery who had contraindication to anticoagulation and were considered high risk for VTE.²⁴ At 11-month follow-up, 23 of 74 patients (31%) developed DVT whereas only 1 patient had PE. Ten out of 17 iliofemoral DVTs occurred on the same side as the side of filter insertion. Insertion site DVT contributed to one-third of the total DVTs. A total of 6 patients died during the follow-up period, but none of the deaths were attributable to PE.  In another study, the authors prospectively followed 22 patients who underwent insertion of an IVC filter following spinal surgery and compared these results to a retrospectively matched cohort.²⁵ Filters were placed preoperatively. All patients received mechanical prophylaxis (i.e., sequential compression devices and thigh-high compression stockings) and none of the patients received chemoprophylaxis (i.e., subcutaneous heparin or low-molecular-weight heparin) postoperatively. There was significant reduction of PE in the IVCF group (0% vs 13%), with 2 patients (9%) developing DVT. However, it is of note that patients with favorable results may have had clinically asymptomatic PEs that were not detected during regular clinical follow-up. The data suggest that IVCF could be useful in this patient population but are associated with developing DVT. 

Prophylactic IVC filter use has been advocated for patients undergoing bariatric surgery. In one series, patients were selected for IVCF placement if they were undergoing open gastric bypass and had history of either BMI>55 kg/m², PE, DVT, or pulmonary hypertension. All of the patients had pre- and postoperative lower extremity duplex ultrasound examination and received mechanical and chemoprophylaxis. Mean time of follow-up was 65±12 months (range 12-96 months).²⁰ At 3-month follow-up, 2 patients developed insertion-site DVT (1 of these patients died) and at 8 years follow-up the remaining 56 patients were without any VTE. Birkmeyer et al assessed the 30-day outcomes of 542 (8.5%) patients out of total 6,376, who received IVC filters before bariatric surgery.²⁶ Characteristics of patients who received filters included old age, male gender, high BMI, and history of VTE. Before risk adjustment, the IVC filter group had high rates of postoperative VTE (2.03% vs 0.53%, P<.0001), complications (7.56% vs 3.62%, P<.0001) and death or permanent disability (1.85% vs 0.51%, P<.0001). The increase in the rates of these outcomes persisted even after risk adjustment, although the difference was not statistically significant. A meta-analysis evaluated 5 studies for the outcomes related to IVCF in bariatric surgery patients.²⁷ The number of patients in these studies who received IVCF ranged from 58 to 1,077 and most studies were retrospective cohorts. Pooled data from these 5 studies suggested an increase rate of PE in patients receiving IVCF (RR 1.21, 95% CI, 0.57-2.56). Rate of DVT and mortality was also higher in the groups who received IVCF, but the difference was not statistically significant. From the available evidence, it appears that IVCF use may be beneficial in the subgroup of patients with very high BMI.

Complications Associated With IVCF Use

Use of IVCFs is associated with significant complications, which could occur any time from the time of insertion, during their time in the vena cava, or during retrieval. Most of the side effects are reported on the basis of case reports and many small case series and it may also be possible that complication rates are underreported and underestimated.^10,28 Complications occurring during or immediately after IVCF insertion include access site thrombosis, contrast reaction, filter malposition, tilting, extravascular penetration, or guidewire entrapment.²⁹ 

Quality Improvement Guidelines for the Performance of Inferior Vena Cava Filter Placement reported a 3%-10% incidence of access site thrombosis with IVCF insertion.⁹ Long-term complications and their incidence with IVCF use may include recurrent PE (0.5%-6%), symptomatic IVC penetration (0%-41%) or thrombosis (2%-30%) and filter movement (0%-18%) or fracture (2%-10%).⁹ As filter technology continues to improve (e.g. smaller size, improved delivery systems, and less thrombogenic potential), the rate of morbidity associated with their use may also decline.

Trends in IVC Filter Use

There is considerable geographical and socioeconomic variation in the utilization of IVCF. A recent study evaluated data on IVCF utilization in 77,695 patients from the National Trauma Databank who were admitted to the hospital for traumatic brain injury or spinal cord injury. A total of 3,331 patients received filters. The Northeast region had the highest utilization of prophylactic IVCF placement (7.4%), whereas the West region had the lowest utilization rate (2%).³⁰ Patients without insurance had the lowest rate of IVCF insertion, while those with Medicaid had the highest rate of IVCF placement (Figure 2). Even among patients with severe trauma (injury severity score of ≥16), insurance factors played a role, with patients who had no insurance receiving fewer IVCF compared with patients who had insurance (4.6% vs 6.7%). This difference persisted even after adjusting for patient- and hospital-related factors. Another study evaluated a large inpatient healthcare cost utilization database from 33 states for IVCF use depending on the prevalence of VTE and observed similar geographic trends.³¹ The study also examined public databases to identify any nonclinical factors (e.g. malpractice statistics, physician density) responsible for the variation in IVCF use. They found that the states with highest utilization of IVCF also had higher paid medical claims per capita, amount of paid malpractice claims, annual physician malpractice premiums, and number of vascular surgeons per capita. These studies suggest that regional variation in the use of IVCF could be partly explained by physicians’ training environment, physicians’ “practice patterns,” state-specific legal standards, and lack of consensus between various guidelines.^30,31

A study of IVCF placement in patients with acute VTE conducted in 263 California hospitals found widespread variation in rates of filter placement even within hospitals in close proximity to one another. Authors found marked variation (lowest vs highest tertile of odds) in the utilization of IVCF within the same geographic areas of Los Angeles Basin and San Francisco Bay Area. Patient characteristics associated with higher IVCF use included patients with bleeding, cancer, patients undergoing surgery, and increasing severity of illness. Hospital characteristics associated with increased utilization of IVCF use included larger hospital (OR, 0.2 [95% CI, 0.2-0.4], <100 vs >200 beds), an urban location (0.4 [0.2-0.5], rural vs urban), and other private vs Kaiser hospitals (1.5 [1.1-2.0]).³² The marked difference in the use of IVCF within hospitals in the same area points out that probably there are other factors responsible for this variation in the utilization of IVCF as compared to the factors responsible for regional differences.

Some patients undergo IVCF placement when in fact they could have received anticoagulation. A retrospective study evaluated 952 patients who received filters at an academic medical center.³³ Indications for IVCF placement included trauma (50%), cancer (16%), and bleeding complication of anticoagulation (11%). Of the patients who underwent filter placement following admission for trauma, 36% (n=174) received the filter 5 or more days after admission, at a time when presumably the risk of bleeding from anticoagulation had passed. Moreover, 24.9% (n=237) of the total 952 patients received some form of anticoagulation before their discharge from the hospital. These findings suggest that many of these filters may have been placed when the transient contraindication of anticoagulation had passed.

With increasing use of optional IVCF, there is growing concern about proper follow-up of patients and removal of these filters. In general practice only about 20% of the optional filters are removed (Table 2). ^34,35 Common reasons cited for nonretrieval were lack of follow-up, physician oversight, patient noncompliance, and change of care to different service.^23,36 A multicenter study looked at the practice patterns of optional IVCF in trauma patients.²³ Out of 446 optional filters placed in 21 centers, 92% were placed for blunt trauma and approximately 75% were placed for prophylactic indications. Retrieval of the filter was attempted in 37% and 24% of the patients who had filters placed for prophylaxis or therapeutic indications, respectively. The two most common reasons for nonretrieval were loss of follow-up (31%) and immobility, which increased the risk of VTE (30%). In institutions in which the service placing the filter was different than the service responsible for follow-up, the rate of nonretrieval was substantially higher (6% vs 45%, P=.001). The US Food and Drug Administration also recommended that implanting physicians and clinicians responsible for the ongoing care of patients with optional IVCFs should consider removing the filter as soon as protection from PE is no longer needed.³⁷

Are Too Many IVCF Placed?

Inappropriate filter placement may be harmful to patients and increase costs to the health care system, whereas appropriate filter placement may reduce risk of PE and improve patient outcomes. Given the explosive increase in IVCF placement, it seems likely that a percentage of filters are placed unnecessarily. Several factors may account for this. Firstly, many patients who are receiving IVCF due to a contraindication to anticoagulation may in fact not have a contraindication.³³ Physicians should evaluate carefully to determine whether there is a contraindication to anticoagulation. If needed, a subspecialist’s help should be sought and the contraindication to anticoagulation documented in the chart. Secondly, patients who received IVCF due to failure of anticoagulation may not have actually failed it. It is important to document if the patient had a new DVT or PE after starting anticoagulation. Another reason for the increase in IVCF placement may be that providers believe that filters are easily retrievable and that the morbidity associated with long-term filter use will be reduced. However, most filters are not removed. In other cases, the filter retrieval is unsuccessful. These patients remain at risk for late complications. Another potential factor driving filter utilization is economic incentive, which may consciously or unconsciously bias a provider’s decision to place a filter. Patients with insurance are more likely to receive an IVCF than those without insurance.³⁰ Another factor that may influence the decision to place a filter is fear of malpractice suit. As noted above, states with highest utilization of IVCF also had higher paid medical claims per capita, amount of paid malpractice claim, and annual physician malpractice premiums. Finally, lack of provider knowledge may also contribute to increasing filter placement. More RCTs and provider education may help improve the utilization of IVCF for these relative indications.

Appropriate use criteria have been devised for coronary intervention and are now being developed for peripheral intervention. These criteria reflect RCTs and expert consensus and serve as a guide to clinicians. Developing such criteria for IVCF may reduce resource utilization without compromising quality of care and outcomes. 

Conclusion

The data to support the widespread use of IVCF are limited. The quality evidence for their placement is only based on one RCT and on many smaller studies with significant limitations. There is significant regional variation in filter placement that may be driven in part by lack of level I data. Placement of IVCF may result in significant short- and long-term morbidity as well as add great cost to the health care system. 

Additional RCTs are needed to address some of the controversies surrounding the relative indications for IVCF implantation. It is expected that filter technology will continue to improve at rapid rate and we will likely see many new filters in the market. Steps must be taken to ensure that appropriate patients receive the filters and that they are removed in a timely fashion to avoid complications and to reduce the financial burden on the health care system.

Editor’s Note: Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no disclosures related to the content of this manuscript. 

Manuscript submitted October 16, 2013; provisional acceptance given November 13, 2013; final version accepted November 26, 2013. 

Address for correspondence: David Paul Slovut, MD, PhD, Montefiore Medical Center, Bronx, New York 10461, United States. Email: dslovut@montefiore.org.

REFERENCES  

1. Becker RC. Aspirin and the prevention of venous thromboembolism. N Engl J Med. 2012 May 24;366(21):2028-2030.
2. Rogers MA, Levine DA, Blumberg N, Flanders SA, Chopra V, Langa KM. Triggers of hospitalization for venous thromboembolism. Circulation. 2012;125(17):2092-2099.
3. Hussain SA. Kazi mobin-uddin, 1930-1999. J Vasc Surg. 2000;32(2):406-407.
4. Stein PD, Matta F, Hull RD. Increasing use of vena cava filters for prevention of pulmonary embolism. Am J Med. 2011;124(7):655-661.
5. Stein PD, Kayali F, Olson RE. Twenty-one-year trends in the use of inferior vena cava filters. Arch Intern Med. 2004;164(14):1541-1545.
6. Smouse B, Johar A. Is market growth of vena cava filters justified? Endovascular Today. 2010;February:74-77.
7. Kearon C, Aki EA, Comerota AJ, et al. Antithrombotic therapy for VTE disease: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012;141(2 Suppl):e419S-94S.
8. 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(3):449-459.
9. Caplin DM, Nikolic B, Kalva SP, et al. Quality improvement guidelines for the performance of inferior vena cava filter placement for the prevention of pulmonary embolism. J Vasc Interv Radiol. 2011;22(11):1499-1506.
10. Aziz F, Comerota AJ. Inferior vena cava filters. Ann Vasc Surg. 2010;24(7)966-979.
11. Decousus H, Leizorovicz A, Parent F, et al. A clinical trial of vena caval filters in the prevention of pulmonary embolism in patients with proximal deep-vein thrombosis. Prevention du Risque d’Embolie Pulmonaire par Interruption Cave Study Group. N Engl J Med. 1998;338(7):409-415.
12. PRECIP 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(3):416-422.
13. Shetty R, Seddighzadeh A, Piazza G, Goldhaber SZ. Chronic obstructive pulmonary disease and deep vein thrombosis: a prevalent combination. J Thromb Thrombolysis. 2008;26(1):35-40.
14. Greenfield LJ, Scher LA, Elkins RC. KMA-Greenfield filter placement for chronic pulmonary hypertension. Ann Surg. 1979;189(5):560-565.
15. Norris CS, Greenfield LJ, Herrmann JB. Free-floating iliofemoral thrombus. A risk of pulmonary embolism. Arch Surg. 1985;120(7):806-808.
16. Radomski JS, Jarrell BE, Carabasi RA, Yang SL, Koolpe H. Risk of pulmonary embolus with inferior vena cava thrombosis. Am Surg. 1987;53(2):97-101.
17. Pacouret G, Alison D, Pottier JM, Bertrand P, Charbonnier B. Free-floating thrombus and embolic risk in patients with angiographically confirmed proximal deep venous thrombosis. A prospective study. Arch Intern Med. 1997;157(3):305-308.
18. Goldhaber SZ. A free-floating approach to filters. Arch Intern Med. 1997;157(3):264-265.
19. Aryafar H, Kinney TB. Optional inferior vena cava filters in the trauma patient. Semin Intervent Radiol. 2010;27(1):68-80.
20. Gargiulo NJ 3rd, O’Connor DJ, Veith FJ, et al. Long-term outcome of inferior vena cava filter placement in patients undergoing gastric bypass. Ann Vasc Surg. 2010;24(7):946-949.
21. Smoot RL, Koch CA, Heller SF, et al. Inferior vena cava filters in trauma patients: efficacy, morbidity, and retrievability. J Trauma. 2010 Apr;68(4):899-903.
22. Rodriguez JL, Lopez JM, Proctor MC, et al. Early placement of prophylactic vena caval filters in injured patients at high risk for pulmonary embolism. J Trauma. 1996;40(5):797-802.
23. 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 Trauma. 2007;62(1):17-24.
24. Leon L, Rodriguez H, Tawk RG, Ondra SL, Labropoulos N, Morasch MD. The prophylactic use of inferior vena cava filters in patients undergoing high-risk spinal surgery. Ann Vasc Surg. 2005;19(3):442-447.
25. Rosner MK, Kuklo TR, Tawk R, Moquin R, Ondra SL. Prophylactic placement of an inferior vena cava filter in high-risk patients undergoing spinal reconstruction. Neurosurg Focus. 2004;17(4):E6.
26. Birkmeyer NJ, Share D, Baser O, et al; for the Michigan Bariatric Surgery Collaborative. Preoperative placement of inferior vena cava filters and outcomes after gastric bypass surgery. Ann Surg. 2010 Aug;252(2):313-318.
27. Brotman DJ, Shihab HM, Prakasa KR, et al. Pharmacologic and mechanical strategies for preventing venous thromboembolism after bariatric surgery: a systematic review and meta-analysis. JAMA Surg. 2013;148(7):675-686.
28. Weinberg I, Kaufman J, Jaff MR. Inferior vena cava filters. JACC Cardiovasc Interv. 2013;6(6):539-547.
29. Ray CE Jr, Kaufman JA. Complications of inferior vena cava filters. Abdom Imaging. 1996;21(4):368-374.
30. Pickham DM, Callcut RA, Maggio PM, et al. Payer status is associated with the use of prophylactic inferior vena cava filter in high-risk trauma patients. Surgery. 2012;152(2):232-237.
31. Meltzer AJ, Graham A, Kim JH, et al. Clinical, demographic, and medicolegal factors associated with geographic variation in inferior vena cava filter utilization: an interstate analysis. Surgery. 2013;153(5):683-688.
32. White RH, Geraghty EM, Brunson A, et al. High variation between hospitals in vena cava filter use for venous thromboembolism. JAMA Intern Med. 2013;173(7):506-512.
33. Sarosiek S, Crowther M, Sloan JM. Indications, complications, and management of inferior vena cava filters: the experience in 952 patients at an academic hospital with a level I trauma center. JAMA Intern Med. 2013;173(7):513-517.
34. Minocha J, Idakoji I, Riaz A, et al. Improving inferior vena cava filter retrieval rates: impact of a dedicated inferior vena cava filter clinic. J Vasc Interv Radiol. 2010;21(12):1847-1851.
35. Janne d’Othée B, Faintuch S, Reedy AW, Nickerson CF, Rosen MP. Retrievable versus permanent caval filter procedures: when are they cost-effective for interventional radiology? J Vasc Interv Radiol. 2008;19(3):384-392.
36. Ko SH, Reynolds BR, Nicholas DH, et al. Institutional protocol improves retrievable inferior vena cava filter recovery rate. Surgery. 2009;146(4):809-814.
37. US Food and Drug Administration. Inferior vena cava (IVC) filters: initial communication: risk of adverse events with long term use. https://www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyAlertsforHumanMedicalProducts/ucm221707.htm. 
38. Antevil JL, Sise MJ, Sack DI, et al. Retrievable vena cava filters for preventing pulmonary embolism in trauma patients: a cautionary tale. J Trauma. 2006;60(1):35-40.
39. Mismetti P, Rivron-Guillot K, Quenet S, et al. A prospective long-term study of 220 patients with a retrievable vena cava filter for secondary prevention of venous thromboembolism. Chest. 2007;131(1):223-229.
40. Zakhary EM, Elmore JR, Galt SW, Franklin DP. Optional filters in trauma patients: can retrieval rates be improved? Ann Vasc Surg. 2008;22(5):627-634.
41. Gaspard SF, Gaspard DJ. Retrievable inferior vena cava filters are rarely removed. Am Surg. 2009;75(5):426-428.
42. Helling TS, Kaswan S, Miller SL, Tretter JF. Practice patterns in the use of retrievable inferior vena cava filters in a trauma population: a single-center experience. J Trauma. 2009;67(6):1293-1296.
43. Johnson MS, Nemcek AA Jr, Benenati JF, et al. The safety and effectiveness of the retrievable option inferior vena cava filter: a United States prospective multicenter clinical study. J Vasc Interv Radiol. 2010;21(8):1173-1184.