Prophylactic vena cava filters for trauma patients: a systematic review of the literature

Thrombosis Research 112 (2003) 261 – 267

Review Article

Prophylactic vena cava filters for trauma patients: a systematic review of the literature Timothy D. Girard a, John T. Philbrick b, J. Fritz Angle c, Daniel M. Becker b,* b

a Division of Allergy, Pulmonary and Critical Care Medicine, Vanderbilt University, Charlottesville, VA, USA Department of Internal Medicine, University of Virginia, Health Center, Box 800671, Charlottesville, VA 22908, USA c Department of Radiology, University of Virginia, Charlottesville, VA, USA

Received 2 December 2003; accepted 4 December 2003

Keywords: Vena cava filters; Pulmonary embolism; Multiple trauma; Prophylaxis; Review; Academic

1. Introduction

2. Materials and methods

Although various methods of preventing venous thromboembolism (VTE) have proven effective in many patient populations [1], neither low-dose heparin (LDH) nor mechanical prophylaxis using sequential compression devices (SCD) has proven better than no prophylaxis in patients who are at high risk for VTE due to major trauma [2]. Additionally, low-molecular-weight heparin (LMWH) may be no better than LDH in the prevention of pulmonary embolism (PE) [2]. In response to the limited effectiveness of standard preventive measures, more and more hospitals have adopted the practice of placing prophylactic inferior vena cava (IVC) filters to prevent PE in high risk trauma patients [2]. Athanasoulis et al. [3] reported the indications for placement of 1753 IVC filters from 1973 to 1998 at the Massachusetts General Hospital. Prophylaxis was not an indication until 1982. From that time until 1998, a total of 83 filters (4.7%) were placed for prophylaxis. In 1998, the percentage of prophylactic filters surpassed 15%. Greenfield et al. [4] reported a similar experience at the University of Michigan. Is there evidence to support the safety and efficacy of prophylactic IVC filter placement in patients at high risk of PE after major trauma? To address this question, we conducted a systematic review of the literature that describes the use of IVC filters in this clinical setting.

We accessed the MEDLINE database to identify Englishlanguage articles published from 1988 to 2002 using the search phrase ‘‘vena cava filter.’’ The abstracts of all articles identified were reviewed for the following inclusion criteria: (1) patients had IVC filters placed; (2) some or all patients had the filters placed prophylactically, i.e., prior to any known VTE disease; and (3) clinical outcomes for at least 1 week after prophylactic filter insertion were provided. To broaden our search, the references of each article chosen from the MEDLINE search were reviewed for articles not previously identified. Each article meeting inclusion criteria was reviewed according to the 10 methodological standards outlined below. These standards were modified from standards developed in previous research [5,6] on the natural history of calf and upper extremity deep vein thrombosis (DVT). They are designed to assess each article’s ability to avoid biased results (standards 1, 2, 6 – 10) and to present evidence that is easily applied to a given patient population (standards 3 –5). Every article was initially rated by one author (TDG) and then independently rated by another (DMB or JTP). Ratings were compared, and a consensus rating was determined among all three reviewers in the case of a disagreement.

Abbreviations: VTE, venous thromboembolism; LDH, low-dose heparin; SCD, sequential compression device; LMWH, Low-molecularweight heparin; PE, pulmonary embolism or emboli; IVC, inferior vena cava; DVT, deep vein thrombosis; RCT, randomized controlled trial. * Corresponding author. Tel.: +1-434-924-5856; fax: +1-434-2432854. E-mail address: [email protected] (D.M. Becker). 0049-3848/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.thromres.2003.12.004

2.1. Standard 1: randomized assignment of patients to treatments We sought a statement in the methods or comparable section of the publication explaining that patients were randomly assigned either to an experimental group to receive an IVC filter or to a control group treated in a

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standard fashion to prevent VTE. Random treatment assignment is intended to equally distribute confounding baseline characteristics between those with and without filters. 2.2. Standard 2: clearly identified comparison group (a) This standard required that two clearly identified groups be studied, one receiving prophylactic IVC filters and the other not, and that these two groups be matched for age and risk for VTE disease. (b) Additionally, apart from the placement of filters, the patients in each group must have been treated in a similar manner. A cohort from another institution or another time period, i.e., a historical control group, would not satisfy this standard. 2.3. Standard 3: adequate description of patient assembly A clear description of the patient selection process, including eligibility criteria and recruitment method, was required to satisfy this standard. With this information a reader would be able to appreciate potential sources of bias, such as selection bias. 2.4. Standard 4: adequate description of patients studied In addition to demographic information (age and sex), we required a description of the clinical factors putting the patients studied at risk for VTE events. This description should have included the type of trauma as well as a measure of trauma severity, e.g., the trauma score. Such information is essential when attempting to apply the results of various studies to a specific patient population.

2.5. Standard 5: adequate description of treatment Satisfaction of this standard not only required a description of the type of IVC filter used, but also the method of insertion, the time of insertion in relation to hospital admission, and a statement regarding the use of other methods of VTE prophylaxis. A statement that no other method of prophylaxis was utilized was appropriate to meet this standard. The treatment description should be detailed enough that physicians in another hospital would be able to treat patients in a similar fashion. 2.6. Standard 6: adequate documentation of adverse filter outcomes This standard required documentation of the occurrence of one or more adverse outcomes, including insertion-site thrombosis, vena cava thrombosis, placement complications or filter migration after placement. Signs and symptoms of adverse events alone were not accepted. We required corroboration with an objective test (e.g., ultrasound for DVT, plain film for filter migration, etc.). 2.7. Standard 7: unbiased surveillance for adverse filter outcomes (a) To be certain that subclinical events were not overlooked, we required serial evaluation of patients at predetermined intervals; and to assure that adverse outcomes were not misdiagnosed, each evaluation must have included use of an objective test (plain film, ultrasound, venogram, etc.). (b) Additionally, the interpreter of the objective test should

Table 1 Summary of patient demographics and clinical characteristics Source

Year

Number treated

Mean age

Male/ female

Patient population

Filter type

Thomas et al. [7] Webb et al. [8] Rogers et al. [9] Rosenthal et al. [10] Leach et al. [11] Winchell et al. [12] Wilson et al. [13] Sue et al. [14] Rogers et al. [15] Khansarinia et al. [16]

1988 1992 1993 1993 1994 1994 1994 1995 1995 1995

3 24 34 29 201 29 15 3 63 108

NR NRa 41.6 NR 37.5 NR 31.4 29.7 38.9 35.9

NR NRa 1.8:1.0 NR 2.7:1.0 NR 4.0:1.0 3:0 2.7:1.0 3.2:1.0

Mixed trauma Acetabular fracture Mixed trauma Orthopedic trauma Mixed trauma Mixed trauma Spinal cord injury Iliofemoral injury Mixed trauma Mixed trauma

Rodriguez et al. [17] Patton et al. [18] Rogers et al. [19] Gosin et al. [20] Rogers et al. [21]

1996 1996 1997 1997 1998

40 110 35 99 132

44.0 47.2 58.4 42.6 39.1

1.4:1.0 1.6:1.0 NR 2.5:1.0 2.7:1.0

Mixed trauma Mixed trauma Orthopedic trauma Mixed trauma Mixed trauma

Langan et al. [22]

1999

187

40.3

3.8:1.0

Mixed trauma

Kim-Ray Greenfield Greenfield Titanium Greenfield, Bird’s nest Greenfield NR NR Titanium Greenfield NR Titanium Greenfield Titanium Greenfield, stainless-steel Greenfield Titanium Greenfield Titanium Greenfield Titanium Greenfield, Bird’s nest Titanium Greenfield, Bird’s nest Titanium Greenfield, stainless-steel Greenfield Titanium Greenfield, stainless-steel, Greenfield

NR = not reported. a Demographic data was not specific to patients receiving IVC filters.

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Table 2 Summary of study methods and methodological standards satisfied Source

Study design

Patient selection

Control type

Standards satisfied

Thomas et al. 1988 [7] Webb et al. 1992 [8] Rogers et al. 1993 [9] Rosenthal et al. 1993 [10] Leach et al. 1994 [11] Winchell et al. 1994 [12] Wilson et al. 1994 [13] Sue et al. 1995 [14] Rogers et al. 1995 [15] Khansarinia et al. 1995 [16] Rodriguez et al. 1996 [17] Patton et al. 1996 [18] Rogers et al. 1997 [19] Gosin et al. 1997 [20] Rogers et al. 1998 [21] Langan et al. 1999 [22]

Case Case Case Case Case Case Case Case Case Case Case Case Case Case Case Case

Retrospective Prospective Prospective Prospective Prospective Retrospective Prospective Retrospective Prospective Prospective Prospective Retrospective Prospective Prospective Prospective Retrospective

N/A Concurrent Historical Historical N/A N/A Historical Historical N/A Historical Historical N/A Historical Historical N/A N/A

4, 6, 8 2b, 3, 4, 6, 7a, 8 3, 4, 5, 6, 7a, 8 6, 8 3, 8 3, 8, 10 3, 4, 5, 6, 7a, 8 2a, 3, 4, 6, 8, 10 3, 4, 5, 6, 7a, 8, 10 2a, 3, 4, 5, 6, 8, 10 2a, 3, 4, 5, 6, 7a, 8, 10 3, 4, 5, 6, 8, 10 3, 4, 5, 6, 7a, 8 4, 6, 8, 10 3, 4, 5, 6, 7a, 8 4, 6, 8

series series series series series series series series series series series series series series series series

N/A = not applicable.

have been blinded to the history of IVC filter placement in order to reduce observer bias. 2.8. Standard 8: adequate documentation of occurrence of pulmonary embolism This standard parallels standard 6, requiring documentation of the occurrence of pulmonary embolism. A statement that no pulmonary emboli were diagnosed was sufficient to satisfy this standard. We required corroboration of all PE diagnoses with an objective test (e.g., perfusion – ventilation lung scan, computerized tomography pulmonary angiogram, pulmonary angiogram). 2.9. Standard 9: unbiased surveillance for occurrence of pulmonary embolism As in standard 7, (a) we required that patients were evaluated at predetermined intervals with an objective test for PE, and (b) that the interpreter of the test be blinded.

sion criteria for review [7 –22]. Tables 1 and 2 summarize patient demographics and clinical characteristics, study design, indications for filter placement and the methodological standards satisfied. There were no randomized clinical Table 3 Rates of pulmonary emboli Source, year

3. Results Sixteen case series, reporting the outcomes of 1112 patients who received prophylactic IVC filters, met inclu-

Filter (%)

Control Filter Control (%) (%) (%)

3 24

0 (0) 0 (0)

0 (0) 0 (0)

Rogers et al., 1993 [9]

34

0

0 (0)

Rosenthal et al., 1993 [10]

29

0

Leach et al., 1994 [11] Winchell et al., 1994 [12] Wilson et al., 1994 [13]

201 29 15

0 0 0

3

0

63

1

Rogers et al., 1995 [15]

Khansarinia et al., 1995 [16] 108

To allow assessment of adequacy of patient follow-up, a study must have reported the number of patients lost to follow-up as well as the reasons for incomplete follow-up. If a large number of patients were lost to follow-up due to death, or if a high proportion of patients lost to follow-up experienced adverse outcomes, the reported effect of IVC filter placement would appear undeservedly optimistic.

Fatal PE

Thomas et al., 1988 [7] Webb et al., 1992 [8]

Sue et al., 1995 [14]

2.10. Standard 10: adequate documentation of patient follow-up

Patients PE

NR 2 (7.4)a (0) 25 (1.0)b (0) 22 (23.4)b (0) NR (0) NR (0) 7 (6.3)b (0) 1 (25)c (1.6) NR

Patton et al., 1996 [18] Rogers et al., 1997 [19]

110 35

Gosin et al., 1997 [20]

99

Rogers et al., 1998 [21]

132

13 (6.0)c 1 (2.5) 14 (17.5)c 0 (0) NR 1 (2.9) 11 (0.9)b 0 (0) 12 (4.8)b 3 (2.3) NR

Langan et al., 1999 [22]

187

1 (0.5) NR

Rodriguez et al., 1996 [17]

40

0 (0)

PE = pulmonary emboli; NR = not reported. a Standard 2(b) was met. b Neither standard 2(a) nor 2(b) was met. c Standard 2(a) was met.

0 (0) 0 (0) 0 (0)

NR 1 (3.7)a 7 (0.3)b 5 (5.3)b NR NR 0 (0)b

0 (0)

0 (0)c

1 (1.6) 0 (0)

NR

0 (0)

0 (0) 0 (0) 0 (0) 0 (0) 1 (0.8) 0 (0)

9 (4.2)c 8 (10)c NR 4 (0.3)b NR NR NR

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trials (standard 1). Three of the case series identified a comparison group that was matched for age and VTE risk [14,16,17]. However, each of these used historical controls (standard 2). One series reported a prospectively developed control group that was noted to have lower risk for VTE than the treatment group [8]. Most series included patients with multiple types of traumatic injuries, but the categories of closed head injury, spine fracture or spinal cord injury, pelvic fracture or multiple long bone fractures accounted for the majority of patients. Although the number of patients with specific injuries was not reported in every series, in the series that did specify type of injury, each of the listed categories accounted for approximately 15– 25% of patients receiving prophylactic IVC filters. An additional 15 – 20% of the described patients sustained more than one type of injury. While all 16 series reported the rate of occurrence of PE (standard 8), no series screened for PE at predetermined intervals (standard 9). Fourteen series reported the rates of occurrence of other adverse events [7– 10,13 –22] (standard 6), and seven series screened for adverse outcomes at predetermined intervals [8,9,13,15,17,19,21] (standard 7a). No study blinded the interpreter of a screening test to IVC filter status (standard 7b). Table 3 reports the number of pulmonary emboli that were diagnosed in treated patients in each series and in control groups, when available. More PE were reported in the control groups. However, all control groups were either historical controls or were not matched for age and VTE risk factors (standard 2). Complete patient follow-up was described in seven series [12,14 –18,20] (standard 10). The longest reported followup period was 42 months. In addition to PE, reported adverse outcomes (Table 4) included complications occurring at the time of filter placement (e.g., filter misplacement or tilt, groin hematoma, femoral arterial venous fistula

formation) as well as filter migration, insertion site thrombosis, IVC thrombosis with or without IVC occlusion and DVT, the most common adverse outcome.

4. Discussion Our review demonstrates a number of methodological shortcomings in each of the articles reviewed. In the absence of a prospective, randomized controlled clinical trial, it is difficult to draw clear conclusions regarding the efficacy and safety of prophylactic IVC filters in the trauma population. With these limitations in mind, we have used the available information to address important clinical questions. 4.1. What is the risk of pulmonary embolism after traumatic injury? In the articles included in this review, the rate of PE reported in historical controls ranged from 1.0% to 23.4%. This variability in reported PE is consistent with previous reports. In 1934, McCartney [23] reported 61 (3.8%) cases of PE following trauma in a study of 1604 autopsies. Since that time, the rate of PE reported in the trauma population has varied from 0.8% to 20.3% [24 –30]. It is possible that the high variability in reported rates of PE in the cited studies is due, in part, to differences in the risk factors of the patients being studied. However, the use of historical controls may introduce a bias. If an institution notes an unusually high rate of PE in trauma patients, it may respond by placing filters in subsequent patients. The resulting low rate of PE in patients with filters may be due to regression to the mean rather than filter effectiveness. Differences in rates over different time periods may also be due to differences in care. The care of patients with major trauma is in constant flux. There are new surgical procedures, new medical

Table 4 Rates of adverse outcomes Source, year

Patients

DVT (%)

IST (%)

IVC OC/T (%)

PC (%)

M (%)

Thomas et al., 1988 [7] Webb et al., 1992 [8] Rogers et al., 1993 [9] Rosenthal et al., 1993 [10] Leach et al., 1994 [11] Winchell et al., 1994 [12] Wilson et al., 1994 [13] Sue et al., 1995 [14] Rogers et al., 1995 [15] Khansarinia et al., 1995 [16] Rodriguez et al., 1996 [17] Patton et al., 1996 [18] Rogers et al., 1997 [19] Gosin et al., 1997 [20] Rogers et al., 1998 [21] Langan et al., 1999 [22]

3 24 34 29 201 29 15 3 63 108 40 110 35 99 132 187

NR 1 (4.2) 6 (17.6) NR 1 (0.5) 1 (3.4) 0 (0) 0 (0) 13 (20.6) NR 6 (15) 14 (12.7) NR NR 12 (9.1) 24 (12.8)

NR 0 (0) NR NR NR NR 0 (0) 0 (0) 2 (3.2) 1 (0.9) NR 3 (2.7) 2 (5.7) 0 (0) 4 (3.0) NR

NR 0 (0) 1 (2.9) 0 (0) 0 (0) NR 1 (6.7) NR 4 (6.3) NR 4 (10) 1 (0.9) 1 (2.9) NR NR 0 (0)

0 (0) 0 (0) NR 1 (3.4) 4 (2.0) 0 (0) 0 (0) 0 (0) NR 5 (4.6) NR 0 (0) 1 (2.9) 0 (0) 0 (0) 3 (1.6)

NR NR NR NR 1 (0.5) NR NR NR NR NR NR 1 (0.9) NR NR NR 0 (0)

DVT = deep vein thromboses; IST = insertion site thromboses; IVC OC/T = inferior vena cava occlusions and/or thromboses; PC = placement complications; M = migration; NR = not reported.

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treatments to prevent and treat complications, new and potentially improved diagnostic tests for VTE, and new and potentially improved measures for VTE prophylaxis. The reviewed series provided no reassurances or data that trauma patients without filters were treated the same way as trauma patients managed with prophylactic filters. Also, it is likely that publication bias contributes to the low PE rates reported in the five retrospective series [12,14,17,18,22]. One (0.3%) PE occurred in the 332 treated patients in these studies compared to six (0.8%) PE in the 780 patients studied prospectively. Perhaps the most accurate estimation of PE risk after trauma was provided by Velmahos et al. [2], who calculated the random-effect incidence of PE and DVT after injury across 73 studies. Their cautious estimate of the incidence of PE was 1.5% (95% CI, 0.011, 0.018). Their estimate of the incidence of DVT was 11.8% (95% CI, 10.4%, 13.1%). 4.2. How often is pulmonary embolism fatal after traumatic injury fatal? Our review of the published data does not allow a precise answer. Among the series we reviewed, the reported rate of fatal PE after traumatic injury ranged from 0% to 10%; 0 – 69% of the PE reported were fatal. Similar rates have been reported in other studies [28,29]. However, as noted above, these rates may be biased. Several studies evaluated more than 250 trauma patients and concluded that the rate of fatal PE was between 0.4% and 0.9% [9,19,27,29,30], which would be consistent with the low incidence of PE, 1.5%, estimated by Velmahos et al. 4.3. What are the short- and long-term adverse outcomes associated with prophylactic IVC filters? The most common adverse outcome reported in the series reviewed was DVT, occurring in 78 (9.3%) of 838 patients who received prophylactic IVC filters. The rate of DVT among the reviewed series varied from 0% to 20.4%. This is similar to the incidence of DVT calculated by Velmahos et al. [2]. Other adverse outcomes occurred at rates similar to those previously reported [5]. Insertion-site thrombosis occurred in 12 (2.0%) of 589 patients, IVC occlusion and/or thrombosis in 12 (1.6%) of 738 patients, complications during filter placement in 14 (1.4%) of 975 patients, and filter migration in 2 (0.4%) of 498 patients. These rates may not be accurate since follow-up was incomplete and surveillance was not complete. Only 6 of the 16 series reviewed documented both adverse filter outcomes (standard 6) and follow-up status on all patients (standard 10) [14 – 18,20]. Only two series reported adverse outcomes at predetermined intervals (standard 7a) and also complete patient follow-up status [15,17]. These methodological problems mean that the true rates of adverse outcomes may be higher than those reported. An additional concern is that the average age of patients receiving pro-

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phylactic IVC filters across the 16 series reviewed was 40.7 years. A relatively young population such as this should be followed for decades before reaching any conclusions about long-term filter safety. Of note, the only randomized control trial to evaluate IVC filters for the treatment of PE found that patients with filters were more likely than controls to develop DVT during a 2-year follow-up period (OR, 1.87; 95% CI, 1.10, 3.20) [31]. 4.4. How effective are other measures in preventing pulmonary embolism after traumatic injury? Although one clinical trial found that both LDH and SCDs were superior to no prophylaxis in high-risk trauma patients [29], other studies, including seven randomized controlled trials (RCTs) and a meta-analysis, have failed to confirm this benefit [2]. Two RCTs concluded that LMWH was superior to LDH in preventing VTE (DVT and PE combined) [32,33], but a meta-analysis showed no difference in PE rates between the two groups [2]. The larger trial, which randomized 265 patients, reported one non-fatal PE in the LMWH group and none in the LDH group [33]. Screening for DVT with serial duplex ultrasound examinations has been suggested as a means of preventing PE in high-risk patients. A positive ultrasound exam would prompt systemic anticoagulation or placement of an IVC filter. Two prospective clinical trials utilized serial ultrasound in patients at high risk for VTE due to traumatic injury and reported the occurrence of PE in one (0.44%) [34] and three (0.87%) [35] patients. In three of these four patients, the PE was fatal. Additionally, a cost-effectiveness analysis concluded that the cost per PE prevented using serial ultrasound is US$46,300 compared to US$93,700 when using prophylactic IVC filters [36].

5. Conclusion PE occurred in 7 (0.6%) of 1112 patients who received a prophylactic IVC filter. Two of these were fatal. However, without randomization and appropriate comparison groups, it is not possible to demonstrate a meaningful treatment effect of prophylactic filters. Only three series reported the clinical outcomes of a comparison group matched to the treatment group for age and risk [14,16,17], and all three utilized historical controls. In fact, the cumulative rate of PE reported in these studies is no better than that seen in trials utilizing serial ultrasound [34,35], a procedure with no adverse effects. In conclusion, the evidence supporting use of prophylactic IVC filters in patients at high risk for VTE after traumatic injury is limited by multiple methodological shortcomings. While the descriptive data available suggest their use may be efficacious, lack of appropriate comparison

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groups, incomplete evaluation for adverse outcomes, and incomplete follow-up make it difficult, if not impossible, to account for possible confounders. Our review documents that there are short-term adverse outcomes of filter placement, and we remain concerned about the potential for longterm complications of filter placement in the relatively young population of trauma patients. If the available evidence does not support routine use of prophylactic filters in this high risk population, what are the alternatives? Retrievable filters would alleviate concerns about long term consequences of IVC filter placement, and while there is now an FDA-approved device that can be left in for months rather than weeks, this technology is still in development [37]. Appropriate utilization of serial ultrasound leads to more focused placement of IVC filters, thereby limiting adverse outcomes as well as cost. This approach, along with judicious use of prophylactic heparin, should be the preferred alternative until large, multi-center RCTs can definitively evaluate the use of IVC filters, whether permanent or retrievable, for primary VTE prevention.

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