The risk of venous thromboembolism (VTE) is very high in trauma patients, secondary to tissue injury, venous status from immobilization, and thrombophilia. As such, early initiation of VTE prophylaxis is essential in this population. The competing risks of life threatening hemorrhage and VTE need to be considered very carefully. Potential approaches to VTE prophylaxis include pharmacologic means, and mechanical devices. For patients unable to receive pharmacologic VTE prophylaxis, retrievable inferior vena cava filters (rIVCFs) may be placed until low molecular weight heparin (LMWH) can be initiated.

The need for mechanical VTE prophylaxis in patients unable to receive pharmacologic therapy is underscored by Geerts and colleagues' prospective study of trauma patients who did not receive anticoagulation. In their study, 58% of their 349 trauma patients sustained deep venous thromboses (DVT). \[Geerts et a., 1994\] Furthermore, a confirmed or clinically suspected pulmonary embolus (PE) was identified in an additional 5% of patients. Importantly, this study excluded patients who died during the first 5 days of admission. However, the highest risk of VTE occurs in the first 4 days after admission and many advocate early insertion of rIVCF \[Owings et al. 1997, O'Malley et al. 1990, Carlin et al. 2002, Haut et al. 2014\]. Coincidentally, VTE prophylaxis is often withheld pending repeat neurologic imaging and / or surgical intervention.

Current guidelines on the use of rIVCFs are contradictory. The Eastern Association for the Surgery of Trauma's (EAST) practice management guideline suggests the use of rIVCFs are advisable in the "very-high-risk trauma patients". Such patients are defined as the those who cannot receive anticoagulation because of increased bleeding risk and have sustained injuries preventing mobilization such as: i) severe closed head injury (GCS \< 8) ii) incomplete spinal cord injury with paraplegia or quadriplegia iii) complex pelvic fracture with associated long bone fractures iv) multiple long bone fractures \[Rogers et al 2002\]. Contrasting this, the American College of Chest Physicians sated in their 2012 Guideline, that there is no role for rIVCFs in primary VTE prevention. \[Gould et al. 2012\]

Reflecting this lack of consensus in guidelines, there is practice variability among major trauma centres. In an American based survey study of 131 Trauma Directors, LMWH was the preferred method for VTE prophylaxis in over half (51%) of the responders, followed by intermittent pneumatic compression devices (IPCD, 42%), Foot pump (8%) Low Dose Heparin (LDH, 7%) and rIVCFs (1%). In patients with contraindications to pharmacologic prophylaxis, the favoured approach for VTE Prophylaxis is IPCD (80%) followed by rIVCF (16%) and foot pump (9%). \[Knudson et al. 2004\] More work is needed to improve our understanding of the optimal role for rIVCFs, particularly considering recent advances in, and physician experience with rIVCF technology.

One of the most cited concerns with the use of rIVCF in trauma patients is the low reported retrieval rates ranging from 21-35% of patients. \[Kirilcuk et al. 2005, Antevil et al. 2006, Karmy-Jones et al., 2007\] The need for VTE prophylaxis in trauma patients is usually temporary, and long term filter use is associated with an increased VTE risk, which was demonstrated in the PREPIC-1 trial and the 8-year follow up study examining the use of permanent IVCF in non-trauma patients with DVT for PE prevention \[Decousus et al. 1998, PREPIC Study Group, 2005\]. Of note, these trials were examining the role of rIVCF in patients for secondary prophylaxis in at risk patients with known VTE disease. The low retrieval rates of rIVCFs that have been reported in the Unites States are not a problem in our Canadian Lead Trauma Centre. We recently demonstrated a 97% retrieval rate in trauma patients surviving to discharge. \[Leeper et al. 2015\] We advocate a trial of early rIVCF use followed by prompt removal once medical prophylaxis is safe.

There is a paucity of data regarding the use of rIVCFs in the Canadian setting, and our group is currently surveying Canadian trauma directors to improve our understanding of current practice. Despite the current deficiency of evidence, many Level 1 North American Trauma centres use rIVCF for primary VTE prophylaxis in their at risk trauma patients, as per EAST guidelines. In a recent meta-analysis by Haut et al. that reviewed 8 studies, they identified a reduction in PE incidence with rIVCF use, but concluded that further studies are required. \[Haut et al. 2014\]

The investigators propose a feasibility study to determine whether or not our center can insert rIVCFs in at-risk trauma patients expeditiously enough to cause a meaningful reduction in the time they are left unprotected to PE.