All good EM/CC clinicians know that venous thrombo embolism (VTE) is a potential complication of traumatic injury. The immobilisation and haematological changes associated with signficant injury are reasonably well described. Additionally there are controversies over the use of drugs such as tranexamic acid, with debates over whether these too may be thrombogenic. What we don’t reallty know is whether we can predict or risk stratify patients as to their risk of VTE post trauma and arguably much of our current VTE prevention practice is extrapolated from elective surgery.
So what is the incidence, and what are the risk factors for VTE in major trauma patients? These questions are tackled in a systematic review published in Injury this month1. The abstract is below, but as always we strongly recommend that you read the full paper and never just the summary and abstract here. 
What kind of paper is this?
It’s a systematic revirew and as such is a review of already published literature. Now you might be expecting the words meta-analysis to be associated with systematic review (as they commonly are) but that’s not the case here. Remember that you can only perform a meta-analysis when you pool data together to come to a larger conclusion. You can only perform a meta-analysis if the data is suitable to be combined, and as we will see in this case it is not.
So who (well what) was included.
In a systematic review the papers are like the participants in a clinical trial, the exclusion criteria and exclusion criteria are really important for our understanding and interpretation of the conclusions. Here papers were included if they were civilian (not military importantly), major trauma patients, aged >16 and where risk factors for VTE were described. Major trauma is not terribly well defined in the paper though, for me the standard definition is related to ISS, and I presume this is what has been used, but I can’t find a clear description of this (in the discussion it suggests that ISS>9 patients are included in some studies). In table 2 it’s clear that the inclusion criteria for what ‘major trauma’ is varies widely, so this is quite a heterogeneous group. They do talk about excluding patients with isolated injury groups were described (so as an example I’m pretty sure that studies of isolated neck of femur patients were not included).
The search was pretty reasonable, electronic and hand searching, with over 1000 papers wittled down to just 8 that were appropriate to answer the clinical question about risk factors for VTE. Considering all the work out there on major trauma and VTE this is a bit suprising really. In all honesty I expected there to be more (though perhaps this SR is a precursor to a ‘proper’ study). The quality of the included studies was pretty low with significant probability of bias, again a little disappointing.
What are the main findings?
The desctibed incidence of VTE after major trauma is incredibly variable, ranging from 0.35% to 24%. The reasons for the variation are complex but probably represent different patient groups, and importantly how hard we look for PE in these patients. The authors draw limited conclusions that lower limb, pelvic and chest injury appear to be associated with VTE. Male sex, higher ISS and age were also factors. The authors also identified a range of other potential risk factors buut the evidence for these was less robust and so the conclusions are really limited and there is no hope from this review of any form of risk assessment or scoring system.
So what does this mean for us as clinicians?
The conclusions are limited as a result of the quality of the included studies and we should commend the authors for not drawing firm conclusions. What we can say is that we don’t really know the incidence or risk factors for VTE in trauma patients and that’s a concern. However, it does seem as though the risk factors may be different from the general hospital population and thus our current practice of extrapolating practice from elective surgery is not evidence based and that’s a worry as we all know that VTE prophylaxis is not without risk, nor do we know which patients might benefit from aggressive VTE prophylaxis, for example through the use of IVC filters 2 , 3 .
We have seen in other studies of PE4 (for example in syncope5) that if you look hard for PE in hospitalised patients then you will find it, but what we don’t know is whether these are all significant and then whether any (or what) intervention is effective in improving patient outcome.
For now we should continue to follow local guidelines on VTE prophylaxis in our trauma patients, but it’s clear that this is an area where we need to know more. A trauma specific risk score for VTE needs development and I hope that this review acts as a springboard to that study.
Final thoughts.
This is what we would describe as a negative study in our journal club in that it does not come to a simple answer. That’s often a disappointment, but it’s important that as evidence based clinicians we understand the strength of evidence for what we do. Understanding uncertainty is arguably more important than simply following protocol.
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