The role of chemical anticoagulation following spine surgery remains unclear, and current NASS guidelines do not suggest the routine use of chemical anticoagulation following elective spine surgery. Cancer and immobility secondary to neurological deficit are known risk factors for venous thromboembolism (VTE), and major decompression and stabilization surgery increases the risk of VTE even further. As such, spine tumor surgery patients are at increased risk of VTE, and there is no consensus on when to start chemical anticoagulation (AC), what AC agent to use, the appropriate dosing of the AC agent, and duration of its use. In order to gain some insight on this topic, Dr. Ramos and colleagues from New York reviewed sixty-five spine tumor surgery cases from a single institution from 2012-2018. All patients had at least 30 days of follow-up. They reported that patients had early surveillance for DVT, though they did not specify what this entailed. The attending surgeon was responsible for the decisions regarding AC (i.e. whether to initiate, timing of initiation, agent, dose, and duration). Overall, they reported a 17% DVT rate in the first 30 days, and a 3% rate of non-fatal PE (no fatal PEs occurred). They then stratified the patients according to post-operative AC status, with an early chemical AC group in which AC was started from post-operative day 1-3 (n=22), a late group started on post-operative day 4 or later (n=14), and a no AC group (n=29). All patients received sequential compressive devices following surgery. For unclear reasons, they did not include the no AC group in their analysis. The early group had a VTE rate of 9% compared to 36% for the late group, and this was statistically significant. While there were no statistically significant baseline differences between the early and late groups, the early group had a higher rate of prior VTE (14% vs. 7%), while the late group included more males (64% vs. 40%), more smokers (50% vs. 23%), and had lower modified Bauer scores (1.7 vs. 2.4). Controlling for these differences did not change the conclusion, and multivariate analysis yielded an odds ratio of 6.4 comparing the odds of VTE in the late vs. early groups. There was one epidural hematoma requiring surgical evacuation in the early group and none in the late group. Based on these data, the authors suggested that early initiation of chemical AC reduced the rate of VTE in spine tumor surgery patients.
This paper shines a light on how little is known about this topic, though the small numbers included preclude any strong conclusions. The most serious concern with this paper is that the authors elected not to include the no AC group, and this decision is not discussed. A back of the envelope calculation demonstrates that the no AC had a VTE rate of 14%. This is not statistically significantly different from the 9% rate in the early group. Given these data, it is not possible to conclude that early anticoagulation reduces the rate of VTE vs. no AC. It is not clear why the late AC group has a higher VTE rate compared to the no AC group, though baseline differences likely account for the finding. The authors did not report the demographic and baseline characteristics of the no AC group, so it is not possible to know how they were different. Given that the surgeons elected not to start AC in this group while they started it on post-operative day number 4 or later in the late group indicates that there were likely clinical differences between the two groups. While this paper does not add much data to the discussion regarding AC following spine tumor surgery, it does shine light on our lack of knowledge on the topic. These patients are at increased risk for both VTE and epidural hematoma, and surgeons are challenged to balance these risks. As this paper demonstrates, it is very difficult to generate a sufficiently large cohort to study the topic, and it would be even harder to perform an RCT on the topic. A large, multicenter observational study is likely the best approach to generate sufficient numbers to answer this question. Until such a study is performed, surgeons will be left with only their judgment to guide this high-risk decision.
Please read Dr. Ramos's article on this topic in the June 1 issue. Does this change how you view the use of chemical AC following spine tumor surgery? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor