External Methods
Although pharmacological measures have been generally the preferred treatment for VTE prophylaxis post SCI, mechanical means of limiting venous stasis can also serve to reduce the incidence of DVT post SCI. Mechanical methods of prophylaxis for venous thrombosis include the use of compression devices. These are generally considered safer forms of prophylaxis than pharmacological methods since there is no risk for bleeding. Compression devices include graduated compression stockings and gradient elastic stockings, as well as IPC/SCD. Compression stockings exert a graded pressure along the lower extremities and are postulated to increase blood flow velocity as well as volume, thereby preventing thrombus formation. IPC and SCD involve an air pump that intermittently and/or sequentially inflates a sleeve fitted around the extremity, and likely involves a mechanism of action that increases femoral vein blood flow. However, it should be noted that use of these devices should be accompanied by twice daily inspection for skin discolouration or breakdown, and broken blood vessels. Pneumatic compression devices are not suitable for individuals with severe arterial insufficiency.
Of the studies evaluating physical methods for the prevention of DVT, five studies evaluated individuals during the acute phase (<3 months), while one study evaluated individuals during the chronic phase (>3 months) of SCI.
Acute Studies
A variety of mechanical measures to reduce the incidence of DVT post SCI have been studied. Becker et al. (1987) studied whether rotating treatment tables would prevent the development and progression of DVT in individuals with acute SCI. The authors noted that rotating treatment tables had been used up to that time in individuals with acute SCI to maintain spinal cord alignment while facilitating nursing care, allowing even distribution of ventilation and preventing pressure sores. It was hypothesized that because these appliances rotated continuously, they might serve to inhibit thrombosis formation by reducing venous stasis. This randomized trial involved 15 individuals with acute SCIs. Four of the five control (non-rotated) individuals developed distal and proximal thrombi, assessed by I125 fibrinogen scanning and impedance plethysmography while only one of the ten treated (rotated) individuals with SCI developed both distal and proximal venous thrombi (p=0.007).
Matsumoto et al. (2015) examined the use of prophylactic pneumatic compression and elastic stockings without anticoagulation. Individuals were on compression devices all day except when they were out of bed. Elastic stockings were on most of the time except when bathing. DVT was diagnosed in 12 individuals out of the 29 enrolled (Matsumoto et al. 2015). The Consortium for Spinal Cord Injury (2008) clinical practise guidelines, supports the application of mechanical compression devices early after injury since it is the period of highest VTE incidence (p. 38).
Winemiller et al. (1999) examined the medical charts of 285 individuals with SCI and found that sequential pneumatic compression devices (SCD) or gradient elastic stockings were associated with a reduced risk of VTE. Multivariate analysis also suggested a decreased risk of VTE in individuals with SCI treated with heparin in the first 14 days or anytime within 42 days. Although this risk reduction was approximately twice that of SCD/gradient elastic stockings it was not statistically significant. A pre-post study by Chung et al. (2011) also examined the use of gradient elastic stockings, external SCD and early ambulation. To better examine the effectiveness of mechanical compression, individuals were not offered pharmacological prophylaxis which may have contributed to the high DVT incidence (43%) across the study.
Maxwell et al. (2002) retrospectively reviewed individuals with acute SCI for an average of 23 days following injury, who used SCD as thromboprophylaxis. The authors found the incidence of DVT and PE to be 7.1% and 2.4%, respectively.
Chronic Studies
In a small randomized controlled trial, Nash et al. (2000) compared the effects of slow SCD and rapid intermittent pulsatile pneumatic compression devices (IPC) on venous hemodynamics in subjects with complete tetraplegia. Doppler examination of the popliteal and femoral veins in each compression condition revealed significant improvements in hemodynamic parameters in both treatment groups from rest. However, resting volume flow per minute and maximal venous velocity was significantly enhanced in the IPC group. As maximal venous velocity is considered a key measure to evaluate the effectiveness of compression devices used for DVT prevention, the authors suggest that IPC is more effective than SCD. It is important to note that incidence of DVT was not recorded in this study. Therefore, further research regarding the incidence of DVT is necessary to truly determine the superiority of one method over the other.
Conclusion
There is level 1b evidence (from one RCT: Becker et al. 1987) that rotating treatment tables reduce the incidence of venous thromboembolism in individuals with acute SCI.
There is level 4 evidence (from one pre-post and two case series: Chung et al. 2011; Maxwell et al. 2002; Winemiller et al. 1999) that sequential compression or gradient elastic stockings are associated with a reduced the risk of venous thromboembolism in acute SCI individuals.
There is level 1b evidence (from one RCT: Nash et al. 2000) that rapid intermittent pulsatile compression devices are more effective than slow sequential compression devices for stimulating venous blood flow in chronic SCI individuals.
