The Role of A-V Foot Pumps in the Prophylaxis of DVT/PE in the Trauma Patient

I.   Statement of the Problem

Gardner and Fox,¹ in 1983, discovered a venous pump on the sole of the foot that consists of a plexus of veins that fills by gravity and empties upon weightbearing, thus increasing femoral blood flow without muscular assistance. A mechanical device, the A-V foot pump, has been developed to mimic this effect of weightbearing. The major advantage of this system is that it only requires access to the foot, which enables it to be used in patients with Jones dressings, casts, or externally fixed limbs that previously were unsuitable for SCD. One study has shown that the pulsatile action of the A-V foot pump increased venous blood flow velocity in the popliteal vein by 250%.²

II.   Process

With the recent clinical introduction of the A-V foot pump, there is a paucity of relevant literature related to this subject. A Medline review dating back to 1980 revealed 12 articles on A-V foot pumps. There were only four articles specifically related to the use of A-V foot pumps in the trauma patient.

III.   Recommendations

A.   Level I

There are insufficient data to suggest Level I recommendations for this topic.

B.   Level II

There are insufficient data to suggest Level II recommendations for this topic.

C.   Level III

A-V foot pumps may be used as a substitute for sequential compression devices (SCDs) in those high risk trauma patients who cannot wear SCDs due to external fixators or casts.

IV.   Scientific Foundation

Most of the studies involving the use of A-V foot pumps are found in the orthopaedic literature, and many of these series involve small numbers of patients. Bradley et al.³ in a randomized prospective trial of 74 patients undergoing total hip replacement assessed the additive effect of A-V impulse venous foot pump to prophylaxis with graduated compression stockings plus LDH plus hydroxychloroquine. All patients were submitted to bilateral ascending venography on the 12th postoperative day. The incidence of DVT was 6.6% in the pumped group and 27.3% (p<0.025) in the non-pumped group. Two patients developed pressure sores due to ill-fitting slippers in the pumped group. Stranks et al.,⁴ in a randomized prospective trial of 82 patients treated for subcapital fractures, compared the A-V foot pump to no DVT prophylaxis. The incidence of DVT as assessed by Doppler ultrasound was 23% in the control group and 0% in those using the device (p<0.0001). Postoperative swelling was also decreased significantly in the treatment group as manifested by a decreased thigh circumference of 3.27cm (p<0.001) and thigh circumference of 1.55cm (p<0.001) in the pumped group relative to the control group. This study suffers somewhat in its design in that a control group which received no prophylaxis is probably not considered a standard treatment for hip fractures with its well known high propensity to develop venous thromboembolism complications. In addition, the comparability of the groups was not presented, and 93% of the DVTs were proximal (this is not sensible). A better comparison would be to compare A-V foot pumps to standard DVT prophylaxis such as subcutaneous heparin. Such a study was done by Santori et al. ¹² in 132 patients randomized to receive heparin vs. A-V footpumps. DVT was diagnosed in 23 patients (35.4%) in the heparin group vs. 9 (13.4%) in the A-V impulse group (p<0.005). In the heparin group there was one fatal PE, and 9 patients had excessive bleeding (13.8%) vs. none in the impulse group. Potential problems with this study include 1) the use of thermography and Doppler ultrasound as outcome measures, 2) the biased application of venography (48% vs 25% of patients), 3) unblinded DVT assessment, and 4) an unblinded bleeding assessment.

Fordyce and Ling⁵ in a similar randomized prospective study compared the use of TED stockings with the A-V impulse system in 84 patients undergoing total hip replacement. Venographically-proved DVT was 40% in the TED group and 5% in the pumped group (p<0.001). Again, the study design was flawed in not providing more aggressive DVT prophylaxis in the control group. Also, they used only unilateral venography which underestimates the true DVT rates. In another prospective study⁶ that included 59 patients undergoing elective knee replacement, venography showed a 19% incidence of proximal DVT in the control group and 0% in the group treated with A-V foot pumps. Westrich and Sculco¹¹ in a Level I study, compared 122 patients (164 knees) scheduled to undergo unilateral or bilateral knee replacement and were randomized to receive either aspirin alone or A-V foot pumps and aspirin. The prevalence of DVT was 27% (22 of 81 knees) in the A-V foot pump group vs. 59% (49 of 83 knees) in the aspirin group (p>0.001). Of note, no proximal thrombi were noted in any patient using the A-V foot pump vs. a 14% incidence (p< 0.0003) of popliteal or femoral DVT in the aspirin treated group. The authors also demonstrated that the total duration of time that the device was worn was related to whether or not the patient developed a DVT. Patients in whom a DVT did not develop used the device for a mean time of 96±23.4 hours while those who developed a DVT wore the device for 67±21.1 hours (p<0.001).

Although little has been done on the effects of the A-V impulse system on DVT in trauma patients, other beneficial effects have been observed. In 71 patients who had operations or casts for traumatic lower extremity injuries, Gardner and Fox⁷ showed a significant decrease in pain, swelling and measurement of compartment pressures in the affected extremities with the use of the A-V foot pumps. In the discussion to this paper, the authors hypothesized that the increased blood flow seen with the pumps is due to hyperemia mediated by endothelial-derived-relaxing factor (EDRF) which is liberated by the endothelium secondary to sudden pressure changes such as could be caused by the A-V pumps. This EDRF release could encourage the opening of critically closed capillaries, enabling reabsorption of fluid, hence the decrease in compartment pressures. In addition, there have been reports of A-V foot pumps improving arterial blood flow with the relief of ischemic rest pain.^8,9

In a recently prospective randomized study by Knudson et al.,¹⁰ A-V foot pumps were one arm of a number of prophylactic measures (low molecular weight heparin and sequential pneumatic compression devices were the other arms) used to prevent DVT in high risk trauma patients. Of 372 patients enrolled in the study, the DVT rate was 5.7% for the A-V foot pumps, 2.5% for the SCDs and 0.8% for the low-molecular weight heparin as determined on follow-up serial duplex ultrasound. Of note, severe skin changes, including blistering and wound problems, occurred in 8/53 patients who wore the foot pumps. This required three patients to be removed early from the study because of wound and skin problems.

V.   Summary

Small clinical series in elective orthopaedic patients support the use of A-V foot pumps to prevent DVT. Only one clinical series in trauma patients compares A-V foot pumps to other standard techniques of DVT prophylaxis. The results from this series are not definitive in terms of the benefits of A-V foot pumps in preventing DVT. However, there is a theoretical advantage for the use of A-V foot pumps in the high-risk trauma patient who has a contraindication to heparin because of their injuries and who cannot have SCDs placed on lower extremities secondary to external fixators or large bulky dressings.

VI.   Future Investigations

More prospective, randomized studies are needed comparing A-V foot pumps to standard prophylactic measures in trauma patients at high risk for the development of DVT.

VI.   References

Reference Conclusions