The Use of Sequential Compression Devices (SCD) in the Prevention of DVT/PE

I.   Statement of the Problem

The role of intermittent sequential compression devices (SCDs) for prophylaxis against DVT has been studied and increasingly utilized in general surgery patients, ¹ orthopedic patients,^2-4 and trauma patients.^5-8

Attacking the long-recognized risk factor of stasis, SCDs have been shown to increase mean and peak femoral venous blood velocities on the lower extremity. ^9,10 Additionally, SCDs have been shown to have a direct effect on the fibrinolytic pathway acting to shorten the euglobulin lysis time, increase levels of coagulation cascade inhibitor molecules, as well as affecting the balance of plasminogen activation.^12-14 In a number of prospective, randomized studies, SCDs have been shown to reduce the incidence of both DVT and PE.^3,6,15,16 Unanswered questions regarding the use of SCDs include the mechanism by which SCDs act, the efficacy of SCDs worn on the upper extremities or a single lower extremity compared to both lower extremities, the nature of risk involved in discontinuing SCDs periodically during use, and the duration of SCD use. Reports suggest that SCDs should be worn with thromboembolism-deterrent stockings (i.e. TEDS), however, this practice has not been widely studied and is not standard. Complications of SCDs have been noted in case reports and have been associated with improper positioning of the lower extremity during surgery which should be avoided.

II.   Process

A Medline search from 1986 to the present produced a large number of articles on this topic. Those articles pertinent to trauma-related thromboembolism prevention were reviewed. Twenty-three of these articles were evaluated to formulate the following guidelines.

III.   Recommendations

A.   Level I

There are insufficient data to support Level I recommendations on this topic.

B.   Level II

Trauma patients at high risk for DVT, such as head-injured patients or those with spinal cord injury and ortho-trauma patients such as pelvis or hip fracture patients, can receive SCDs for prophylaxis against DVT.

C.   Level III

1.   For patients in whom the lower extremity is inaccessible to place SCDs at the calf level, foot pumps may act as an effective alternative to lower the rate of DVT formation.

2.   Patients who have surgery in lithotomy position or have evidence of significant weight loss should have precautions taken in positioning to prevent the occasional complications of peroneal nerve compression.

IV.   Scientific Foundation

Since their description in 1858 by Rudolf Virchow, the factors that are felt to form the basis of the pathophysiology of venous thromboembolic disease are stasis (reduction of blood flow in the veins), injury (to the intimal surface of the vessel) and hypercoagulability. Scientific and clinical evaluations of SCDs strongly suggest that the nature of their effect on DVT prophylaxis derives from their ability to increase mean and peak femoral vein velocity as well as their effect on the systemic coagulation and fibrinolytic mechanisms.

The sequential pattern of compression has been well described: chambers of the extremity garment are sequentially inflated from ankle to knee (or mid thigh) to a maximum pressure of 45-50mm Hg at the ankle, 35 mm Hg at the calf, and 30mm at the thigh (hence the term "gradient" compression). The duration of compression is 11 seconds with a 60 second relaxation period between compressions.

Keith et al.⁹ measured peak venous velocity (PVV) at the common femoral vein in postoperative (non-trauma) patients and in healthy control subjects using Doppler ultrasound. In the control subjects, PVV was increased from a mean velocity of 23.8 cm/sec at rest to 45.5 cm/sec with knee-high SCDs and 53.2 cm/sec with thigh-high SCDs. In postoperative patients, the PVV was similarly raised from a resting velocity of 21.8 cm/sec to 55.1 cm/sec. In both of these evaluations, the differences were statistically significant when compared to controls and were not further augmented by the concomitant use of compression stockings (e.g. TEDS). Spectral recording of blood flow velocity during inflation and deflation of the SCDs reveal a temporal association with inflation and increased PVV which suggests a mechanical effect derived from inflation of the SCDs. Another study examined the role of SCDs on femoral vein flow velocity in patients undergoing laparoscopic abdominal procedures.¹⁰ It was noted that the effect of pneumoperitoneum to lower the velocity of flow through the femoral vein could be abrogated with the use of lower extremity SCDs.

Several studies in the selected bibliography^12-14 have evaluated in vivo fibrinolytic effects of SCDs. Inada et al.¹² reported a prospective study comparing euglobulin lysis times and a fibropeptide concentration in a cohort of cancer patients with and without SCDs. Both of these measurements are non-specific indicators of the relative activity of the fibrinolytic pathway in humans. They showed that the presence of SCDs vs. no-SCDs shortened the euglobulin lysis time and by the fifth postoperative day had increased the fibropeptide concentration suggesting increased plasminogen activity. In a well-designed study, Jacobs et al.¹⁴ showed that euglobulin lysis times were not reproducible as a marker for fibrinolytic activation, and their study focused on measured changes in tissue plasminogen activator (tPA), plasminogen activator inhibitor (PAI-1) and tPA-PAI-1 complex. They demonstrated a significant increase in tPA-PAI-1 (hence an obligatory decrease in PAI) in patients undergoing SCD and postulated a (complex and incompletely proven) role of SCDs in the systemic balance of plasminogen activation and inhibition. In Jacobís study, they found that fibrinolytic activity begins to decay within minutes of discontinuing SCDs. This observation has important clinical implications in that SCDs must be worn continuously in order to avoid rapid decay in fibrinolytic activity. A recent study has documented patients in whom SCDs have been ordered, spent less than 50% of the time actually wearing the devices, possibly decreasing their effectiveness.¹⁷ Another important finding in Jacobís study was that there appeared to be an incremental decrease in fibrinolytic activity when blood was sampled in sites remote form the area of placement of the SCDs. This difference in local and systemic effects has important implications on the ability of SCDs worn on the arms to prevent DVT in the legs.

Hoppensteadt et al.¹³ studied levels of tissue factor pathway inhibitor (TFPI) in surgical patients before and after one hour of intermittent pneumatic compression. The authors describe TFPI as the key feedback inhibitor of the extrinsic activation of coagulation, a protease molecule which acts by binding to Factor Xa to inactivate the TF-FVIIa complex. They demonstrated a significant increase in TFPI concentrations in patients following pneumatic compression. The authors describe TFPI as being stored intima-bound on the endothelial cells, and suggest its release is mediated from these cells by the action of SCDs. This would represent a speculative mechanism whereby SCDs have a direct inhibitory effect on thrombin generation as well as the primary effect on flow enhancement.

There is a paucity of studies specifically regarding the use of SCDs in the multiply-injured trauma patient. In a prospective study in which 113 trauma patients received either SCDs and TED stockings or low dose heparin (LDH), Knudson et al. ⁵ showed a 12% rate of venous thromboembolism (VTE) in the SCD vs. 8% in the LDH group, which was not significantly different. This study did not demonstrate that either method of attempted prevention (LDH or SCD) was better than no prophylaxis. Dennis et al.,⁶ in a prospective, nonrandomized study of 395 trauma patients admitted with an ISS > 9 who received either SCD, LDH or no prophylaxis, demonstrated a VTE rate of 8.8% in the no prophylaxis group, 2.7% with SCD and 3.2% in the LDH group. There was no statistically significant difference in VTE rate in the prophylaxis groups, but there was a significant difference in those who received prophylaxis vs. no prophylaxis (p<0.02). Two very high risk groups seemed especially to benefit from prophylaxis were the head and spinal cord-injured patients. Overall risk reduction of VTE with prophylaxis was from 16.7% to 1.4% in head injured patients and from 27.3% to 10.3% in spinal cord-injured patients. The study suffers from the fact that there were randomization problems during the course of the study in which 67 patients (37%) originally assigned to receive no prophylaxis were switched to receive some sort of prophylaxis at the discretion of the attending surgeon. In a prospective trial, Knudson et al.¹⁸ compared SCD, LDH and no prophylaxis. Neither LDH or SCD appeared to offer any protection to multiply-injured trauma patients, except in the specific subgroup of patients with neurotrauma in which SCD was more effective than control in preventing DVT (p=0.057). In contrast to Knudsonís study, Gersin et al.⁷ in a non-randomized prospective study, looked at the incidence of VTE in a group of 32 severely head-injured patients(GCS < 8). Fourteen patients received SCD and 18 did not because of concomitant lower extremity fractures. Within the group receiving SCD, four (28%) developed PE; none developed DVT. In the group not receiving prophylaxis, two developed PE and two developed DVT. Although the study population was small, the findings in this study call into question the efficacy of SCD even in severe head-injured patients. In a group of 304 orthopaedic trauma patients with hip and pelvic fractures, SCDs were found to reduce thromboembolic events significantly over those who had no prophylaxis (11% vs. 4%; p=0.02). In subgroup analysis, SCD was only effective in the hip fracture group, not in those with pelvic fractures.

Compression devices appear to be well-tolerated with minimal side effects. Isolated case reports of pressure necrosis from a too tightly fitted SCD have been reported. ¹⁹ Also peroneal palsy and compartment syndromes have been reported with SCDs. ²⁰ A potential complication of SCD is to elevate intracranial pressure in those patients with severe head-injury. This question was addressed by Davidson et al.²¹ in 24 severely brain-injured patients (mean GCS=6) who had intracranial pressure (ICP) and cerebral perfusion pressure (CPP) calculated after 0, 10, 20, and 30 minutes of intermittent pneumatic leg compression. The authors found no significant increase in ICP or CPP at any time points studied with the use of SCDs, and concluded that SCDs can be used safely in stable head-injured patients.

VI.   Summary

The use of SCDs worn on the lower extremity in patients at high risk for DVT and to reduce the rate of DVT is widely accepted, however, clinical studies demonstrating their effectiveness in trauma patients are few. While the exact mechanism of action of SCDs is not known, their effect is felt to be based on a combination of factors addressing stasis and hypercoagulability. Until these mechanisms are better studied and understood, answers to specific questions regarding the appropriate use of SCDs are forthcoming.

VII.   Future Investigation

More studies need to be done specifically related to the use of SCDs in trauma patients at risk for VTE. Questions regarding the efficacy of using the device on one lower extremity vs. two, and whether an arm vs. a leg provides equal protection, all need to be addressed. There are a number of commercial vendors of compression devices. Whether they all provide equal protection or one vendor is superior needs to be determined. Finally, the role of multimodality therapy (mechanical and pharmacologic) to provide any additional protection from VTE needs to be ascertained.

VI.   References

Reference Conclusions