Venous Thromboembolism: Role of Ultrasound in Diagnostic Imaging for DVT in Trauma

Authors

Rogers, Frederick B. MD; Cipolle, Mark D. MD, PhD; Velmahos, George MD, PhD; Rozycki, Grace MD; Luchette, Fred A. MD

Author Information

From the University of Vermont, Department of Surgery, Fletcher Allen Health Care (F.B.R.), Burlington, Vermont, Department of Surgery, Lehigh Valley Hospital (M.D.C.), Allentown, Pennsylvania, Department of Surgery, Division of Trauma and Critical Care, University of Southern California (G.V.), Los Angeles, California, Department of Surgery, Emory University School of Medicine, Atlanta, Georgia, and Department of Surgery, Division of Trauma, Critical Care, and Burns, Loyola University Medical Center (F.A.L.), Maywood, Illinois.

Submitted for publication September 1, 2001.

Accepted for publication March 15, 2002.

Any reference in this guideline to a specific commercial product, process, or service by trade name, trademark, or manufacturer does not constitute or imply an endorsement, recommendation, or any favoritism by the authors or EAST. The views and opinions of the authors do not necessarily state or reflect those of EAST and shall not be used for advertising or product endorsement purposes.

Address for reprints: Frederick B. Rogers, MD, University of Vermont Department of Surgery, Fletcher Allen Health Care, 111 Colchester Avenue, Burlington, VT 05401; email: frederick.rogers@vtmednet.org.

Statement of the Problem

Early identification of DVT in trauma patients would allow treatment to be initiated and decrease the frequency of complications. Ultrasound scanning has the advantage as a diagnostic tool to detect DVT because it is noninvasive, requires no contrast medium, can be performed at the bedside, and is able to detect nonocclusive thrombus. Two types of ultrasound scanning will be discussed. Doppler ultrasound involves a hand-held probe placed over the skin of the vein being studied. Duplex ultrasonography uses real-time B-mode sonography that produces a two-dimensional image using high-frequency sound waves and Doppler ultrasound. The addition of color flow to duplex provides additional advantages. It may help with identification of the deep venous system, especially the veins below the knee. Partially occluding thrombi may be noted as a defect in the lumen's color, and completely occlusive thrombi as the absence of color from the vein. It is important for the reader to distinguish between these two technologies for accuracy of ultrasound to detect DVT. Furthermore, in the critical review of ultrasound technology in detecting DVT, a dichotomy exists in the sensitivity of ultrasound in symptomatic versus asymptomatic patients.

Process

A MEDLINE search from 1966 to the present revealed several thousand articles related to the diagnosis of DVT using ultrasound. Several of the more seminal articles and review articles related to the ultrasound diagnosis of DVT in the nontrauma patient are included to provide a perspective on the current state of the technology. Sixteen articles related to the ultrasound diagnosis of DVT in the trauma patient are discussed in this review (Table 7).

Recommendations

A. Level I: Duplex ultrasound may be used to diagnose symptomatic trauma patients with suspected DVT without confirmatory venography.^[83][84]

B. Level II: A Level II recommendations cannot be supported on this topic because of insufficient data.

C. Level III: Serial duplex ultrasound imaging of high-risk asymptomatic trauma patients to screen for DVT may be cost-effective and may decrease the incidence of PE.^[15][85-90]However, the use of ultrasound in screening asymptomatic patients is burdened by a low sensitivity when compared with venography.^[7][91][92]

Scientific Foundation

A. Ultrasound Diagnosis of DVT in the Nontrauma Patient

1. Doppler Ultrasound.

The use of a Doppler flowmeter for the diagnosis of DVT has some appeal because of its relatively low cost and the additional benefit of being able to be performed at the bedside or on an outpatient basis. The accuracy is very much dependent on the experience of the user.^[83] Wheeler and Anderson^[84] compiled a meta-analysis of 23 studies examining the accuracy of Doppler ultrasound compared with venography. Overall, in symptomatic patients, Doppler ultrasound had a sensitivity of 85% (722 of 847) and a specificity of 88% (1,415 of 1,615) to detect proximal DVT.

2. Duplex Ultrasound.

Duplex ultrasound using both real-time B-mode scanning and Doppler ultrasound allows for noninvasive visualization of the veins of the leg. In most patients, it is easy to visualize the common femoral, proximal superficial femoral, and popliteal veins. It can be difficult to visualize the superficial femoral vein in Hunter's canal and also to detect calf DVTs. An acute DVT is identified by the presence of a dilated vein, lack of compressibility, and absence of Doppler flow sounds. Again, the technical quality of the study is very much user-dependent. In patients who present with symptoms of DVT, ultrasound has a high sensitivity and specificity. Comerota's collective review of 25 studies in which duplex was used to diagnose proximal DVT in symptomatic patients had a sensitivity of 96% (1,132 of 1,178) and a specificity of 96% (1,384 of 1,450).^[31] In the 10 series in which duplex was used to diagnose calf DVT in symptomatic patients, it had a sensitivity of 80% (122 of 153).

In asymptomatic high-risk patients, duplex ultrasound does not appear as accurate as a screening technique for DVT; however, the reports are quite variable in success rates. Most of these studies have been performed in orthopedic patients undergoing elective surgery. Agnelli et al.^[91] attempted to shed some light on the diagnostic accuracy of duplex ultrasonography in patients with asymptomatic DVT by performing an overview on the studies, taking into account their study methodology. A study was classified as Level I if consecutive patients were admitted, bilateral venography was performed, and ultrasonography was performed and judged before venography. Studies not fulfilling these criteria were considered Level II. Overall, there were four Level I studies and eight Level II studies (Table 8).

B. Ultrasound Diagnosis of DVT in the Trauma Patient

Several studies exist on the use of ultrasound to screen for DVT in asymptomatic patients at high risk for DVT. Unfortunately, most of these studies had significant methodologic flaws, and few if any used a confirmatory venogram to check the accuracy of their techniques. Of additional concern was the fact that several of these series reported on a number of PEs that occurred in the absence of documented DVT, leading to speculation on the possibility that ultrasound screening missed a clinically significant DVT. One must be reminded, however, that other sources of PE, such as the upper extremity and heart,^[93] would not be picked up by ultrasound of the lower extremity. Prandoni and Bernardi^[93] noted that upper extremity DVT accounts for 1% to 4% of all DVTs and that PEs can occur in up to 36% of these cases. Nevertheless, these ultrasound studies do offer a glimpse of the incidence of the occult DVTs that occur in high-risk trauma patients, and they provide additional data as to their location and origins as well as the role that prophylaxis plays in decreasing the incidence of DVT.

Burns et al.^[85] performed a comprehensive color Doppler ultrasound examination twice weekly of all major venous structures in 57 patients classified as high risk during an 8-month period. Both upper and lower extremities were examined as well as the internal jugular, subclavian, and axillary veins; the inferior vena cava; and the common iliac, internal, and external veins. Twelve high-risk trauma patients (21%) were identified as having occult DVT. A complete ultrasound examination was unable to be attained in 23% of patients. No confirmatory study was performed in those who tested positive on ultrasound. Of note, there were two PEs in this high-risk patient group (confirmed by pulmonary angiography), and both patients at the time had screened negative for DVT. Napolitano et al.^[86] retrospectively reviewed the results of biweekly duplex screening in 458 trauma patients admitted to their ICU over a 5-year period. The incidence of DVT was 10%, and all were asymptomatic. Multiple logistic regression revealed age, length of stay, spinal cord injury, ISS, and TRISS scores as being significant risk factors for the development of DVT. No confirmatory study was used in those patients who tested positive for DVT, and a PE occurred in this population. In a commentary that accompanied the article, Knudson pointed out several methodologic flaws with the study. The issues were the timing of the scans obtained, the retrospective nature of the study, and the use of only ICU patients in the screening protocol, which introduces a bias eliminating other high-risk patients such as those with pelvic or lower extremity fractures that may not need ICU admission.

Meythaler et al.^[87] performed a cost analysis of routine screening for proximal DVT using color-Doppler ultrasound in 116 head-injured patients being admitted to a rehabilitation unit over a 21-month period. Fourteen (8.5%) patients were found to have DVT on initial screening. No confirmatory studies were performed and all were asymptomatic. The authors conducted a complicated cost-benefit analysis of ultrasound screening for DVT in this population and found that the cost per year of life saved was $2,977.65 ($129,527.83/43.5 years). This compared favorably to the $8,280 per year of life saved for biennial mammograms for women aged 50 to 59 years and the $35,054 per year of life saved for annual fecal occult blood tests beginning at age 65. As is indicative of such an analysis, a number of underlying assumptions exist that may not reflect reality; nevertheless, it does lend perspective on the cost issues relative to other screening programs.

In a study of 60 patients with major fractures of the pelvis, White et al.^[88] performed serial duplex sonography to determine the incidence of DVT. In this study, confirmatory contrast venography was used in those who tested positive for DVT on ultrasound. Eight (15%) patients developed DVT, of which six were proximal and two were distal (calf). All were asymptomatic for DVT. One PE presented in this population in a patient who subsequently tested positive for a proximal DVT. One weakness of the study was that the screening ultrasound was first performed 7 days after admission. The authors stated that they checked the accuracy of duplex ultrasound as a screening test in 32 high-risk orthopedic patients (including those with lower extremity and pelvic fractures) by comparing it to ascending venography. Eleven patients had positive duplex sonograms, and all had positive venograms. One patient had a negative duplex but a positive venogram. Overall, the predictive value of a positive duplex sonogram in this study population was 100% (11 of 11) and that of a negative duplex sonogram was 95% (21 of 22).

Chu et al.^[94] looked at the 21 spinal cord-injured patients admitted to a rehabilitation unit over an 11-month period who were screened with Doppler ultrasound and impedance plethysmography on alternate weeks. Only two patients developed DVT during an 8-week period, and both were detected clinically before diagnostic testing. It should be noted that this study somewhat contradicts other studies of DVT in spinal cord-injured patients in which the incidence of DVT approached 100%.^[95][96] In addition, the authors of this study used Doppler ultrasound with an unknown sensitivity and specificity as a screening procedure in the asymptomatic patient.

Meredith et al.^[89] looked at the incidence of DVT with femoral vein catheterization using 8.5 French Swan-Ganz introducer catheters. Patients were followed with serial duplex ultrasonography. Not surprisingly, these large-bore catheters were associated with a 14% iliofemoral DVT rate on the side of the catheter. All were clinically occult.

In a study examining modes of prophylaxis in 281 high-risk trauma patients, Dennis et al.^[7] scanned for DVT at admission and every 5 days thereafter with a duplex scanner or Doppler ultrasound. Approximately 25% were scanned using duplex and 75% using Doppler. The authors did not indicate the reason for different modes. No confirmatory study was performed in patients who tested positive on ultrasound, and in 20% of examinations the study was incomplete. There were 18 cases of DVT (4.6%) and 4 cases of PE (1%) in the absence of DVT, three of which were fatal. Of concern in all three fatal PEs, none had shown evidence of DVT on routine surveillance with ultrasound before their deaths. In a similar prospective study examining prophylaxis of DVT in trauma patients, Knudson et al.^[15] used serial duplex ultrasound to detect thigh vein thrombus. In a few cases, the authors used venography to confirm a positive duplex result that was 100% accurate. Overall, approximately a 10% DVT rate was reported, but again there were four cases of PE in the absence of detectable DVT, leading to speculation on the sensitivity of duplex to detect clinically significant DVT. In a larger study, again examining modes of DVT prophylaxis in trauma patients, Knudson et al.^[3] used weekly serial duplex ultrasound as the diagnostic modality to detect DVT. Of 251 patients in this randomized prospective study, 15 (6%) developed DVT as detected by duplex. Only 20% had clinical symptoms of DVT, and the rest were occult. Again, two patients developed PE, one of which was fatal, after repeated negative ultrasound examinations.

Brasel et al.^[90] examined the cost-effectiveness of biweekly ultrasound screening versus placement of prophylactic VCFs on reducing PE in high-risk trauma patients using a decision-tree type of analysis. The authors found that ultrasound was more cost-effective than VCF, with a cost per PE prevented of $46,3000 versus $97,000. However, ultrasound screening became more expensive than VCF when the anticipated length of stay was greater than or equal to 2 weeks. Again, a number of assumptions exist that underlie such a decision-tree analysis that may not reflect clinical reality. In contrast, Satiani et al.^[97] concluded that the cost ($18,586 per DVT identified) of routine screening did not justify its use in patients receiving routine prophylaxis.

Summary

Numerous studies in the nontrauma literature attest to the overall accuracy of both Doppler and duplex ultrasound in the detection of DVT in the symptomatic patient. The overall accuracy of screening ultrasound in the asymptomatic patient is less clear. Many reports on the use of screening ultrasound (either Doppler or duplex) lack corroboration of accuracy with contrast venography. Of concern is that many of these studies report on PEs in the presence of negative screening ultrasound examinations, leading one to speculate on the ability of duplex to detect clinically significant DVT.

Future Investigation

To serially screen all trauma patients for DVT is not cost-effective; therefore, the high-risk trauma patient who is prone to develop DVT likewise needs to be identified. The emphasis in future research ought to be placed on (1) identifying the source of DVT in patients with negative duplex but who develop PE, (2) cost-effectiveness of ultrasound screening in high-risk patients, (3) determining the clinical significance of asymptomatic calf DVT, and (4) the role of serial duplex in calf DVT progression and in patients with equivocal ultrasound examinations.

Acknowledgment

We thank Jody Ciano for her help in the preparation of this article.

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Ultrasound