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Comparison of the Accuracy of Emergency Department-Performed Point-of-Care-Ultrasound (POCUS) in the Diagnosis of Lower-Extremity Deep Vein Thrombosis

Nathan Denicoff, MD
Published 11/23/20

Probetrotters | Medical Education

García, Jorge Pedraza, et al. Comparison of the Accuracy of Emergency Department-Performed Point-of-Care-Ultrasound (POCUS) in the Diagnosis of Lower-Extremity Deep Vein Thrombosis. The Journal of Emergency Medicine, vol. 54, no. 5, 2018, pp. 656–664., https://doi:10.1016/j.jemermed.2017.12.020

Objective and Study Design

This was a prospective cross-sectional study and diagnostic test assessment with the goal of determining the accuracy of emergency physician-performed three-point compression ultrasound to diagnose DVT in comparison to the standard radiology-performed Doppler ultrasound.

Methods

This study was conducted between March 2012 and May 2014 in an emergency department in Spain. Patients with suspected above-knee lower extremity DVT were enrolled and risk-stratified using a Wells score and D-dimer algorithm, as shown in the article’s Figure 1 below.

Fig. 1 Proposed new diagnostic approach incorporating ultrasound to rule out DVT. DVT = deep vein thrombosis; DD = D-Dimer; ED = Emergency Department; US = Ultrasound

* note the DD- and DD+ under “3 point ultrasound in the ED” should be US- and US+

Figure 2: Three-point compression ultrasound anatomy[1]

Those with a low Wells score of <2, indicating DVT unlikely, were tested with a D-dimer. If the D-dimer was negative, no further testing was pursued. If positive, patients underwent three-point compression ultrasound, with the sites of compression highlighted the figure below. If US positive, patients were anticoagulated and followed up with a Doppler US within 48 hours. If US negative, they were not anticoagulated, but were still followed up with Doppler within 48 hours. For patients with a moderate/high risk of DVT on the modified Wells score, all were tested with D-dimer, ED ultrasound, and follow up Doppler. All patients who underwent compression ultrasound were followed up in a DVT clinic for one year to monitor for complications and resolution of the DVT.

Results

As per the above algorithm, 109 patients underwent an EM-performed compression ultrasound. The results are summarized in the article’s Figure 2:

These results demonstrate that POCUS DVT is an effective diagnostic method, as summarized in Table 1:

Table 1: Diagnostic accuracy of POCUS DVT

Discussion and Limitations

Extensive training and practice in POCUS DVT prior to data collection may skew the results towards increased accuracy and limit generalizability to physicians less experienced in this diagnostic method.
The study was conducted in Spain, which may limit generalizability to other populations.
The study identifies the following pitfalls in accurate diagnosis of DVT by compression ultrasound: not placing the probe perpendicular to the skin when compressing, patient obesity or edema, and mistaking a lymph node or Baker’s cyst for a DVT.
Both the POCUS and Doppler ultrasounds did not examine the calf veins, which may not in fact be problematic, as these distal DVTs may not have clinical significance, with lower risk of embolization.
Incorporation bias: the gold standard test, the Doppler ultrasound, incorporates or relies on the studied test, the three-point compression ultrasound. The up to 48 hour delay in Doppler may allow for proximal DVTs identified on POCUS to resolve prior to Doppler, or for unidentified distal DVTs to extend proximally, thus changing the result. This limitation could have been mitigated by performing a Doppler ultrasound minutes after the POCUS, but this was likely not feasible.
Convenience sampling rather than consecutive sampling was used, as there were times when no POCUS-trained attendings were in the department, such as from midnight to 8am.

Takeaways

With sufficient training, emergency physicians can effectively use three-point compression ultrasound to diagnose proximal lower extremity DVTs.
POCUS DVT is less time consuming than comprehensive ultrasound, and it was performed in an average of five minutes in this study. This speed can reduce ED length of stay.
POCUS DVT can be especially helpful at times when radiology technicians are not in the hospital to perform a Doppler ultrasound, which is often the case at night.
While not touched upon in this study, POCUS DVT is also part of the expanded RUSH exam (Rapid Ultrasound for Shock and Hypotension) when PE is suspected.[2] This significantly broadens the potential applications of POCUS DVT in my clinical practice to patients with undifferentiated shock with concern for PE.
This study was initiated in 2008 at a time when the attending physicians may not have had much experience with ultrasound, and they benefited from dedicated training prior to this study. Today, EM residency programs have much more robust ultrasound teaching and higher expectations of residents’ ultrasound skills. This study is convincing evidence that I should make POCUS DVT part of my practice as a resident, and that I should perform this study consistently in order to become proficient.

References

Ahn J and Dinh V et al. DVT Ultrasound Made Easy: Step-By-Step Guide. POCUS 101. www.pocus101.com/dvt-ultrasound-made-easy-step-by-step-guide/.
Seif D, Perera P, Mailhot T, et al. Bedside ultrasound in resuscitation and the rapid ultrasound in shock protocol. Crit Care Res Practice. 2012;2012:503254. https://emcrit.org/wp-content/uploads/2011/03/New-RUSH-Review-Article1.pdf

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