3 Point Ultrasound Study to Rule out DVT

3 Point Ultrasound Study to Rule out DVT

Abstract

Study objective:

This study was performed to evaluate whether emergency medicine physicians are able to use a quick(less than 10 minute) 3 point method to evaluate and accurately diagnose DVT in patients, so that they are able to treat the patients that are positive in a timely manner.

Methods:

This was a prospective study of a small sample of ED patients with suspected lower extremity dvt, performed at a single center, community hospital with an emergency medicine residency program. The bedside ultrasounds were obtained by the emergency medicine residents, after a short didactic lecture and hands on training session. The ED ultrasound exam was performed prior to the patient having a formal venous duplex scan performed by the ultrasonographer in the radiology department. Formal ultrasound exam was read by board certified radiologists. ED exam included transverse views with and without compression obtained at 3 specific points, to evaluate the common femoral, superficial and popliteal veins. Results were recorded on a survey form and at the conclusion of the study they were compared to the formal radiologic report.

Results:

A total of 29 patients were evaluated for DVT from 4/2015 to 9/2015 by 6 emergency medicine residents. Three studies were rejected, as there was no formal study ordered for evaluation of DVT. Out of 26 patients there were 23 true negative studies, 2 true positive studies, 1 false negative study, and zero false positives. Our study shows a sensitivity of 66.67% (95% CI 9.43 to 99.16%), and specificity 100% (95% CI 85.18 to 100%) overall for DVT. Our positive predictive value is 100% (95% CI 15.81 to 100%) and a negative predictive value of 95.83% (95% CI 78.8 to 99.89%). Emergency medicine residence performed well when comparing inter-rater reliability (κ = 0.78, SE = 0.211, 95% CI 0.367 to 100%).

Conclusion:

This was a limited study with poor power secondary to the ultrasound linear transducer breaking, as well as not having the machine available to the residents for an extended period of time during the time period that our study was taking place. However, we feel that our study demonstrates that emergency medicine residents seem to perform well when compared to radiologists when evaluating for DVT.

Introduction

Deep venous thrombosis (DVT) falls within a spectrum called venous thromboembolism (VTE), which carries significant risks for morbidity and mortality. Complications related to DVT are recurrent DVT, postphlebitic syndrome, phlegmasia cerulean dolens, phlegmasia alba dolens, pulmonary embolism.(1, 6) From 2006-2009, there was an estimated annual visit of 123,000 patients to emergency departments with a primary diagnosis of DVT. (10) The total annual health care cost for DVT is an estimated $7.5 to $39.5 billion dollars. (8) It is a disease process that is costly and carries significant health complications, which has driven research towards bedside ultrasound for quicker disposition and treatment in the emergency department.

This has been well studied in large academic centers, with physicians and residents who may not have had formal ultrasound training, with good results. (2-5, 7, 9) Unfortunately, there are many community hospitals that do not have accessibility to ultrasound overnight. Our goal would be to investigate the accuracy of 3-point bedside ultrasound screening for DVT by emergency medicine residents, in a community hospital setting, trained by a certified ultrasound technician.

Materials and Methods

This was a prospective study designed to evaluate whether emergency medicine trained physicians can accurately diagnose deep venous thrombosis(DVT) by performing a limited 3 point DVT exam using bedside ultrasound in the emergency department, when formal ultrasound is not available.

This study was performed at a small community hospital in York, Pennsylvania with an emergency medicine residency program, and an annual ED census of approximately 50,000 patients. The exams were performed by the residents in the program. Residents in the program undergo a limited formal two week ultrasound rotation in their second year of training, where they learn and practice how to perform the basic exams used in ultrasound. Emergency Medicine attendings and midlevel providers did not take part in the study.

The residents involved in the study underwent a short didactic lecture, as well as a hands on demonstration on how to perform the 3 point compression venous duplex above the calf ultrasound exam. The lecture included the anatomy of the lower extremity, a short explanation of how to obtain the views needed for the study, and images of normal versus abnormal studies. Both the didactic lecture and the hands on training was provided by a senior emergency medicine resident who is also RDMS certified from a previous career as an ultrasound technologist. The residents were shown the 3 points to obtain an image and how to perform the compression views. Each resident had time to practice obtaining the images on a live model to become comfortable performing the exam. A total of 6 residents were took part in the exam. The intern class of residents were not included, as they were on scheduled rotations outside of the emergency department at the time the study took place. The senior resident who is RDMS certified was excluded from taking part in the study.

Patients selected for the study, were self-referred patients that presented to the ED between April 2015 and September 2015. Patients were enrolled in the study after a medical history and physical exam was performed by the emergency medicine resident involved in the case. Inclusion criteria for the exam included patients in which a formal venous duplex study of the lower extremity was ordered. Patients in the study also had to have documented suspicion for dvt to include: 1) patient reported lower leg pain and swelling; 2) leg swelling, edema, or tenderness of leg noted by physician on their physical exam; 3) suspicion of possible PE. The only exclusion criteria was patients who had a known diagnosis of a recent deep venous thrombosis.

The bedside ultrasound exam was performed by the resident prior to the patient having their formal ultrasound scan obtained in the radiologic department. Results were recorded on a survey form that included the date, the medical record number of the patient, the initials of the resident performing the exam, and the 3 views obtained where the resident could record positive or negative results.

The resident emergency medicine residents in this study performed their bedside studies on a GE Logiq e (Wisconsin). Views were obtained using the 8MHz linear probe. Transverse views were obtained at the groin to evaluate the common femoral vein, mid-thigh to evaluate the superficial femoral, and posterior to the knee to evaluate the popliteal vein. Compression views were performed at each level to evaluate for thrombus within the vessel. The exam was considered to be positive if there was visualized thrombus within the vessel or if the vessel was non-compressible. Non compression of a vessel was defined as the anterior wall not coming in contact with the posterior wall of the vessel when pressure was applied with the transducer.

After performing the exam, the resident then recorded their results on the survey form and placed it within the collection envelope. Each resident was instructed to record their results prior to obtaining the formal radiologic performed exam and/or visualizing the formal ultrasound report. At the conclusion of the study, the survey forms with the results of the emergency medicine resident’s exams were compared with the formal radiologic report findings that were read by board certified radiologists.

Results

During the study period from April 2015 to September 2015 a total of 29 patients were evaluated for DVT by emergency medicine residents. Residents performed three-point ultrasonography on leg of concern, and then filled out a study survey. Survey was then placed in an envelope for evaluation. Resident evaluations were compared to official report as performed by an ultrasound technician and read by a board certified radiologist. Three studies were rejected, as there was no formal study ordered for evaluation of DVT. Out of 26 patients there were 23 true negative studies, 2 true positive studies, 1 false negative study, and zero false positives. The patient with the false negative study was found to have a DVT in the superficial femoral vein. One patient was found to have a chronic DVT of the opposite leg evaluated by our resident, as our institution requires bilateral evaluation when sent for formal DVT studies. This study was counted as a true negative.

Our study shows a sensitivity of 66.67% (95% CI 9.43 to 99.16%), and specificity 100% (95% CI 85.18 to 100%) overall for DVT. Our positive predictive value is 100% (95% CI 15.81 to 100%) and a negative predictive value of 95.83% (95% CI 78.8 to 99.89%). Emergency medicine residence performed well when comparing inter-rater reliability (κ = 0.78, SE = 0.211, 95% CI 0.367 to 100%).

Unfortunately the study sample is small secondary to technical problems with our ultrasound machine, which was removed from the emergency department for an extended period of time.

Discussion

In our study it is difficult to obtain an accurate conclusion. In the small community setting where residents are relied upon to help evaluate, diagnose and disposition patients at a fast pace, taking the time to perform an ultrasound study when ultrasonography is available 24 hours a day may not be the best use of a resident’s time. However residents did obtain valuable skills with both knobology and technique when it comes to ultrasonography.

Results show that residents performed relatively well when compared to studies performed by an ultrasound technician and read by a radiologist. Our one false negative study was a patient who had a superficial femoral artery blood clot.

Our study used a three-point approach for DVT detection. We did not have residents evaluate from common femoral through and into the superficial femoral vein, which could explain the one false negative obtained. However technique and inexperience may have played a role.

This study was limited by a small sample size. Technical problems with our ultrasound machine, and a busy work environment may be the culprit. Our machine underwent repairs during several months of this study. Also residents were more likely to send a patient to the radiology suite during a busy shift foregoing their own study for time management issues.

Selection bias also comes into play in our study. Residents were allowed to select patients that they felt had a high pre-test probability of having a DVT. This in turn may have resulted in an increase number of true negative studies. We did not perform a chart review of the patient’s symptoms or co-morbidities. Residents also filled a formal survey that they would submit after they completed their study and before official radiologist read was obtained. This was to be done anonymously, however during chart review, ordering physician (resident) of the formal study would be revealed. All residents had access to the folder within the ED with their survey. We feel it is unlikely, but a resident may have filled their study after formal reading was obtained.

In conclusion residents seem to perform well when compared to radiologists when evaluating for DVT. Complete evaluation of common femoral vein and superficial femoral vein should be obtained in the bedside study for completeness.

Works Cited

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