Welcome to another ultrasound-based case, part of the “Ultrasound For The Win!” (#US4TW) Case Series. In this peer-reviewed case series, we focus on real clinical cases where bedside ultrasound changed management or aided in diagnoses. In today’s case, a 74-year-old woman presents to the Emergency Department with painful right arm paresthesias.
A 74-year-old female with history of atrial fibrillation presents to the Emergency Department with 45 minutes of painful right arm tingling that are now resolving. She has been off warfarin for the past 2 weeks for knee surgery. She reports no right arm weakness or color change. She reports left shoulder pain 12 hours prior to presentation. No complaints of shortness of breath or chest pain.
- BP 150/52 mm Hg left arm, 30/- mm Hg right arm (automatic BP cuff)
- P 96 bpm
- RR 18 respirations/min
- O2 94% on room air (left arm); 85% on room air (right arm)
- T 37.3 C
- Right arm:
- No palpable radial or brachial pulses
- Normal strength and sensation
- Capillary refill 3 seconds
- Left arm:
- Normal radial and brachial pulses
- Normal strength and sensation
- Capillary refill <2 seconds
- Lower Extremities:
- Normal and symmetric bilateral femoral, posterior tibial and dorsalis pedis pulses.
- Normal strength and sensation bilaterally
- Cardiac and lung exams:
- Arterial thromboembolism of right arm
- Stroke/cerebrovascular accident
- Thoracic aortic dissection
Labs revealed a subtherapeutic INR of 1.5. A CT angiogram of the chest and abdomen was performed due to concern for possible dissection versus thromboembolism, and revealed:
- No evidence of thoracic aortic dissection
- Normal right brachiocephalic artery seen to axillary artery
- Multiple areas of atherosclerotic disease
POINT-OF-CARE (POC) ULTRASOUND
Given the ongoing concern for possible thrombo-embolic disease, a point-of-care ultrasound of the right upper extremity was performed:
Axillary artery visualized with pulsations in B-Mode (left) and with color doppler (right)
With significant external compression with the probe, a visualized thrombus (blue arrow) is seen within a non-compressible brachial artery
ULTRASOUND IMAGE QUALITY ASSURANCE (QA)
Ultrasound evaluation of the vascular system in the extremities is performed using the high-frequency linear transducer. It is important to optimize positioning of the patient when performing any point-of-care ultrasound; when evaluating the vessels of the upper extremity, the patient should be supine, with the shoulder abducted and externally rotated, and elbow flexed . Evaluation should include vessel identification, and assessment of vessel compressibility and blood flow. When using B-mode (normal gray scale) the angle of the probe in relation to the vessel should be as close to 90 degrees as possible, which will improve the definition of the vessel as well as the clot. Color doppler is used to assess direction of flow and can help to differentiate vascular from non-vascular structures such as nerves, lymph nodes, and bursae.
The use of color doppler is based on measurements of movement. Specifically in this case, it was used to measure the movement of blood in vessels, which is processed as a color flow display. A common misconception is that red is arterial flow, and blue is venous flow, however this is not necessarily always the case. In fact, by default, red is simply indicative of flow moving towards the probe, and blue is indicative of flow moving away from the probe. This is important to note as the doppler ultrasound beam must be aligned to the direction of flow (angle of insonation), or more parallel to the flow (typically <60 degrees), as opposed to perpendicular to the flow. The figure below illustrates this concept.
Effect of transducer position (angle of insonation) on color doppler signal interpretation. Image courtesy of Dr. Mike Mallin.
Also keep in mind your scale when using color doppler. The higher the flow state (e.g. an artery), the higher your scale should be. If the scale is set too low (as is the case in these clips), you will see more artifact including aliasing, which is an artifact where the color signal “folds over” and falsely appears to be reversing flow. In general when using color and pulsed wave doppler, the scale should be optimized to minimize aliasing, and the gain should be turned up until color artifact is seen, then turned down just below that point.
Use of a low scale (4 cm/s in this case) on a high-flow vessel can produce an aliasing artifact, falsely appearing as reversal of flow
DISPOSITION AND CASE CONCLUSION
Given the patient’s symptoms and point-of-care ultrasound findings of a non-compressible right brachial artery with visible thrombus, a heparin bolus and infusion were initiated. Vascular surgery was emergently consulted, and the patient was taken for emergent right brachial artery thrombectomy with removal of a large subacute thrombus with restoration of normal perfusion in her arm. She was discharged home the next day on enoxaparin as a bridge back to warfarin.
Point-of-care ultrasound for evaluation of arterial thrombus is an advanced skill, and there is limited evidence on its use by emergency physicians. If there is a concern for arterial thromboembolism in a patient, a vascular surgeon should be consulted given the emergent nature of the process. Revascularization of an ischemic limb within 12 hours has an amputation rate of 6%, and rises to 20% at 24 hours . Given the need for timely diagnosis, point-of-care ultrasonography can be a beneficial skill for the emergency physican to have, as it can potentially shorten both time-to-diagnosis and time-to-embolectomy.
- While there is limited evidence on the use of point-of-care ultrasound by emergency physicians for the detection of acute limb ischemia, classic positive findings of arterial thrombus can decrease time-to-definitive care.
- Sonographic findings of arterial thrombo-embolic occlusion :
- Non-compressive artery
- Lack of or altered color doppler flow in artery
- Intraluminal echogenic material in artery
- Optimize your probe position when using color doppler to visualize flow within a vessel (i.e. more parallel to direction of flow), and adjust your scale to suit the flow conditions (i.e. higher flow = higher scale, to optimize your image and reduce aliasing).
- If your images will not be readily available for the surgeon, consider marking the patient to demonstrate the location of the clot:
- Cook T, Nolting L, Barr C, Hunt P. Diagnostic ultrasonography for peripheral vascular emergencies. Crit Care Clin 2014;30(2):185-206. PMID: 24606773
- Rolston DM, Saul T, Wong T, Lewiss RE. Bedside Ultrasound Diagnosis of Acute Embolic Femoral Artery Occlusion. J Emerg Med. 2013;45(6):897-900. PMID: 23988137
November 13, 2014
Great post on a case of nontraumatic arterial limb ischemia (ALI), diagnosed by bedside ultrasonography. I removed a few periods and commas which were extraneous. I also reorganized how the exam findings were listed to distinguish between left and right arm findings. Changed medication names to generic rather than brand names. Some questions and suggestions:
- You may be over-reaching the scope of a the main teaching point of using ultrasound to detect an arterial thrombus. Would remove some of the take-home points and any mention of content which reviews the pathophysiology/ basic issues on ALI. These points seem to detract from your main message.
- FYI in a journal review article, I think your writeup would be perfectly fine to include the broader scope of talking about ALI. In this series, we were aiming for a clean, short, “simple” message on how ultrasound can be done to save time and improve patient care — more on the mechanics and technique.
- Videos: Can you crop out as much text (especially the date and any ultrasound company logos) from the videos? FYI for all blog posts, I’d remove any mention of date or time of day (e.g. afternoon, night) to avoid ANY risk of HIPAA issues.
- Image: Is the diagram from Cook et al copyrighted? Do you have permission to use? Would draw your own original, if not.
- Image of arm with “clot” text: Nice inclusion to mark location of clot.
- Take home point #1: Did you mean “In retrospect” instead of “on repeat exam”?
- Take home point #3 and #7 seem similar. Basically it sounds like even though you think you see a peripheral arterial thrombus, a second study such as a formal ultrasound or CT angiogram may be indicated to confirm the diagnosis before an intervention is made. Can you combine this teaching point somehow?
- I like take-home point #2. Emphasizes the importance of timeliness in this diagnosis.
- Can you accompany each ultrasound video with a screen shot of the most important view and label it? See other #US4TW posts. Labeling will be key to help readers understand what you are talking about.
- Sounds like the pulse wave doppler wasn’t used. You may consider removing mention of this to avoid confusion. I defer that to you, your prepub critique reviewer, and expert peer reviewer.
- A bit lost on the 5 points under Point of Care Ultrasound. I’m hoping some labelled diagrams might help (point #8).
Great save using ultrasound!
[AUTHOR RESPONSE: Thanks Michelle.
I have made the text improvements, and will wrestle with adding the .GIF’s this weekend and cleaning up the explanations of the images. I will create my own diagram to replace the one from Cook et. al. — Rob]
Michelle Lin, MD, ALiEM Editor in Chief; Associate Professor of Emergency Medicine, UC San Francisco
November 14, 2014
Hi Dr Bryant,
Great case and another new tool I will be utilizing. I do a have a few comments on the post:
- There is a good amount of time dedicated to the use of Doppler in your post, but it was not needed for this case. Can you comment on the utility of using with/without Doppler.
- Can you comment on utilization of this technique in the lower extremity? Key locations to scan or any differences in technique?
- Agree with Michelle on cropping the videos/GIF. Feel free to email me if you are having difficulty in doing so. Also ideally their resolution should be the same so their size is handled similarly in WordPress.
- I like the “CLOT” drawing on a the arm.
Otherwise, I made a few subtle modifications to the Case Presentation for readability. A few tweaks to ‘slang’ terms as well (angio)
Overall very informative, good read, emphasizes the important points.
[AUTHOR RESPONSE: Thanks Sameed,
I will add the details about evaluating lower extremities and will add the .GIF files with doppler this weekend. The doppler views, and the trouble shooting of those views should be useful to other US neophytes. Even in the setting of seeing clot within a vessel, doppler evaluation provides secondary confirmation of vessel occlusion that would justify taking the patient to the OR based on our US exam.]
Sameed Shaikh, MD, ALiEM-CORD Fellow, Emergency Medicine Resident, Wayne State School of Medicine
Expert Peer Review
November 23, 2014
Great case Rob!
Here are my thoughts:
- I like how you emphasize the importance of angle of insonation when using doppler ultrasound. Your figure is good, but could you add a little “) <60″ to denote exactly which angle you’re talking about?
- I would emphasize that while an angle of insonation.
- While by convention red is towards the probe, this setting can be changed in the machine, and you could just point out the scale in your figure on aliasing which shows red at the top, meaning towards, and blue at the bottom, meaning away from the probe.
- It’s unclear exactly what is meant by “scale” when talking about color doppler. I think you mean Nyquist limit, which would normally be set around 60m/s for higher velocity studies and about half that for lower flow venous studies. While the Nyquist limit will control the velocity at which aliasing occures, in this case we’re more interested in optimizing the gain, which is the sensitivity to flow in general. Rather than go into this in depth, I would simply give the tip that when using color doppler, the gain should be turned up until spontaneous color artifact occurs, then turned down just below that point.
- Lastly, I recommend a link that will play an audio recording of Rob reading this blog post so that we can hear his dulcet Kiwi-tones while learning about this excellent use of ultrasound.
Jimmy Fair, MD, Ultrasound Fellow, Division of Emergency Medicine, Department of Surgery, University of Utah School of Medicine
Expert Peer Review
November 26, 2014
Great catch and nice work on the write-up Rob. Generally, I think this is an exceptional use of ultrasound in the emergency department. I have personally seen several similar presentations, although in the femoral or common femoral artery. An additional take home point I would make is that you can perform this exam at the bedside in a stable patient before they go to the CT scanner. While I understand your concern for an aortic catastrophe, I imagine an acute thromboembolism diagnosis by ultrasound may have saved some time to consultation, or at least allowed you to get a more directed CT scan to include the upper arm.
A couple of specific comments:
- Your description of the direction of flow is important. Red does NOT mean arterial and blue venous. You explain that well. However, the direction of flow can be switched on most machines too. So while the standard is that red = towards the probe and blue = away (BART: Blue Away Red Towards). That can change too. The easiest way to tell for sure is to look at the color legend on the ultrasound screen. Your “Aliasing” image for example has the red on top and the blue on bottom. This means the red is towards the probe and the blue is away. This can be flipped on almost all machines out there. Usually not important, and not necessary for diagnosis in this case.
- Regarding the angle of insonation: I have another image that might suit your needs better and shows how the Doppler waveform changes with probe angulation. Here you can see the actual Doppler shift, represented by velocity, changes with the angle of insonation the probe makes with the moving blood cells.
- This statement is a little misleading: “In general when using color doppler, the scale should be turned up until spontaneous color artifact occurs, then turned down just below that point.” When adjusting color and pulsed wave doppler the SCALE (cm/s) should be adjusted so that aliasing is minimized (Except in the cardiac exam where aliasing is expected with regurgitant lesions). Conversely, the color “GAIN” should be adjusted by turning up the gain until color artifact is seen (Noted by little color speckles where there is no flow) and then turning the gain down just so that artifact disappears. On most machines the gain button that makes the image brighter or darker turns into a color gain when you put the machine into the color setting. So typically, you can just adjust the gain to increase the brightness and sensitivity of the color settings.
- Take home point #2, bullet 2: Sometimes you can see color flow around the thrombus. In this case, the velocity is often increased causing aliasing you would not see in the normal portion of the artery. I have attached an image. Recommend changing this bullet to “Lack of or altered color doppler flow in the artery.
- Take home point #4. See above for exceptions to direction of flow. Although an interesting aspect of this case, I do not believe this is important enough in the diagnosis of the thromboembolism to be one of your take home points. I would recommend removing.
Great work Rob, thank you for the opportunity to review this excellent USFTW.
[AUTHOR RESPONSE: Thanks Mike for your expert peer review! I’ve made the suggested changes to the post which helps clarify things.
I also do think your image better illustrates the point we were trying to get across. Can we use yours in the post? Is there a reference that we can put next to it?
Thank you again for being a part of the US4TW case series!
Mike Mallin, MD, Assistant Professor of Surgery, Director of Emergency Ultrasound, Division of Emergency Medicine, Department of Surgery, University of Utah School of Medicine, Co-Creator: Ultrasound Podcast