Tips and Tricks: Probe Rotation

Probe Manipulation – Rotation from Sinai EM Ultrasound on Vimeo.

How do you obtain that nice long image of the peripheral blood vessel for a longitudinal approach? It is easy to say ‘rotate the probe 90 degrees from the transverse view,’ but there are many subtleties to probe rotation. Many times when we rotate the probe, we do not get the desired longitudinal view, but rather the vessel is seen in part, or obliquely sectioned. Also, the vessel may appear on the left side of the screen or the right side and further fine rotation often makes the vessel disappear. How do we correct for this?

The trick is to understand the many different axes of probe rotation. See the video for an example of :

(i) probe rotation along an axis that goes through the proximal end of the probe (incorrect)

(ii) probe rotation along an axis through the distal end of the probe (incorrect)

(iii) CORRECT probe rotation along an axis through the central portion of the probe (through the transducer wire)

In order to move from a transverse to longitudinal view of a blood vessel without losing track of it, you must:

  1. Visualize the vessel in the center of the screen (thus, directly beneath the center of the probe)
  2. Rotate the probe on its CENTRAL axis (through the wire)
  3. Watch as the vessel transitions from a circle (transverse) to an ellipse (oblique) to two parallel lines (longitudinal)

Go try this on a phantom and with some practice, everyone can get that nice elongated view of the vessel.

Top 3 Articles: Ultrasound guided Central Venous Catheter Insertion

The literature for using ultrasound guidance in placing a central venous line is robust. There are many articles espousing the benefits of ultrasound guidance: reduced number of attempts, reduced complication rate, increased first pass success rate. So, it is indeed difficult to narrow down to a finger count of 3 articles. But if one were to spend time reading just 3 articles that define the topic, these 3 should be as good as any. Continue reading “Top 3 Articles: Ultrasound guided Central Venous Catheter Insertion”

Top 3 Articles: Abdominal Aortic Aneurysm

AAA

While an uncommon condition, a leaking abdominal aortic aneurysm (AAA) is deadly if not recognized quickly.

How good is the physical examination for excluding AAA? Even if the physical exam is specifically directed to look for AAA, the sensitivity is still not good enough to rule out its presence (Sensitivity of 29% for AAAs of 3.0 to 3.9 cm, to 50% for AAAs of 4.0 to 4.9 cm, and 76% for AAAs of 5.0 cm or greater in diameter). So go pick up that ultrasound probe to look for it.

Lederle, F. A. et al. The rational clinical examination. Does this patient have abdominal aortic aneurysm? JAMA. 1999;281(1), 77.

Can ultrasound define the diameter of a AAA as accurately as a CT scan? Pretty close, though ultrasound will probably underestimate the diameter. Where it matters (at and around the bifurcation with a longitudinal view), ultrasound can come within 1cm of the CT diameter 95% of the time.

Knaut, A. L.et al. Ultrasonographic measurement of aortic diameter by emergency physicians approximates results obtained by computed tomography. The Journal of Emergency Medicine, 2005; 28(2), 119-26.

Finally, how good are emergency physicians in detecting AAAs? Pretty good it seems, with 100% sensitivity (95% CI 1⁄4 89.5 to 100), 98% specificity (95% CI 1⁄4 92.8 to 99.8), 93% positive predictive value (27/29), and 100% negative predictive value (96/96).

Tayal VS, et al. Prospective study of accuracy and outcome of emergency ultrasound for abdominal aortic aneurysm over two years. Acad Emerg Med. 2003;10:867-871.

Top 3 Articles: Pelvic US

Miscarriage in progress from Sinai EM Ultrasound on Vimeo.

Pelvic ultrasound is one of our core US applications. It has been incorporated within many emergency departments and it is a bread and butter skill for the EP. So, how do we fare in our performance?

This early study showed that ED ultrasound was very similar to radiology department findings (or final outcome, or both) in 96% of the study cohort. Also, when ED ultrasound accurately identified IUPs, ectopic pregnancies were effectively ruled out with a NPV of 100%.

1. Durham, B., Lane, B., Burbridge, L., & Balasubramaniam, S. (1997). Pelvic ultrasound performed by emergency physicians for the detection of ectopic pregnancy in complicated first-trimester pregnancies. Annals of Emergency Medicine, 29(3), 338-47.

Also, why do we do it in the first place, and not send all the cases to radiology for ultrasound? The answer lies in the reduction of both ED length of stay as well as cost. Any means to reduce ED overcrowding and decrease spending are welcome!

2. Shih, C. H. (1997). Effect of emergency physician-performed pelvic sonography on length of stay in the emergency department. Annals of Emergency Medicine, 29(3), 348-51; discussion 352.

Lastly, when ectopic pregnancy is suspected, remember to perform a FAST exam as a positive finding (free fluid in Morison’s pouch) can predict the need for operative intervention.

3. Moore C, Todd WM, O’Brien E, Lin H. Free fluid in Morison’s pouch on bedside ultrasound predicts need for operative intervention in suspected ectopic pregnancy. Acad Emerg Med. 2007;14:755-758.



Tips and Tricks: Paracentesis

The first and most important step in paracentesis is confirming there is ascites to begin with!

Physical examination findings can be misleading, and inserting a needle blindly into the abdomen can cause complications unnecessarily. Note the black free fluid in the image, with echogenic bowel loops floating within.

Several approaches are commonly used. Each one starts with an assessment for peritoneal fluid, localization of area suitable for paracentesis (no nearby vessels, large enough pocket, etc.). Next, measure the distance from skin to peritoneum to establish a sense of how far the needle lust penetrate before expecting to yield ascites. This is followed by either:

  1. Real time (dynamic) ultrasound guidance. Probe held in non-dominant hand (or by assistant); dominant hand guides needle with real-time guidance using short- or long-axis technique
  2. Static guidance: Mark the location for paracentesis (use a pen, pressure from a pen cap or fingernail, or even using a nearby mole/skin blemish as a landmark!), and then proceed with the tap using that mark as a guide. It is critical that the mapping is performed immediately before the paracentesis, and the patient remains in the same position. If the patient moves or is re-positioned,  the patient must be scanned again because the pocket of fluid would have shifted due to the highly mobile floating bowel loops.

As the needle is inserted into the abdomen using either technique, it is wise to hold slight negative pressure on the plunger of the syringe. This way, as soon as fluid or blood is encountered, the operator will note both a pressure change and a flash of fluid into the syringe.

Top 3 Articles: FAST

The FAST exam is the prototypical application of emergency ultrasound. However, it is important to know that there are limited randomized controlled trials assessing the utility of the FAST exam. Despite this, let’s look at three good articles that  all emergency residents should know.

1. In this Cochrane review, the authors’ conclusion was that there was insufficient evidence for the use of ultrasound-based clinical pathways in the initial diagnostic workup of patients with blunt abdominal trauma. Ultrasound was not sensitive and lacked diagnostic accuracy. However, the use of ultrasound did reduce the use of CT scans. The take-home message is that ultrasound should not be used as a single rule-out test for significant intra-abdominal injury and the ED resident should be aware of ultrasound’s limitations.

Stengel D, Bauwens K, Sehouli J, Rademacher G, Mutze S, Ekkernkamp A, Porzsolt F. Emergency ultrasound-based algorithms for diagnosing blunt abdominal trauma (Review). The Cochrane Collaboration. February 18th, 2008.

2. Interestingly, this review used the same methodology as the Cochrane review and found that an adequately performed FAST exam can predict the need to send a patient to the operating room, with a high degree of sensitivity (98.9%) and specificity (98.1%).

Melniker LA. The value of focused assessment with sonography in trauma examination for the need for operative intervention in blunt torso trauma: a rebuttal to “emergency ultrasound-based algorithms for diagnosing blunt abdominal trauma (review)”, from the Cochrane Collaboration. Critical Ultrasound Journal. 2009;1:73-84.

3. Thoracic ultrasound has become part of the standard assessment of the trauma patient. Ultrasound has been shown to be much more sensitive than CXR in the detection of pneumothorax when compared to CT as the gold standard. There are many studies proving this point and this is a good example.

Blaivas M, Lyon M, Duggal S. A prospective comparison of supine chest radiography and bedside ultrasound for the diagnosis of traumatic pneumothorax. Acad Emerg Med. Sep 2005;12(9):844-849

Tips and Tricks- The gallbladder / duodenum conundrum

One of the most common pitfalls in gallbladder sonography is confusion with the structure which abuts it in the right upper quadrant – the duodenum. This loop of bowel can easily be mistaken for the gallbladder especially if it contains a mixture of fluid and solid materials. So how can we tell them apart?

The gallbladder:

  • has a bright (echogenic) wall
  • is surrounded by liver
  • attaches to the middle hepatic ligament
  • is a contained structure
  • can be traced to the portal vein

The duodenum:

  • has a darker (hypoechoic) wall
  • is next to the liver, not in it
  • cannot be traced to the middle hepatic ligament
  • is a tubular structure
  • does not connect to the portal vein

More images and explanation after the break!

Continue reading “Tips and Tricks- The gallbladder / duodenum conundrum”