Mount Sinai Emergency Medicine Ultrasound

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.

With each new course, rotation, or group of novice sonographers we often give the same advice on scanning. Although I don’t mind the repetition, I’ve codified some of the most common tips below so I don’t forget them.

These are mainly directed towards novices, but there may be something useful in there for everyone to remember. Note that I used self-restraint and did NOT list “clean the machine” among the tips. I assume everyone has already built up an impressive list of excuses for not cleaning the machine. That sounds like another post in itself!

• Start with one indication and become comfortable with it, then expand your repertoire
• Before picking up the probe, think about how the results of the scan will change your management and clarify your clinical question (good advice for any diagnostic test)
• Familiarize yourself with the most useful buttons first (every machine has these):
  • Power, probe selection, depth, gain, save/print
• Remember you are scanning three-dimensional structures- be sure to fan the ultrasound beam through several planes to visualize the full anatomy
• Practice, and keep practicing. Ultrasound IS operator dependent, just like everything else you do in your practice. So get good at it, just as you became proficient in EKG interpretation or laceration repair.
• When you can’t see anything:
  • Use more gel, find a better acoustic window, and check the common buttons (transducer, depth, gain)
• Proper hand position is crucial- hold the probe so you are comfortable and stable
• Check follow-up studies if they are performed, and compare your bedside results to CT scan, operative findings, etc.
• Position the patient, the machine, and yourself for optimal visibility and comfort whenever possible
• Share positive findings with your colleagues! Although pregnancies and gallstones are common, sharing aortic aneurysms or deep vein thromboses will be appreciated.
• Share ‘saves’ with your colleagues! Although most applications for bedside ultrasound are evidence-based, never underestimate the power of the anecdote in changing practice patterns.

Please leave YOUR best scanning tip in the comments.

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.

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!

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