Mount Sinai Emergency Medicine Ultrasound

The subxiphoid four chamber view is commonly used in cardiac assessments and the FAST exam and for many is the initial “go-to” view of the heart. Difficulty obtaining this window can frustrate novice and seasoned operators, and there are a few tips which can help optimize the view.

1. It’s called SUB-xiphoid for a reason. Don’t jam the probe up against the xiphoid process. Imaging through bone is difficult, the patient will be in pain, and the angle is too steep. Instead, place the probe a few centimeters south of the xiphoid process and work up from there.
2. Get a good view of the liver, THEN use that to get a good view of the heart. You may find that starting to the patient’s right of midline gives a better liver window, since the stomach tends to obscure the subxiphoid view as you go further left.

This video illustrates the huge difference that left vs. right can make. It was taken with the probe in a midline subxiphoid position. Starting with the probe angled towards the patient’s left, the entire screen is obscured by gas in the stomach. As the operator changes the angle towards the patient’s right, we see the liver come into view. This yields an excellent window through which the heart can be visualized.

The figure below, taken from the midpoint of the video, illustrates the point a bit more clearly. To the right of the green line (patient left), superficial stomach gas (arrow) obscures everything behind it, creating a terrible view. On the other side of the green line, liver (L) is visualized which creates a good window for viewing the heart behind it.

Finding the right angle is critical to optimal imaging. In fact ‘right angle’ or perpendicular imaging is the best way to get a clear image. At 90 degrees, many more sound beams reflect back to the transducer than at more shallow angles.

In addition, the ultrasound energy is more spread out when it connects to the tissue at an angle, as seen above.
In this image of the kidney, notice the inferior aspect of the kidney (right arrow) is imaged at nearly 90 degrees. The white lines represent the plane of the kidney.

It has the sharpest border and is well-distinguished from the liver. The middle arrow represents the path of ultrasound energy hitting the the kidney off 90 degrees.  Not a bad image but doesn’t look as good as the one imaged at 90 degrees. Finally, the left arrow represents the beam hitting the kidney almost parallel. Note that the kidney-liver interface looks fuzzy and there is a great loss of detail. Most of the ultrasound energy is reflecting off the surface AWAY from the transducer- hardly any is available to reflect back towards the transducer and yield a good image.

Thus, angling the probe 90 degrees to the structure you want to image can increase resolution and improve your image quality.

We’ve all seen ultrasound augment the physical examination and even allow for assessments we could not otherwise accomplish at the bedside. One great example is the use of ultrasound to check the pupillary light reflex. If you are wondering why a pen light would not suffice for this physical examination standby, you have never encountered a patient with facial trauma whose eyes were swollen shut.

We already know what to look for without ultrasound (thanks to Greyson Orlando and Wikipedia for the GIF):

By directing the beam of a high-frequency linear array transducer through the plane of the iris, you can obtain the following image (while shining a light through the closed eyelid of the same or contralateral eye):

It takes a bit of practice to align both planes, and not worth the trouble if the patient can open their eyes.

Placing a Tegaderm over the closed eye prior to applying gel can make cleanup much easier afterwards (a useful tip for any type of ocular ultrasound).

Further reading:

• Sargsyan AE, Hamilton DR, Melton SL, et al. Ultrasonic evaluation of pupillary light reflex. Critical Ultrasound Journal. 2009 1(2): 53-57.
• Harries A, Shah S, Teismann N, Price D, Nagdev A. Ultrasound assessment of extraocular movements and pupillary light reflex in ocular trauma. Am J Emerg Med. 2010 Oct; 28(8):956-9.

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.