Learning Ultrasound – 6 – The Abdominal Ultrasound Scan

All of the posts of the series Learning Ultrasound are excerpts from the book Point-Of-Care Ultrasound for Emergency Physicians — “The EDE Book”. I purchased the e book two years ago. The e book is only available on Apple devices. The e book is only about $15 and it is simply the best there is on learning  to perform point of care ultrasound (POCUS). You need to buy it now.

I have posted these Learning Ultrasound series, temporarily, for a friend who does not currently have access to an Apple device.

In this post you will watch four YouTube videos on what you will see in a correctly performed abdominal ultrasound exam.

Then we will go over the often difficult technical points of conducting the exam from Point-Of-Care Ultrasound for Emergency Physicians — “The EDE Book”.

You may notice that there are some differences in the recommendations on performing the scans between the YouTube videos and “The EDE Book”. And that is because there is often more than one way to perform an effective scan.

The following are excerpts from Point-Of-Care Ultrasound for Emergency Physicians — “The EDE Book” on how to perform the abdominal ultrasound scan:

[Abdominal Ultrasound Scan Technique]

Because the abdominal scan begins in the upper quadrants, the admonition to “Dive the Depth” (i.e., set the depth to maximum) does more to ensure than ensure the anatomy is not missed by scanning at an inappropriately shallow level. The abdomen presents two obstacles to scanning: bowel gas and rib shadows. These impediments will blur the picture. Starting at a healthy depth will give you a sharp image in the near field, which can be magnified later when the anatomy has been clearly the anatomy has been clearly identified.

A mid-range frequency (e.g., 3.5  MHz) will work best for most patients. Consider using a lower frequency (e.g., 2.5 MHz) if your patient is quite obese. In contrast, a higher frequency (e.g., 5 MHz) will often sharpen your image in children. Start the scan with the default gain setting, but be prepared to adjust it to suit your own eyes as the scan proceeds. In particular, consider decreasing your gain to enhance the appearance of black free fluid as described below. The curved array probe is your best bet [but you can also use the phased array probe].

Apply gel to the probe itself rather than to the patient [because it would fall off if applied to the patient].

[Don’t hold the probe in a death grip. Hold it relaxed] and make a four fingered platform for the probe (Figure 1 below) [to stabilize the probe].

How To Perform The Abdominal EDE [Ultrasound Scan]

Abdominal [ultrasound scan] includes examination of the right upper quadrant (RUQ), the left upper quadrant (LUQ), and the pelvis.

The scan begins in the RUQ. This is the single most important part of the scan. The RUQ has the hepatorenal space (also known as Morrison’s pouch), the second lowest part of the supine abdomen. However, the lowest part – the pelvis – has very little volume. Any clinically significant intraperitoneal bleed, even if it is of pelvic origin, will quickly overflow into the right upper quadrant via the right paracolic gutter. As for bleeding in the LUQ, it will be diverted into the RUQ (without going to the relatively lower pelvis) by the phrenocolic ligament and the mesentary of the transverse colon. For these reasons, if a scan is positive in only one view, it will be the RUQ in more than 80% of cases.

Although it lies higher in the abdomen than either the pelvis or the RUQ, it is nonetheless essential to scan the LUQ. There is enough potential space in the LUQ for a clinically significant bleed to accumulate. Early bleeding from a splenic injury is therefore best accomplished with this scan.

The Upper Quadrants

Scans of the upper quadrants require the greatest technical ability of any of the  basic [ultrasound] scans, so you must be very methodical. Most importantly, you must move the probe in one plane at a time. The upper quadrant scan is performed in the longitudinal plane.

Step 1

Locate the xiphoid process. Since the kidney is located in the retroperitoneum, place the probe at the posterior axillary line (Figure 2a below) at the level of the xiphoid (Figure 2b) [meaning that the superior margin of your probe will be at the level of the xiphoid process.

Starting on or at least near the posterior axillary line will help you avoid the most common beginner mistake: placing the probe too anteriorly. Make sure that the probe is in the true longitudinal plane (parallel to the stretcher). The goal is to have the beam intersect the liver and the right kidney on the right (Figure 3 below) and the spleen and left kidney on the left (Figure 4 below).

Step 2

The kidney is the internal landmark for your Area of Interest.

If you see the kidney at your starting point, you can skip Step 2 and proceed to Step 3. Otherwise, locate the kidney as follows.

Slide the probe posteriorly from your starting point (Figure 6 below).

You may even find that your knuckles touch the stretcher at the end of your slide. If you see the kidneys, great! Move to Step 3. If not, slide the probe anteriorly, roughly to the mid-axillary line. Whether or not you see the kidney at this point, move to Step 3. Step 3 will help you both  focus in on your Area of Interest and find that elusive kidney.

It is vital to do the posterior-anterior (PA) slide while keeping the probe in the longitudinal plane such that the beam is aimed straight across the body. It is very common to let the probe handle drop. This causes the beam to angle up and pass anterior to the Area of Interest.

Step 3

The goal of Step 3 is to find the best possible view of your Area of Interest: the interface between the liver (or spleen) and the kidney (Figures 5 and 7 Below)

 

This potential space is where intraperitoneal blood most commonly collects in trauma. To one side of this potential space is the liver (or spleen), and the other side is Gerota’s fascia. This tough fascia appears as a bright white line which outlines the contour of the kidney. Your window to the interspace is the liver (or spleen); the beam travels through the solid organ to reach the interface.

The interface is defined as that part of the kidney that is adjacent to the solid organ. In most people, the liver and spleen end roughly at the mid-kidney. But in some patients the solid organ keeps right on going, even beyond the kidney’s inferior pole. The solid organ defines the interface. It is therefore essential to identify the solid tip of the solid organ every time you scan the hepatorenal (or splenorenal) space (Figure 8 below). Only then can you be certain that you have seen the entire Area of Interest.

Once the kidney has been located in step two, slide the probe cephalad or caudad until the kidney is is clearly seen and properly centered on the screen (Figures 9 and 10 below). It is vital to keep the probe in the longitudinal plane when performing this slide. When this maneuver is properly executed, the kidney should move left to right without its appearance changing in any way.

It is very common for beginners to move the probe out-of-plane, almost always by coming anteriorly. You will be able to tell if you are doing this if the kidney changes shape as you move posteriorly. If you lose the kidney, stop and go back to Step 2 to locate the kidney once again.

If your slide in the longitudinal plane fails to provide an excellent view of the interface, find the best possible view, then improve it by rotating the cephalad end of the probe towards the stretcher (Figure 11 below). Rib shadows commonly obstruct part of the interface, and this rotation will remove the rib shadows from your view.

If you were unable to locate the kidney in Step 2, your initial probe placement was very likely cephalad to the kidney. The kidney will therefore be caudad to where you performed your PA slide. You can use the longitudinal slide of Step 3 to help you. Return to your starting point and then slide the probe along the posterior axillary line one or two intercostal spaces. Then repeat the PA slide of Step 2 from this more caudal location. Once you locate the kidney, proceed with Step 3 to center the interface.

Step 4

Step 5

 

 

 

 

Resources:

Point-Of-Care Ultrasound for Emergency Physicians — “The EDE Book”; “The clearest and most concise approach to emergency ultrasound.” There is an inexpensive ebook available for Apple devices and I strongly recommend you purchase it right away.

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