When the Transeptic spray bottle won’t spray, it is often because the pump has become disconnected from the plasticÂ tubingÂ within the bottle. Instead of trying to fish it out with forceps, just turn the whole bottle upside-down.
To image something which moves, you must remain still. To image something which is still, you must move.
If you think on this long enough, the point is self-evident and requires no explanation. Or, just see some examples below.
We are pretty well adapted to seeing three dimensions at a time. Thus when imaging a moving structure like the heart, we hold the probe in a fixed position to obtain standard views. This allows us to focus on the movement, and cardiac presets optimize temporal resolution at the expense of spatial resolution. We are then seeing two spatial dimensions and one temporal dimension (heart moving in time).
It is very difficult to appreciate the anatomy and function of the heart, for example,Â when the probe is moving.
In contrast, imaging the right upper quadrant for fluid in Morison’s pouch requires a slow fan through the liver, diaphragm, and kidney. This allows us to appreciate the entire potential space where fluid can collect. Abdominal imaging is optimized for spatial resolution at the expense of temporal resolution, so be sure to move the probe slowly. Fanning through the entire structure of interest will often reveal pathology which was missed with a single-plane scan. Small gallstones, small amounts of peritoneal or pleural fluid, saccular aneurysms, and other maladies can fool a novice sonographer who isn’t thorough. In this case we are seeing three spatial dimensions.
Thoracic sonography is one of the most rapidly growing areas of emergency and critical care ultrasound. One very important emerging indication is to assess for lung consolidation. The characteristic appearance of consolidated lung is very sensitive and specific for pneumonia, but novices should heed some important pitfalls in making the diagnosis.
Special thanks to Jim Tsung, MD, MPH and Brittany Jones, MD for their tips, videos, and ongoing research in this important field! For further reading on this topic, please see this article.
Pitfall #1 – confusing thymus for a consolidation
Normal thymus in sagittal view:
Thymus (top half of screen) and heart (bottom right). Don’t confuse thymus for lung consolidation. Note there are no air bronchograms, but thymus has a faint speckled appearance.
Normal thymus in transverse view:
Thymus (top half of screen) and heart (bottom right). Don’t confuse thymus for lung consolidation. Note there are no air bronchograms, but thymus has a faint speckled appearance
Pneumonia adjacent to Thymus in transverse view:
Lung consolidation with air bronchograms (top left) adjacent to normal thymus (speckled appearance on top right) with heart (bottom right)
Pitfall #2 – mistaking spleen for consolidation.
This is an important pitfall for everyone to know about. The same issue applies to the liver & stomach. The sensitivity of lung US for pneumonia rises >90% if this mistake is avoided.
Left lower chest- sagittal view:
Be careful scanning the left lower chest (left anterior and left axillary line) – air in stomach and spleen may look like pneumonia if you don’t realize that you have scanned inferior to the diaphragm and past the end of the pleural line. Most common error by novices.
Left lower chest- transverse view:
Be careful scanning the left lower chest (left anterior and left axillary line) – air in stomach and spleen may look like pneumonia if you don’t realize that you have scanned inferior to the diaphragm and past the end of the pleural line.
Pitfall #3- missing pleural effusion
Here are a few examples to refresh your memory.
Left pleural effusion:
Pleural effusion (anechoic wedge just beneath ribs and pleura)
Air in stomach
Do not confuse spleen and air in stomach for pneumonia.
We already know it is helpful to use ultrasound to guideÂ placementÂ of central venous catheters.
How can we use ultrasound to help confirm proper placement of an internal jugular catheter?
There are several methods which have been described:
Visualize the needle entering the vein (optimally in the long axis)
Visualize the guide wire in the vein
Visualize the tip of the triple lumen catheter in the right atrium, then pull back 2 cm
Bubble test (more on this below)
In addition there are non-ultrasound-related methods to confirm placement (but who cares about those?):
Blood gas drawn through central venous catheter port
Pressure transduction (quantitative- manometry)
Pressure transduction (qualitative- attach IV tubing and checkÂ heightÂ of blood column)
So let’s get back to that bubble test. In order to confirm that the catheter has been placed in the superior vena cava, inject 5-10 cc normal saline through the catheter while visualizing the right heart on a subxiphoid 4-chamber view. Â When done rightÂ should look something like this :
So this is a neat trick after the catheter is in, but the horse is out of the barn at that point. Ideally you should confirm proper venous placement prior to dilating the vessel and placing the central line. You could do this while the needle is in the vessel, but that’s a bit unstable. Instead consider using the long angiocatheter found in most central line kits to puncture the internal jugular vein.
After the flash (and ultrasound confirmation of venous puncture) advance the catheter and remove the needle. You then have an angiocatheter in the central venous system, which can be used for manometry, blood gas analysis, or the saline pushÂ necessaryÂ for the bubble test. SomeÂ peopleÂ have used this angiocatheter during ACLSÂ situationsÂ to administer a few doses of code medications in a shorter time than it would take to complete a “full” central line.
Once proper venous placement is confirmed, you can advance the guide wire through the angiocatheter and continue the procedure as normal.
For a great overview of central venous catheterization, check out this post by Haru Okuda and Scott Weingart at EMCrit.org.
Prekker ME, Chang R, Cole JB, Reardon R. Â â€œRapid confirmation of central venous catheter placement using an ultrasonographic “Bubble Test.â€Â Acad Emerg MedÂ 2010;17(7):e85-6. (PMID:Â 20653578)
In this post we’ll illustrate the optimal imaging angle for Doppler evaluation. Let’s start with basic Doppler physics.
Where to police officers situate themselves to aim a radar gun at speeding cars?
The maximal Doppler shift will be seen at 180 degrees. In fact at the instant the car passes the officer, (90 degrees) there will be zero Doppler shift. At that instant there is no movement between the object and the listener. So they aim the gun directly at the oncoming traffic, so the direction of their beam is parallel to the direction of [traffic] flow.
The image below illustrates Doppler shift of ultrasound reflected off a red blood cell:
Top: A normal ultrasound wave
Middle: Doppler shift reflected off the RBC moving toward the transducer (thus increasing the frequency of the returning wave)
Bottom: Doppler shift reflected off the RBC moving away from the transducer (thus decreasing the frequency of the returning wave).
Thanks to equipmentexplained.com for the image. Imaging at 180 degrees is impractical forÂ diagnosticÂ ultrasound, since the optimal B-mode imaging angle is 90 degrees. Therefore, most authorities recommend an imaging angle between 45-60 degrees for Doppler ultrasound imaging . If you are imaging a vascular structure at 90 degrees and getting no Doppler signal, try lowering your angle.