When the Transeptic spray bottle won’t spray, it is often because the pump has become disconnected from the plastic tubing 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, 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 guide placement 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 check height 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. When done right 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 push necessary for the bubble test. Some people have used this angiocatheter during ACLS situations 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. “Rapid confirmation of central venous catheter placement using an ultrasonographic “Bubble Test.” Acad Emerg Med 2010;17(7):e85-6. (PMID: 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 for diagnostic 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.
Hopefully you are using ultrasound to guide your insertion of central venous catheters. Once they are in, you still have to suture them at some point. Straight suture needles are often used to secure arterial and venous catheters to the skin. These types of suture needles have been demonstrated to be more dangerous than curved or blunt suture needles, with up to seven times higher rate of injury for health care workers. By utilizing the plastic needle sheath present in most central venous line kits as a “thimble,” counter pressure and skin puncture may be achieved without bringing the fingers near the sharp end of the suture. Here’s an image from Bret Nelson’s article on the technique.
Panel A shows counter-pressure being applied with the cap to direct the tip of the needle. Panel B shows the needle tip safely sheathed within the cap.
The video below demonstrates this technique in real time:
Other authors have illustrated alternative techniques to reduce the risk of self-injury when using straight suture needles. Steven Bauer uses a 5-mL syringe to ensconce the emerging straight needle. This can provide even more distance, and he also uses it to guide tying an ‘air knot’ when needed!
Haney Mallemat has just posted a video where he demonstrates using the paper envelope the suture is packaged in to distance the needle tip from your fingers.
Keep in mind NONE of these techniques has been studied- there is no evidence that they reduce needlesticks. We DO know that using curved, blunt-tip suture needles used with needle drivers and forceps is safer than using straight sutures. Whichever method you use please be careful!
Nelson BP. Making straight suture needles a little safer: a technique to keep fingers from harm’s way. J Emerg Med. 2008 Feb; 34(2):195-7. Epub 2007 Oct 1. (PMID: 18282537)
Centers for Disease Control and Prevention. Evaluation of blunt suture needles in preventing percutaneous injuries among healthcare workers during gynecologic surgical procedures—New York City, March 1993–June 1994. MMWR Morb Mortal Wkly Rep 1997;46:25–9. (PMID: 9011779)
Edlich RF, Wind TC, Hill LG, Thacker JG, McGregor W. Reducing accidental injuries during surgery. J Long Term Eff Med Implants 2003;13:1–10. (PMID: 12825744)
The normal gallbladder wall should measure less than 3-4mm. It is recommended that this measurement be taken through the anterior wall of the gallbladder, since posterior acoustic enhancement will often make posterior measurements inaccurate. The image above was taken in a patient with cirrhosis, chronic ascites, and no acute complaints of upper abdominal pain. While a thickened gallbladder wall is one sign of cholecystitis, there are a number of normal and pathologic states which can lead to this finding as well.
Normal contracted gallbladder
Alcoholic liver disease
Increased portal venous pressure
Acute viral hepatitis
Why does this occur? A normal gallbladder can exhibit a thickened wall of 4-5mm due to contraction alone. Typically this will occur in the setting of a lower-than-normal gallbladder volume.
For the rest, hypoalbuminemia is a major culprit in gallbladder wall thickening; alone or as a secondary mechanism in patients with cirrhosis, heart failure or renal disease. Other speculated mechanisms of gallbladder wall thickening in the disease states above are increased portal venous pressure and generalized edema. Going back through radiology journal articles older than the ones below (1970s-80s), the same mechanisms are invoked repeatedly, and other older articles are referenced. There seems to be no definitive mechanism proven to cause the gallbladder wall thickening, though many articles demonstrate that it does in fact occur, and distinct from incomplete contraction of the gallbladder itself.
Gallbladder wall thickening is often evident in adenomyomatosis and gallbladder cancer as well. In these settings the gallbladder wall diameter is directly a part of the pathology, and not a side effect of some other process as in the cases above.
Thus, this finding is not specific to acute cholecystitis. It is present in many other disease states and may even signal the clinician that there is some other pathology at play.
Wegener M, Borsch G, Schneider J et al. Gallbladder wall thickening: a frequent finding in various nonbiliary disorders–a prospective ultrasonographic study. J Clin Ultrasound 1987 Jun;15(5):307-12. (PMID: 3149957)
van Breda Vriesman AC, Engelbrecht MR, Smithuis RH et al. Diffuse gallbladder wall thickening: differential diagnosis. Am J Roentgenol 2007 Feb;188(2):495-501. (PMID: 17242260)