Educational Pearls from Today's Ultrasound Course

by Bob Stuntz


Here are the major take home points from the EUS course our US team put together today.  

US Basics and Physics

  • Hold the probe near the scanning surface, and place a hand on the patient to balance your probe.  Many of your views require fine manipulation of the probe
  • Higher frequency (shorter wavelength) = better resolution but worse penetration
  • Lower frequency (longer wavelength) = worse resolution but better penetration
  • Optimize your gain and depth to obtain the best images
  • Time gain compensation (TGC, or near and far field gain) can be helpful to change your gain at different depths
  • When using doppler, red and blue have nothing to do with artery and vein.  Red means motion toward the probe, and blue is motion away from the probe.  
  • In general, your probe indicator is to the right of the patient for transverse windows and towards the patient’s head for saggital images.  Throw this point out the window when doing US guided procedures and cardiac US.  

eFAST

  • Do not confuse an epicardial fat pad for a complex pericardial fluid collection
    • Fat pad: Anterior, more echoic, and rhythmically moves with he heart
    • Effusion: Can be anechoic or contain swirling complex echoes that do not move rhythmically
  • Do not confuse hemothorax for intraperitoneal fluid
    • Look for the hepato-renal interface to ensure you are in the peritoneum
    • Look for the diaphragm to localize fluid in the chest
  • To get your splenorenal view, you may need to place the probe more posterior and cephalad than your RUQ view
  • Solid organ injury can be seen with US (there is poor sensitivity for solid organ injury, but high specificity)
  • Make sure to visualize the diaphragms in the upper quadrant views, especially the LUQ.  Blood will often collect between the spleen and diaphragm, and this also allows you to evaluate for hemothorax.  
  • False positives in the FAST exam
    • Distended stomach (full of liquid)
    • Peritoneal dialysis
    • Ascites
    • Seminal vesicles
  • Look for echogenic as well as anechoic fluid on the FAST exam.  As blood accumulates and clots, it will begin to be echogenic
  • The sensitivity of a supine chest XR for pneumothorax is 50%, and and upright CXR has a sensitivity of 94%.  Studies have shown US to be 98% sensitive for the detection of pneumothorax, no matter if they are supine or upright. 
  • Pneumothorax is seen with absence of lung sliding, the “stratosphere sign” on M mode.  
  • Look out for false positives when performing US for lung sliding and pneumothorax
    • Apnea or mainstem intubation
    • Transtracheal jet ventilation
    • Pleural adhesions/pleural based cancers
    • Bullous lung disease

US Guided Procedures

  • Procedures are an exception to the standard views.  Your probe indicator should always be to your left when doing procedures to match up with what you are doing on the screen
  • US guidance for vascular access increases success rate, especially first pass success rate, and reduces time to cannulation of the target vessel compared to landmark techniques
  • When placing your sterile sheath over the US probe, remember that you need gel between the probe and the sheath, and then sterile gel on to of the sheath
  • Always keep your needle tip in view.  If you do not know where your needle tip is, stop moving the needle!
  • Make sure to check for vessel compressibility prior to sticking to ensure the vessel you are going for is fully collapsible and patent. 
  • Anchor your probe hand on the patient when performing procedures
  • When performing US guided peripheral access, use the largest, most superficial vein available
  • Use ultrasound before paracentesis to evaluate for optimal fluid collection and to evaluate for adherent bowel or loculated ascites. 

Echo in the ED

  • Tamponade is a diastolic phenomenon.  Look for right ventricular collapse during end diastole either by using M mode of by looking at the RV free wall when the V is at its most full point.  
  • If you are concerned for tamponade or elevated R sided heart pressure, look at the IVC in a saggital plane and look for respiratory variability (the lumen becoming larger and smaller with respiration). 
  • The amount of fluid around the heart is not as important as the rate of accumulation.  
  • Do not confuse an epicardial fat pad for a complex effusion.  Epicardial fat pads are anterior, echoic, and move rhythmically with the heart.  Complex effusions may be posterior, and swirl, notmoving rhythmically with the heart.  
  • Remember where the LV is on your different views. 
    • Parasternal long: LV posterior, apex to the left of the screen
    • Parasternal short: LV circular and posterior/right
    • Apical 4 chamber: LV is to the right, apex on the top of the screen
    • Subxyphoid: LV posterior, apex to the right of the screen
  • Signs of right sided heart strain (D sign, McConnel’s sign, large RV) can be clues to a PE in the right setting, but are only helpful if they are known to be acute.  
  • Look for EF in the parasternal long and apical 4 chamber views.  Look for concentric squeeze with change in the size of the LV cavity, and look to see the anterior leaflet of the mitral valve hitting the septum. Categorize EF as normal or low when you are just starting out.  

AAA

  • Look for the spine.  The spine is a bony structure with posterior shadowing, and that is your landmark for finding the aorta.  The aorta will lie just anterior to the spine.  
  • Perform a quick sweep of the entire transverse aorta before you start measuring.  You want to find a AAA as soon as possible.  
  • Measure the abdominal aorta outer wall to outer wall.  
  • Try to find the takeoff of the SMA.  If a AAA is present within 2 cm of the SMA takeoff, it likely involves the renal arteries, and thus surgical approach will be different. 
  • A normal aorta is < 3 cm, becomes more anterior as you move distally, and tapers as you move distally.  
  • AAA that are > 5 cm or that contain thrombus are more likely to rupture.  
  • Remember that you may not see free fluid or any retroperitoneal blood in a patient with AAA rupture as US is poor at visualizing retroperitoneal blood.  
  • Common AAA pitfalls
    • Not finding the spine and measuring other structures (SMA, Bladder)
    • Backwards probe
    • Measuring the lumen only in patients with a AAA with thrombus