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What is Ultrasound?

Ultrasound is a common imaging modality that allows visualisation in real time.  As such it is becoming increasingly popular on the wards for diagnosis and management purposes.  You should be familiar with its operation and know in which situations it may help your clinical decision making.

 


Where will I see Ultrasound in the Hospital?

  • Assessment of jugular venous pressure (JVP)
  • Venipuncture
  • In the Emergency Department for FAST (Focused Assessment for Screening in Trauma)
  • Lumbar puncture
  • Thoracentesis
  • Paracentesis
  • Evaluation of abdominal organs
  • Biopsy
  • Pregnancy

 


Ultrasound Basics

How Does Ultrasound Work? ¹

  • High-frequency sound waves are transmitted from a transducer
  • These sound waves are then reflected by different tissue types in different ways
  • The reflected sound waves are then picked up by the ultrasound transducer
  • The sound waves are then transformed into an image by special software

 

How do tissue types differ in their reflection of sound waves?

  • Hyperechoic = bright (most waves reflected)
    • Bones, fat, stones
  • Hypoechoic = dark (most waves pass through)
    • Cartilage, muscle
  • Anechoic = black (no reflection)
    • Any fluid or fluid-filled structure
  • Shadow = hypoechoic area behind a hyperechoic structure

 

Getting Started

1. Turn the machine on (easy, but often overlooked; often a button in the upper left or right corner of the keypad)

2. Enter the patient’s information

3. Select an appropriate ultrasound probe

 

Probe Basics

How do I know which probe I should use?

Typically there are 3 types of probes:

  • Linear: high frequency (7-15MHz)
    • High resolution but superficial (1-6cm) depth
    • Good for vascular access, nerve blocks, assessment of testes and superficial lung tissue
  • Curvilinear: low frequency (2-5MHz)
    • Low resolution, but greater depth (10-20cm)
    • Useful for abdominal, pelvic, obstetric and deep lung tissue
  • Phased: lowest frequency (1-3MHz)
    • Useful for echocardiography

 

How do I hold the probe?

Correct ultrasound probe grasp

Figure 1: Correct ultrasound probe grasp ²

 

 

Probe orientation

  • Typically, there is a dot or a cross on the probe, this correlates with a dot on the left side of the screen
  • This marker should be toward the patient’s right in transverse and head in longitudinal
  • If you are unsure, it is best to place your finger on one side of the probe and look for movement on the screen (the side that shows movement by the dot is the side that should face the patient’s right)

 

Final Steps

4. Apply gel to the probe and patient

5. Place the probe onto the patient and observe the images on the screen

6. Adjust settings to achieve an optimal view

 

Common settings

  • Gain:
    • Gain = brightness
    • Usually a knob
    • Toggle until fluid is black and soft tissue is mid-grey with some parts of the image appearing white
  • Depth:
    • Usually two buttons (up and down)
    • Depth measures are shown in cm on the side of the screen
    • Start at high depth to orientate yourself, then work more superficially to bring the object of interest into the middle of the screen

 

Tips for good images

  • Use lots of gel
  • Press hard (but ensure the patient is comfortable)
  • Dim the lights
  • Ensure the probe is perpendicular to the skin

 


Measuring the JVP with Ultrasound

1. Position your patient as you would when assessing the jugular venous pressure (JVP) in a clinical exam (supine, head of bed at 45°, patient’s head laterally rotated to the side not being scanned)

2. Set the gain to mid-range

3. Apply gel to the patient’s neck

4. Place the probe in a transverse orientation within 2cm of the clavicle

5. Identify the internal jugular vein (IJV) and the carotid artery, assessing the following:

  • Wall thickness
    • Arteries have thicker more muscular walls than venous structures
  • Shape
    • The carotid will be circular whereas the IJV can be oval or irregularly shaped
  • Compressibility
    • Veins are easily compressed
    • Pro tip: if you only see one vessel, use less pressure as you may have fully compressed the IJV
  • Respiratory variability
    • Central venous structures will fluctuate in size with respiration
  • Position
    • The IJV is usually (but not always) lateral to the carotid

 

Figure 2: Cross section of the Carotid and IJV ³

 

6. Centre the probe so the IJ is centred on the monitor

7. Slowly rotate the probe keeping the IJ in the centre until a sagittal view is achieved (ensure you are not foreshortening the vein by carefully moving the probe medially and laterally)

8. Locate the point of the initial collapse of the IJV (centre the probe over this point)

9. Measure the JVP height above the sternal angle as normal

Point of initial collapse of IJ in the sagittal plane

Figure 3: Point of initial collapse of IJ in the sagittal plane (middle arrow) 4

 

 


Ultrasound Guided Intravenous Access 5,6

In this section, we will be focusing on peripheral intravenous access, however, similar principles are applied for central venous line insertions.

Indications

  • Multiple failed attempts
  • History of difficult cannulation

 

Contraindications

  • Ultrasound-guided IV access should not supplant intraosseous (IO) access in life-threatening situations

 

Which Probe?

  • Choose a high frequency (5-12 MHz) linear transducer, as high frequency permits a better resolution of structures close to the surface of the skin
  • A lower frequency curved probe may be more effective in obese patients

 

Steps

1. Select a vein (as per non-ultrasound guided peripheral IV placement)

2. Machine set up:

  • Turn on
  • Choose appropriate examination pre-set: typically “peripheral vascular venous” or “superficial vascular, venous”

3. Clean the ultrasound probe

4. Apply a tourniquet

5. Apply gel to the ultrasound probe

6. Identify the target vein in the transverse plane:

  • Note depth of the anterior wall of the vein
  • Pay attention to any adjacent structures

7. Once identified, rotate the probe into the longitudinal plane:

  • Hold the probe with the thumb, index, and middle fingers as shown, using the remaining fingers as an anchor

Figure 4: Correct hand placement for ultrasound-guided IV access 5

8. Clean the patient’s skin

9. Align the needle prior to insertion

10. Insert the needle just distal to the transducer probe:

  • You should be able to see the needle throughout the procedure on the screen, if you cannot, you must realign
  • You can gently rock the probe to help see the flash of the needle tip if needed
  • Do not advance the needle unless you are able to clearly see the tip

11. Advance the needle into the vein

 

Figure 5: Ultrasound showing needle tip in the lumen of the vein 5

 

12. Hold the needle still and watch as you advance the catheter into the vein

 

Figure 6: Ultrasound showing catheter in the vein 5

Common Pitfalls

  • Applying too much pressure and thus collapsing the vein
  • Incorrect settings on the ultrasound machine

 


Focused Assessment with Sonography for Trauma (FAST)

  • Used in emergency settings to rule out free fluid in the abdomen as well as pericardial effusions
  • Remember, fluid shows up as black, so the scanning clinician is inspecting for black lines surrounding organs
  • FAST assessment uses a curvilinear probe

 

Probe locations

Figure 7: FAST scan probe locations

Figure 7: FAST scan probe locations 2

 

 

Right Upper Quadrant View (Morison’s pouch)

  • The ultrasound probe is positioned in the coronal plane in right mid-axillary line (between rib 11 and 12)
  • Once positioned correctly, the ultrasonographer inspects  for evidence of free fluid between the liver and the kidney
  • Ribs are often in the way;  so the probe often requires some tilting/rotating to align it with an intercostal space

Figure 8: Ultrasound showing fluid between the right kidney and liver  7

 

 

Left Upper Quadrant View (Perisplenic view)

  • Similar to Morison’s pouch, but the transducer is placed approximately half a probe length more superior and posterior (as the left kidney is more superior and posterior than the right)
  • The ultrasonographer observes for free fluid between the kidney and spleen

Figure 9: Ultrasound showing fluid between the left kidney and spleen 8

Cardiac View

  • The ultrasound probe is positioned in the transverse plane, within the sub-xiphoid region (with the probe aimed at the heart)
  • The ultrasonographer inspects for evidence of pericardial effusion

Figure 10: Ultrasound showing a pericardial effusion 8

Pelvic View (Suprapubic)

  • The ultrasound probe is positioned in the suprapubic region, pointing towards the bladder
  • The ultrasonographer inspects for free fluid outside of the bladder
  • Both transverse and longitudinal images are typically assessed

Figure 11: Ultrasound showing free fluid around the bladder 8

 


References

1. Toronto Notes 2016: Medical Students Essential Med Notes.

2. Clay Kurtz (Author’s own work)

3. Emergency Ultrasonography (http://www.emergencyultrasoundteaching.com). Resources and Tutorials on EM Ultrasound. [LINK]

4. Canadian Internal Medicine Ultrasound (CIMUS) website [LINK]

5. Joing S, Strote S, Caroon L, et al. Ultrasound-guided peripheral IV placement. N Engl J Med. 2012;366(25):e38. https://doi.org/10.1056/NEJMvcm1005951. doi: 10.1056/NEJMvcm1005951.

6. UpToDate. Principles of ultrasound-guided venous access. Jeremiah J Sabado, MD and Mauro Pittiruti, MD. [LINK]

7. Wikipedia. Public Domain. [LINK]

8. The POCUS Atlas (http://www.thepocusatlas.com) [LINK]

 


 

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