Hocus POCUS

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What is POCUS?

POCUS is point-of-care ultrasound that is FOCUSED, DEDICATED, and meant to answer SPECIFIC questions at the bedside.

It is in contrast to COMPREHENSIVE (not “real,” not “formal”) ultrasounds, which evaluate an entire anatomical region.

POCUS is generally used to achieved a specific goal, e.g. rule in or rule out, “yes or no” questions.

What POCUS is NOT

  • A replacement for radiology
  • Comprehensive ultrasound
  • A replacement for sub-specialists
  • All the answers

Why do POCUS?

  • Extension of the physical exam
  • Usually can get answers quickly
  • Offers something for patients who might not be able to get more extensive or repeat imaging easily or quickly (inpatient and outpatient)
  • Review anatomy (without cadavers)
  • Cost-effective
  • Portable
  • Still a relatively new and expanding field

Ultrasound Physics

  • Sound waves are emitted by piezoelectric material inside the transducers
  • As they move through tissue, the sounds waves are reflected, refracted, scattered, transmitted, and absorbed by tissues depending on the tissue property
  • Ultrasound images are produced by the sounds waves reflected back to the transducer

Ultrasound Modes

2D or B-mode (“brightness” mode)

  • Most commonly used and usual default mode for most ultrasounds

M-mode (“motion” mode)

  • Tracks motion through a single line over time

Doppler imaging

  • Uses Doppler effect to measure relative motion

Spectral Doppler

  • Quantitative assessment of velocities

Transducers

Linear probe

  • Frequency: 5-15 mHz
  • Imaging depth: 6-9 cm
  • Common applications: 
    • Arteries/veins
    • Procedures
    • Skin/soft tissue
    • Eyes
    • Thyroid
    • Lymph notes

Curvilinear probe

  • Frequency: 2-5 MHz
  • Imaging depth: 20-35 cm
  • Common applications: 
    • Gallbladder
    • Liver
    • Kidney
    • Spleen
    • Abdominal aorta

Phased array probe

  • Frequency 2-5 MHz
  • Imaging depth: 20-35 cm
  • Common applications: 
    • Heart
    • Lung
    • Can also be used for abdominal applications

Terminology & Orientation

Imaging planes: 

  • Sagittal (Longitudinal) 
  • Transverse (Axial) 
  • Coronal (Frontal) 

Orientation:

  • Top of the screen is closer to the footprint of the probe.
  • Indicator is (usually) on the left side of the screen.
  • Test marker side with gel.
  • For most images, probe marker will be to the patient’s RIGHT or HEAD.

Image acquisition

General advice: 

  • To get better images, consider more gel and more pressure
  • Hold the probe close to the patient’s skin
  • Object of interest should take up about 2/3 of the screen (depth adjustment)
  • Can adjust brightness (gain)
  • If it moves, hold the probe still
  • If it does not move, scan through the object of interest
  • Call what you are comfortable calling—always fine to order a comprehensive or other testing if unsure
  • Save images!

Enemies of US: 

Acoustic windows: 

Cardiac US

Four primary views:

  • Parasternal long
    • Probe marker pointed to the patient’s right shoulder
    • Classic view is the “three-and-one” view
  • Parasternal short
    • Probe marker pointed to the patient’s right hip (ED convention) or left shoulder (cardiology convention)
    • Location is the same as parasternal long, just rotated 90º 
    • Classic view is the “donut and croissant” view
  • Sub-xyphoid
    • Placement of probe under the xiphoid, with an overhand grip on the probe
    • Best view for effusion
  • Apical four-chamber
    • Left mammillary crease, with probe pointed towards right shoulder
    • Easiest if patient is able to lay on their left side

Five E’s: 

  • Effusion
  • Ejection
  • Equality
  • Exit
  • Entrance

FAST

Four views:

  • RUQ
  • LUQ
  • Sub-xyphoid
  • Bladder

Lung

Mid-clavicular line anteriorly, axillary, posteriorly.

B-lines: 

Pneumothorax: 

  • Use linear probe when patient is lying flat.
  • 1st, 2nd, 3rd intercostal spaces anteriorly have the most sensitivity.

Further reading!

  • Soni, N. J., Arntfield, Robert, Kory, Pierre. (2019). Point of Care Ultrasound (2nd ed.): Elsevier.
  • Tavares J, Ivo R, Gonzalez F, Lamas T, Mendes JJ. Global Ultrasound Check for the Critically lll (GUCCI)—a new systematized protocol unifying point-of-care ultrasound in critically ill patients based on clinical presentation. Open Access Emerg Med. 2019;11:133-145
  • Moore, C. (2008). Current issues with emergency cardiac ultrasound probe and image conventions. Acad Emerg Med, 15(3), 278-284. doi:10.1111/j.1553-2712.2008.00052.x
  • Smith, Z. A., & Wood, D. (2014). Emergency focussed assessment with sonography in trauma (FAST) and haemodynamic stability. Emerg Med J, 31(4), 273-277. doi:10.1136/emermed-2012-202268

Blog post based on Med-Peds Forum talk by Burton Shen, MP Core Faculty

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