Looking for Glass?

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Point-of-care ultrasound can help detect foreign bodies in murky water. 

Once upon a time you were working a Fast-Track shift with the usual rapid turnover of colds, UTI’s, lacerations, abscesses, sprains and the like when you look at the chief complaint for your next patient. It reads “Foreign Body for 3 months”. What emergency physician doesn’t appreciate both the novelty and the challenge of a foreign body, be it in the ear, eye, nose, throat or somewhere more embarrassing. Reading the nurses narrative, you obtain a bit more information and detail on just why someone has had a foreign body in their body for three whole months: “Fell on outstretched hand 3 months ago. States there is a piece of glass in his palm. Has been to the ED three times previously as well as PMD twice and was referred to see a specialist who ended up not taking his insurance. Has appointment to see another specialist but it is over a month and a half from now. Doesn’t want to wait that long.”

You waltz in cautiously, smile, introduce yourself and hand your patient one of your business cards. The nurses HPI was a great summary of the case. The patient basically gives you the same information peppered with his frustration of what seems to him to be a simple problem. He ends with the statement that he has had it “up to here” with his HMO. He begs you to try to take it out and then shows you his palm (see image 1 above).

You note a chronic appearing granuloma and decide you would like to do the right thing. But you also worry that if you injure the patient, the lawyers will come after you. Obviously, there is no rush to getting it done today in anyone’s mind but the patient’s. But isn’t it his opinion that matters most? You place an order for an I & D tray as well as a written informed consent. You also order an x-ray which confirms a radio-opaque foreign body is indeed present. You then decide to use the ED ultrasound machine, specifically the small parts probe, to get a better idea of how deep the foreign body is so you can decide if you are willing to go digging for glass. You obtain image 2.

glass2

You are not certain what you are looking at and feel that the uneven surface of the patient’s palm is affecting your image quality. You wonder if there is a way to get a better image. Is there?

Yes, there is. You have a few options. One is a stand-off pad. A 500 mL bag of IV fluid sandwiched between two layers of ultrasound will give you better image quality and negate the trouble caused by the uneven surface of the patient’s palm. Another option is water immersion ultrasound. By placing the patient’s hand underwater in a basin and hovering the ultrasound probe above the area of interest a much enhanced image can be obtained (see image 3 below).

glass3

It’s actually quite beautiful to see. The starry night artifact above the area of interest is from floating bits of ultrasound gel that was still on the patient’s hand when he submerged it. It’s not a recommended part of the process, but looks so cool! The foreign body appeared to be close to the surface. An incision was made and a piece of glass removed (see image 4 below). The procedure was more difficult than anticipated, which is frequently the case for foreign bodies in the hands or feet.

glass4

Pearls & Pitfalls for Point-of-Care Ultrasonography

  1. Probe & Positioning: Use a high frequency linear array transducer (10-13 MHz) for superficial structures and scans.  For very superficial structures use a stand-off pad (you can improvise with a bag of saline) or a water immersion.
  2. Target Confirmation: Obtain images in multiple planes (longitudinal, transverse, oblique) and utilize the contralateral side for comparison if necessary for clarification.
  3. Sensitivities: Know the Sensitivity of X-ray (XR) and Ultrasound (US) for different types of foreign bodies.  Basically, x-ray is about 98% for gravel, metal and glass but almost useless for plastic and organic material.  X-ray can also not be used real-time at the bedside to help localize.  Ultrasound is about 30-50% sensitive for various types of foreign bodies.  They will appear hyperechoic to different degrees and depending on material may produce different artifacts such as reverb, shadowing or even enhancement (glass).  Sensitivity is lower for smaller objects like a cactus spine and also may lose sensitivity for organic material as time goes on and water is absorbed into the material.  Below are some sensitivities for the study cited in the reference section
    – Gravel: XR: ~98%, US: ~40%: hyperechoic with shadowing
    – Metal: XR: ~98%, US: ~45%: reverberation or comet tail artifact
    – Glass: XR: ~98%, US: ~50%: may have posterior enhancement rather than shadowing
    – Cactus: XR: ~0%, US: ~30%: sensitivity of US lower due to smaller size
    – Wood: XR: ~0%, US: ~50%: sensitivity of US worse as time progresses (absorbs water)
    – Plastic: XR: ~0%, US: ~40%
  4. Know Your Limitations: Ultrasound may help clarify findings elicited by a thorough history and physical exam. When used correctly, it can lead to a more rapid diagnosis and/or improve diagnostic accuracy, especially for critical conditions or unstable patients.  Verify abnormal findings with formal imaging, either by CT, formal ultrasound or other modalities when indicated.  Find out if your department has a quality improvement program set up that is approved by both ED administration and radiology.
  5. Practice, Practice, Practice: The best way to minimize errors is through experience, so scan lots of normal anatomy.  The more scans you do, the better you will be able to differentiate abnormal from normal, even when you may not be sure exactly what the abnormality is.

ABOUT THE AUTHOR

EMERGENCY ULTRASOUND SECTION EDITOR
Dr. Pregerson manages a free online EM Ultrasound Image Library and is the editor of the Emergency Medicine Pocketbook series. He is also an author for EPM's soundings column.

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