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| Ultrasound Innovation Award |
| Online Abstract Submission |
| (Author: Chris Mitchell ) |
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| Abstract |
| Type: New equipment design |
| Title: Echogenic Mitchell needle |
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| Disclosure Statements |
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My research & development of my invention is not supported by a commercial company |
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| Abstract |
| * Background:
Progressive improvements in ultrasound technology and the development of new techniques have driven the rapid uptake of ultrasound guided regional anaesthesia (UGRA). The Achilles’ heel of UGRA is poor needle visibility / echogenicity.
When needles are inserted perpendicular to the ultrasound probe the highly reflective tissue-metal interface makes the needle highly echogenic and therefore visible. However as the needle is inserted at progressively steeper angles, the highly reflective surface results in the ultrasound waves striking the needle and being directed away from the transducer. Most needle shafts are nearly invisible when inserted at angles greater than 30 degrees from perpendicular.
Where possible, proceduralists modify their technique to maintain a shallow needle insertion angle. Regional blocks which demand a steep angle of insertion are typically referred to as difficult. Experienced proceduralists compensate for the lack of needle shaft echogenicity with excellent hand-eye co-ordination and the utilisation of more subtle, but less reliable signs, which include following the mildly echogenic tip of the needle, observing tissue movement and utilising hydrodissection.
* The ideal characteristics of a regional anaesthesia needle would include:
1. Equally visible / echogenic at all angles of insertion.
2. The tip of the needle should be clearly visible
3. Insulated to allow electrical peripheral nerve stimulation
4. Range of gauges available. Small gauge to minimise tissue trauma (eg 22G or 24G), large gauge to allow insertion of catheters
5. Polished needle surface to allow smooth passage of needle through tissues
6. Echogenic measurement markers on the needle to allow easy assessment of distances under ultrasound
7. Cheap
8. Single use.
* Invention:
The echogenic Mitchell needle (patent pending) was designed to address these ideal characteristic outlined above.
All prototypes in the following videos and still images have been produced by modifying a commercially available 22G stimulating peripheral nerve needle. The modifications have all been achieved with home built equipment so it is anticipated that further improvements will be possible with commercialisation. The echogenicity is produced by the addition of numerous small echogenic markings into the wall of the needle. The markings do not protrude from the needle wall, so do not alter the smooth characteristics of the needle in the tissue. The addition of the markings does slightly constrict the internal diameter of the needle, but the injection of local anaesthetic is not appreciably restricted. The markings are compatible with the insulating layer used by the manufacturer of the modified needles.
In multiple phantom and cadaveric experiments the new Mitchell echogenic needle is reliably highly visible up to 75 degrees from perpendicular. Attached is a series of images and a video demonstrating the needle in both pork and gelatin phantoms.
An earlier prototype of the echogenic Mitchell needle has been subjected to one independent study titled “Peripheral nerve block needle tip localisation under ultrasound – blinded assessment of five different needles in human fresh cadaveric tissue” by Edgcombe and Hocking. The poster of this trial is attached and the full study has been submitted for publication. In the study the Mitchell needle is referred to as needle T. This trial provided statistically significant evidence that the Mitchell needle was superior to other currently available needles in the ability to identify the needle tip at steep angles of insertion. This has significant implications for the practice and teaching of ultrasound guided regional anaesthesia.
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| Clinical Significance |
| The echogenicity of the Mitchell needle improves needle visualisation and tip identification. It will modify the ultrasound guided techniques used for most blocks.
It will:
• allow steeper needle insertion angles and shorter skin to target needling distance
• allow a skin entry point next to the transducer making it easier to pass the needle into the plane of view of the ultrasound
• reduce both blind and visualised movements of the needle in the tissues
• reduce the learning curve involved with ultrasound guided techniques and make teaching easier
• decrease the time taken for difficult blocks
• have application in all fields of medicine using ultrasound guided needle techniques.
Most importantly it should ultimately improve patient safety and increase the use of ultrasound guided regional anaesthesia.
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| Ultrasound Equipment |
| Manufacturer: Sonosite |
| Model: S-Nerve |
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| Probe Used |
| Type: L25 |
| Size: 25-mm |
| Frequency: 13-6 MHz |
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| Files |
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1. Filename: ISURA video presentation.wmv
2. Filename: Ultrasound images of the Mitchell echogenic needle in 2 phantoms.doc
3. Filename: Poster Needle Tip Localisation Edgcombe Hocking.ppt
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