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Basics of Ultrasound Guided Nerve Blocks
Dr Shiv Kumar Singh Consultant Anaesthesia
Royal Liverpool University Hospitals [email protected]
www.anaesthesiaworld.com
Know your machine
Probes: Frequency and ResoluJon
Curvilinear Probe: Low frequency , deeper structure
Linear Probe: High Frequency, superficial structures
High (8–12 MHz), Medium (6–10 MHz), and Low (2–5 MHz)
Transducer selecJon
• Where is the area of interest?
• Deep/superficial
• Size of scanning window
• Size of paJent?
Frequency vs resoluJon
• Higher frequency = beRer resoluJon
• Decreased penetraJon
• Superficial scanning
Aspect markers
Aspect Marker
The aspect marker (green dot) on the screen corresponds to the NOTCH on this probe NOT THE DOT
Important Knobs on the machine
Preset Knob: Most Important
Press patient button and once the screen appears, use track pad to move the arrow and then press select
Nerve Preset
• Set of sophisJcated algorithms that the machine uses automaJcally, appropriate to what you are doing
• Gives the machine some idea of what you want to do!
• Correct preset, a great starJng point
Gain Knobs
Increase gain = Brighter image
Decrease gain = darker image
Adjust gain unJl same level of brightness displayed regardless of depth
Gain se\ngs
Too dark
Balanced
Too bright
Auto gain: Similar to preset
Micro Maxx
M Turbo
Depth Knobs
Adjusts displayed data
Start deep to see all anatomy
Adjust to fill display with area of interest
Depth Too
shallow Too deep
Correct depth
As you increase the depth the widow will become narrower
This
This to
AdjusJng the frequency
These are called RESoluJon, GENeral and PENetraJon
Use highest resoluJon you can without compromising far field echoes and without impacJng frame rate
Frequency buRons
Colour Doppler
Flow toward transducer = RED
Flow away from transducer = BLUE
For the machine: Keep it simple
Get used to working with:-‐
• PRESET
• DEPTH
• GAIN
• FREQUENCY
• COLOUR DOPPLER
A`er you know the machine; know your anatomy
Landmarks are sJll important
Know your anatomy
Can’t see anything!!!
apply PART(S)
What is PART(S)
• Pressure
• Alignment by
• RotaJon and
• Tilt and Slide
PART
Apply little pressure and tilt the probe so that it is perpendicular and parallel to the structure you are trying to visualize
Beam not returning to the probe
PART
Medial Lateral
Caudal
Cranial
RotaJon on the Axis
Try this with Femoral Nerve
Can you idenJfy the femoral nerve in the next pic?
Where is the nerve?
Where is the nerve?
Fascia Lata
Fascia Iliaca Femoral Artery
Femoral Nerve
Try again and again
• Not all paJents are the same
• ECHOGENIC Vs PHOTOGENIC: Some people are more photogenic than others, similarly some are more echogenic than others
• Anatomy is variable, so don’t expect to see textbook picture all the Jmes
A`er idenJfying the nerves
Next difficult part is hand eye co-‐ordinaJon
Improving Needle visibility
Learning Hand-‐eye-‐coordinaJon
Everything in your “field of vision” (ergonomics)
NOT THIS!!!
PracJce hand eye coordinaJon
• Use Phantoms (Costly)
• Or Turkey/chicken Legs!!!
• Or make your own
phantoms using jelly
or agar
Why do we fail to visualize the needle
1mm thick beam
Beam: Credit card thin, 1mm slice
Aligning the thin needle with the beam can be difficult and need practice
Beams need to return back!!!
If the needle is more than 60o to the probe, you will not visualise the needle
Align by Jlt, rotaJon and slide
Heel in maneuver
Method of reducing the angle between the needle and the probe to collect the returning beam
Heel in maneuver: collecJng the returning beam
The beam from the probe are hi\ng it perpendicularly
Move only one part at a Jme
• Only move the ultrasound transducer or the needle to opJmize procedure needle Jp visualizaJon
• USRA is a dynamic process
• Do not inject LA Jll you can visualise the Jp
Good Luck