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Basics of US Regional Anaesthesia
November 2008
Essential Physics
HIGH frequency = great resolution but poor penetrationpoor penetration
LOW frequency = poor resolutionpoor resolution but great penetration
Potential Advantages of US
• No ionising radiation
• Portability• Portability
• Robust
• Advent of NICE has
increased machine
accessibility
Potential Advantages of US• Identify target nerve - fascicular pattern, 90% of peripheral nerves have
this pattern.
• White / hyperechoic is peri/epineurium
• Black / hypoechoic is nerve tissue
Transverse Longitudinal
Left interscalene
More proximally where the nerve tissue is more dense the nerve can appear more hypoechoic –
black bubbles with white borders.
Potential Advantages of US
• Identify surrounding structures e.g. blood vessels,
pleura, peritoneum
• Determine best approach to target nerve• Determine best approach to target nerve
• Real time guidance
• Patients with neuropathy do not respond normally
to PNS
• Observe local anaesthetic distribution
Normal Anatomy ?
Potential Advantages of US
• Faster onset of block
• Assess catheter position
• Repeat block if extended surgery
• Paralysed patient!
Additional Advantages in Children
• Under GA – warning signs of intravascular or intraneural injection may be masked
• Smaller mass so nerves more superficial so • Smaller mass so nerves more superficial so allowing higher frequencies to be used
• Less margin for error as vulnerable structures such as pleura are closer to nerves
Additional Advantages in Children
• Less ossification allows better neuroaxial imaging
• Variable landmarks with age (neonate to teenager) teenager)
• Congenital abnormalities can lead to misleading surface landmarks
• Decreased volume of LA required thus diminishingthe risk of toxicity and allowing multiple blocks
PNS ?
OOP out of plane approach
Needle - Probe Orientation
OOPOOPOOPOOP - ? Familiar if used for vascular, 3 axis, inferior
guidance
IP in plane approach
Needle - Probe Orientation
IP – unfamiliar, 2 axis, better control,
may be less comfortable in awake patient
Needle gauge and visibility
Schafhalter-Zoppoth et al: RAPM Sept-Oct 2004
Varying needles seen at 0º& 45 ºSchafhalter-Zoppoth et al: RAPM Sept-Oct 2004
18G - Hustead epidural needle
18G - UP Tuohy needle18G - UP Tuohy needle
18G - Standard Sprotte (pencil tip) needle
18G - Spinal (Quincke tip) needle
Sterility
Sheath – catheters
1. Degrades the picture
2. Interferes with grip
NO touch or IV 3000
Technique
Ensure an ergonomic setup in your anaesthetic room
PatientOperator
Technique
• Assess surface anatomy
• Remove all air from injectate and needle
• Select appropriate probe – footprint size, depth
• US machine set for ‘small parts’ or nerve and high resolution ( if target
greater than 4cm consider using lower resolution)greater than 4cm consider using lower resolution)
• Ensure multibeam activated
• Use adequate US gel to provide an air free interface
• Orientate probe and image
• Probe hand – non-dominant hand
• Mapping scan (scanning hand on patient provides proprioception and
better probe fixation when needling)
Technique
• Start deep, then work up (generally 4cm is adequate )
• Nerve should be viewed in middle depth of screen
• Orientate again
• Choose entry point
• Out of Plane target in middle of screen
• In Plane target on opposite side that needle enters• In Plane target on opposite side that needle enters
• aim needle to one side of nerve- OOP approach 3/9 O’clock , IP approach 6/12 O’clock ( 12 O’clock is performed second)
• PNS to confirm nerve
• Aspirate then inject 0.5ml LA / saline
• Assess spread
• If you lose the needle image first check your hands not the monitor
Five quality-compromising patterns of behavior were identified:
• failure to recognize the maldistribution of local anesthesia
• failure to recognize an intramuscular location of the needle tip before injection
• fatigue
SIX
• fatigue
• to correctly correlate the sidedness of the patient with the sidedness of the ultrasound image
• poor choice of needle-insertion site and angle with respect to the probe preventing accurate needle visualization
• Over insertion of needle ~ 20% know where your tip is!
Difficulties of US
• Depth - improving with use
of curvilinear probes and
software eg Tissue Harmonic
ImagingImaging
• Ossification – US can’t pass
through it , sector probes
can help view between
bones eg ribs
Anisotropy – the nerves have a now you see
me now you don’t quality. They reflect US ,
thus if the US beam doesn’t hit the nerve
perpendicularly then it is less likely to
return to the probe and an image formed.
Artefact– if the target is only visible in one plane it is probably
isn’t real!
Arrows indicate areas of post cystic areas of post cystic enhancement in the infraclavicular
region. Not brachial plexus cords.
Difficulties of US
• Learning curve, some blocks are harder than others.
• Greater anatomical • Greater anatomical knowledge required, get that Schnell out and dust it off
Conclusion
• Practice on yourselves and staff FIRST
• Start with simple (e.g. forearm and femoral blocks) and
familiar blocks in teenagers
• Always use a PNS until you master US• Always use a PNS until you master US
• Use the highest frequency available for the depth of
target in tissues
• US is only as good as the operator
• Remember it takes 3 years to train as a
radiographer!