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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!