Basics of US Regional Anaesthesia. November 2008

Transcription

1 Basics of US Regional Anaesthesia November 2008

2 Essential Physics HIGH frequency = great resolution but poor penetration LOW frequency = poor resolution but great penetration

3 Potential Advantages of US No ionising radiation Portability Robust Advent of NICE has increased machine accessibility

4 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

5 Left interscalene More proximally where the nerve tissue is more dense the nerve can appear more hypoechoic black bubbles with white borders.

6 Potential Advantages of US Identify surrounding structures e.g. blood vessels, pleura, peritoneum Determine best approach to target nerve Real time guidance Patients with neuropathy do not respond normally to PNS Observe local anaesthetic distribution

7 Normal Anatomy?

8 Potential Advantages of US Faster onset of block Assess catheter position Repeat block if extended surgery Paralysed patient!

9 Additional Advantages in Children Under GA warning signs of intravascular or intraneural injection may be masked 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

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11 Additional Advantages in Children Less ossification allows better neuroaxial imaging Variable landmarks with age (neonate to teenager) Congenital abnormalities can lead to misleading surface landmarks Decreased volume of LA required thus diminishing the risk of toxicity and allowing multiple blocks

12 PNS?

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15 OOP out of plane approach

16 Needle - Probe Orientation OOP -? Familiar if used for vascular, 3 axis, inferior guidance

17 IP in plane approach

18 Needle - Probe Orientation IP unfamiliar, 2 axis, better control, may be less comfortable in awake patient

19 Needle gauge and visibility Schafhalter-Zoppoth et al: RAPM Sept-Oct 2004

20 Varying needles seen at 0º& 45 º Schafhalter-Zoppoth et al: RAPM Sept-Oct G - Hustead epidural needle 18G - UP Tuohy needle 18G - Standard Sprotte (pencil tip) needle 18G - Spinal (Quincke tip) needle

21 Sterility Sheath catheters 1. Degrades the picture 2. Interferes with grip NO touch or IV 3000

22 Technique Ensure an ergonomic setup in your anaesthetic room Patient Operator

23 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) 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)

24 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 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

25 Five SIXquality-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 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!

26 Difficulties of US Depth - improving with use of curvilinear probes and software eg Tissue Harmonic Imaging Ossification US can t pass through it, sector probes can help view between bones eg ribs

27 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.

28 Artefact if the target is only visible in one plane it is probably isn t real! Arrows indicate areas of post cystic enhancement in the infraclavicular region. Not brachial plexus cords.

29 Difficulties of US Learning curve, some blocks are harder than others. Greater anatomical knowledge required, get that Schnell out and dust it off

30 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 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!