Ultrasound Guided Nerve Blocks:

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Ultrasound Guided Nerve Blocks

• Raymond Graber, MD
• University Hospitals Case Medical Center
• Case Western Reserve University School of Medicine

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Goals

• Discuss rationale for US guidance.
• Learn proper techniques of US guidance.
• Discuss interesting findings seen with US.
• Discuss specific nerve blocks.

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Landmark Technique For Nerve Blocks

• Traditional nerve block techniques are based on
  the ability to palpate muscles, bones, and
  pulses.
• A normal consistent anatomic relationship between
  nerves and these other structures is assumed.

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Problems with Landmark TechniquesAnatomic
Variations

• There are normal variations in anatomy.
• Some patients have landmarks that are difficult
  to palpate.

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History of US Guidance

• 1989 Ting et al used US to examine spread of
  local anesthetic after axillary blocks.
• 1994 Reed Leighton used doppler to identify
  the axillary artery in an obese patient, and
  marked the skin prior to axillary block.
• 1994 (Kapral et al) supraclavicular blocks.
• 1998 ( Marhoffer) femoral blocks.

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Benefits of US Guidance

• Ability to see nearby vascular structures
• Ability to see nerves (sometimes!)
• Ability to visualize the needle approaching the
  nerve.
• Ability to see local anesthetic spread.
• Possibility of reducing complications.
• Can do postop without nerve stim.
• Less painful to use US instead of nerve stim when
  patient has a fracture.
• Can perform rescue blocks without nerve stim.

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Spread of Local

• US guidance has demonstrated one possible cause
  of patchy blocks incomplete surrounding of the
  nerve with local anesthetic.
• If after half the volume of local is injected,
  inadequate spread is seen, the needle can be
  repositioned.

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How Accurate is Nerve Stimulation?

• We used to assume a linear relationship between
  the threshold stimulating current (the lowest
  current you can still achieve a twitch at) and
  the distance from the needle tip to the nerve.
• Many authors recommend a current of 0.2-0.5 ma as
  a goal. Higher threshold currents would lead to
  more searching with the needle. Lower currents
  would mean increased risk of intraneural
  injection.
• The 2 following studies called this dogma into
  question.

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• In this study, interscalene blocks were done with
  paresthesia technique. Paresthesia is assumed to
  indicate contact with the nerve. When a
  paresthesia was obtained, the nerve stimulator
  was turned on.
• Results All patients had easily elicited
  paresthesias Only 30 of patients exhibited any
  motor response to electrical stimulation up to
  1.0 mA
• Conclusion Elicitation of paresthesia does not
  translate to an ability to elicit a motor
  response to a peripheral nerve stimulator in the
  majority of patients.

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• In this study, needles were placed into pig
  nerves, then nerve stim turned on to see at what
  current motor response occurred.

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• Thus, intraneural placement occurred despite
  presumed safe nerve stim currents in 66 of the
  nerves.

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Demonstration of Intraneural Injection with US
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Does US Improve Success Rate?

• RAPM May-June 2008
• US guidance improves success rate of interscalene
  brachial plexus blockade (99 vs 91). (Kapral et
  al)
• US guidance improves the success of sciatic nerve
  block at the popliteal fossa (89.2 vs 60.6).
  (Perlas et al)
• Both these studies allowed the US group to
  reposition to needle to ensure good spread of
  local anesthetic, whereas the nerve stim groups
  were singe injection.

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US Guided Nerve Blocks Equipment, Terminology
Technical Aspects
The equipment is evolving. High resolution
imaging is now available in laptop size
equipment. The better the resolution, the easier
it is to image nerves. Some equipment examples
follow, but more systems are coming on the market.
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Sonosite 180C11 Probe

• 11-mm broadband curved array transducer.
• Imaging modes 2D, M-mode, color power Doppler,
  directional color power Doppler
• Physical characteristics
• Frequency broadband 7-4 MHz
• Maximum Depth 10 cm
• Maximum Field of View 90º
• Our original device images hard to interpret.
  Good for IJ placements.

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Sonosite C11HFL38 Probe

• 38 mm broadband flat array transducer.
• Imaging modes 2D, M-mode, color power Doppler,
  directional color power Doppler
• Physical characteristics
• Frequency broadband 10-5MHz
• Maximum Depth 6 cm

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GE 12L-RSUS Probe

• 42 x 7 mm broadband flat array transducer.
• Imaging modes 2D, M-mode, color Doppler,
  harmonic and compound imaging.
• Physical characteristics
• Frequency 5-13 MHz
• Maximum Depth 6-8 cm
• Maximum width of View 39 mm.
• Most of the images in this talk are from this
  device.

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Equipment Supplies

• Block kit.
• Needles block, skin wheal
• Nerve stimulator
• Sterile sheath kit (contains gel, sleeve, rubber
  bands.)
• Local anesthetic
• US machine

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SAX Imaging

• Most commonly used.

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LAX Imaging

• Rarely used.

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SAX Out of Plane (OOP) Approach
Needle is at best seen only in cross section.
More commonly, tissue movement is seen as the
needle approaches the target.
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SAX In Plane (IP) Approach
With this approach, one can see the needle
approach the target. However, be aware that it
is easy to be a little oblique, and to not
actually see the needle tip.
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Needle Type

• Typical 22 g insulated block needles can be used.
  
• Alternatively, 18 g Touhy needles sometimes are
  used, because are easier visualized, or for
  catheter placement.
• OOP approach Needle diameter would not matter,
  since the needle is not visualized with this
  technique.
• IP approach A larger diameter needle can be
  helpful, especially if the nerve is relatively
  deeper, and a longer needle is required.

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Technique (1)

• IP approach line up needle in middle of US
  plane. Penetrate skin and enter under probe. If
  needle not seen, move probe slightly and slowly
  to find needle.

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Technique (2)

• Move needle to desired location.
• Inject 1 ml to verify needle location.
• Reposition needle if needed.

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Technique (3) Local Anesthetic Spread

• Examine spread of local.
• Reposition to next location if desired.

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With US guidance, is nerve stimulation still
required?
As you get better with US, you rely less and less
on nerve stim. However, may be advantageous to
leave nerve stim on at low current for extra
feedback on needle tip location.
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Femoral Nerve Block