ultrasound guided nerve block part i

8/10/2019 Ultrasound Guided Nerve Block Part I

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Ultrasound Guided

Nerve Blocks:Raymond Graber, MD

University Hospitals Case Medical Center

Case Western Reserve University School of Medicine
http://www.nysora.com/techniques_ultrasound/equipment/files/1.jpg


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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 Techniques:

Anatomic 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 thenerve.

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 whenpatient has a fracture.

Can perform rescue blocks without nerve stim.


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Spread of Local:

US guidance has demonstrated one possible cause ofpatchy blocksincomplete 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 indicatecontact with the nerve. When a paresthesia was obtained,the nerve stimulator was turned on.

Results:All patients had easily elicited paresthesias Only30% 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 nervestimulator in the majority of patients.


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In this study, needles were placed into pignerves, 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 repositionto 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 180+

C11 Probe

11-mm broadband curved arraytransducer.

Imaging modes: 2D, M-mode,color power Doppler, directionalcolor power Doppler

Physical characteristics:

Frequency: broadband 7-4MHz

Maximum Depth: 10 cm

Maximum Field of View: 90

Our original deviceimageshard to interpret. Good for IJplacements.


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Sonosite C11

HFL38 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-RS

US Probe 42 x 7 mm broadband flat array

transducer.

Imaging modes: 2D, M-mode,color Doppler, harmonic andcompound imaging.

Physical characteristics:

Frequency: 5-13 MHz

Maximum Depth: 6-8 cm

Maximum width of View: 39

mm.

Most of the images in thistalk are from this device.
http://www.nysora.com/techniques_ultrasound/infraclavicular/files/3.jpg


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Equipment & Supplies

Block kit.

Needlesblock, 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, anda 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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Move needle to desired location. Inject 1 ml to verify needle location.

Reposition needle if needed.

Technique (2)


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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, isnerve 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

ultrasound guided nerve block part i

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