Ultrasound Guided Nerve Blocks:

1. Ultrasound Guided Nerve Blocks: Raymond Graber, MD University Hospitals Case Medical Center Case Western Reserve University School of Medicine

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

3. 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.

4. Problems with Landmark Techniques:Anatomic Variations • There are normal variations in anatomy. • Some patients have landmarks that are difficult to palpate.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

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

11. Thus, intraneural placement occurred despite presumed “safe” nerve stim currents in 66% of the nerves.

12. Demonstration of Intraneural Injection with US:

14. 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.

15. 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.

16. Sonosite 180+C11 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.

17. 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

18. 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.

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

20. SAX Imaging • Most commonly used.

21. LAX Imaging • Rarely used.

22. 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.

23. 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.

24. 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.

25. 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.

26. Technique (2) • Move needle to desired location. • Inject 1 ml to verify needle location. • Reposition needle if needed.

27. Technique (3) Local Anesthetic Spread • Examine spread of local. • Reposition to next location if desired.

28. 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.

29. Femoral Nerve Block