Regional Anesthesia





Key Words

ultrasound-guided regional anesthesia, post-operative pain, peripheral nerve blocks, local anesthetic, local anesthetic systemic toxicity

 




Synopsis


The use of ultrasound (US) has revolutionized regional anesthesia and become an important component of surgical anesthesia and acute pain management. Its relative safety and ease of performance make it a perfect option for surgeries in resource-poor settings. Specifically, regional anesthesia is used to desensitize a precise body part to painful stimulus. Research suggests that acute post-operative pain continues to be undertreated. US-guided regional anesthesia (UGRA) may be used to address acute post-operative pain and improve outcomes as well as provide surgical anesthesia for specific procedures. There are several applications for UGRA that are beyond the scope of this text. This chapter will focus on upper- and lower-extremity blocks. The overall purpose of this chapter is to provide step-by-step instruction on how to perform the most commonly used nerve blocks and to highlight their contribution in the context of reconstructive surgery in resource-poor settings.




Clinical Issues


Presentation


Acute post-operative pain is a recognized and challenging problem. UGRA is appropriate whenever post-operative pain control is a concern and can sometimes be used as the sole anesthetic, avoiding a general anesthesia altogether.


General Risks


The most worrisome risks for all peripheral nerve blocks include:



  • 1.

    Nerve injury


  • 2.

    Bleeding


  • 3.

    Infection



Associated Conditions


Patients with an existing nerve injury, or with skin or systemic infection (i.e., sepsis), or who have a coagulopathy of any etiology may not be good candidates for UGRA. The risks and benefits of a nerve block must always be considered.


Additional Considerations


Although this guide describes single-injection techniques, it is possible to place perineural catheters at the nerve targets to provide longer analgesia. Special equipment and pumps to provide continuous infusions are necessary and beyond the scope of this chapter.




Management




  • 1.

    Choice of local anesthetic (LA): There are many acceptable LAs that can be used to meet specific patient needs. In general, LA can be classified by duration and depth of block. The most commonly used LAs and their concentrations are listed in Table 1.4.1 .



    TABLE 1.4.1

    Local Anesthetics and Their Concentrations
































    Local Anesthetic Concentration
    Analgesic Block Surgical Block
    Short-Acting
    Lidocaine n/a 1.5%–2%
    Mepivacaine n/a 1.5%
    Long-Acting
    Ropivacaine 0.25% 0.5%
    Bupivacaine 0.25% 0.5%


  • 2.

    Equipment:



    • 1.

      US probe: High-frequency linear probe (10–15 MHz)


    • 2.

      Needle: 100-mm insulated needle



      • a.

        There are several regional anesthesia needles commercially available that all share these qualities



    • 3.

      An extension tube to attach a syringe of LA


    • 4.

      Blunt tip to minimize risk of nerve or vascular injury


    • 5.

      Skin preparation: chlorhexidine, Betadine, or alcohol


    • 6.

      Probe cover: helpful to maintain strict aseptic technique. When using a probe cover, limit air bubbles from gel because they will distort the US image.


    • 7.

      Monitors: pulse oximeter (audible heart rate tone), continuous ECG, and non-invasive blood pressure


    • 8.

      Sedation: titrate to the needs of your patient. Nerve blocks can be performed with little or no sedation. Midazolam 2 mg, fentanyl 100 mcg, or propofol 20 to 50 mg are commonly used dosages.



  • 3.

    Preparation:



    • 1.

      Position: ensure proper and comfortable patient positioning as well as ergonomic positioning of the US machine.


    • 2.

      US image: obtain best US image of the target by adjusting depth, gain, focus, and frequency of the probe.


    • 3.

      Skin preparation: strict aseptic technique is important at needle insertion site to minimize risk of infection.


    • 4.

      Safety pause: immediately before performing block, confirm:



      • a.

        Correct patient


      • b.

        Correct surgery and side


      • c.

        Correct block and side


      • d.

        No contraindications to nerve block


      • e.

        All equipment including resuscitation equipment is available, including 20% lipid emulsion.



    • 5.

      Injection technique:



      • a.

        An in-plane needle technique is described for all blocks included in this chapter, except for the ankle block.


      • b.

        Incremental injection of 5 mL with frequent aspiration for blood is important to minimize risk of complications.


      • c.

        High injection pressures may signify an intraneural injection, and redirection of the needle may be necessary.


      • d.

        Use slow injection of LA.







Techniques



Facial Block


Infra-Orbital Block


Intro: The infra-orbital block anesthetizes the infra-orbital nerve, a branch of the maxillary division (V2) of the trigeminal nerve, and provides sensory innervation to the upper lip, lower eyelid, and nasal vestibule area in between. It is easy to perform and can provide substantial analgesia for cleft lip surgeries in children.


Indications: Cleft lip surgery


Technique




  • 1.

    Patient Positioning:



    • a.

      Supine, anesthetized patient



  • 2.

    Technique:



    • a.

      Draw an imaginary line parallel to midline at mid-pupillary location.


    • b.

      Palpate the infra-orbital foramen just below the infra-orbital margin on the mid-pupillary line. This is your target.


    • c.

      Rest the index finger of your other hand on the infra-orbital ridge during injection to prevent inadvertent needle entry into the globe.


    • d.

      Injection: using a 30-gauge needle, start needle at mid-pupillary line even with the lateral border of nares and angle upward toward the infra-orbital foramen. Walk off bone into foramen; then deposit 0.5 to 1 mL of LA just outside foramen.


See Fig. 1.4.1 : Infra-Orbital Block.

Key Principles





  • Injection near the infra-orbital foramen allows sensory block of all branches of the infra-orbital nerve, which branches quickly after exiting the foramen.



  • A finger on the orbital ridge protects against globe injury.



  • Avoid injection inside the foramen to protect against compartment pressure and ischemic injury to the nerve. Be sure to pull out of the foramen before injection.



  • Bilateral blocks are recommended even for unilateral cleft lip, because surgery often crosses the midline.



  • For routine cleft lip repair, this block can enable avoidance of any opioids in small infants.



  • This block may not be completely effective if significant nasal reconstruction is required.





Fig. 1.4.1


Infra-Orbital Block.



Upper Extremity (Brachial Plexus)


Interscalene Block


Intro: The interscalene block is performed at the level of the nerve roots, between the anterior and middle scalene muscles of the neck within the interscalene groove. Blockade of the brachial plexus at the interscalene level reliably blocks C5 to C7 nerve roots but frequently spares the ulnar nerve distribution, resulting in failure to block the ring and small fingers.


Indications: surgery involving the shoulder, distal clavicle, and proximal humerus.


Technique




  • 1.

    Patient Positioning:



    • a.

      Supine, back elevated 30 to 45 degrees with patient’s head turned away from block site. Consider positioning a pillow under the ipsilateral shoulder if needling area is limited.



  • 2.

    Home Base:



    • a.

      Supraclavicular fossa. The nerve plexus and relevant vasculature are easily identifiable here by US. This is the same position as with a supraclavicular nerve block. Identify the subclavian artery and surrounding plexus, which appears as a “bunch of grapes.”



  • 3.

    Scanning:



    • a.

      Slide the probe in the cephalad direction while keeping the nerve plexus in the center of the screen, holding the probe perpendicular to the skin.


    • b.

      The nerve plexus will begin to appear as discrete hypoechoic or dark circles between the scalene muscles.



  • 4.

    Target:



    • a.

      Scan cephalad until the three distinct nerve roots are viewed stacked on top of one another within the interscalene groove. These are typically the C5 nerve root and two fascicles of C6.



  • 5.

    Needling:



    • a.

      Advance the needle anteriorly toward the target. For safety, it is recommended to deposit the LA posteriorly to the plexus. It is not necessary to puncture between the dark circles.


    • b.

      The needle may be redirected above or below the target to obtain adequate spread.



  • 6.

    Injection:



    • a.

      15 to 20 mL.


See Fig. 1.4.2 : Interscalene Block.

Key Principles





  • Unique side effects include Horner’s syndrome, hoarse voice from recurrent laryngeal nerve blockade, and ipsilateral hemi-diaphragmatic paresis from phrenic nerve palsy.



  • Lower volumes of LA and/or injecting posteriorly may reduce the incidence of phrenic nerve palsy.



  • Occasionally, the nerve roots may course through the scalene muscle (<5%). Target individual nerve roots if this is the case.



  • Be wary of neck vasculature traversing through the plexus. Use a Doppler if indicated to identify blood vessels.



  • The interscalene block spares the ulnar nerve distribution and proximal (above elbow) medial portion of arm near the axilla (intercostal-brachial nerve).





Fig. 1.4.2


Interscalene Brachial Plexus Block.

(A) Needle/probe/patient position for block on right shoulder. (B) Ultrasound image. (C) Ultrasound anatomy labeled with needle path (dashed black arrow).


Supraclavicular Block


Intro: The supraclavicular block is performed just above the clavicle at the level of the first rib where the trunks and divisions of the brachial plexus course. This block has grown in utility with the increase in utilization of US, because it allows the practitioner to view vital structures such as the pleura and arterial branches of the thyrocervical trunk, which traverse the plexus at this level.


Indications: Surgery below the shoulder, including the hand


Technique:



  • 1.

    Patient Positioning: Supine with head elevated approximately 45 degrees, turned away from surgical side.


  • 2.

    Home Base: Place the probe in the supraclavicular fossa with the beam aimed into the thorax as if to image “behind” the clavicle.


  • 3.

    Scanning:



    • a.

      Slide the probe medially until the subclavian artery is visualized as a pulsatile black circle.


    • b.

      The nerves can be seen at this level as a “cluster of grapes,” or round hypoechoic structures lateral to the artery.


    • c.

      Identify the first rib and pleura. There should be near complete dropout, or shadowing, deep to the first rib, whereas the image will appear hazy or shimmering deep to the pleura.


    • d.

      Tilt and slight rotation of the probe can improve the image of the nerves if they do not appear crisp.


    • e.

      Occasionally the first rib is not seen directly below the artery, depending on probe position. Care must be taken to avoid advancing the needle beyond the first rib or edge of the pleura.



  • 4.

    Target:



    • a.

      The trunks and divisions typically are found immediately lateral to the artery but can also extend far laterally and medial to the artery.


    • b.

      Doppler can be used to identify blood vessels that course through the plexus at this level.



  • 5.

    Needling:



    • a.

      Direct the needle from lateral to medial toward the “corner pocket” formed by the artery and first rib.


    • b.

      A single injection at the “corner pocket” is usually sufficient.


    • c.

      Other injection techniques have been described, including a second injection above the plexus and an “intra-cluster” injection. We recommend using the single-injection technique unless the spread is deemed inadequate.



  • 6.

    Injection:



    • a.

      20 to 30 mL.


See Fig. 1.4.3 : Supraclavicular Block.

Key Principles





  • Phrenic nerve palsy occurs in 1/3 of patients.



  • The carotid artery can be confused for the subclavian artery. Care should be taken to identify the first rib and pleura to help locate the appropriate target. The subclavian artery lies lateral to the carotid artery.



  • Ulnar nerve sparing is possible, and the block should be monitored as it sets up if the ulnar nerve distribution is important for surgery. Supplementation for the ulnar nerve can easily be done at or above the elbow if needed.


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Dec 24, 2019 | Posted by in Reconstructive surgery | Comments Off on Regional Anesthesia
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