• Clinical science

Local and regional anesthesia

Abstract

Local and regional anesthesia, in contrast to systemic, general anesthesia, involves the reversible numbing of a specific region of the body to prevent any sensation of pain. Pain may be blocked on different levels of its signal transduction pathway, e.g., at the site of origin, along the nerves, or in the brain. Accordingly, local and regional anesthesia can be divided into local topical and infiltration anesthesia, regional peripheral nerve blocks (PNB), and neuraxial anesthesia (e.g., spinal and epidural). Local anesthesia can be combined with general anesthesia, allowing the doses of anesthetic and analgesic drugs to be reduced during surgery, and may eliminate the need for other measures to achieve sufficient anesthesia (depending on the timeframe of surgery, risk profile, patient's consent). In general, local anesthesia carries less risk than general anesthesia, as essential body functions (e.g., respiration) are not affected. However, specific complications (e.g., bleeding, infection) and contraindications (e.g., patient's refusal, allergies) to local anesthesia must be considered. The drugs used for anesthesia can be found in the learning card local anesthetic agents.

Overview

Local and regional anesthesia are used prior to certain medical procedures to reduce perioperative pain; see “Indications” in local anesthetic agents.

  • Types of anesthetic agents and pathophysiology: See local anesthetic agents.
  • Contraindications
    • Absolute contraindications
      • Patient refusal
      • Allergies to local anesthetic drugs
    • Relative contraindications
      • Active inflammation/infection at the injection site
      • Neurological deficits in the area of distribution
  • Techniques

References:[1]

Local anesthesia

  • Definition: : Local anesthesia reversibly blocks nerve endings and pain conduction near the site of administration (limited area).
  • Indications: See local anesthetic agents.
  • Procedure
    • Topical anesthesia: : application of gels, ointments, sprays, or patches → anesthetic agent gets absorbed through the skin
    • Infiltration anesthesia: injection of local anesthetic directly into a painful area or one to be operated on
      • Technique:
        • Hygiene is crucial and depends on the specific intervention!
        • Sufficient infiltration of the target area (e.g., wound margins of a cut) by injecting the local anesthetic drug from all sides with as few punctures as possible; (avoid vascular infiltration with regular aspiration control! )
      • Injection site: injected locally subcutaneously and/or submucosally wherever required (e.g., wound margins of a cut)

The effect of local anesthetic drugs is very limited in inflamed tissues (e.g., abscess)! The acidic environment of inflamed tissues leads to protonation of the anesthetic drug, which in turn reduces its lipophilicity and prevents the spread of the drug to the site of action.

References:[2]

Peripheral nerve block

Definition

  • Local anesthetic is injected near a specific nerve or nerve bundle.

Indications

  • Surgery of the upper extremities
    • Interscalene block
    • Supraclavicular plexus block
    • Vertical infraclavicular plexus block
    • Axillary brachial plexus block
  • Surgery of the lower extremities
    • Sciatic and femoral nerve block
    • Lumbar plexus (psoas compartment) block
    • Inguinal block and paravertebral plexus block
  • Surgery of the scalp, neck, and trunk
  • Block of selected peripheral nerves (e.g., digital nerve block): technique to anesthetize the digits to perform surgery on the fingers or toes.

Relative contraindication

Procedure

  • Injection site: depends on the nerves that need to be blocked
  • Technique
    1. The patient is placed in a position that is tolerable for him or her and allows the practitioner to access the relevant nerve easily (e.g., to apply an axillary plexus block, the hand is placed underneath the head with the arm abducted and bent.)
    2. Hygiene: hand disinfection, sterile gloves, sterile face mask, utensils for wipe disinfection of the puncture site afterward, (if catheter is inserted, also sterile gown and sterile fenestrated drape)
    3. Identification of the relevant nerve guided by specific landmarks and
      • Ultrasound: ultrasound-guided needle advancement towards the target nerve
        1. Needle advancement towards the target nerve is vision-guided (the movement of the needle tip should always be monitored), aspiration tests should be performed continuously. The needle may be navigated, e.g., using the out-of-plane technique. or the inline technique
        2. Injection of the local anesthetic drug around the target nerve, no injection if high resistance is encountered, needle retraction if injection evokes pain or paresthesia!
      • Nerve stimulation test
        1. Oriented approach: The needle is inserted and advanced towards the target nerve with high current intensity (standard values: amplitude: 1.0–1.5 mA, stimulus duration: 0.1 ms, frequency: 2 Hz) until a motoric nerve response becomes detectable in the desired innervation area.
        2. Precise approach: The intensity of the stimulus is reduced (e.g., to 0.5 mA) while the needle is repositioned to elicit a motoric nerve response just above the response threshold.
        3. Injection of the local anesthetic drug (during nerve stimulation) until the nerve response has subsided.
    4. Two approaches to inject the local anesthetic drugs are available:
      1. Single-shot technique: A single dose of the local anesthetic drug is injected (e.g., bupivacaine).
      2. Catheter placement with the advantage of repeated/continuous administration of anesthetic drugs

Peripheral nerve blocks are preferred over general anesthesia in patients with respiratory problems and preferred over epidural/spinal anesthesia in patients who are at high risk for urinary retention or other side effects of these procedures.

References:[3]

Epidural anesthesia

Definition

  • Local anesthetics are injected into the epidural space and act on the spinal nerve roots.

Indications

Puncture site Surgery/area of surgery
Th5–7
Th6–9
Th7–9
  • Right hemicolectomy
Th8–10
  • Colorectal surgery (left hemicolectomy, complete colectomy, rectal resection)
  • Aortoiliac and aortobifemoral bypass surgery
  • Wertheim-Meigs operation, radical hysterectomy
Th9–11
  • Pelvic exenteration
L2/3–4

Contraindications

Procedure

  • Injection site
    • May be performed at any vertebral level (cervical, thoracic and lumbar spine)
    • Needle inserted into the epidural space between the ligamentum flavum and dura mater
  • Approaches to inject the local anesthetic:
    1. Catheter placement, which has the advantage of repeated/continuous administration of anesthetic drugs (most commonly performed)
    2. Single-shot technique: A single dose of the local anesthetic drug is injected (e.g., bupivacaine), if necessary in combination with sufentanil.
  • Needle: traumatic needle (e.g., Tuohy needle), atraumatic needle (e.g., Sprotte needle)
  • Preparation: The patient is seated with the back being curved/hunched over at the level of the puncture site.
  • Technique
    1. Selection of the injection site/spinal level as required
    2. Hygiene: face mask, hand disinfection, sterile gown, sterile gloves, disinfectants for the puncture site following injection, application of a sterile fenestrated drape
    3. Local anesthetic drug containing lidocaine
    4. Accessing the epidural space:
      1. The spinal needle punctures the skin at the median or paramedian line of the spine.
      2. The needle is gently inserted into the interspinal ligament (2–3 cm).
      3. Remove the mandrin.
      4. Attach a special, smooth-running syringe filled with physiological saline solution to the needle adapter.
      5. Move the needle slowly forward by pushing the plunger of the syringe with constant, gentle pressure.
      6. When the needle breaches the ligamentum flavum the resistance usually first increases before suddenly decreasing again, allowing saline solution to be more easily injected (Loss of resistance technique).
        • An alternative approach to detect the epidural space based on the lower pressure within the epidural space is the Hanging drop technique.
    5. Negative aspiration test: neither CSF nor blood may be aspirated!
      • If CSF is aspirated: The needle must be retracted! Repeat puncture if necessary.
      • If blood is aspirated: repeat puncture
    6. At this point one of two alternatives may be chosen:
      1. Single shot: A single dose of the local anesthetic drug is injected (e.g., bupivacaine), if necessary in combination with sufentanil.
      2. Catheter insertion (advantage: repeated/continuous drug administration possible)
        1. A catheter may be inserted into the needle (without major resistance) and advanced not more than 3 cm into the epidural space.
        2. Epidural test dose: A test dose of 2–3 mL local anesthetic drug in combination with 10–20 μg epinephrine is injected to exclude intravascular or intrathecal (= spinal) catheter placement.
        3. Fixation of the catheter at the insertion site using transparent tape , proper fixation of the connecting tube to the patient's back with tape, injection of the full drug dose and attachment of a PCEA pump (patient-controlled epidural analgesia)

Complications

References:[4][4][5][6][7][8]

Spinal anesthesia

Definition

Indications

Used for a variety of lower extremity, lower abdominal, pelvic, and perineal procedures; (e.g., cesarean delivery, hip and knee replacement)

  • C-section: Th4–6 (mamillary line)
  • Pelvic, urethral, and renal pelvic surgery: Th6–8 (xiphoid)
  • Transurethral surgery including stretching of the bladder, vaginal birth, hip surgery: Th10 (navel)
  • Transurethral surgery without stretching of the bladder: L1 (inguinal ligament)
  • Knee and foot surgery: L2/3
  • Perineal surgery: S2–5

Duration and site of action of spinal anesthesia

  • Local anesthetic drugs are selected based on the expected duration of surgery (e.g., mepivacaine in a concentration of 4% for interventions taking up to 1 h; bupivacaine 0.5% for interventions longer than 1 h (duration of anesthesia ∼ 2.5 h))
  • The specific spinal levels that are affected by the anesthesia depends on the dose of the local anesthetic drug.

Contraindications

Procedure

  • Injection site
    • Injection usually performed below L2 to avoid damage to the spinal cord
    • Needle inserted into subarachnoid space between the arachnoid and pia mater/medulla
  • Needle: atraumatic (e.g., Sprotte needle)
  • Preparation: The patient is seated (pregnant women may lie on one side, if necessary) with the back being curved at lumbar level.
  • Technique:
    1. Identification of the puncture site by palpation of the iliac crests: The puncture site (L3–4 or L4–5) may be found at the intervertebral space on an imaginary line between the two iliac crests.
    2. Hygiene: hand disinfection, sterile gown, sterile gloves, face mask, utensils for wipe disinfection of the puncture site afterward, application of a sterile fenestrated drape if necessary (e.g., patient in a lateral position)
    3. Local anesthetic drug, combined with lidocaine (optional)
    4. Insertion of a wider but shorter needle (introducer needle) to guide the thin spinal needle.
    5. Puncture of the skin in the cranial direction (∼ 10–30°) up to the dural sac
      • Bone contact: retract needle, repeat needle insertion in an even more cranial direction
      • Paresthesia: retract needle and repeat needle insertion in a more median direction
      • Blood: wait for the CSF to clear up again; if CSF does not clear up, retract needle and repeat insertion at a different lumbar level.
    6. After removal of the mandrin, CSF drops out of the spinal needle if the needle tip is in the correct position (in the subarachnoid space, so far same procedure as lumbar puncture)
    7. Gentle attachment and fixation of the syringe filled with the local anesthetic drug to the needle, followed by quick injection
  • Approach: almost always single-shot technique

Combined spinal and epidural anesthesia

  • Identification of the puncture site and needle insertion as describe above, followed by one of two options differing in the sequence of spinal and epidural anesthesia. The choice depends on the CSE equipment:
    1. First spinal anesthesia, then insertion of the epidural catheter (needle with one working channel)
      1. A very thin spinal needle is inserted into the same working channel as the epidural catheter later on. This needle is used to breach the dura mater and inject the local anesthetic drug into the dural space which results in the spinal anesthesia.
      2. Quick placement of the epidural catheter
    2. First insertion of the epidural catheter, then spinal anesthesia (needle with two working channels)
      1. Two separate working channels run parallel in a single needle. This enables the practitioner to insert the epidural catheter first, including an epidural test dose to check the correct placement.
      2. Spinal anesthesia

References:[9][10]

Complications

All procedures

Epidural/spinal anesthesia

References:[11][5][10][12][13][14][15]

We list the most important complications. The selection is not exhaustive.