Local and regional anesthesia

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 article local anesthetic agents.

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

• Types of anesthetic agents and their pharmacology: See “Local anesthetic agents”.
• Contraindications
  • Absolute contraindications: allergies to local anesthetic drugs
  • Relative contraindications
    • Active inflammation/infection at the injection site
    • Neurological deficits in the area of distribution
• Techniques
  • Local anesthesia: topical or infiltrative
  • Regional anesthesia
    • Peripheral nerve block
    • Neuraxial: See epidural anesthesia and spinal anesthesia.

References:^[1]

• 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 or mucosa
  • 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 by aspirating before injecting!)
    • 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]

Definition

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

Indications

• Surgery of the upper extremities
• Surgery of the lower extremities
• 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

• Coagulopathy

Procedure

• Injection site: depends on the nerves that need to be blocked
• Technique
  1. Identification of the relevant nerve guided by specific landmarks and/or:
     • Ultrasound: ultrasound-guided needle advancement towards the target nerve
     • Nerve stimulation test
  2. 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]

Definition

• Local anesthetics with or without opioids and alpha-adrenergic agonists are injected into the epidural space and act on the spinal nerve roots.

Indications

• Used for a variety of surgeries of the lower body (e.g., cesarean delivery, hernia repair, appendectomy, prostate and bladder surgeries, knee surgery)
• During labor
• Perioperatively
• Chronic pain management (e.g., spinal stenosis, disc herniation)

Contraindications

• Absolute contraindications
  • Uncorrected hypovolemia
  • Increased intracranial pressure
  • Infection at the puncture site
• Relative contraindications
  • Coagulopathy
  • Spinal deformities
  • Sepsis, systemic bacteremia, amniotic infection syndrome
  • Neurological deficits caused by, e.g., disc prolapse, paraplegic syndrome, and multiple sclerosis

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

Complications

• Pain at the injection site
• Dural puncture
• Spinal-epidural hematoma
• Epidural abscess
• Hypotension
  • Pathophysiology: sympathetic blockade causes vasodilation and decreases venous return → reduced cardiac output
  • Clinical features: hypotension, dizziness, lightheadedness, and nausea shortly after administering anesthetic
  • Diagnosis: clinical diagnosis
  • Treatment: IV fluid resuscitation + small doses of epinephrine

References:^{[4][4][5][6][7][8]}

Definition

• Local anesthetics with or without opioids and alpha-adrenergic agonists are injected into the cerebrospinal fluid (CSF) in the lumbar spine and act directly on the spinal cord

Indications

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

Contraindications

• See “Contraindications of epidural anesthesia” above.

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
• Approach: almost always single-shot technique

References:^[9][10]

All procedures

• Bleeding complications (e.g., hematoma) → nerve compression → neurological symptoms depending on the localization and degree of the hematoma
• Infections: local inflammation/abscess formation
• Allergic reactions
• Toxic reactions
  • Local tissue toxicity
  • Systemic toxicity (see “Side effects” in local anesthetic agents)

Epidural/spinal anesthesia

• Post-dural puncture headache
• Spinal epidural hematoma and spinal epidural abscess
• Septic/aseptic meningitis
• Sympathetic block → peripheral vasodilation, bradycardia, and hypotension (Bezold-Jarisch reflex) → relative hypovolemia
• Urinary retention and overflow incontinence : treat with indwelling catheter for 24 hours if postvoid residual volume > 50 ml and/or the patient is unable to empty the bladder voluntarily
• Total spinal anesthesia: complete spinal space affected by local anesthetic drug

References:^{[5][10][11][12][13][14][15]}

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