Regional Anesthesia (anesthesia 2024)

Local Anesthesia Overview

  • Preference for either local or imported anesthesia

Types of Anesthesia

  • Local Anesthesia

    • Drugs injected/absorbed peripherally to block nerve conduction at a specific site for minimally invasive procedures.

  • Regional Anesthesia

    • Drugs injected to specific areas to block "regions" of nerve conduction for more invasive procedures.

  • General Anesthesia (Inhalational)

    • Drugs injected systemically or inhaled to depress the central nervous system.

Local Anesthesia Mechanism and Effects

  • Function of Local Anesthetics

    • Block pain signals

    • Prevent sensation of pain

    • Common medications end with "...caine": Cocaine, Lidocaine, Bupivacaine, Procaine, Ropivacaine.

Mechanism of Action (MOA) of Local Anesthesia

  • Local anesthetics produce anesthesia by inhibiting excitation of nerve endings or blocking conduction in peripheral nerves.

  • Reversibly bind to and inactivate sodium channels, preventing action potentials from propagating.

Administration of Local Anesthesia

  • Routes of Administration:

    • Subcutaneous

    • Topical

    • Inhalation

    • Intrathecal

  • Provides anesthesia without loss of consciousness.

  • Sedation may be used as an adjunct.

Spread of Local Anesthesia After Injection

  • Core Bundle

    • Deeper in nerve fiber, takes longer for anesthetic effect.

  • Mantle Bundle

    • Innervates proximal tissue sites, exhibits anesthetic effects first.

Minimum Blocking Concentration (Cm)

  • Definition: Lowest concentration of local anesthetic that blocks impulse conduction along a given nerve fiber.

  • Factors Affecting Cm:

    • Nerve fiber diameter

    • Tissue pH

    • Increased rate of nerve firing

    • Length of nerve exposed to LA

  • Order of Loss of Function:

    1. Pain

    2. Temperature

    3. Touch

    4. Proprioception

    5. Skeletal Muscle Tone

Local Anesthesia Medications

  • Amides: Lidocaine, Mepivacaine, Bupivacaine, Ropivacaine

  • Esters: Procaine, Benzocaine, Chloroprocaine, Tetracaine, Cocaine

  • Note: Systemic absorption can attenuate the drugs effect.

Vasoconstrictive Agents

  • Used with locals to constrict blood vessels around the injection site, extending local anesthetic action.

  • Common Agent: Epinephrine

Lidocaine Specifics

  • Anesthetic for localized use, metabolized in the liver.

  • Typical duration: 1-2 hours.

  • Also used for intravenous antiarrhythmic and in inhalation for awake intubation.

Adverse Effects of Local Anesthesia

  • Allergic Reactions: More common with Esters (rash, hives, itchy skin, swelling).

  • LAST (Local Anesthetic Systemic Toxicity): Life-threatening reaction from local anesthetics reaching significant systemic concentrations.

    • Causes: High concentration injection into systemic circulation, excessive doses, rapid absorption.

    • Symptoms

Management of LAST

  • Stop injection or infusion.

  • Establish IV access and apply monitors.

  • Provide aggressive supportive care (airway, breathing, and cardiovascular support).

  • Use 20% Intralipid if necessary.

Regional Anesthesia

  • Spinal Anesthesia:

    • Injected into spinal fluid using a single needle, freezes legs and abdomen, simpler procedure.

  • Epidural Anesthesia:

    • Catheter placed in epidural space for continuous infusion, used in pain management (e.g., during childbirth).

Complications of Epidural/Spinal Anesthesia

  • Hypotension: Due to decreased peripheral resistance.

  • Post-dural Puncture Headache: Caused by CSF leakage from punctured dura.

  • Extensive Spread of Anesthetic: Potential for complications if blocks progress too high.

Peripheral Nerve Blocks

  • Alternative to general anesthesia for surgery on extremities and trunk.

  • Involves bathing nerves with anesthetic for more extensive areas.