Regional Anesthesia (Anesthesia 2024)

LOCAL ANESTHESIA

• Preference for local anesthesia over general anesthesia is common among patients.

TYPES OF ANESTHESIA

• Local Anesthesia:

  • Drugs injected or absorbed to block nerve conduction at a specific site.

  • Suitable for minimally invasive procedures.

• Regional Anesthesia:

  • Involves injecting drugs to block nerve conduction in specific regions.

  • Typically used for more invasive procedures.

• General (Inhalational) Anesthesia:

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

LOCAL ANESTHETICS

• Function of Local Anesthetics:

  • Block pain signals and prevent the sensation of pain.

• Common Local Anesthetics:

  • Medications end with the suffix “...caine”:

    • Cocaine

    • Lidocaine

    • Bupivicaine

    • Procaine

    • Ropivicaine

• Effect:

  • Transient effects, not permanent.

MECHANISM OF ACTION

• Sodium Channel Blockade:

  • Local anesthetics inhibit action potential conduction by binding and inactivating sodium channels.

  • Intracellular pH varies, affecting permeability and action potential.

LOCAL ANESTHESIA MITIGATION (MOA)

• Blocks impulse conduction in nerves at a localized area.

• Provides anesthesia without loss of consciousness.

• Sedation can be used as adjunct therapy.

• Routes of Administration:

  • Subcutaneous

  • Topical

  • Inhalation

  • Intrathecal

SPREAD OF LOCAL ANESTHESIA

• Core vs. Mantle Bundles:

  • Core bundles innervate distal tissue and take longer for anesthetic effects.

  • Mantle bundles innervate proximal tissues and exhibit effects first.

MINIMUM BLOCKING CONCENTRATION (Cm)

• Definition:

  • Lowest concentration of local anesthetic blocking impulse conduction.

• Varies by individual nerve fiber characteristics:

  • Size, myelination, and depth.

• Factors Affecting Cm:

  • Nerve fiber diameter

  • Tissue pH

  • 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 ANESTHETIC MEDICATIONS

• Types:

  • Amides:

    • Lidocaine

    • Mepivicaine

    • Bupivicaine

    • Ropivacaine

  • Esters:

    • Procaine

    • Benzocaine

    • Chloroprocaine

    • Tetracaine

    • Cocaine

• Systemic absorption can reduce efficacy, improperly directing the drug.

VASOCONSTRICTIVE AGENTS

• Commonly used with locals to constrict blood vessels at the injection site.

• Epinephrine is the most frequently used agent.

• Important to prevent systemic circulation of the agent.

LIDOCAINE

• Used topically or subdermally for localized anesthesia.

• Metabolized in the liver via cytochrome P450.

• Duration is typically 1-2 hours.

• Also used intravenously for antiarrhythmic purposes and during awake intubation.

ADVERSE EFFECTS

• Allergic Reactions: More common with esters than amides.

• L.A.S.T (Local Anesthetic Systemic Toxicity):

  • A serious reaction from local anesthetics reaching significant levels in systemic circulation.

  • Causes:

    • High concentration injection into systemic circulation

    • Exceeding maximum dosage

    • Rapid absorption in vascular areas

  • Symptoms:

    • Refer to resources for detailed symptoms.

MANAGEMENT OF LAST

• Steps to manage LAST:

  • Stop the injection.

  • Establish IV access.

  • Apply monitoring devices.

  • Provide aggressive supportive care:

    • Ensure airway and breathing (administer 100% FiO2).

    • Treat cardiovascular collapse (consider epinephrine).

    • High-quality CPR with minimal interruptions.

    • Consider sodium bicarbonate for severe acidosis.

    • Administer lipid emulsion (20% Intralipid).

REGIONAL ANESTHESIA

• Divided into Spinal and Epidural Anesthesia.

SPINAL ANESTHESIA

• Involves injection into spinal fluid, affecting both legs and abdomen.

• Requires a single needle insertion, generally quicker than epidural procedures.

EPIDURAL ANESTHESIA

• Indications:

  • Pain management, obstetrics, and surgeries.

• Catheter placement in the epidural space allows for a continuous infusion.

• Anesthetic drugs interrupt information transfer along nerves.

COMPLICATIONS OF EPIDURAL/SPINAL ANESTHESIA

• Potential issues include:

  • Hypotension due to peripheral dilation of blood vessels.

  • Post-dural puncture headache from CSF leakage.

  • Risks of extensive anesthetic spread, particularly towards the diaphragm.

PERIPHERAL NERVE BLOCKS

• Serve as an alternative to general anesthesia for surgery on limbs or trunk.

• Involves more extensive area coverage than local anesthesia.