Local anaesthesia

Overview

Local anaesthetics produce a reversible loss of pain sensation, although other sensory modalities may also be affected. When administered to specific nerve pathways, they can also produce motor blockade (paralysis).

Local anaesthetic agents

Lidocaine

Lidocaine (local infiltration)

• Maximum dose without a vasoconstrictor (adrenaline): 4.5 mg/kg

• Maximum dose with a vasoconstrictor (adrenaline): 7 mg/kg

Note: Lidocaine is not recommended for spinal anaesthesia.

Bupivacaine

Bupivacaine (local infiltration)

Available concentrations include:

• 625 micrograms/mL (0.0625%)

• 1.25 mg/mL (0.125%)

Hyperbaric bupivacaine

Bupivacaine + glucose

• Bupivacaine hydrochloride: 5 mg/mL (0.5%)

• Glucose: 80 mg/mL

This preparation has a specific gravity of 1.026. The addition of glucose produces a hyperbaric solution relative to cerebrospinal fluid.

Management of local anaesthetic overdose

Severe local anaesthetic systemic toxicity with cardiovascular or neurological impairment should be treated with:

Lipid emulsion (20% or 30%) (IV)

• Initial bolus: 1.5 mL/kg over 1 minute.

• Continuous infusion: 0.25 mL/kg/minute.

• Repeat the bolus 1–2 times if cardiovascular collapse persists.

• Increase the infusion rate to 0.5 mL/kg/minute if blood pressure remains low.

• Continue the infusion for at least 10 minutes after cardiovascular stability is achieved.

Maximum recommended dose

• Approximately 10 mL/kg of lipid emulsion during the first 30 minutes.

Epidural and combined spinal-epidural anaesthesia

Epidural anaesthesia is a form of neuraxial anaesthesia in which local anaesthetic is injected into the epidural space to block the spinal nerve roots.

Common indications include:

• Abdominal surgery

• Pelvic surgery

• Lower limb procedures

• Selected thoracic procedures

Epidural local anaesthetics

Lidocaine (epidural)

• 1–2%

OR

Bupivacaine (epidural)

• 0.25–0.75%

Epidural labour analgesia

Bupivacaine (epidural)

• 0.1–0.25%

May be administered with or without fentanyl (50–100 micrograms).

Example:

• Bupivacaine 0.1% plus fentanyl 2 micrograms/mL administered as an epidural infusion at 0–12 mL/hour.

Peripheral nerve blocks

Peripheral nerve blocks are commonly used for:

• Surgical anaesthesia

• Postoperative analgesia

• Non-surgical pain management

They are frequently chosen to:

• Reduce the adverse effects of general anaesthesia

• Minimize respiratory complications

• Reduce opioid requirements while providing effective analgesia

Local anaesthetics for peripheral nerve blocks

Lidocaine

Lidocaine (perineural)

• 1–2%

OR

Bupivacaine

Bupivacaine (perineural)

• 0.25–0.75%

OR

Bupivacaine + glucose

Bupivacaine + glucose (perineural)

• 0.25–0.75%

Adjuvant agents

Adrenaline

Adrenaline (perineural)

• Typical concentration: 5–10 micrograms

OR

Dexamethasone

Dexamethasone (perineural)

• 4–10 mg

OR

Clonidine

Clonidine (perineural)

• 0.5–2 micrograms

Topical anaesthesia

Lidocaine gel

Lidocaine gel (topical)

• 2–5%

OR

Lidocaine topical spray

Lidocaine topical spray

• Available as 2% and 10% solutions.

Indications include topical anaesthesia of the:

• Oropharynx

• Vocal cords

• Trachea

• Nasal passages