Local anaesthetic- types

• Topical local anaesthetic can be:

  trans-mucosal: absorbed across mucus membrane

  Trans-cutaneous: Due to poor absorption, a carrier compound is used alongside LA.
• May be ocular, nasal or laryngeal.

  Eyes (corneal): Proxtmetacaine, Amethocaine.

  Skin: ELMA, lidocaine

  Larynx: Lignocaine spray
• Advantages of topical LA:

  Enables minor surgery eg. corneal debridement following ocular application of local anaesthetic drops.
• Disadvantages of topical LA:

  Only superficial analgesia is achieved 1-2mm, absorption affects effectiveness.
• Risks of topical LA:

  • Nerve fibre may cause temporary / permanent loss of function
  • Tissue irritation
  • Animal chewing areas, causes irritation and pain.
  • Allergic reaction
• Example of local infiltration?

  Ring/ line block
• local infiltration: how is LA administered?

  LA injected near the nerve to be affected. Given S/C, intradermally or between muscles.
• what affect does adding adrenaline have to an area?

  Causes constriction of blood vessels which decreases the rate of absorption, prolonging the effect of LA. Vasoconstriction reduces concentration of LA in circulation, reduces toxicity of the drug.
• Local infiltration is used for surgeries involving superficial tissues. e.g. removal of small skin tumours.
• local infiltration is used with care in cardiac disease patients.
• Local infiltration- Duration depends on drugs used and rate of absorption by local blood vessels.
• 2 types of local infiltration?

  Nerve block- needs location of nerve.

  Line block- injection of continuous line of local analgesia in S/C or subcuticular tissue immediately proximal to target area.
• what is regional LA?

  Causes blockage of relatively large areas (e.g. limb)
• How is regional LA acheived?

  by injecting into a major nerve plexus/close to spinal cord.
• What are some regional techniques?

  • Epidural
  • Limb blocks
  • Digital nerve blocks
  • Mandibular/maxillary nerve blocks
• regional LA is used for fast onset of anaesthesia
• What is epidural anaesthesia?

  LA injected into epidural space to allow the drug to circulate between the vertebrae and dura matter.
• Regional LA is used in pelvic and tail surgeries and orthopaedic procedures.
• What is spinal anaesthesia?

  LA injected through dura and into subarachnoid space where it mixes with CSF.
• Spinal anaesthesia is faster than epidural and lower doses of anaesthetic required.
• Regional LA- care in hypotensive patients.
• Regional LA- what are splash blocks?

  involve directly applying the LA solution to the area of interest, usually by dripping the agent from a syringe onto the exposed tissue during surgery.