Local anaesthetic

"reversibly prevent transmission of nerve impulses, without affecting consciousness."

• Most local anaesthetics contain an aromatic ring, and are basic and lipid soluble
• Inactivates voltage-gated sodium channels so no further depolarisation can occur, and nerve impulses cannot propagate proximally.
• Progresses sequentially though loss of pain, temperature, touch, proprioception, skeletal muscle tone.
• Promotes vasoconstriction at low concentrations, and vasodilation at high

Dosages

• 1% solutions contain 10mg/mL, 2% contains 20mg/mL, etc
• Easiest just to use 3mg/kg for both rupivicaine and lignocaine
• All these agents are cleared by the liver

Drug	Dose (plain)	Dose (adren)	Onset (m)	Duration (h)	Comments
Lignocaine	2-4mg/kg	7-9mg/kg	5-10 'fast'	1-2 (p) 2-3 (a)	Rapid onset, good for short procedures
Bupivicaine	2.5	2.5	10-15 'fastish'	3-4 (p) 3-5 (a)	Slower onset. Can precipitate arrhythmias
Prilocaine	5	5	5-10 'fast'	1-2 (p) 2-3 (a)	Can be used IV (Bier's block)
Ropivicaine	3mg/kg / 200mg total	N/A	1-15 'slow'	2-6

Contraindications

• Hypersensitivity
• Bupivicaine for regional anaesthetic
• Prilocaine in anaemia/methaemoglobinaemia
• Adrenaline in end-arteries… sometimes
• CVS instability

Toxicity

• Neurological early: mouth and tongue tingling numbness, fingertip numbness, tinnitus, anxiety, drowsiness/confusion, tremor
• Neurological late - progresses to fitting, coma, resp distress, death
• CVS
• Respiratory
• Allergic
• If suspected - cease drug, give oxygen via facemask, call MET, give diazepam if convulsion

Treatment of toxicity

• High-flow oxygen
• Treat seizure with midazolam
• Monitoring - may need IVF and other haemodynamic support

Reduced effectiveness

• Acidic environments
  • Inflammation
  • Sepsis
  • Ischaemia
• Increased vascularity leading to higher rate of washout

EMLA

• Eutectic Mixture of Local Anaesthetics
• Mix of lignocaine and prilocaine