see also: [[EMLA|topical anaesthesia]], [[Local anaesthetic systemic toxicity]] [Dunn - local anaesthesia](x-devonthink-item://AC3AF794-C5DB-4BBD-ABB6-D5F124092548) - [[Sodium channel blocker|Na-channel blocker]] - block nerve impulses by: - increasing threshold for excitation - slowing propagation of impulse - reduce rate of rise of action potential - weak bases - need to be unprotonated to reach site of action -- less effective in acidic enviornment - faster onset if mixed with HCO3 order of loss of nerve function from first to last: 1. pain 2. temp 3. touch 4. proprioception 5. skeletal muscle tone # LA safe doses > 1% = 1g/100mL = 10mg/mL | drug | max dose | | ------------------------ | ------------------------------------- | | lignocaine | 3 mg/kg max 350 | | lignocaine + adrenaline | 7 mg/kg max 500mg | | bupivacaine | 2 mg/kg max 200mg | | bupivicaine + adrenaline | 3 mg/kg max 225mg | | ropivicaine | 2 mg/kg max 200mg | | prilocaine | 6mg/kg<br>3mg/kg for [[Bier's block]] | # specific LA considerations ## prilocaine - less CNS ototox than lignocaine - can cause [[Methemoglobinemia]] with doses >400mg - prilocaine 0.5% solution (5mg/mL); 2.5 mg/kg [[Bier's block]] (1/2 pt weight is mL required) - interactions with sulfonamides, antimalarials, ntric compounds (pre-dispose to methemoglobin) ## Bupivacaine - more cardiotoxic - more lipid soluble than lignocaine - duration 6H ## ropivicaine - less cardiac and CNS toxic than bupivacaine - 0.75% = 7.5mg/mL - duration 6 h