Editing 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

{| class="wikitable"
|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

[[Category:Anaesthetics]]