Local anaesthesia

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Local anaesthesia

  1. 1. Local Anaesthetics produce loss of sensation to pain in a circumscribed area of the body by inhibiting the conduction process in the peripheral nerves.
  2. 2. In order for us to understand how local anaesthetics work, we first have to look at the the electrical impulse and take you back to first year physiology
  3. 3. This picture shows how membrane potential changes with an action potential. As we have learnt, Nerve impulses are conducted by a wave of action potentials. When a stimulus is great enough to reach the threshold potential of -55mV, sodium ions flow into the neurone. It does so via sodium gates to produce depolarisation. When depolarised, the membrane potential is reversed to +40 mV. At the same time, there is passive outwards diffusion of potassium ions to bring about repolarisation and the membrane potential is again reversed to -70mV
  4. 4. Local anaesthetics work by preventing the entry of sodium ions to prevent the propagation of action potentials.
  5. 5. There are two theories on the subject of how sodium channels are blocked: 1. Non-specific membrane expansion theory 2. Specific receptor theory
  6. 6. Non-specific membrane expansion theory: The lipophilic part of the local anaesthetic attaches to the cell membrane to cause swelling. This then reduces the size of the sodium channel to obstruct the flow of sodium ions.
  7. 7. Specific receptor theory: The hydrophilic charged amino terminal binds to specific receptors of the sodium gates to block the passage of sodium ions
  8. 8.  Lignocaine  Prilocaine(Citanest)  Articaine  Bupivacaine(Marcaine)
  9. 9. First found by Nils Lofgren in 1943, and has been in clinical use since 1948 used as 2% plain or 2% with 1: 80000 adrenaline Short onset of 2-3 minutes Duration of action for ~ 2hrs Each 2.2ml cartridge contains 44mg of lidocaine Max dose with vasoconstrictor is 7mg/Kg
  10. 10. Less toxic and metabolises quicker than lignocaine Used as 4% plain or 3% with IU/ml Felypressin; Felypressin is an analogue of Oxytocin. Oxytocin induces labour hence its use should be avoided in pregnant women Slower onset of 4 minutes Max dose is 6mg/Kg A metabolite of prilocaine can very rarely oxidise heme to cause methemoglobinemia. This of course, reduces the oxygen carrying capacity of haemoglobin. Consequently the patient becomes hypoxic.
  11. 11. The molecular structure of articaine is different from other local anaesthetics due to the presence of a thiophene ring. It also contains an additional ester group which is metabolized by estearases found in the blood and tissues. For this reason. Articaine is hydrolysed quicker than other anaesthetics -used as 4% solution with 1:100000 or 1:200000 adrenaline More rapid onset Anaesthesia is more profound Maximum dose 7mg/kg
  12. 12. used as 0.25% or 5% solution with 1: 200000adrenaline Onset of 5 minutes Can last for ~8 hours Used for longer duration surgery, post- operative pain control and pain control for intractable facial pain Maximum dose 1.3mg/kg
  13. 13. THIS IS THE END OF THE SLIDE SHOW ON LOCAL ANAESTHETICS

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