Class local anaesthetics 2

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Class local anaesthetics 2

  1. 1. LOCAL ANAESTHETICS
  2. 2.  Drugs that cause reversible loss of sensory perception specially of pain in a restricted area of the body, when applied topically or local injection.  LA if applied to a mixed nerve—sensory and motor impulses are interrupted—resulting in muscular paralysis and loss of autonomic control.
  3. 3.  Reversibly block the impulse conduction  Transient loss of sensation  Local anaesthesia blockade  C,B > Aδ > Aα,ß,γ
  4. 4. AMIDETYPE  Long acting- BUPIVACAINE, LEVO- BUPIVACAINE, ROPIVACAINE, DIBUCAINE  IntermediateActing-LIDOCAINE, MEPIVACAINE, PRILOCAINE,ARTICAINE ESTERTYPE-  LONGERACTING-TETRACAINE,
  5. 5.  IntermediateActing-COCAINE  Short Acting- PROCAINE, CHLORPROCAINE, BENZOCAINE, PROPARCAINE  Miscellaneous- PRAMOXINE, DYCLONINE,OXETHAZINE
  6. 6. E S T E R S  Short duration of action  Less intense anesthesia  Higher risk of hypersensitivity -PABA.  Hydrolyzed by Plasma Cholinesterase in blood.  Rarely used for Infiltration anesthesia But useful for topical anesthesia on mucous membranes. A M I D E S Produce more intense and longer lasting anesthesia Bind to alpha1 acid glyco- protein in plasma Rarely cause hypersensitivity reactions- no cross reactivity with ESTER L A s Not hydrolyzed by Plasma Cholinesterase, but in liver
  7. 7.  Vasoconstrictor is a substance used to keep the anesthetic solution in place at a longer period and prolongs the action of the drug  Vasoconstrictor delays the absorption which slows down the absorption into the bloodstream  Vasoconstrictor used ---the natural hormone called epinephrine (adrenaline).
  8. 8.  Blockage of membrane depolarisation in all excitable tissues, usually intended on peripheral nerve  Membrane stabilizer  They prevent the  Initiation and propa-  Gation of the nerve  Impulse by reducing  the passage of Na
  9. 9.  Effects of LA: injection as acid (hydrochloric salt)= ionized form  at physiological pH dissociation to free base (lipid soluble) passage through cell membrane to interior of axon re-ionisation enter and blockage of Na+-channel and thereby preventing influx of Na+ no generation of AP conduction blockade  They block nerve conduction by reducing the permeability of Na ions during depolarisation
  10. 10.  Should not be coadministered for nerve block in areas such as fingers and toes that are supplied with end-arteries because it may cause ischemia or necrosis  It should be used cautiously in patients in labour and in patients with thyrotoxicosis or cardiovascular disease.
  11. 11.  Usually at range 7.6 – 8.9  Decrease in pH shifts equilibrium toward the ionized form, delaying the onset action.  Lower pH, solution more acidic, gives slower onset of action  Presence of Pus and inflammation will retard the action of LA. ( probably low acidic pH)
  12. 12.  Most widely used Amide linked LA and most versatile ana.  Has variety of applications like Local, nerve block, spinal, epidural, IVRA.  When used locally action starts within 3 mts and causes vasodilatation.  Overdose causes muscle twitchings, convulsions, cardiac arrhythmias, fall in BP, coma, respiratory arrest.  Most popular ant arrhythmic drug
  13. 13. • Standard agent for infiltrations, regional blocks or topical • Short onset time, intermediate duration of action • Class Ib antiarrhythmic properties • Medium toxicity • Maximal recommended dose: 3 mg/kg, 6 mg/kg with vasconstrictor
  14. 14.  A potent long acting ---Amide linked LA available in India, most widely used allover.  Not used for IVRA but all others like local, spinal epidural blocks.  Action lasts for 2 to 3 hours. Strength for epidural is 0.25 to 0.5 % solution.  Has high lipid solubility, distributes more in tissues than in blood
  15. 15.  It is similar to Bupivacaine  One of the metabolites are toxic and can cause Methamoglobinemia  Used for Nerve Blocks and IVRA.
  16. 16.  Causes more sensory block, than motor block the advantage taken in during Caesarean Section. (Walking Epidural)  Bupivacaine is more prone to prolong QTc interval and induce ventricular tachycardia or Cardiac depression----( Membrane Stabilization action ) ( toxic doses and accidental entry into vessel)-should not be used for IVRA.  Longest acting LA available in India now.
  17. 17. 1. Surface anesthesia 2. Infiltration anesthesia 3. Conduction block a. Field block b. Nerve Block 4. Spinal anesthesia 5. Epidural anesthesia 6. I V R A (Bier’s Block)
  18. 18.  Amethocaine ---eye, throat, urethra, rectum and skin.  Benzocaine and Lidocaine hydrochloride—same --- except for eye.  Procaine is unsuitable as a surface ana. Because of its poor penetrating power  Lignocaine --4 % topical solution, 2 % Jelly 2 % vials for injections
  19. 19.  Eutectic : Lowering of melting point of two solids when they are mixed.  combination of Lidocaine and Prilocaine.  For Pediatric purpose. It can penetrate intact skin.  I v .cannula inserting.  Split skin graft harvesting  Other superficial procedures.
  20. 20.  Mech. of action : Nerve endings as exposed to the drug there by action.  Procaine, Lignocaine 2 % are used either with or without Adrenaline 1 : 2,00,000  C/I : blocking where end arteries are involved either for Penis, or for Digits, C A D patients.
  21. 21.  Drug is injected close to the nerve or big nerve trunks eg. Brachial Block, Sciatic, Femoral Nerve, Radial, Ulnar Nerves.
  22. 22.  LA is injected into the subarachnoid space. Injection is made heavy by adding dextrose or light by adding saline.  When the anesthetic in injected outside the dura, the technique is known as Epidural anesthesia.  Lignocaine, Bupivacaine the two agents most commonly used regularly in anesthesia practice.
  23. 23. EPIDURAL EPIDURAL EPIDURAL
  24. 24.  Intravenous regional anesthesia  Agent of choice------ Lignocaine (Xylocaine )  20 to 40 ml of 0.5 % Lidocaine is used  Used for only for Upper Limb orthopedic surgeries and others on Up. Limb.
  25. 25.  We have seen all Local actions of LA s  Systemic action when given IV : Bupivacaine is relatively more cardiotoxic , produces ventricular tachycardia or fibrillation.  Lidocaine has little effect on contractility and conductivity, used as antiarrhythmic.  The prominent cardiac action of Xylocaine is suppression of automaticity in ectopic foci.
  26. 26.  Depression of function of CNS and CVS when high plasma concentrations are reached  CNS toxicity : usually before cardiovacular effects First signs of excitation due to initial blockade of inhibitory pathways mild: circumoral tingling, metallic taste, tinnitus, visual disturbance, slurred speech moderate: altered consicous state, convulsions Later sings of generalized CNS depression with potentially fatal toxicity: coma,respiratory arrest
  27. 27.  1.Bradycardia, 2.Hypotension 3.Headache  4.Cauda Equina syndrome 5.Septic meningitis  EPIDURAL ANESTHESIA :  Here the drug is injected outside the dura. Drug spread is restricted to a specific region causes fewer complications.
  28. 28.  Allergic reactions: common with ESTERS like Procaine, caused by para-aminobenzoic acid (also found to cause arachnoiditis), less common with AMIDES, then mostly through preservatives  Drug interactions: i.e. Anticholinesterases, other competing drugs hydrolyzed by Plasma CE  Attention with heavy sedation with anticonvulsants: may mask early signs of toxicity  Methaemoglobinaemia: after large doses Prilocaine

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