LAST: PREVENTION AND TREATMENT PART A

PART A: OVERVIEW What are local anesthetics Classification MOA Anesthetic potency Clearance Uses Prolongation of action

PART B: ADVERSE EFFECTS&SYSTEMIC TOXICITY Allergic reaction Local toxicity Systemic toxicity

What are LA Weak bases which produce a transient and reversible loss of sensation (analgesia) in a circumscribed region of the body without loss of consciousness. Normally, the process is completely reversible.

Classification Local anesthetics - esters or amides. Major difference is their potential for producing adverse effects and the mechanisms of their metabolism.

Esters Eg: Procaine, Cocaine, tetracaine The ester linkage is cleaved by plasma cholinesterase. Short half life( abt 1min). Amides: Eg: lidocaine, Marcaine(Bupivacaine), ropivacaine. Amide linkage is cleaved in the liver. Half life is about 2-3 hrs

MECHANISM OF ACTION LA block nerve conduction by impairing propagation of action potential in axons. Interact directly with Na+ channels and stop Na+ ion influx. May also act on K+ & Ca+ channels. LA need to diffuse passively in uncharged state (lipophilic) to reach target-axoplasmic side of Na+ channel.

HOW MUCH IS TOO MUCH? ESTERS MAX DOSE(mg/kg) DURATION (HOURS) Chloroprocaine 12 0.5 – 1 Procaine Cocaine 3 Tetracaine 1.5 – 6

Amides Max Dose (mg/kg) Duration (h) Lidocaine 4.5/(7 with epi) 0.75 – 1.5 Mepivacaine 1– 2 Prilocaine 8 0.5 – 1 Bupivacaine 3 1.5 – 8 Ropivacaine

ANESTHETIC POTENCY The more LA is lipophilic the more potent it is ( increased rate of diffusion). More protein binding prolongs the effect. Bupivacaine is approximately 95% protein-bound. Intermediate-duration LAs (lidocaine and mepivacaine) have a smaller protein-bound fraction (60-70%). pH; higher pH speeds action (keeps LA uncharged). pKa: lower pKa faster onset. Concentration; higher conc. =rapid onset (mass effect).

CLEARANCE ESTERS hydrolysis via tissue cholinesterase AMIDES metabolism via hepatic enzymes

USES Surface anesthesia Infiltration anesthesia Regional anesthesia

SURFACE ANESTHESIA On intact skin – eutectic mixture of Local anesthetics (EMLA) Slow absorption, Action up to ½ Hr

INFILTRATION ANESTHESIA LA infiltrates locally into tissues to numb the area. Purpose of pain free procedures-before injections with large needles, lumbar puncture

REGIONAL ANESTHESIA Nerve block Intravenous Epidural/Extradural Intrathecal block/ spinal anaesthesia

NERVE BLOCKS Inject a drug around the nerve Anaesthetise a region

INTRAVENOUS ANESTHESIA 0.5-1% lidocaine without adrenaline Bier’s Block

EPIDURAL Thoracic, lumbar, sacral Act on nerve roots Less hypotention

SPINAL BLOCK Sympathetic nerve block hypotension