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[email protected] ---local anaesthetics for under graduates


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LOCAL ANESTHETICS Dr.Rakesh Chintalapudi, M.D., D.A ., Asst.Professor – King George Hospital, Visakhapatnam –Andhra Pradesh-INDIA mail id : [email protected]



Definition ::

Definition : 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.

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History :

History All LA originated from COCAINE (alkaloid in leaves of Erythroxylum coca), first used as LA by KOLLER, an ophtalmic surgeon in Vienna In 1884, he used the first local anesthetic on a patient with glaucoma General formula: aromatic group joined to an amine by an intermediate group with either ESTER or AMIDE link PROCAINE (Ester) first used 1904 LIDOCAINE (Amide) introduced 1940s

L A drugs:

L A drugs Cocaine Procaine Chloroprocaine Tetracaine Benzocaine Lidocaine Bupivacaine Dibucaine Prilocaine Ropivacaine


Chemistry Hydrophilic amine Lipophilic aromatic residue AMIDE ESTER A l k y l C h a i n

Ester-linked Amide - linked:

Ester-linked Amide - linked Cocaine Procaine Chloroprocaine Tetracaine Benzocaine Lidocaine Bupivacaine Dibucaine Prilocaine Ropivacaine ESTERS AMIDES

Differences :

Differences E S T E R S Short duration of action Less intense analgesia Higher risk of hypersensitivity ESTER linked LA s are rarely used. Hydrolyzed by Plasma Cholinesterase in blood. Rarely used for Infiltration anesthesia But useful for topical ana on mucous membranes. A M I D E S Produce more intense and longer lasting ana . Bind to alpha1 acid glycoprotein in plasma Not hydrolyzed by Plasma Cholinesterase, but in liver Rarely cause hypersensitivity reactions- no cross reactivity with ESTER L A s.

Resting Membrane Potential:

Resting Membrane Potential There is an electrical charge across the membrane. This is the membrane potential. The resting potential (when the cell is not firing) is a 70mV difference between the inside and the outside. inside outside Resting potential of neuron = -70mV + - + - + - + - + -

Action Potentials:

Action Potentials At rest: Na+& K+ channels closed. -70mV Fibre stimulated: Na+channel opens, Na+ enters cell. Potential rising Cell depolarised, Na+ channel closes. +20mV K+ channel opens, K+ exits cell, potential falling Fibre repolarised, Na+& K+ channels closed. Na/K pump restores balance. -70mV Result is a voltage gradient along axon, causing a current. This causes configurational change in Na-channels in the next segment conduction

L A - Mode of action:

L A - Mode of action Blockage of membrane depolarisation in all excitable tissues, usually intended on peripheral nerve  Membranestabilizer

Membrane Stabilizing effect:

Membrane Stabilizing effect The action affecting the process of depolarization, leading to failure of propagation of an impulse without affecting the resting potential, is known as Membrane stabilizing effect. AUTONOMIC SENSORY MOTOR MOTOR SENSORY AUTONOMIC

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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 Mode of Action contd.,

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Na + Na +

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Drug should reach Nerve through tissue Drug should enter Neuron ( Nerve ) Hydrophilic Lipophilic

Systemic Actions ::

Systemic Actions : When applied locally gets into the blood ----either absorbed from tissues or—accidental entry into blood Discuss----toxicity

Factors Affect the Reaction of Local Anesthetics :

Lipid solubility All local anesthetics are weak bases. Increasing the lipid solubility leads to faster nerve penetration, block sodium channels, and speed up the onset of action. The more tightly local anesthetics bind to the protein, the longer the duration of onset action. Local anesthetics have two forms, ionized and nonionized. The nonionized form can cross the nerve membranes and block the sodium channels. So, the more nonionized presented, the faster the onset action. Factors Affect the Reaction of Local Anesthetics

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Lipid solubility is an important characteristic. Potency is related to lipid solubility, because 90% of the nerve cell membrane is composed of lipid. This improve transit into the cell membrane

pH influence:

pH influence 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)

Vasodilation :

Vasodilation 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).

Therapeutic Uses ::

Therapeutic Uses : 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)

1. Surface anesthesia :

1. Surface anesthesia 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 --

Xylocaine (Lignocaine ):

Xylocaine (Lignocaine ) 4 % topical solution 2 % Jelly 2 % vials for injections with or without adrenaline 2% Viscous 5 % Ointment

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5 % Heavy for Spinal Anesthesia 0.25 to 0.5 % solution for Epidural Anesthe. 10 % Spray for Intubations and 4 % endoscopic exams.

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E M L A Cream : E utectic M ixture of L ocal A nesthetic, combination of Lidocaine and Prilocaine. For Pediatric purpose. It can penetrate intact skin. I v .cannula inserting. Split skin graft harvesting Other superficial procedures. (before 1 hr.) Eutectic : Lowering of melting point of two solids when they are mixed.

Infiltration anaesthesia ::

Infiltration anaesthesia : 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.

Nerve block or Conduction block:

Nerve block or Conduction block Drug is injected close to the nerve or big nerve trunks eg. Brachial Block, Sciatic, Femoral Nerve, Radial, Ulnar Nerves.

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Superior Laryngeal Nerve Median Nerve Axillary nerve glassopharyngeal nerve

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Choice of drug : Depends on the type of surgery whether short duration or long duration i.e. either Lignocaine or Bupivacaine or both together, or with a opioids.

Spinal Anesthesia:

Spinal Anesthesia 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.

Complications of Spinal Anesthesia:

Complications of Spinal Anesthesia 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.

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I V R A (Bier’s Block):

I V R A (Bier’s Block) 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.

Systemic Actions ::

Systemic Actions : 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.

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When given by iv route action last for 10 to 20 mts. because of rapid redistribution. 1to 2 mg/kg body wt initially followed by half of it every 10 to 20 mts. Useful for only ventricular tachyarrhythmias. It is a Class I B anti arrhythmic.

Individual LA Agents:



PRILOCAINE It is similar to Bupivacaine One of the metabolites are toxic and can cause Methamoglobinemia Used for Nerve Blocks and IVRA.

Lignocaine ( Xylocaine ) :

Lignocaine ( Xylocaine ) 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

Lignocaine ( Xylocaine ) contd…:

Lignocaine ( Xylocaine ) contd… 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

Bupivacaine ( Sensorcaine ):

Bupivacaine ( Sensorcaine ) 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

Bupivacaine cont.....:

Bupivacaine cont..... 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.

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Long duration of action, no need for repetitive doses Hard to resuscitate, large doses of inotropes required Plain / hyperbaric (5%Glucose) Levobupivacaine: Chirocaine, less cardio toxic, newer---Liposomal Bupivacaine Max recomm. Dose: 2 mg/kg Bupivacaine cont.....

Systemic Toxicity:

Systemic Toxicity Due to same membrane stabilizing effect 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

Systemic Toxicity contd....:

Systemic Toxicity contd.... CVS-toxicity: direct myocardial depression and peripheral vasodilation AP-duration decreased in ventricular muscle, increased PR intervals and QRS duration, sinus bradycardia, sinus arrest, negative inotropy Ventricular arrhythmias---VF, difficult to resuscitate, esp with Bupivacaine Reentrant type tachycardia with Bupivacaine Dose dependent vasoconstriction or vasodilation


ROPIVACAINE A newer Bupivacaine congener, equally long acting but less cardio toxic. Sensory block is more compared to Motor. Continuous epidural Ropivacaine is being used for relief of postoperative and Labour pain. I t can also be used for nerve blocks. It is available in USA not in India.

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Shorter block More differential block (reduced diffusion to large A beta fibres) Cardiac resuscitation more successful than after Bupivacaine. Max. recomm.dose: 3 mg/kg

Amethocaine ( Tetracaine ):

Amethocaine ( Tetracaine ) It is a potent and toxic ester linked LA Hydrolyzed by Pseudo cholinesterase in plasma. Useful for topical application to the eye, nose, throat, tracheobronchial tree and rarely for spinal , or epidural. Topical action is so fast as IV.

Oxethazaine :

Oxethazaine A potent topical anesthetic, unique in ionizing to a very small extent even at low pH values. It is, therefore, effective in anaesthetizing gastric mucosa despite acidity of the medium. Swallowed along with antacids, it affords symptomatic relief in gastritis, drug induced irritation, gastro esophageal reflux and heartburn of pregnancy.

Other side effects:

Other side effects Xylocaine (Lignocaine) Sensorcaine (Bupivacaine) Membrane stabilizing Action : Local tissue toxicity: Neurotoxicity (mainly after continuous spinal injection with microcatheters) transient neurological Sx after single shot spinal (rare)

Other side effects contd....:

Other side effects contd.... 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

Spinal Additives:

Spinal Additives NaOH, HCl -- pH Glucose, H2O -- baricity Preservatives (multi dose vials, not for subarachnoid / epidural use) Vasoconstrictors: Epinephrine, Felypressin. CO2—speed onset of blockade by decreasing intracellular pH Certain Opioids like Fentanyl, Buterphenol

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