Introuduction to local anesthesia
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Local anesthetics work by blocking sodium channels in nerves, limiting the propagation of action potentials and preventing pain sensation. Lidocaine was the first modern local anesthetic introduced in 1940. Local anesthetics are either esters or amides, with amides like lidocaine causing less allergic reactions. The onset and duration of local anesthetics is influenced by their lipid solubility, pH, presence of vasoconstrictors, and peak circulation levels to avoid toxicity.
Introuduction to local anesthesia
- 1. Local AnestheticsLocal Anesthetics HOSSAM M. ATEF;MDHOSSAM M. ATEF;MD SUEZ CANAL UNIVERSIITYSUEZ CANAL UNIVERSIITY ANESTHESIA DEPARTMENTANESTHESIA DEPARTMENT
- 2. What are local anesthetics?What are local anesthetics? Local anesthetic: produce loss ofLocal anesthetic: produce loss of sensation to pain in a specific area of thesensation to pain in a specific area of the body without the loss of consciousnessbody without the loss of consciousness
- 3. Local anesthetics -Local anesthetics - MechanismMechanism Limit influx of sodium, thereby limitingLimit influx of sodium, thereby limiting propagation of the action potential.propagation of the action potential.
- 4. LidocaineLidocaine In 1940, the first modern localIn 1940, the first modern local anesthetic agent was lidocaine, tradeanesthetic agent was lidocaine, trade name Xylocaine®name Xylocaine® It developed as a derivative of xylidineIt developed as a derivative of xylidine Belongs to the amide class, cause littleBelongs to the amide class, cause little allergenic reaction; it’s hypoallergenicallergenic reaction; it’s hypoallergenic Sets on quickly and produces aSets on quickly and produces a desired anesthesia effect for severaldesired anesthesia effect for several hourshours It’s accepted broadly as the localIt’s accepted broadly as the local anesthetic in United States todayanesthetic in United States today
- 5. Differences of Esters and AmidesDifferences of Esters and Amides All local anesthetics areAll local anesthetics are weak basesweak bases. Chemical structure of local. Chemical structure of local anesthetics have an amine group on one end and an aromatic ring on theanesthetics have an amine group on one end and an aromatic ring on the other . The amine end is hydrophilic (soluble in water), and the aromaticother . The amine end is hydrophilic (soluble in water), and the aromatic end is lipophilic (soluble in lipids)end is lipophilic (soluble in lipids) Two classes of local anesthetics are amino amides and amino esters.Two classes of local anesthetics are amino amides and amino esters. Amides:Amides: Esters:Esters: --Amide link b/t intermediate--Amide link b/t intermediate --Ester link b/t intermediate chain and chain--Ester link b/t intermediate chain and chain and aromatic ringand aromatic ring aromatic ringaromatic ring --Metabolized in liver and very--Metabolized in liver and very --Metabolized in plasma through soluble in--Metabolized in plasma through soluble in the solutionthe solution pseudocholinesterases and notpseudocholinesterases and not --stable in the solution--stable in the solution --Cause allergic reactions--Cause allergic reactions
- 6. Local anesthetics - Classes (RuleLocal anesthetics - Classes (Rule of “i’s”)of “i’s”) EstersEsters CocaineCocaine ChloroprocaineChloroprocaine ProcaineProcaine TetracaineTetracaine Am”i”desAm”i”des BupBupiivacainevacaine LLiidocainedocaine RopRopiivacainevacaine EtEtiidocainedocaine MepMepiivacainevacaine
- 7. Structures of Amides and EstersStructures of Amides and Esters The amine end is hydrophilic (soluble in water), anesthetic moleculeThe amine end is hydrophilic (soluble in water), anesthetic molecule dissolve in water in which it is delivered from the dentist’s syringe into thedissolve in water in which it is delivered from the dentist’s syringe into the patient’s tissue. It’s also responsible for the solution to remain on eitherpatient’s tissue. It’s also responsible for the solution to remain on either side of the nerve membrane.side of the nerve membrane. The aromatic end is lipophilic (soluble in lipids). Because nerve cell is madeThe aromatic end is lipophilic (soluble in lipids). Because nerve cell is made of lipid bilayer it is possible for anesthetic molecule to penetrate through theof lipid bilayer it is possible for anesthetic molecule to penetrate through the nerve membrane.nerve membrane. The trick the anesthetic molecule must play is getting from one side of theThe trick the anesthetic molecule must play is getting from one side of the membrane to the other.membrane to the other.
- 8. MechanismMechanism The mechanism of local anesthetics connects withThe mechanism of local anesthetics connects with the ion channels,the ion channels, nerve, and depolarization.nerve, and depolarization. Local anesthetics block the conduction in peripheral nerves that inhibitedLocal anesthetics block the conduction in peripheral nerves that inhibited the nerve to excited and created anesthesia.the nerve to excited and created anesthesia. The anesthetic is a reversible reaction. It binds and activates the sodiumThe anesthetic is a reversible reaction. It binds and activates the sodium channels.channels. The sodium influx through these channels and depolarizes the nerve cellThe sodium influx through these channels and depolarizes the nerve cell membranes.membranes. As a result, the nerve loses depolarization and the capacity to create theAs a result, the nerve loses depolarization and the capacity to create the impulse, the patient loses sensation in the area supplied by the nerve.impulse, the patient loses sensation in the area supplied by the nerve.
- 9. Local anesthetics - FormulationLocal anesthetics - Formulation Biologically active substances are frequentlyBiologically active substances are frequently administered as very dilute solutions whichadministered as very dilute solutions which can be expressed ascan be expressed as parts of active drug perparts of active drug per 100 parts of solution (grams percent)100 parts of solution (grams percent) Ex.: 2% solution =Ex.: 2% solution = __2 grams2 grams__ = ___ = _2000 mg2000 mg_ = ___ = __20 mg20 mg____ 100 cc’s 100 cc’s 1 cc100 cc’s 100 cc’s 1 cc
- 10. Local anesthetics - FormulationLocal anesthetics - Formulation Biologically active substances are frequentlyBiologically active substances are frequently administered as very dilute solutions whichadministered as very dilute solutions which can be expressed ascan be expressed as parts of active drug perparts of active drug per 100 parts of solution (grams percent)100 parts of solution (grams percent) Ex.: 2% solution =Ex.: 2% solution = __2 grams2 grams__ = ___ = _2000 mg2000 mg_ = ___ = __20 mg20 mg____ 100 cc’s 100 cc’s 1 cc100 cc’s 100 cc’s 1 cc
- 11. Factors Affect the Reaction of Local AnestheticsFactors Affect the Reaction of Local Anesthetics Lipid solubilityLipid solubility All local anesthetics haveAll local anesthetics have weak basesweak bases. Increasing the. Increasing the lipid solubilitylipid solubility leads to faster nerve penetration, block sodium channels, and speedleads to faster nerve penetration, block sodium channels, and speed up the onset of action.up the onset of action. The more tightly local anesthetics bind to the protein, the longer theThe more tightly local anesthetics bind to the protein, the longer the duration of onset action.duration of onset action. Local anesthetics have two forms, ionized and nonionized. TheLocal anesthetics have two forms, ionized and nonionized. The nonionizednonionized form can cross the nerve membranes and block theform can cross the nerve membranes and block the sodium channels.sodium channels. So, the more nonionized presented, the faster the onset action.So, the more nonionized presented, the faster the onset action. pH influencepH influence Usually at range 7.6 – 8.9Usually at range 7.6 – 8.9 Decrease in pH (acidosis) shifts equilibrium toward the ionized form,Decrease in pH (acidosis) shifts equilibrium toward the ionized form, delaying the onset action.delaying the onset action.
- 12. Factors Affect the Reaction of Local AnestheticsFactors Affect the Reaction of Local Anesthetics (cont.)(cont.) VasodilationVasodilation Vasoconstrictor is a substance used to keep the anesthetic solution inVasoconstrictor is a substance used to keep the anesthetic solution in place atplace at a longer period and prolongs the action of the druga longer period and prolongs the action of the drug vasoconstrictor delays the absorptionvasoconstrictor delays the absorption Lower vasodilator activity of a local anesthetic leads to a slowerLower vasodilator activity of a local anesthetic leads to a slower absorption and longer duration of actionabsorption and longer duration of action Vasoconstrictor used the naturally hormone called epinephrineVasoconstrictor used the naturally hormone called epinephrine (adrenaline).(adrenaline). Side effects of epinephrineSide effects of epinephrine Epinephrine HR,BP and arrythmiaEpinephrine HR,BP and arrythmia
- 13. ToxicityToxicity Toxicity is the peak circulation levels of local anestheticsToxicity is the peak circulation levels of local anesthetics Levels of local anesthetic concentration administered to patients areLevels of local anesthetic concentration administered to patients are varied according to age, weight, and health.varied according to age, weight, and health. Maximum dose for an individual is usually between 70mg to 500mgMaximum dose for an individual is usually between 70mg to 500mg The amount of dose also varied based on the type of solution usedThe amount of dose also varied based on the type of solution used and the presence of vasoconstrictorand the presence of vasoconstrictor Example:Example: ---For adult whose weight is 100kg and up, maximum dose of lidocaine---For adult whose weight is 100kg and up, maximum dose of lidocaine is about 500mgis about 500mg ---For children, the dosage reduced to about 1/3 to ½ depending on---For children, the dosage reduced to about 1/3 to ½ depending on their weight.their weight. The doses are not considered lethal.The doses are not considered lethal. Some common toxic effects:Some common toxic effects: --light headedness--light headedness ---shivering or twitching---shivering or twitching --seizures--seizures --hypotension (low blood pressure)--hypotension (low blood pressure) --numbness--numbness
- 14. Local Anesthetics - AllergyLocal Anesthetics - Allergy True allergy is very rareTrue allergy is very rare Most reactions are from ester class - esterMost reactions are from ester class - ester hydrolysis (normal metabolism) leads tohydrolysis (normal metabolism) leads to formation of PABA - like compoundsformation of PABA - like compounds Patient reports of “allergy” are frequently due toPatient reports of “allergy” are frequently due to previous intravascular injectionsprevious intravascular injections
- 15. Local Anesthetics - ToxicityLocal Anesthetics - Toxicity Tissue toxicity - RareTissue toxicity - Rare Can occur ifCan occur if administered in highadministered in high enough concentrationsenough concentrations Usually related toUsually related to preservatives added topreservatives added to solutionsolution Systemic toxicity - RareSystemic toxicity - Rare Related to blood level ofRelated to blood level of drug secondary todrug secondary to absorption from site ofabsorption from site of injection.injection. Range fromRange from lightheadedness, tinnituslightheadedness, tinnitus to seizures andto seizures and CNS/cardiovascularCNS/cardiovascular collapsecollapse
- 16. Factors of circulation levelsFactors of circulation levels Factors of circulation levels are the rates of absorption,Factors of circulation levels are the rates of absorption, distribution, and metabolism.distribution, and metabolism. Absorption depends on the speed of administration andAbsorption depends on the speed of administration and levels of the doses.levels of the doses. Distribution allows absorption to occur in three phases.Distribution allows absorption to occur in three phases. First, the drug occurs at highly vascular tissues in theFirst, the drug occurs at highly vascular tissues in the lungs and kidneys. Then it appears less in vascularlungs and kidneys. Then it appears less in vascular muscle and fat. Then the drug is metabolized.muscle and fat. Then the drug is metabolized. Metabolism involves in the chemical structure based onMetabolism involves in the chemical structure based on two classes, amide and ester .two classes, amide and ester . Decreasing the potential toxicity resulted in rapidDecreasing the potential toxicity resulted in rapid metabolism.metabolism.
- 17. ConclusionConclusion AnestheticAnesthetic pKapKa OnsetOnset Duration (withDuration (with Epinephrine)Epinephrine) in minutesin minutes Max DoseMax Dose (with(with Epinephrine)Epinephrine) ProcaineProcaine 9.19.1 SlowSlow 45 - 9045 - 90 8mg/kg –8mg/kg – 10mg/kg10mg/kg LidocaineLidocaine 7.97.9 RapidRapid 120 - 240120 - 240 4.5mg/kg –4.5mg/kg – 7mg/kg7mg/kg BupivacaineBupivacaine 8.18.1 SlowSlow 4 hours – 84 hours – 8 hourshours 2.5mg/kg –2.5mg/kg – 3mg/kg3mg/kg PrilocainePrilocaine 7.97.9 MediumMedium 90 - 36090 - 360 5mg/kg –5mg/kg – 7.5mg/kg7.5mg/kg ArticaineArticaine 7.87.8 RapidRapid 140 - 270140 - 270 4.0mg/kg –4.0mg/kg – 7mg/kg7mg/kg
- 18. Local anesthetics - DurationLocal anesthetics - Duration Determined by rate of elimination ofDetermined by rate of elimination of agent from site injectedagent from site injected Factors include lipid solubility, doseFactors include lipid solubility, dose given, blood flow at site, addition ofgiven, blood flow at site, addition of vasoconstrictors (does not reliablyvasoconstrictors (does not reliably prolong all agents)prolong all agents) Some techniques allowSome techniques allow multiplemultiple injections over timeinjections over time to increase duration,to increase duration, e.g. epidural cathetere.g. epidural catheter
- 20. Local anesthetics - vasoconstrictorsLocal anesthetics - vasoconstrictors Ratios Epinephrine is added to local anesthetics in extremely dilute concentrations, best expressed as a ratio of grams of drug:total cc’s of solution. Expressed numerically, a 1:1000 preparation of epinephrine would be 1 gram epi 1000 cc’s solution 1000 mg epi 1000cc’s solution = 1 mg epi 1 cc =
- 21. Local anesthetics - vasoconstrictorsLocal anesthetics - vasoconstrictors Therefore, a 1 : 200,000 solution of epinephrine would be 1 gram epi 200,000 cc’s solution = 1000 mg epi 200,000 cc’s solution or 5 mcg epi 1 cc solution
- 22. Local anesthetics - vasoconstrictorsLocal anesthetics - vasoconstrictors Vasoconstrictors should not be used in theVasoconstrictors should not be used in the following locationsfollowing locations FingersFingers ToesToes NoseNose Ear lobesEar lobes PenisPenis
- 24. Regional anesthesia - DefinitionRegional anesthesia - Definition Rendering a specific area of the body,Rendering a specific area of the body, e.g. foot, arm, lower extremities,e.g. foot, arm, lower extremities, insensate to stimulus of surgery orinsensate to stimulus of surgery or other instrumentationother instrumentation
- 25. Regional anesthesia - UsesRegional anesthesia - Uses Provide anesthesia for a surgicalProvide anesthesia for a surgical procedureprocedure Provide analgesia post-operatively orProvide analgesia post-operatively or during labor and deliveryduring labor and delivery Diagnosis or therapy for patients withDiagnosis or therapy for patients with chronic pain syndromeschronic pain syndromes
- 26. Regional anesthesia - typesRegional anesthesia - types TopicalTopical Local/FieldLocal/Field Intravenous block (“Bier” block)Intravenous block (“Bier” block) Peripheral (named) nerve, e.g. radial n.Peripheral (named) nerve, e.g. radial n. Plexus - brachial, lumbarPlexus - brachial, lumbar Central neuraxial - epidural, spinalCentral neuraxial - epidural, spinal
- 27. Topical AnesthesiaTopical Anesthesia Application of local anesthetic toApplication of local anesthetic to mucous membrane - cornea, nasal/oralmucous membrane - cornea, nasal/oral mucosamucosa Uses :Uses : awake oral, nasal intubation, superficialawake oral, nasal intubation, superficial surgical proceduresurgical procedure Advantages :Advantages : technically easytechnically easy minimal equipmentminimal equipment Disadvantages :Disadvantages : potential for large doses leading to toxicitypotential for large doses leading to toxicity
- 30. Local/Field AnesthesiaLocal/Field Anesthesia Application of local subcutaneously toApplication of local subcutaneously to anesthetizeanesthetize distal nerve endingsdistal nerve endings Uses:Uses: Suturing, minor superficial surgery, lineSuturing, minor superficial surgery, line placement, more extensive surgery withplacement, more extensive surgery with sedationsedation Advantages:Advantages: minimal equipment, technically easy, rapidminimal equipment, technically easy, rapid onsetonset Disadvantages:Disadvantages: potential for toxicity if large fieldpotential for toxicity if large field
- 31. IV Block - “Bier” blockIV Block - “Bier” block Injection of local anesthetic intravenously forInjection of local anesthetic intravenously for anesthesia of an extremityanesthesia of an extremity UsesUses any surgical procedure on an extremityany surgical procedure on an extremity Advantages:Advantages: technically simple, minimal equipment, rapid onsettechnically simple, minimal equipment, rapid onset Disadvantages:Disadvantages: duration limited by tolerance of tourniquet pain,duration limited by tolerance of tourniquet pain, toxicitytoxicity
- 33. PeripheralPeripheral nerve blocknerve block Injecting local anestheticInjecting local anesthetic near thenear the course of a named nervecourse of a named nerve Uses:Uses: Surgical procedures in the distribution ofSurgical procedures in the distribution of the blocked nervethe blocked nerve Advantages:Advantages: relatively small dose of local anesthetic torelatively small dose of local anesthetic to cover large area; rapid onsetcover large area; rapid onset Disadvantages:Disadvantages: technical complexity, neuropathytechnical complexity, neuropathy
- 36. Plexus BlockadePlexus Blockade Injection of local anesthetic adjacent to aInjection of local anesthetic adjacent to a plexus, e.g cervical, brachial or lumbar plexusplexus, e.g cervical, brachial or lumbar plexus Uses :Uses : surgical anesthesia or post-operative analgesia insurgical anesthesia or post-operative analgesia in the distribution of the plexusthe distribution of the plexus Advantages:Advantages: large area of anesthesia with relatively large doselarge area of anesthesia with relatively large dose of agentof agent Disadvantages:Disadvantages: technically complex, potential for toxicity andtechnically complex, potential for toxicity and neuropathy.neuropathy.
- 39. Central neuraxial blockade -Central neuraxial blockade - “Spinal”“Spinal” Injection of local anesthetic into CSFInjection of local anesthetic into CSF Uses:Uses: profound anesthesia of lower abdomen andprofound anesthesia of lower abdomen and extremitiesextremities Advantages:Advantages: technically easy (LP technique), high success rate,technically easy (LP technique), high success rate, rapid onsetrapid onset Disadvantages:Disadvantages: ““high spinal”, hypotension due to sympathetic block,high spinal”, hypotension due to sympathetic block, post dural puncture headache.post dural puncture headache.
- 42. Central Neuraxial Blockade -Central Neuraxial Blockade - “epidural”“epidural” Injection of local anesthetic in to the epiduralInjection of local anesthetic in to the epidural space at any level of the spinal columnspace at any level of the spinal column Uses:Uses: Anesthesia/analgesia of the thorax,Anesthesia/analgesia of the thorax, abdomen, lower extremitiesabdomen, lower extremities Advantages:Advantages: Controlled onset of blockade, long duration whenControlled onset of blockade, long duration when catheter is placed, post-operative analgesia.catheter is placed, post-operative analgesia. Disadvantages:Disadvantages: Technically complex, toxicity, “spinal headache”Technically complex, toxicity, “spinal headache”
Editor's Notes
- #4: This slide depicts the effect of sodium influx on overall membrane potential. By limiting influx, local anesthetics inhibit the depolarization of the membrane thereby interfering with propagation of the action potential.