Soft Tissue WorkshopSoft Tissue WorkshopLocal Anesthetics and Regional Local Anesthetics and Regional

Anesthesia of the Head and NeckAnesthesia of the Head and Neck

Local AnestheticsLocal Anesthetics

Local AnestheticLocal Anesthetic

A local anesthetic is an agent that A local anesthetic is an agent that interrupts pain impulses in a specific interrupts pain impulses in a specific region of the body without a loss of patient region of the body without a loss of patient consciousness. Normally, the process is consciousness. Normally, the process is completely reversible-completely reversible--the agent does not -the agent does not produce any residual effect on the nerve produce any residual effect on the nerve fiber. fiber.

Advantages of Local AnesthesiaAdvantages of Local Anesthesia

The patient is conscious during surgery.The patient is conscious during surgery. Smooth postoperative course. Smooth postoperative course. Patient awake and maintains his own airway. Patient awake and maintains his own airway. Less pain needs less narcotics, lighter Less pain needs less narcotics, lighter

anesthesia in general cases.anesthesia in general cases. Less nursing care after procedures, less Less nursing care after procedures, less

admissions.admissions. Less expensiveLess expensive

Disadvantages of Local AnesthesiaDisadvantages of Local Anesthesia

The patient may prefer to be asleep The patient may prefer to be asleep Specialized skill necessary. Specialized skill necessary. Some blocks require up to 30 minutes to Some blocks require up to 30 minutes to

be fully effective. be fully effective. Analgesia may not always be totally Analgesia may not always be totally

effective, and general anesthesia may be effective, and general anesthesia may be required anyway.required anyway.

Disadvantages of Local AnesthesiaDisadvantages of Local Anesthesia

Generalized toxicity may occur if local Generalized toxicity may occur if local anesthetic drugs are given intravenously anesthetic drugs are given intravenously by mistake or an overdose is given. by mistake or an overdose is given.

Widespread sympathetic blockade can Widespread sympathetic blockade can result in hypotension. result in hypotension.

There is a small but definite incidence of There is a small but definite incidence of prolonged nerve damage. prolonged nerve damage.

Characteristics of the Ideal Local Characteristics of the Ideal Local AnestheticAnesthetic

Effective when injected or applied topicallyEffective when injected or applied topically Short onset of actionShort onset of action Duration long enough for procedureDuration long enough for procedure Non-Irritating to tissuesNon-Irritating to tissues Non-damaging to nerve structuresNon-damaging to nerve structures High margin of safetyHigh margin of safety Soluble in water, stable in solutionSoluble in water, stable in solution Inexpensive and availableInexpensive and available

HistoryHistory

First local anesthetic - Cocaine which was isolated First local anesthetic - Cocaine which was isolated from coca leaves by Albert Niemann in Germany in from coca leaves by Albert Niemann in Germany in the 1860s. the 1860s.

Very first clinical use of Cocaine was in 1884 by Very first clinical use of Cocaine was in 1884 by Sigmund Freud who used it to wean a patient from Sigmund Freud who used it to wean a patient from morphine addiction.  morphine addiction. 

It was Freud and his colleague Karl Kollar who first It was Freud and his colleague Karl Kollar who first noticed its anesthetic effect.  Kollar first introduced it noticed its anesthetic effect.  Kollar first introduced it to clinical ophthalmology as a topical ocular to clinical ophthalmology as a topical ocular anesthetic. anesthetic. 

Also in 1884, Dr. William Stewart Halsted was the Also in 1884, Dr. William Stewart Halsted was the first to describe the injection of cocaine into a first to describe the injection of cocaine into a sensory nerve trunk to create surgical anesthesia. sensory nerve trunk to create surgical anesthesia.

ChemistryChemistryAll local anesthetics are weak bases, classified as tertiary amines. 

EstersEsters

These include cocaine, procaine, These include cocaine, procaine, tetracaine, and chloroprocaine. tetracaine, and chloroprocaine.

They are hydrolyzed in plasma by pseudo-They are hydrolyzed in plasma by pseudo-cholinesterase. One of the by-products of cholinesterase. One of the by-products of metabolism is paraaminobenzoic acid, the metabolism is paraaminobenzoic acid, the common cause of allergic reactions seen common cause of allergic reactions seen with these agentswith these agents

AmidesAmides

These include lidocaine, mepivicaine, These include lidocaine, mepivicaine, prilocaine, bupivacaine, and etidocaine. prilocaine, bupivacaine, and etidocaine.

They are metabolized in the liver to They are metabolized in the liver to inactive agents. True allergic reactions are inactive agents. True allergic reactions are rare (especially with lidocaine) rare (especially with lidocaine)

Mechanism of ActionMechanism of Action

Local anesthetics are weak bases that work to Local anesthetics are weak bases that work to block nerve conduction by reducing the influx of block nerve conduction by reducing the influx of sodium ions into the nerve cytoplasm.sodium ions into the nerve cytoplasm.

Sodium ions cannot flow into the neuron, thus the Sodium ions cannot flow into the neuron, thus the potassium ions cannot flow out, thereby inhibiting potassium ions cannot flow out, thereby inhibiting the depolarization of the nerve.  the depolarization of the nerve. 

If this process can be inhibited for just a few If this process can be inhibited for just a few Nodes of Ranvier along the way, then nerve Nodes of Ranvier along the way, then nerve impulses generated downstream from the impulses generated downstream from the blocked nodes cannot propagate to the ganglion. blocked nodes cannot propagate to the ganglion.

Mechanism of actionMechanism of action

local anesthetics bind local anesthetics bind directlydirectly to the to the intracellularintracellular voltage-dependent sodium voltage-dependent sodium channelschannels

Block primarily Block primarily openopen and and inactiveinactive sodium sodium channels, at specific sites within the channels, at specific sites within the channelchannel

Mechanism of actionMechanism of action

1) slow rate of depolarization1) slow rate of depolarization 2) reduce height of action potential2) reduce height of action potential 3) reduce rate of rise of action potential3) reduce rate of rise of action potential 4) slow axonal conduction 4) slow axonal conduction 5) ultimately prevent propagation of action 5) ultimately prevent propagation of action

potentialpotential 6)6) do not do not alter resting membrane potential alter resting membrane potential 7) increase threshold potential7) increase threshold potential

Factors affecting Factors affecting local anesthetic actionlocal anesthetic action

Effect of pHEffect of pH charged (cationic) form binds to receptor site charged (cationic) form binds to receptor site

and does not readily cross the cell membrane, and does not readily cross the cell membrane, thus, tissue acidosis (abscesses and cellulitis) thus, tissue acidosis (abscesses and cellulitis) renders local anesthetic agents ineffective renders local anesthetic agents ineffective

uncharged form penetrates membraneuncharged form penetrates membrane efficacy of drug can be changed by altering efficacy of drug can be changed by altering

extracellular or intracellular pH extracellular or intracellular pH

Susceptibility to block by local Susceptibility to block by local anesthetics of types of nerve fibers anesthetics of types of nerve fibers In general, small nerve fibers are more In general, small nerve fibers are more

susceptible than large fibers; however, susceptible than large fibers; however, the type of fiberthe type of fiber degree of myelinationdegree of myelination fiber length and fiber length and frequency- dependence are also important in frequency- dependence are also important in

determining susceptibilitydetermining susceptibility

Order of sensory function block Order of sensory function block

1. pain1. pain 2. cold2. cold 3. warmth3. warmth 4. touch4. touch 5. deep pressure 5. deep pressure 6. motor6. motor

Recovery in reverse order

Recovery from local anesthesiaRecovery from local anesthesia

After injection, the drug is absorbed into After injection, the drug is absorbed into the blood and removed from the areathe blood and removed from the area

Absorption varies with the vascularity of Absorption varies with the vascularity of the area injectedthe area injected

Epinephrine is potent vasoconstrictor and Epinephrine is potent vasoconstrictor and results in decreased blood flow…slower results in decreased blood flow…slower absorption…decreased likelihood of absorption…decreased likelihood of systemic reaction and prolonged systemic reaction and prolonged anesthetic effectanesthetic effect

TOXICITIES OF LOCAL TOXICITIES OF LOCAL ANESTHETICSANESTHETICS

Essentially all systemic toxic reactions Essentially all systemic toxic reactions associated with local anesthetics are the associated with local anesthetics are the result of over-dosage leading to high blood result of over-dosage leading to high blood levels of the agent given. Therefore, to avoid levels of the agent given. Therefore, to avoid a systemic toxic reaction to a local a systemic toxic reaction to a local anesthetic, the smallest amount of the most anesthetic, the smallest amount of the most dilute solution that effectively blocks pain dilute solution that effectively blocks pain should be administered.should be administered.

Hypersensitivity of Local Hypersensitivity of Local AnestheticsAnesthetics

Some patients are hypersensitive (allergic) to Some patients are hypersensitive (allergic) to some local anesthetics. some local anesthetics.

Although such allergies are very rare, a careful Although such allergies are very rare, a careful patient history should be taken in an attempt to patient history should be taken in an attempt to identify the presence of an allergy. identify the presence of an allergy.

There are two basic types of local anesthetics (the There are two basic types of local anesthetics (the amide type and the ester type). A patient who is amide type and the ester type). A patient who is allergic to one type may or may not be allergic to allergic to one type may or may not be allergic to the other type. the other type.

Central Nervous System Central Nervous System ToxicitiesToxicities

Local anesthetics, if absorbed Local anesthetics, if absorbed systematically in excessive amounts, can systematically in excessive amounts, can cause central nervous system (CNS) cause central nervous system (CNS) excitement or, if absorbed in even higher excitement or, if absorbed in even higher amounts, can cause CNS depression. amounts, can cause CNS depression.

CNS toxicity continuedCNS toxicity continued

Excitement. Tremors, shivering, and Excitement. Tremors, shivering, and convulsions characterize the CNS convulsions characterize the CNS excitement.excitement.

Depression. The CNS depression is Depression. The CNS depression is characterized by respiratory depression characterized by respiratory depression and, if enough drug is absorbed, and, if enough drug is absorbed, respiratory arrest.respiratory arrest.

Cardiovascular ToxicitiesCardiovascular Toxicities

Local anesthetics if absorbed Local anesthetics if absorbed systematically in excessive amounts can systematically in excessive amounts can cause depression of the cardiovascular cause depression of the cardiovascular system. system.

Peripheral vascular action arteriolar dilation Peripheral vascular action arteriolar dilation (except (except cocainecocaine which is vasoconstrictive) which is vasoconstrictive)

Hypotension and atrioventricular block Hypotension and atrioventricular block characterize such depression. These may characterize such depression. These may ultimately result in both cardiac and ultimately result in both cardiac and respiratory arrest. respiratory arrest.

Signs of toxicitySigns of toxicity

Signs of toxicity occur on a continuum. From Signs of toxicity occur on a continuum. From early to late stages of toxicity, these signs are: early to late stages of toxicity, these signs are: circum-oral and tongue numbness, circum-oral and tongue numbness, lightheadedness, tinnitus, visual disturbances, lightheadedness, tinnitus, visual disturbances, muscular twitching, convulsions, muscular twitching, convulsions, unconsciousness, coma, respiratory arrest, unconsciousness, coma, respiratory arrest, then cardiovascular collapse. then cardiovascular collapse.

Treatment of ToxicityTreatment of Toxicity OxygenOxygen by face mask or intubation by face mask or intubation Anticonvulsants such as Anticonvulsants such as benzodiazepinesbenzodiazepines and and barbiturates barbiturates

(diazepam 5-10 mg, thiopental 50-100 mg) are the drugs of choice (diazepam 5-10 mg, thiopental 50-100 mg) are the drugs of choice for seizure control. for seizure control.

Phenytoin is not effective and should be avoided. Phenytoin is not effective and should be avoided. SuccinylcholineSuccinylcholine is sometimes also used to terminate the is sometimes also used to terminate the

neuromuscular effects of seizures. Because succinylcholine neuromuscular effects of seizures. Because succinylcholine paralyzes all muscles, the patient requiresparalyzes all muscles, the patient requires intubation intubation.. In severe reactions, monitor the cardiovascular system (CVS) and In severe reactions, monitor the cardiovascular system (CVS) and

support the patient with support the patient with intravenous fluidsintravenous fluids and and vasopressorsvasopressors as as required.required.

Metabolic acidosis may develop, and the use of Metabolic acidosis may develop, and the use of sodium bicarbonatesodium bicarbonate can be considered, although, as in other instances of acute metabolic can be considered, although, as in other instances of acute metabolic acidosis, this is controversial.acidosis, this is controversial.

LidocaineLidocaine

Amide, vasodilator (use epinephrine)Amide, vasodilator (use epinephrine) 4% solution for topical use4% solution for topical use 0.5%-1% solution for injection into soft 0.5%-1% solution for injection into soft

tissuestissues Maximum dose 5mg/kg without Maximum dose 5mg/kg without

epinephrine; 7mg/kg with epinephrineepinephrine; 7mg/kg with epinephrine 10mg/ml in 1% lidocaine10mg/ml in 1% lidocaine 20mg/ml in 2% lidocaine20mg/ml in 2% lidocaine

Mepivacaine (Carbocaine)Mepivacaine (Carbocaine)

Efficacy and toxicity similar to lidocaine but Efficacy and toxicity similar to lidocaine but diffuses more readily through tissues and diffuses more readily through tissues and has a longer half-lifehas a longer half-life

Bupivacaine (Marcaine)Bupivacaine (Marcaine)

Long duration of action, used for nerve Long duration of action, used for nerve blocks or infiltrated into wound closure for blocks or infiltrated into wound closure for postoperative pain reliefpostoperative pain relief

Total dose 3mg/kg alone; 4mg/kg with epiTotal dose 3mg/kg alone; 4mg/kg with epi

RopivacaineRopivacaine

Newer agent, efficacy similar to Newer agent, efficacy similar to bupivacaine but is less toxic and less bupivacaine but is less toxic and less moor block for he same degree of sensory moor block for he same degree of sensory blockblock

S stereoisomer of bupivacaine and has the S stereoisomer of bupivacaine and has the substitution of a propyl for a butyl substitution of a propyl for a butyl

Slightly less potent and has safer Slightly less potent and has safer cardiotoxicity profilecardiotoxicity profile

CocaineCocaine

Unique among topical anesthetics because it is a potent Unique among topical anesthetics because it is a potent vasoconstrictorvasoconstrictor

Can be used alone in upper aerodigestive tract for both Can be used alone in upper aerodigestive tract for both anesthesia and control of hemorrhageanesthesia and control of hemorrhage

Limited to mucous membranes of the head and neckLimited to mucous membranes of the head and neck 4% solution for direct application to mucous membranes4% solution for direct application to mucous membranes Quick onset of action (5-10 minutes) and duration of Quick onset of action (5-10 minutes) and duration of

action as long as 6 hoursaction as long as 6 hours Blocks uptake of epinephrine and norepinephrine by Blocks uptake of epinephrine and norepinephrine by

adrenergic nerve endings – potentiates the effects of adrenergic nerve endings – potentiates the effects of catecholaminescatecholamines

Total dose limited to 1.5 mg/kgTotal dose limited to 1.5 mg/kg

BenzocaineBenzocaine

Topical spray before endoscopic Topical spray before endoscopic proceduresprocedures

Can cause methemoglobinemia if used in Can cause methemoglobinemia if used in large doseslarge doses

Local AnestheticsLocal Anesthetics

DrugDrug Chemical Chemical CharacteristicCharacteristic

Metabolism Metabolism Max dose Max dose (mg/kg)(mg/kg)

Onset/Onset/

DurationDuration

CocaineCocaine EsterEster CholinesteraseCholinesterase 1.51.5 5-10 min5-10 min

6 hours6 hours

LidocaineLidocaine AmideAmide LiverLiver 5-75-7 2-5 min2-5 min

1-3 hrs1-3 hrs

BenzocaineBenzocaine EsterEster CholinesteraseCholinesterase 33

BupivicaineBupivicaine AmideAmide LiverLiver 3-43-4

Regional Blocks in Head and NeckRegional Blocks in Head and Neck

Scalp BlocksScalp Blocks

Scalp BlocksScalp Blocks

Trigeminal Nerve BlocksTrigeminal Nerve Blocks

Mandibular Nerve BlocksMandibular Nerve Blocks

Inferior Alveolar Nerve BlockInferior Alveolar Nerve Block

Inferior Alveolar Nerve BlockInferior Alveolar Nerve Block

Inferior Alveolar Nerve BlockInferior Alveolar Nerve Block

Inferior Alveolar Nerve BlockInferior Alveolar Nerve Block