L.a- Neurophysiology and Mode of Action

7/25/2019 L.a- Neurophysiology and Mode of Action

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Local anesthesia- defnition, neurophysiology and mode o

Seminar on..

Moderator

Dr. Arun Kumar K.V. Dr. Neeraja Singhla


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Contents.

Introduction Historical

background

Definition

Desirable

characteristic

Anatomic

consideration

Physiologic

considerations

Mode and site of

action of local

anesthetic

Kinetics of L.A.

Pharmacology of

LA.

Potentiation of

action of local

anesthetics-

vasoconstrictors ecent advances

and future trends in

!ain control

"hronic !ain-

current modes of

treatment

"onclusion

eferences


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Introduction


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Historical background

#$%#& Prave' -hy!odermic syringe. #(%)& Ale*ander +ood -hollo, metal needle.

""AI/ -first local anesthetic agent-isolated by

ieman -#(01 -from the leaves of the coca tree. Its anesthetic action ,as demonstrated by Karl

Koller in #((2.

3irst effective and ,idely used synthetic localanesthetic -P"AI/ -!roduced by /inhorn in

#$1% from ben'oic acid and diethyl amino ethanol.


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It anesthetic !ro!erties ,ere identified by 4iberfieldand the agent ,as introduced into clinical !ractice by

4raun.

LID"AI/- Lofgren in #$2(. 5he discovery of its anesthetic !ro!erties ,as

follo,ed in #$2$ by its clinical use by 5. 6ordh.

5hereafter& series of !otent anesthetic soon follo,ed,ith a ,ide s!ectrum of clinical !ro!erties.

Historical background


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Definition

Local anesthesia

Local anesthetic agent


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Various methods of inducing

local anesthesia Mechanical trauma

Lo, tem!erature

Ano*ia

"hemical irritants

eurolytic agents such as a

alcohol and !henols

"hemical agents such as local

anesthetics.


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Desirable characteristics

of local anesthesia . on irritating

ot cause any !ermanent alteration of nerve

structure

Lo, systemic to*icity

Must be effective regardless of ,hether it is

in7ected into the tissue or a!!lied locally to

mucous membranes.

8hort onset of anesthesia


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Desirable characteristicsof local anesthesia .

Duration of action must be long

Potency sufficient to give com!lete

anesthesia ,ithout the use of harmful

concentrated solutions.

3ree from !roducing allergic reactions

stable in solution and readily undergobio-transformation in the body.

8terile


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Anatomic

considerations

Structure of nerve fibers

Neuron

Sensory Motor


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Histochemistry


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Schwann cells and myelin


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Anatomy of a mixed nerve


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Physiologicconsiderations

Im!ulse 9 action !otential


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Electrophysiology electrochemistry of

ner!e conduction 85/P- #


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INTRACELLULAR AND EXTRACELLULAR IONICCONCENTRATIONS

Ion Intracellular(MEQ/L)

Extracellular(MEQ/L)

Ratio

Potassium (K+) 1101!0 "# $!%1

Sodium (Na+

) #10 1&0 1%1&

'hloride ('l) #10 110 1%11


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85/P- :


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85/P - )


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Membrane

channels


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IMPULSE PRPA!A"IN


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IMPULSE SPREA# Unmyelinated nerves


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Myelinated nerves


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"ode of action oflocal anesthetic

local anesthetic agents interfere ,ith e*citation !rocess in

a nerve membrane in one or more of the follo,ing ,ays;

Altering basic resting !otential

Altering the threshold !otential

Decreasing the rate of de!olari'ation

Prolonging the rate of re!olari'ation


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8ite - nerve membrane


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Mechanism of action

HH < H"lH"L < H:

+eak strong acid ,ater

4ase acid salt

H"IH< < "I-


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RN$% dis&laces calcium ions for the sodium channel rece&tor site'

( which causes

)indin* of the local anesthetic molecules to this rece&tor site

( which &roduce

)loc+ade of sodium channel

( and

#ecrease in sodium conduction ( which leads to

#e&ression of the rate of electrical de&olari,ation

( and

-ailure to achieve the threshold &otential level

Lac+ of develo&ment of &ro&a*ated action &otentials

( called

.onduction bloc+ade


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Effect of pH

Acidic environment =lo, !H>

H< ? < H

H< @ < H 9 vasoconstriction

#e*citatory 9 !ost syna!tic

:inhibitory 9 !ost syna!tic.

4eta => - vasodilation and bronchodilation < cardiac

stimulation

#3ound in heart F small intestines F res!onsiblefor cardiac stimulation F li!olysis

:found in bronchi& vascular beds& F uterus F

!roduces bronchodilation and vasodilation


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Epinephrine Most !otent and ,idely used vasoconstrictor in

dentistry 8ource; (1B of medullary secretion& also available as a

synthetic

Moa- both and & ,ith being !redominate

Systemic Effects of E&ine&hrine

Myocardium - G heart rate F cardiac out!ut

Pacemaker - G risk of dysrhythmias

"oronary Artery-Dilation of coronary artery

4 P- G systolic !ressure& effect on diastolic !ressure is

dose related

"ardiovascular -Decrease cardiac efficiency


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asculature

asoconstriction in skin& mucous membrane

F kidneys

asodilation in skeletal muscle in small

doses

es!iratory - 4ronchodilator

"8 - ot a !otent "8 stimulant

Metabolism

Increase o*ygen consum!tion

6lycogenolysis- G blood sugar

5ermination of /!ine!hrine


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! !

eu!take

"M5 and MA /*creted unchanged in urine =#B>

"linical Manifestations of /!ine!hrine verdose

"8 stimulation - fear& an*iety& tremor& !allor& di''iness

"ardiac dysrhythmia

entricular fibrillation

Drastic increase in 4P - can cause cerebral hemorrhage

Angina in !atients ,ith coronary insufficiency

Ma*imum Dose for Dental A!!ointment


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!!

ormal healthy !atient

1.: mg. !er a!!ointment

8ignificant cardiovascular im!airment

1.12 mg !er a!!ointment

"linical A!!lications for /!ine!hrine Acute allergic reaction

4ronchos!asm

"ardiac arrest

Hemostasis

Produce mydriasis

asoconstrictor

ore!ine!hrine


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ilutions of vasoconstrictors!

Dilution Mg/l T!era"eutic u#e

1%1000 1.0 mergen* medi*ine(,m-S* anahla/is)

1%$#00 0.& Phenlehrine

1%10000 0.1 mergen* medi*ine (,V*ardia* arrest)

1%$0000 0.0# eonorde2rin

1%"0000 0.0"" Noreinehrine

1%#0000 0.0$ o*al anesthesia

1%30000 0.01$# o*al anesthesia

1%100000 0.01 o*al anesthesia

1%$000000 0.00# o*al anesthesia


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+ecent ad!ances and future

trends in pain control .entbucridine

Euinalone derivative

five to eight times the !otency of

lidocaine

8ignificantly is does not effect "8

F "8


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o!ivacaine

long- acting amide anesthetic

!re!ared as a isomer

greater margin of safety

decreased cardio-to*icity

/MLA


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/MLA


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&$ alterations

Alkalini'ation - G

"arbonation


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$yaluronidase

Ultra lon* actin* local anesthetics


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Ultra 7lon* actin* local anesthetics

5etradoto*in -!uffer fish

sa*ito*in -dinoflagelates.


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-ely&ressin

Electronic dental anesthesia


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Electronic dental anesthesia

5/8- :H'- try!to!han& Gserotonin F endor!hins

esidual analgesic effect

Jsed in management of;

"ausalgia

Phantom limb !ain

Post her!etic neuralgia

Intractable cancer !ain Lo,er back !ain

Ileus

Peri!heral nerve in7ury

4ursitis

Parturition

Polycythemia vera

"ervical back !ain

Post o!erative !ain

Diabetic ulceration

/DA- #:1 H' or more- !ain modulation


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/DA- #:1 H' or more- !ain modulation

serotonin F endor!hins- secondary role

Indications

5MMPD =chronic !ain>

Administration of local anesthesia

Acute !ain

onsurgical !eriodontal !rocedure

3i*ed !rosthodontic !rocedures

estorative dentistry

"ontraindications


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"ardiac !acemakers

eurological disorders9 8tatus !ost 9 cerebrovascular accident

9 History of transient ischemic attacks

9 History of e!ile!sy

Pregnancy

Immaturity =in ability to understand> the conce!t

of !atient control of !ain>

9 ery young !ediatric !atient

9 lder !atients ,ith senile dementia

Language communication difficulties

Ad


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Advantages

o need for needle

o need for in7ection of drug

Patient is in control of the anesthesia

o residual anesthetic effect at the end of

!rocedure

esidual analgesic effect remain for several

hours

Disadvantages


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Disadvantages

"ost of the unit

5raining

Learning curveinitial success may

be lo, but ,ill increase ,ith

e*!erience.

Intra oral electrodes 9 ,eak link in the

entire system.

Chronic pain # current


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Chronic pain # currentmodes of treatment

#ru* thera&y

Anti-inflammatory and analgesic

+eak o!ioids

8trong o!ioids

Re&eated local anal*esic and

neurolytic bloc+s

)loc+s of ANS


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.ryoanal*esia

Radiofre8uency heat lesion .hemical hy&o&hysectomy

Percutaneous cordotomy

Electro stimulation and

electrical non1invasive thera&y

Acu&uncture Psychothera&y

$y&nosis

+eferences


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+eferences Principles of anesthesiology& )rdedition& vol- :& incent .

"ollins

Local anesthesia-mechanism of action and clinical use-

4en7amin 6 "ohino

Handbook of local anesthesia& %thedition& 8tanley 3.

Malamed

Monehims local anesthesia and pain control,4enett

Current trends in pain research and therapy,ol 2&

chronic !ain reactions& mechanism and modes of

thera!y


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Local anesthesia-M. L. Ku'in

D"A- Local anesthetics revie,ed&20 =2>& :11: Internet references;

6oogle.com

Alta vista.comAllthe,eb.com

"anadian ournal of anesthesiology.org

Medvi'ion.net

/medicine.net.


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%hank you

L.a- Neurophysiology and Mode of Action

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