local anesthesia i lecture

8/16/2019 Local Anesthesia I lecture

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Local Anesthesia

Andrew G. Drollinger, DDS

Assistant Professor

Roseman University

College of Dental Medicine


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!tcomes

– De"ne local anesthesia

– #dentify chemical con"g!ration and characteristics oflocal anesthetics

– #dentify the desira$le %ro%erties of a local anesthetic

– Descri$e methods to ind!ce anesthesia

– Understand the anatomy of a nerve and nerve cellmem$rane

– Understand the %rocess of anesthetic di&!sion and

electro%hysiology of nerve cond!ction – Descri$e saltatory cond!ction and !nderstand its

im%ortance in nerve cond!ction

– Understand the mechanism of local anesthetics


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Lect!re !tcomes

• Understand dissociation of LA's and tiss!e %(

• Understand how low tiss!e %( )infection* altersdissociation of LA's

• Understand rate of onset and dissociation constants

• Descri$e the factors that a&ect LA action• Understand the sites of meta$olism of LA's

• Understand the role and action of vasoconstrictors in LA's

• Understand the systemic e&ects and dr!g interactions of

vasoconstrictors• De"ne methemoglo$inemia

• Understand the ma+im!m dosages of LA's for children andad!lts


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Lect!re !tcomes

• Calc!late amo!nt of LA andvasoconstrictor fo!nd in a dentalanesthetic cartridge

• Understand anesthetic deliverye!i%ment

• Descri$e medications !sed in %ost o%%ain management


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A-S/(S#A

An0000000000witho!t

Esthesia000a$ility to e+%erience sensation

• (and$oo1 of Local Anesthesia 2th edition

3y Stanley 4. Malamed• Reading assignments5

– Part 6 )cha%ters 607*

– Cha%ter 62

– Cha%ter 86 9!estions

)local anesthetics : vasoconstrictors*


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;(A/ #S LCALA-S/(S#A<

Loss of sensation in circ!mscri$edareas of the $ody witho!t loss ofconscio!sness ca!sed $y de%ression ofe+citation in nerve endings

0 /his is a %hysiologic %rocess 0


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M/(DS / #-DUC A-S/(S#A<• Mechanical tra!ma )com%ression of tiss!es*

•Sensory nerves over0"re %rod!cing loss of sensation d!e to de%letion of -/M)n!clear trans%ort mod!lation*

• Low tem%erat!re

• Ano+ia

•

de%rivation or relative decrease in 8

• Chemical irritants

•Can ca!se nerve damage e&ecting transmission of nerve im%!lse

•+am%le5 Sargenti method of endodontics made %ts li%s go n!m$ after RC/

•3enadryl = has wea1 analgesic %ro%erties

•

-e!rolytic agents s!ch as alcohol and %henol•Alcohol : %henol $loc1s

•Ris1 of develo%ing Anesthesia Dolorosa

• Chemical agents s!ch as local anesthetics


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DS#RA3L PRPR/#S 4 A LCALA-S/(/#C

• -on0irritating to the tiss!es• addition of sodi!m $icar$onate can ma1e it non0irritating and s%eed its onset of action

• -o %ermanent alteration of nerve• Alcohol will 1ill %art of the nerve str!ct!re

• 4ormaldehyde, Sargenti, and alcohol will denat!re the %rotein in the nerve mem$rane

• ;e need to $e ca!tio!s in what we choose to !se

• Low systemic to+icity• All dr!gs will dis%erse thro!gho!t the $ody and there will AL;A>S $e a systemic conse!ence

• 3!%ivicaine )Marcaine* avoid !se in %ediatrics d!e to %rolonged anesthesia – htt%5??www.aa%d.org?media?Policies@G!idelines?G@LocalAnesthesia.%df

• &ective as a to%ical and inecta$le

• Short onset of action : a%%ro%riate d!ration of action• Lidocaine is a good LA for dentistry, lasts a$o!t B min )longer with e%ine%hrine*

• 3!%ivicaine has the longest d!ration of action, 20 ho!rs


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09!ic1 side note a$o!tanesthesia0

A%%lica$le information and vital toyo!r s!ccessE


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A-A/M> 4 A -RF

• /he ne!ron is the $asic str!ct!ral !nitof the nervo!s system

• /wo ty%es of ne!rons 0 f!nctionally• Sensory a&erent

• Motor e&erent

•

/wo ty%es of ne!rons = mor%hologically• 3i%olar )%se!do!ni%olar*

• m!lti%olar


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A-A/M> 4 A -RF

• /he a+on ty%ically has a s!%er"ciallayer called myelin (Schwann cells)

• Cell body of a motor neuron isinvolved in transmission (nodes ofRanvier, speed of transmission)

• Cell body of a sensory

Neuron is only available

For nutritional support


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• Myelin5 – Li%io%roteinaceo!s s!$stance )s%ecialied

Schwann cells* – #ncreases the s%eed of transmission

– Acts as a $arrier to LA

• Site of action for LA – -odes of RanvierHevery .B0.I mm, but can $e

!% to 8 mm

Profo!nd anesthesia when 80B adacent -odes ofRanvier are $athed in LA and?or a minim!m of 0

6 mm


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SAL/A/R> PRPGA/#-

•

/he JmessageKlea%s from one-ode of Ranvier tothe ne+t

• htt%s5??www.yo!t!$e.com?watch


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#nferior alveolar nerve


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• A+ons in a $!ndle are called fascic!li andcovered in endone!ri!m

#nnermost layer of the %erine!ri!m is calledthe perilemma which is the main $arrier todi&!sion of LA


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Cell Mem$ranes )nerve mem$rane*

• ;hat's the general ma1e!% of a cellmem$rane< – Phos%holi%id $ilayer


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Cell?nerve mem$rane

• 3loc1s di&!sion of water sol!$lemolec!les

• Semi0%ermea$le to certain molec!lesvia channels or %ores

• /ransd!ce information from theextracell!lar s!rro!ndings )matri+*intracell!larly via %roteinsem$edded in the mem$rane


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• ;hat can interact with these %roteinsem$edded in the mem$rane<

6. -e!rotransmitters )i.e. hormones,chemicals*

8.Press!re

B. Light

7.Fi$ration


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Proteins

• ;hat are the two main ty%es ofmem$rane %roteins<

6. /rans%ort %roteins )channels,carriers or %!m%s*

8. Rece%tor %roteins


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/rans%ort %roteins

• Contin!o!s channels – %assive Oow of ions )-a, , Ca*

• Gated channels – Gate m!st $e o%en to allow %assage


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Dr!m Roll PleaseE

• /he %assage of ions thro!gh thesegates allow a nerve im%!lseEEE


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Myelinated nerve "$ers

• ;hat is myelin< – #ns!lating li%id layer

• ;hat act!ally forms the myelin< – Schwann cells


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Unmyelinated nerve "$ers

• Act!ally s!rro!nded $y a schwanncell sheath or myelin

• CaveatH – M!lti%le nerve "$ers share the same

sheath


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;hy is this im%ortant to1now<

• /he ins!lating %ro%erties of themyelin ma1e nerve cond!ction m!chfaster than the !nmyelinated "$ers


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Saltatory cond!ctionJsaltareK to lea%


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SoH

• D!ring an inection which nerves lose sensation "rst<

A. Small unmyelinated nerves or

3. Large myelinated nerves

• ;hy< – Smaller diameter means less Jst!&K to go thro!gh

• Myelin – Myelin ins!lates the a+on $oth electrically and %harmacologically

–-aQ channels fo!nd mainly at nodes of Ranvier

– An electrical im%!lse can J!m%K over 608 nodes of Ranvier

– 80B s!ccessive nodes need to $e $loc1ed to halt %ro%agation

– /he more myelinHthe f!rther a%art the nodes, hence the harder to $loc1


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Anesthetic Di&!sion

• LA $ecomes increasingly

dil!ted $y tiss!e O!ids and

removed $y ca%illaries and

lym%hatics

• Core bers are e+%osed to a decreased concentrationof LAHmore dic!lt to achieve %rofo!nd anesthesiaHdistal distri$!tion

• !antle bers )s!rface* are e+%osed to higher

concentration LA Heasier to achieve %rofo!ndanesthesiaH%ro+imal distri$!tion

• Profo!nd anesthesia can $e more dic!lt for %remolarsthan molars.


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lectro%hysiology of -erveCond!ction


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Slow depolari"ation# /heinterior $ecomes lessnegativeAt a critical level )thresholdlevel) the de%olariationincreases

Stim!l!s a%%lied

/his rapid depolari"ationca!ses a change in the%olarity across themem$rane. #nterior nowmore %ositive.

Repolari"ation $ac1 to the0NmF


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ions

• ;hich cation is %redominately fo!ndintracell!larly< – QHremains in a+o%lasm d?t electrostatic

attraction

• ;hich ions are fo!nd %redominatelye+tracell!larly< – -aQHtravels inward d?t concentration

gradient and electrostatic attraction

– Cl0Hstays o!tside d?t electrostatic attraction


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Resting %otential of thenerve

• ;hat is the resting %otential< – A negative electrical %otential of 0NmF across the

mem$rane

• ;hat %rod!ces this %otential< – /he di&ering concentrations of ions on either side of

the mem$rane

• ;hich is negative, the e+terior of the nerve orthe interior< – #nterior


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/ransmission of -e!ronal#nformation

• Mem$rane channelsHfo!nd in allne!rons – -ongated

– Modality gated )sensory ne!ron, C- F*

– Ligand gated

– $olta%e %ated )voltage0de%endent -aQ

channels*


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-aQ channel

-AQ


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-erve at rest

• -aQ is a$o!t half the sie of Q andCl0

• ;hat )%rimarily* 1ee%s -aQ in thee+tracell!lar s%ace< – H2O

• ;hen -aQ $ecomes hydrated it cannot %ass

thro!gh its channel, whereas Q and Cl0 can


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-erve at Rest )resting mem$rane*channel closed

(ydrated-aQ


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Activated nerve )de%olariation*channel o%en

(ydrated-aQ


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Slow de%olariation. /heinterior $ecomes lessnegativeAt a critical level )thresholdlevel* the de%olariationincreases

Stim!l!s a%%lied

/his ra%id de%olariationca!ses a change in the%olarity across themem$rane. #nterior nowmore %ositive.

Re%olariation $ac1 to the0NmF


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Saltatory cond!ction


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SoHhow do local anesthetics wor1<

• 3loc1 the transmission of the action%otential $y inhi$ition of voltage0gated -aQ channels

• -aQ channel $loc1ers

• Decreasing the rate of de%olariation


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• LA's do not alter the restingmem$rane %otentialHMiller, 3asics ofAnesthesia, 2th edition

•

Malamed, (and$oo1 of Local Anesthesia, 2th edition

•

LA's have very little e&ect on thethreshold %otential


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;hat's #m%ortant

• Primary e&ect of local anesthetics isto decrease the rate of de%olariation – 3asicallyHthey $loc1 the de%olariation

%haseH

• Remem$er -aQ inO!+


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S%eci"c Rece%tor /heory

• local anesthetics )and venoms* act$y $inding to s%eci"c rece%tors in thesodi!m channel


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Sodi!m channel

-ote local anesthetic $loc1sfrom the a+o%lasm side

local anesthesia i lecture

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