local anesthesia i lecture
TRANSCRIPT
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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