Local anesthesia sheet #2 - Dana Al omosh

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Local anesthesia sheet #2 - Dana Al omosh

Post by Shadi Jarrar on 3/10/2011, 2:06 am

4shared.com la2.html



BY THE NAME OF ALLAH

PHARMACOLOGY OF LOCAL ANESTHESIA

This lecture will talk about the pharmacology of local anesthetics, but just before that the dr. talked about many subject about local anesthesia we should know it by heart …
Everyone should know the molecular physiology of pain , from pain definition, neurotransmitters , the important of substance B and pain pathology .
Then the dr. asked what the substance B ??
It is one of the neurotransmitters that has relation to the pain , when does exist its mean that painful process is going on .
Substance B exist in sabstantia gelatenosa .
We should know the effect of substance B on threshold , does it increase it or decrease it ??
You have to know the physiology of neurons and what are the fibers that included in the transitions of pain from the site of injury until the perception of this pulse in cortex , and what the mandatory factors that affect the pain pathway.
We should concern on the " Gate control theory " , because the pain is modulating , so imagine if the pain transmitted from the site of injury to the cortex without modulating , it will be in high magnitude and that will be harmful so thx god for modulating mechanism which make inhibition on this pathway.
We have to know what are the nerve fibers that are incorporated from the site of injury until reach the thalamus
there is many type of fibers :
- C fiber
A fiber -
- B fiber
- delta fiber
The different between the different type of fibers is very important and we should know them very well.
Those fibers go to spinothalamic tract then come out frome the dorsothalamic tract to the thalamus .
{ dr. talked about the quiz for the oral surgery lab, will be in the third week "this week L " will be about the enervations of facial area , branches of trigeminal nerve , motor nucleus , sensory nucleus, substantia gelatenosa , substance B , spinothalamic tract and the whole journey of pain pathway and gate control theory } bas hadool L
Dr. say that she focus on the " pain pathophysiology " because the pain is very important in the international exams ( national Bord exams , MFD exama ..) so pain is international topic J
To study all the previous subjects , that u should know it as your names as dr said , the dr advice us by reading MALAMED BOOK which is " el ketab el mo3tamad " .
Now we start our today subject , the new idea in this lecture is the
" Pain Clinic " , one of the most developed things in medicine is the presence of pain clinic to manage the pain , dental pain procedure is one of the most painful technique that need to be manage very well ,specially manage the pain of the first procedure "injection of local anesthesia" because many patients have phobia from needle injection .
In pain clinic there is no one specialist of pain , this clinics have team work of consultant , one of them is a dentist or is an oral surgeon to manage dental pain and other forms of pain that is related to dental procedures like trigeminal neuralgia , so every one should study or revision the trigeminal nerve .
Pain threshold is variable , and pain tolerance is different between individuals and even in the same person it is different from time to time , there is many factors that contribute this issue you take it last lecture .
In last lecture you took that local anesthesia (L.A) work basicly on the action potential , or depolarizing , or prolonging the repolarization .
That is the summary of the action of L.A .
In today lecture we will focus on the pharmacology of L.A

Definition of local anesthesia :
Loss of sensation in circumscribed area of the body caused by depression of excitation in nerve ending or an inhibition of conduction process in peripheral nerves
, L.A not only mean loss of pain sensation but also we should considered other parameters which are :
Touch , Pressure, Temperature otherwise it will not be L.A , it will be local analgesia only .
Types of local anesthesia :
1- Topical Anesthesia :
local anesthesia are absorbed at differing rates after application to mucus membrane , topical L.A either cream , gel , ointment , spray or any other preparations.
One of the newest topical oral L.A is the "lozenges" by taking one lozenges as " mlabaseh " in oral cavity it will make topical local anesthesia to the mucus membrane of oral cavity .
Spray topical L.A is one of the most common use in dental clinic and our homes , some patients come to ur clinic with gray mucus membrane due to heavy use of these sprays which cause burn in oral mucosa .
Mostly we use topical anesthesia in pediatric clinic , before we give the injection we put some topical anesthesia at the site where we will give the needle in .
2- Infiltration :
Deposit of solution in the region to be anesthetized and permeates through the tissue to affect fine nerve endings .
Many types for infiltration will be discuses later , ( supraperiostial , subperiostial ,….)
In filtration we affect the free nerve ending , to inhibit the action potential on it .
3- Regional or Block anesthesia :
To anesthetize a region by blocking the conduction in the nerve trunk supplaing the area.
we go to the nearest nerve trunk in the area or to the large division of the nerve and we block it .
e.g : ID block ( inferior dental alveolar nerve block ) or mental nerve block , or in upper jaw : posterior superior alveolar nerve block .
developmental history of L.A :
1- Mechanical Trauma :
In the past when the dentist need to make extraction for example he was hurt the patient to make mechanical trauma which make part of L.A .
2- Low Temperature :
Use of ice to get anesthetic action .
3- Chemical Irritant :
Mainly alcohol , by using alcohol injection but the problem with this technique is the permanent damage to nerve fibers because the effect of alcohol is irreversible .
The ideal agent that we look for is reversible , affordable, injectable, and easy to be used .
4- Chemical Agent such as L.A in its newly form
The develop of L.A start in 1948 , " msh mn zman kteer " .
Local agent are basicly 2 groups :
1- ester type
2- amide type
- ketone –linkage (ketonic group) class of anesthesia has relatively little clinical importance ,and mainly use as topical anesthesia because it is not suitable to injection because its highly lipophilic .
Amide and ester groups have 2 parts in their structures :
- lipophilic part: is the largest portion of the molecule . aromatic in structure , and it is derived from benzoic acid or aniline .
- hydrophilic part : is an amino derivative of ethyl alcohol or acetic acid .
So this molecule called amphepathic ( has 2 portion hydrophilic and lipophilic at the same time ) .
Hydrophilic part of L.A make it indictable , and can prepared in aqueous solution , so L.A without hydrophilic part ,they are not stable for injection ,and they mainly act as topical anesthesia .
The anesthetic structure completed by intermediate hydrocarbon chain either an ester or an amide and according to it L.A classified .
Amide can be secondary or tertiary amide according to the structure .
-.A are basic compounds , poorly soluble in water and unstable if it is exposed to air .
So always when we take about the content of L.A carpool we should talk about the preservative materials or antioxidant materials in the solution of L.A .
- L.A are weak base or hydrolytic salt of this base , they combined with acids , and to know the action of L.A we should know :
- ph of L.A solution .
- ph of the oral cavity tissues .
- pka of L.A . ( to know how much of L.A available ) dissociation constant .
RNH+ RN + H+


From this equation the active part of L.A is the RN molecule which can bind to membrane receptor and prevent the action potential .
H+ ions determine the ph of the tissue if it is acidic or basic , so if the concentration of H+ ions increase ,the ph will be low and the tissues will be acidic , then the rxn will shifted to the left , to the RNH+ side , the non active form ,that cant bind to the receptors of membrane , so no effect of L.A .
That what happens when the tissues of oral mucusa are inflamed ,that mean they are acidic and the acidic environment prevents good dissociation of L.A drug ,so no effect to it .
So in surgery the X-ray is mandatory to show any periapical radiolucency that guide us to know if there is any inflammation or not ,and precaution is very important clinical test for any tenderness in tooth , because tenderness mean inflammation ,and we should not give any infiltration of L.A in inflamed area cause that will be useless .
The percentage of drug in L.A can be determined from the
Handerson – Hasselblach equation :
base
Log = ph - pka
Acid
When pka = ph that mean anionic form = cationic form
When pka increase that mean ther is many RN molecule ( the active form) and the onset of action will be faster .
Potency of the agent :
The disadvantage of ester compound is the allergy .
the prototype of ester is procain , procain itself not cause allergy but the byproduct of metabolization of it , that which cause allergy >> PABA
( paramine benzoic acid ) causes allergic rxn.
We choose the agent of L.A according to potency of that agent , because different agents have different potencies , for example if we give procain no. 1 , we will give other agents numbers according to it , Etidocain ( amide) its no. = 140 , that mean Etidocain is extremely potent , so we only need small concentration of it to achieve the desired value of L.A .

Duration of anesthesia :
The bonds between L.A and receptors reflects the duration of L.A , so high and strong bonds mean that the duration will be longer .
In case of pediatric procedure , we look for L.A with short duration .
All L.A are vasodilator except Cocain is the only local anesthetic consistently producing vasoconstriction , but the initial action of cocain is vasodilation ,which followed by an intense and longed vasoconstriction .
Which agent have the most vasodailation ability ??
It is the Procain .
So we can use it in the management the case of medication toxicity , we can give it intra-arterial injection because it hase potent vasodilating ability .
Sometimes when we give L.A fast as one shot , it will go to the circulation faster then the patient suddenly will faint due to the side effect of L.A , but now we have vasoconstrictor added to L.A like epinephrine and felypressin etc . ,that reduce the escape of L.A to circulation , so duration of L.A will be longer .
Addition of vasoconstrictor and antioxidant reduce the ph of L.A solution
Most solution of local anesthetics without a vasoconstrictor have ph between 5.5 and 7 .
Local anesthetic solutions that contain a vasopressor (e.g., Epinephrine) are acidified by the manufacturer to retard oxidation of the vasoconstrictor, thereby prolonging the period of the drug effectiveness
Sodium bisulfite is commonly used, in a concentration between 0.05% and 0.1 %;
A 2 % solution of Lidocaine, with a pH of 6.8, is acidified to 4.2 by the addition of Sodium bisulfite.











Solution of local anesthesia
L.A. drug-
-Vasopressor drug ------------preservative for vasopressor
-sodium chloride
-distilled water
Biotransformation of L.A :
The site of metabolism depends on the type of L.A :
ester type is metabolized in the blood by pseudocholineestarase which found in plasma of blood , so ester L.A are contraindicated inpatient with this enzyme deficiency.
Amide type is metabolized in liver , so these type is contraindicated in patient with liver cirrhosis , due to alcohol or who is in end stage of hepatitis b ,or liver cancer .
Reinjection of L.A :
Repeat injection of local anesthesia sometime is necessary in some dental procedure .
Sometimes when we make reinjection there is no response or effect to L.A that called Tachyphylaxis
Tachyphylaxis : is an increasing tolerance to a drug that is administered repeatedly . (from book )
Tachyphylaxis is probably brought about through some or all of the following factors :
- edema
- localized hemorrhage
- clot formation
- decrease ph of the tissue
- nerve itself in refractory period
- haypernatremia (frm book)

- transudation (frm book)
There is some materials that share the same structure with L.A which is :
1- antihistamine drugs
2- anticolinergic drugs
Home work : dr said that we should know about general anesthesia , and its relation with apnea and succinylcholine enzyme . (dr. malik zo7lof talked about it I think )
Best of luck J

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Dana issa alomoush
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Shadi Jarrar
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عدد المساهمات : 997
النشاط : 12
تاريخ التسجيل : 2009-08-28
العمر : 26
الموقع : Amman-Jordan

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