Local anesthesia sheet #1 - Abrar sa3adeh

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Local anesthesia sheet #1 - Abrar sa3adeh

Post by Shadi Jarrar on 30/9/2011, 11:25 pm

4shared.com LA_1.html


Anesthesia lecture #1

For Dr. Al-shayyab.

Done by Abrar Sa’adeh




Neurophysiology

Today we r going to talk about neurophysiology…(anatomy and physiology)

All that are important in the local anesthesia (LA) procedure which we r gonna to deal with every single day of our career,, and without performing it correctly ,,you won’t get your patient confidence and trust ,, which is a problem by it’s own .





“70-80 % of doctors do not provide appropriate LA even after their graduate study ”,,guess this is the doctor’s opinion :P





We will start speaking about some terms that will give us some type of understanding through the treatment .

In general as u know LA will be applied in :

· Restorations or fillings .

· Periodontal procedures.

· RCTs.

· Minor and major surgeries .

· Extractions.





The history of Dental anesthesia :

1884 à Collar “nt sure of the name sry ,,x)” discovered topical anesthesia (cocaine) .

1884 à William … discovered the injectable form of Cocaine .

1904 à Albert prescribed procaine + 4 years Cocaine was synthesized ,,+4 yrs Lidocaine was used in dental clinics.









Definition of some terms in local anesthesia :

Block local anesthesia :

We deposit the LA just close to the nerve trunk .



Infiltration local anesthesia :

Deposition of LA close to the terminal nerve branches .



Field block :

Which is the most appropriate or the method of choice when we do biopsies is deposition of LA solution in the surrounding structures ,, not in the area of interest BECAUSE the LA destroys the histological structures ,,, SO it will affect the value of the biopsy .



We have different methods in Dentistry or even on Medicine in order control the pain which is very imp in our life work for us and for our patients .



We have general anesthesia where we get loss of consciousness and loss of sensation at the same time ,but local anesthesia we just get loss of sensation without loss of consciousness .

We have topical anesthesia which are drugs that are applied on the mucosa AND THE SKIN in order to make the insertion of the needle “pain free”.



The third type of controlling the pain is the Sedation ,,

The sedative methods are :

· Relative anesthesia

· Inhalational anesthesia

· Oral sedative drugs .

· ID sedation .

We will talk about all of them in the last lectures by dr Ibrahim..





Neurophysiology :

Anatomy of the nerve cell “neuron” which is the main structural unit in the CNS .

· Physiology of the peripheral nerve .

· Electrophysiology about nerve conduction then we will start to understand he LA works.



Now we could say LA could be Induced by different methods , if u follow the history ,, you can find that …

· mechanical trauma could induce anesthesia or loss of sensation .

· low temperature or freezing of the tissue could lead to loss of sensation

· anoxia ,,chemical irritants .

· alcohol or phenol ,some times used or applied for the treatment of the neuralgia or sever pain.

You can see that all these methods that cause loss of sensation are not appropriate for our work ,, those will lead to permanent damage to the tissues.



So the LA or the material to be used for LA should process many properties in order to be suited in our clinical practice.

· Not irritant doesn’t cause any permanent damage or alterations of the nerve structure .

· Non-toxic.

· Free of producing allergic reactions .

“So ,, Easter type of LA are excluded from our dental practice” .

· Should have short time of onset of action

· Provide long duration to let us complete our procedure.

· Stable in solution

· Not liable to be deteriorated when exposed to air

· Readily undergoes biotransformation in the body on order to decrease the risk of toxicity .

· Sterile or can be sterilized by different methods of sterilizations.





The neuron :

It’s the structural unit of the CNS could be :

· Sensory .

· Motor.

· Mixed.

Sensory neurons : will transmit the impulses from the peripheral nerves or tissues to the higher centers .



Motor neurons : the opposite way of the sensory ones ,, where there is transmission of the information from the CNS to the peripheral structures “commonly the muscles” .

The structures of the sensory neurons :

Three main compartments of the sensory neuron of the nerve cell ..

1. The first part : the peripheral nerve endings which consist of many “….” That connect the axon ,, this axon will transmit the impulses from the peripheral tissues to the CNS where we have many “….” That synapse to specific sites or receptors in the CNS.

2. the second part : the central part .

3. cell body : which consists of cytoplasm and nucleus like any other cell in the body…which is located at a distance from the axon which is a very important aspect of it.

So we can say it’s not involved in the process of impulse transmission ,, because of its position.

It’s role is just to provide metabolic support for the entire neuron.





Axon:

Is the nerve fiber that are surrounded by a membrane called nerve membrane ,, which is the most imp component of the neuron coz it’s the only part that is involved in the transmission of the impulse , not the nerve fiber itself nor the structure inside the axon or what’s called axo-plasm.

So the structures of the interior of the nerve are called axo-plasm,, but the extra cellular compartment is separated from the intracellular by the nerve membrane .

the intracellular compartment or the axo-plasm and the cell body are nt involved in the impulse transmission ,, just the nerve membrane as we said they just provide metabolic support.



Motor neuron :

Which is a little bit similar to the sensory one with some differences.. .

· The cell body is located at the same axis of the neuron not at a distance from the neuron ,, so from it’s position we can expect it’s evolvement in the impulse transmission.

Again we have central part and peripheral part .

· Where the impulses here are transmitted from the CNS to the peripheral structures or tissues,. by the axon through the nerve membrane .so here the cell body is involved in the impulse transmission.



The microstructure of the nerve membrane :

It consists of bi-lipid layer ,, mainly lipid tissue .

But we can find some intervening proteins , these proteins are of two types ,, some of them are

· transport proteins

and the others are ..

· receptor sites ,,But mainly it consists of bi-lipid layer .



Myelinated nerve fibers and Un-mylinated nerve fibers ,The difference here is so imp in the clinical work .



Where the nerve fibers are surrounded by myelin that nerve there is only single axon ,, so myelinated nerve fiber means single axon surrounded by myelin and Schwann cells .

Schwann cells play an imp role in the regeneration of the sensory abnormalities ,,

ex: if we did a surgery for a 3rd molar ,, and then we had an injury to the IDs ,, the most imp factor in the repair of this nerve will be th Schwann cells.

But myelin plays an important role in the transmission of the impulses ,, so for that reason the nerve fiber that is surrounded by myelin has a faster transmission property for impulses.





You can find nodes of ranvier (Myelin sheath gaps or nodes of Ranvier) at an interval of about 0.5-3 mm .where u can’t find myelin or even Schwann cells surrounding the axon ,, the impulse in this case is .transmitted or jumping from one node to another ,, not a creeping process



Saltatory: conduction which is a very rapid way if we compare it with the transmission if the un-myelinated nerves…where there is no nodes of ranveir ,, so we have creeping process .,,so we just find Schwann cells in the un-myelinated nerve fibers no myelin :p,, and the saltatory conduction in the myelinated ones exclusively …



Q was put to be answered :

What is the type of nerve fibers that has the most rapid way of transmission of impulse??

A: Alpha A fibers



Trigeminal nerve consists mainly of 4 types of nerve fibers :

· Alpha a.

· Alpha b

· Delta a

· C fibers

All of them are myelinated except for C fibers .



That’s imp in some cases such as a patient who has a sensory problems after a surgical procedures ,, -all our surgical procedures may cause sensory problems -,, like when u do a wisdom tooth extraction ,, u may cause trauma for the lingual nerve or for the ID nerve .

“you have to know sth ,, not to confirm every single word from the patient so you “yourself” have to determine the degree of sensation altering or abnormality ” and that’s all determined by :

CNT : Clinical Neuro Sensory Test.



Level A à a alpha fibers has a rapid transmission of the impulse or stimulus ,,like when u touch somebody lightly .

Level B à when u touch somebody a little bit stronger

Level C à when u insert the needle and the sensation occurs.

So by this we are determining the level of sensory disturbance (mild, moderate or sever .)

Example: someone that didn’t feel neither A nor B and he felt C that indicates that he has a sever problem ,, your clinical tests are so imp cause they determine the prognosis of the case ,, for example if a patient has sensory disturbance after a surgical work ,, and it lasted for a couple of months ,, then u can tell that he has a permanent damage or loss of sensation “w 3ayydaat m3o”.





Normal status of the nerve “resting potential ” :

Normally we have a kind of balance between the charges that are found in the extra cellular compartment and the intra cellular compartment .

The charge of the nerve will be about -70 mega volts ,,, here in this state No PAIN .

This is associated with closure of Na channels which are in the nerve membrane and u can’t see it unless u use a microscope.

When the -70 turns into -50 called the “firing threshold” .

Here we have the action potential and the impulse starts to move or transfer.

When the action potential starts the sodium channels are opened and the influx of Na inside the nerve membrane begins ,, so there is a deposition on what’s called Pain sensation .

When it reaches +40 that means the period of depolarization ended and repolarization starts again which is associated with sodium channels closure.



So depolarization ONLY occurs when Na channels are opened or when Na(s) ions are entering the interior of the nerve.

No Na entering à no action potential “resting state”

The most common two methods that explain the mechanism of action of local anesthesia are :

· The membrane expansion theory :

When the local anesthesia deposit near the peripheral nerve we induce kind of expansion to the nerve and that would close the Na channels so then no action potential ,,NO PAIN.

· Local anesthesia are able to bind to the specific receptor inside the sodium channels .

When they bind to these receptors they block any entry of the Na àso then no action potential à no pain .

(the first one useful when we use topical anesthesia ,, the second when we use injectable one) .



Kinetics of local anesthesia.



We will speak about :

· Onset.

· Duration of action.

· Depth of anesthesia .



Cross section of the nerve fiber :

Epi-neural sheath :

The outer layer That encloses the nerve,, this is the first barrier to the diffusion of local anesthesia ,, but it’s not the greatest barrier towards diffusion.

It has loose connective tissue and vessels ,,

The axon is enclosed by epineuria (perineuria) which is the greatest barrieragainst the diffusion of Local anesthesia .

Those bundles that are located close to the surface are called mantle bundles ,, but those who are located in the center are called Core bundles,, so the local anesthetic solution reach the mantle bundles before the core ones.



Clinical significance :

Mantle bundles usually supply the proximal tissues like molars,, but the central ones usually supply the distal tissues like incisors or the lips.



Now if we took a cross section of the ID nerve,, the peripheral bundles supply the molars while the central supply the incisors.

So sometimes when we want to do RCT to a molar we give ID block ,, there will be no pain ,, but when we want to do RCT for the incisors the patient may feel pain ,, that’s because

· the LA hasn’t reached the central bundles yet

· OR inadequate volume,,

SO in this case u have to wait 2-5 min till the LA reaches those central bundles or to increase the volume.



So the diffusion of LA depends on :

· The concentration of LA à the more the concentration is àthe faster the diffusion that we have .

· Barriers .

· PH of the LA.

· The diffusion constant of the drug mainly.



Induction of general anesthesia :

Means the time between the first deposition of the drug until the patient is unconscious .

Induction of LA:

the time between the first deposition of LA until sensory loss occurs .



We have phenomena that called tachiphlaxis “not sure of the spelling”,, this occurs when you give the patient anesthesia and u take long time in the procedure so then u give anesthesia for another time but it doesn’t work,, and that’s due to

· edema formation that would prevent the diffusion of LA ,,

· or maybe due to hemorrhage

· or hematoma.

**The most important factor that determine the duration of LA is Protein binding characteristics of the LA .

Highly vascular tissue means à high absorption of LA so there will be short duration of the LA ,,when vasoconstriction is used that means there is preservation of LA in the tissue of interest .



Depth of Local anesthesia :

It depends on the lipid solubility .



A Q was asked …. If we faced such a case that the effect of LA stopped ,, what to do?? ,, the doctor said STOP your procedure. J



The end






Best wishes for all of you Future DENTISTS J
Corrections and additions are more than welcomed.
**Your colleague ,,,,, Abrar Sa3adeh **
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Shadi Jarrar
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تاريخ التسجيل : 2009-08-28
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