Local Anesthetic .cont

8/3/2019 Local Anesthetic .cont

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The dr started the lecture telling that the avg in our first exam is 70% which is very

good and 92% passed the exam.

Local anesthetics Drugs that reversibly block nerve conduction and produce transient loss of

sensation in local areas of the body when applied locally to a nerve tissue in

appropriate concentration.

Chemically speaking, local anesthetics are of two types; the ester and the amide

which composed of lipophilic group its aromatic usually connected by hypophilic

amine by ester or amide.

Depending on the ester or amide ??? which communicate the lipophilic group to

hydrophilic amine..

You have to understand these chemical structures cause it has a relationship with

the rate of metabolism of these drugs.

Usually amide type are mainly metabolized in both the liver and the peripheral

tissue specially the plasma by esterase enzyme.

So we can expect that the rate of metabolism of the ester type is faster and greater

than the rate of metabolizing of amide type.

It means that the duration of action of ester is shorter than amide.

Therefore hepatic diseases decrease the metabolism of local anesthetics.

Example of ester : cocaine, Procaine, benzocaine, tetracaine.

Example of amide : lidocaine, Prilocaine, mepivacaine, ropivacaine.

- All the names of local anesthetics end with the suffix "Caine" Unluckily we have to understand and memories all of them because Theres no

dental procedure which is painful could be performed without the use of local

anesthetics.


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thats our destination because we are dentists and we have to know sth about

these names

They are a basic compound, their PKa is more than 7 8 to 9.

The inflamed tissues have acid PH increase ionized fraction and decrease the effect

of these local anesthetics, like when we go to the dentist with inflamed tooth, he

might prescribed to us an antibiotics and analgesics and tell us to come back after

one to two days later to perform the surgical procedure.

The effect of local anesthetics is very low or vary in its minimum degree.. why?

Because itll be highly ionized and it wont be absorbed to nerve tissue and will not

produce its proper effect.

Their action is to prevent both the generation and conduction of nerve impulse,inhibit the initiation or generation of nerve impulse and then they can inhibit the

propagation of nerve impulse to adjacent area or to remote area.

The main site of action is the cell membrane, nervous cell membrane. They bind

to specific receptor in sodium channel.

How the impulse is transmitted normally?

Sodium channel will be opened and sodium ion will enter from the outside of cell

membrane to the inside of cell membrane, making depolarization of the cell

membrane, making an initiation of nerve impulse and the propagation or

conduction or distribution of nerve impulse.

The ion channel should be opened to block the initiation and generation of this

nerve impulse, sodium channel should be blocked. in other word, the membrane

will be stabilized so there will be no initiation or generation or conduction of nerve

impulse.

local anesthetics block the sodium channel so sodium ion will not enter or pass the

cell membrane and will not enter to the inside.


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Briefly :

Mechanism of action of local anesthetics is simply by blocking the sodium ion

channels which are located in the cell membrane and therefore preventing the

generation and conduction of a nerve impulse.

local anesthetics compete with calcium ion for ?sike? in cell membrane that control

the passage of sodium across the membrane and by this way competing with

calcium, they can block the transition through sodium channel, so increasing

calcium ions will partially antagonize the action of local anesthetics.

Its a matter of competition, local anesthetics compete with calcium ion to prevent

sodium ion from entering the cell.

Simply. If we increase the concentration of calcium, we will decrease the effect oflocal anesthetics.

The net affect depend on concentration of competing drugs. For example;

acetylcholine with atrophine, one compete with the other on cholinergic receptors

so the net effect whether is due to acetylcholine or atrophine depend on

concentration of each other, which is the higher has prominent effect.

* Small non- Myelinated before long Myelinated?

It means that the small nerve terminals are better affected by drugs local

anesthetics than on larger nerves. Why? Because the small non-mylinated affected

before the Myelinated.

In Non- Myelinated the effect of local anesthetics will be direct. The cell

membrane is exposed to the effect of the drug and its not covered by Myelinated

sheath naked .

While the Myelinated nerves, the majority of them is covered and Myelin sheath

will act as a barrier for local anesthetics to come in contact with cell membrane or

the nerve in certain small area called Myelin sheath gaps or nodes of Ranvier.

Sensations are blocked in following sequence :

Pain touch temperature pressure motor tone .


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After injection of local anesthetics to a painful tooth for example, the first

sensation which is lost is that the patient is relieved of his Pain then touch

sensation that he cant feel his cheek with his finger, then temperature and pressure

and later on you cant feel the sensation of pressing the area and lastly the

movement of the area.

Note : the movement of the mandible will not affected because the muscles are

higher from site of injection of local anaesthetics.

The recovery of local anesthetics :

It will be in the reverse order like this

Motor tone pressure temperature touch pain .

Pharmacokinetics:

The rate of absorption and duration of action dependson :

1- Site of injection

2. Dose and concentration

3. Local vascularity: the higher the blood supply the faster the onset of action and

the shortest is the duration of action .

4. Presence of vasoconstriction:

We know that one of therapeutic uses of adrenaline is to prolong the duration of

local anesthetics.

Dentists usually have two types of local anesthetics, the plain one and the mixed

with vasoconstrictor either adrenaline or noradrenaline to increase the duration of

local anesthetics action.

For example if the duration of action of local anesthetics is half an hour as a plain,

the mixed with vasoconstrictor duration action might extended up to 2 hours or

more.


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And the advantage of the mixed local anesthetics for the patient that instead of

giving the plain local anesthetics with repeated injection we can replace it with

single injection of mixed local anesthetics.

As you know that not all patients can use adrenaline or noradrenaline.

- Suppose a patient with hypertension comes to your clinic and he needs asurgical dental procedure which you should give him local anesthetics,

what would you choose to give; plain or mixed?

Either you give this patient plain local anesthetics with repeated injection every

half an hour or every time he feels pain or we can use another type of

vasoconstrictorbut doesnt belong to sympathetic amine which can produce

minimum effect on CVS.

That vasoconstrictor that we can use in these cases is felypressin.

Felypressin: vasoconstrictor preferred in patients with heart disease and

hypertension.

So we concluded that we should ask the patient about his history whether he has

diseases like HTN and heart diseases or diabetic cause if we give him the wrong

vasoconstrictor we might kill him.

Sympathetic drugs should not be mixed with local anesthetics whether adrenaline

or noradrenaline or felypressin to anesthetize lacrimal terminal organs like fingers

or toes, ear lot and nose because they have limited blood supply and if we did so

we might induce ischemic changes.

Other terminal organs in male children in surgical procedure of circumcision, we

should not use vasoconstrictor because the penis is also having limited blood

supply, it will be regarded as the finger or the toes.

any type of vasoconstrictor is contraindicated to be used in these sides of the

body


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Pharmacological actions of local anesthetics :

1- Prevent initiation & generation and conduction of nerve impulse.2- On CVS, like the heart. They depress the conduction of the heart as we

use it to treat the ventricular arrhythmias Xylocaine & lidocaine .3- On CNS brain:CNS neurons are of two type; inhibitory and stimulatory, so the net affect of

local anesthetics depend on the net effect on whether neurons are inhibitory or

stimulatory.

So after high doses, some of it will be absorbed to the blood and can produce

CNS effect, small doses locally the CNS effect is very law or very mild, thats

why we call them local anesthetics, they are producing their main effect locally

but if they are given in very high doses, some of it will be absorbed to the

circulation and can produce a remote effect on CNS or if we give these drugs

IV. For example, treatment of ventricular arrhythmia which need not to use

local anesthetics injection but IV injection.

excitatory effect will be: restlessness, tremor and clonic convulsion this may

be followed by

1- depression and death due to respiratory depression.2- The stimulation maybe due to inhibition of inhibitory cortical synapses.

So inhibition of inhibition is stimulation.

Higher doses depress both the inhibitory and the excitatory neurons which will

lead to depression.

At the beginning there will be stimulation. Why? Due to inhibition of inhibitory

neurons.

Later on , both types of neurons will be inhibited and the net result will be

depression.


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Toxicity of local anesthetics :

Allergic reaction especially by ester type local anesthetics, while it's very rare in

the amide type. Thats why the amide type usually preferable in dental practice

because they have longer duration of action and less allergic reaction.

The dangerous allergic reaction will be in form of asthma and anaphylaxis shock

severe allergy and hypersensitivity that can be treated by using adrenaline .

To relieve CNS toxicity, diazepam and Valium is used to decrease CNS

STIMULATION.

Diazepam is one ofanxiolytic drugs or CNS depressor drug which well discuss

later on.

What are the therapeutic uses of local anesthetics ?

1) minor operation the most important one, like dental procedure.

2) ophthalmic surgery.

3) surface anesthesia of the skin & the mucus membrane.

For example, gel could be applied on a painful dermatological conditions or burns,

they could be rubbed by gel and the pain will be relieved immediately and

completely.

Mucus membrane, local anesthetics gel could be used in young children who have

for example mouth ulcer or stomatitis or pharyngitis or inflammation of buccul

mucus membrane that might lead to pain.

4) spinal anesthesia, which is injecting of local anesthetics into the CNS to

anesthetize the lower part of the body.

5 ) anti arrhythmia especially Xylocaine & lidocaine or lignocaine that can be usedin treatment if ventricular arrhythmia which might be life threatening arrhythmia.

In general, there should be desire properties in chosen local anesthetics:

1- it should Not be irritant and should not damage the local tissues.


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2- it should have high therapeutic index (TI), which means less incidence of toxic

manifestations.

3. it Should be effective topically and by injection.

4. It should have rapid onset and enough duration of action to perform the surgical

procedure.

Method of administration of these local anesthetics :

1- Topical at surface anesthesia in form of gel whether on mucus membrane orskin.

2- Nerve block : to anaesthetize mandibular tooth which is supplied bymandibular nerve; its is the largest of the three branches of the trigeminal

nerve. And it can be easily identified or located in the mandible behind thelast molar and if you give single injection at this site youll anesthetize the

hall mandibular teeth that are distal to this site .

3- Infiltration : if we want to anaesthetize a maxillary tooth which is suppliedby nerves that cant be easily identified. Therefore, we give one injection

near the affected tooth and the other at the back of the hard palate.

4- (IV) anesthesia biers block

A Biers block is an injection of local anesthetic into a vein in your arm or leg.

This numbs the nerves that supply that limb. The limb stays numb for 1-2

hours. During this time the operation can be performed on the arm or leg

without causing you any pain.


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The advantage of a Biers block is that you do not need a general anesthetic.

You can stay awake for the operation. The anesthetist can give a sedative drug

to make you feel relaxed and less anxious.

5. Spinal, injection of local anesthetics directly to the CNS

6. Epidural anesthesia; Epidural anesthesia is regional anesthesia that blocks

pain in a particular region of the body. The goal of an epidural is to provide

analgesia, or pain relief, rather than complete anesthesia.

-This table will show you examples of LA, their routes of administration, their

potencies and some properties:

Esters:

- Cocaine: rarely used and only topically , it was the first one discovered, it

differs from the other local anesthetic in having high addictive property and it

can produce vasoconstriction so it has a long duration of action.

The dr just moved on to the next subject!! O.o

General anesthesia Its a Reversible and controllable state of

Analgesia. (relief of pain) amnesia. (memory disturbance or loss) loss of coconsciousness. (the patient will be unaware of himself) inhibition of sensory and autonomic reflexes. Variable degree of skeletal muscle relaxation by neuromuscular blocker.The main deference between general and local anesthesia is the loss of

coconsciousness.

No general anesthesia without the loss of coconsciousness. But localanesthesia the coconsciousness is present .

Preanasthetic medication:


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The drugs which are given to the patient before the administration of general

anesthesia.

Why we need to give a drug before general anesthesia ?

Produce sedation and decrease anxiety and apprehension by using diazepam

, antihistamine, phenothiazine.

To provide amnesia.

To produce analgesia when there is pain such as opioids.

Potentiate weak GA as nitric oxide (N2O).

Facilitate induction without prolonging recovery.

Reduce some undesirable side effects of general anesthesia such as H2

blockers as Cimetidine and anti-emetic as metoclopramide .

To produce vagolytic effects the vagus is parasympathetic or anti-

cholinergic effect as atropine and hyocine.

Inhibiting vomiting and decrease the acid secretion of the stomach to reduce

some undesirable effect by metoclopramide; its anti-emetic which can prevent

vomiting.

Classification of GA:

Its either Inhalational or IV Intravenous depending on their route of

administration.

1- Inhalational GA:It should be administered through endotracheal intubation passing a rubber

endotracheal tube to the larynx to ensure that the patient inhaled all the gas or

the volatile liquid and this procedure needs complete muscle relaxation and

cannot be performed without the administration of neuromuscular blocker as

succinylcholine.

- Volatile liquids :


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and its either and mainly the halogenated compounds or ethers .

- Gases what's the difference between Volatile liquids and gases?

Liquid evaporates into vapor and the gas is already in its gaseous state.

The gas such as nitric oxide which commonly used nowadays , its gas under

pressure, they come in cylinder. When the pressure is relieved it will be

administrated in its gas state an inhaled by the patient .

The process of GA is induction, maintenance, recovery:

The time between the administration of GA until the patient start to lose his

consciousness until complete loss of consciousness is called induction.

Our aim in general anesthesia is to reach the state of complete loss of

consciousness in which the sensation, motor activity, reflexes might be lost.

The time of losing consciousness is called the period of effective anesthesia or

maintenance of general anesthesia.

Then after performing the surgical procedure the patient should be recovered, the

consciousness should be back and retain to this patient. How ? by stopping the

administration of general anesthesia.

The time of stopping the administration of GA until the patient regain his whole

consciousness is called the period of recovery.

So good ideal anesthetic should have short induction period and short recovery

period.

Properties of an ideal GA:

Should produce safe and pleasant anesthesia Good muscle relaxation Be potent, stable, non-irritant, and non-inflammable.


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General anesthesia started by ether and its highly inflammable and it has done

enough fire accident during surgeries and it replaced by halogenated hydro

compounds which is less inflammable or non inflammable

Non-toxic and free of side effects .

Produce rapid and smooth induction and rapid or fast recovery

Unfortunately, this ideal general anesthetic that has all this properties is still

beyond our reach especially free side effects .

Mechanism of action of inhalational GAs:- They depress CNS neuron activity by increasing their threshold and

reducing the rise of the action potential by interfering with sodium influx.

- They have similar mechanism of action of the local anesthetic, theyprevent the entry of sodium into the CNS locally ..

The GA administer the sodium influx systemically by inhalation or by IV

administration.

- They can increase transmission of inhibitory synapses as GABA transmitter.The main rout of administration of GA is inhalation, so they are taking to the

systemic circulation by lungs.

The first compartment to which GA reach is the alveolar air, then from AA to

blood and then by the process of distribution it reaches the tissue; The target

tissue for GA is the brain.

So uptake and distribution depend on the depth of GA and its directly

proportional with the tension of GA in the brain and the tension in the brain

proportional to the tension in the blood and tension in the blood proportional to

the tension in alveoli .

-In other drugs we were talking about concentration but in GA we mention

tension-


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Tension : the partial pressure of the drugs .

In a mixture of gases therell be a pressure this pressure is derived from the partial

pressure of each component of these gases. Here the AA we dont have only GA ;

we have GA and we have oxygen and nitrogen and carbon dioxide , all these formcertain pressure . the partial pressure of GA is proportional to the depth of GA. In

other words, The higher the partial pressure the higher the depth of GA and vice

versa .

So the rate of induction and recovery depend on the rate of change of tension in

the brain and tension of the GA in AA nearly equivalent to the tension in the

blood and nearly equivalent to the tension in the brain.

The tension of the alveolar air is gradually increase when the patient start to inhale

until it produce complete loss of consciousness and this maintenance period will

continue as far as the valve of the container of gas or liquid is opened, then the

recovery of GA when the anesthetist start to close the valve of the container of GA

and the tension of GA in the brain, in the blood in the AA start to decline gradually

by process of expiratory washing out till we reach minimum partial pressure and

full recovery .

The main organ of elimination of general anesthetic is the lung while in other

drugs is the liver first and then the kidney.

-and finally I reached the end of my damn lecture-

Nada was with me in the lecture and during writing this lecture, raising me up and

standing up with me to let this suicidal thing finish in peace, Thanks is meaningless

here cause every part mn l tafree3 we made a story about it, love you.

Dafdouf , the silence is our frienemy and theres no one in the world gets me lyk u

This year I wish for nth but happiness to me and to you all specially do7a, walaaeman, 7aneen, haya, raja2,raneem, raya o lamees and my lady tuqa o samouraa

o asraa ;), o my happiness fara7 o rawan o l sherera nouur :P o meen Kaman?

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Raghas ..

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Local Anesthetic .cont

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