13. general anaesthesia.docx
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( Maybe it is a long script .. but its very easy and enjoyable to study .. GOOD LUCK ^_^ Eman Nazzal )
General Anaesthesia (GA) Definition : General anaesthesia is defined as a condition in which
the patient has lost :
1-consciousness
2- analgesia : loss of pain sensation .
3- amnesia : loss of memory . Why amnesia ??
((Bcz in Any surgery the patient become in a fear situation so it is preferredthat the patient loss his memory, in order not to remember anything))
4-muscle relaxation. Why muscle relaxation ??
((In order to enhance surgery we need a good muscle relaxation ))
5- loss of autonomic reflexes .
General anaesthetic has . That are administered for induction tomake any general anaesthetic which is VERY important before anysurgery , in which once the patient go to surgery ( it is a must )
must have lost of consciousness , no pain sensation , amnesia in
which the patient cant remember anything .
So, general anaesthesia is a condition which characterized byanalgesia, amnesia, loss of consciousness, inhibition of sensory andautonomic reflexes, and, in many cases, skeletal muscle relaxation.
Local anaesthesia : we induce analgesia, without loss of
consciousness , and administered locally to certain area , in which the
atient cant sense the ain at the side o administration .
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General anaesthesia Drugs:
So general anaesthesia Drugs it is a reversible loss of consciousness
( many of us think that anesthesiologists career is very easy , But it is Not bcz u
induce a consciousness , u induce a reversible comma , and in the case of over
dose this lead to death .But when the dose calculated carefully this will induce or
maintain general anesthesia to facilitate surgery.
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4 Stages of General anaesthesia :
The anesthesia goes in 4 main stages , and also some sub stages :
1-Analgesia2-Excitement3-Surgical anaesthesia4-Medullary paralysis
stage 1 : Analgesia
Analgesic effect is the partial loss of pain sensation with impairment
loss of consciousness , ( start with impairment loss of consciousness. )
Analgesia is partial until stage II is about to be reached.
stage 2 : Excitement
It is stage of excitement or stage of dis-inhibition.
Here there are excitement , involuntary movement , irregular BP& irregular respiration .
## What did u think ! We now in this stage >> should we go to the
next stage rapidly ? or keep the patient in this stage ?? did u think
that this is the stage of surgical anaesthesia ??
No , We should go to the next stage as rapid as we canBcz this as the stage of excitation , there are undesirable effect on
the patient and we should go to the next stage rapidly
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stage 3 : Surgical anaesthesia :
here we get the anesthetic purpose ( which we mentioned at the
beginning of Lecture. e.g : analgesia etc) ,
at the same time respiratory and the cardiovascular system are
maintained , and there is regular respiration , Blood pressure is
controlled at the same time I will get the anesthetic purpose >
Once we reach this stage the surgery is proceed.
stage 4 :Medullar paralysis:
Stage of medullary depressor that seen in the case of anestheticover-Dose and we will have respiratory and cardiovascular
depression center in the medulla , and without full control or
support : death will occur ( in the case of over-Dose ) .
Induction of anaesthesia
3 group of drugs can be administered :1-Drugs that administered as Pre-anesthetic medication ( prior to surgery)2-Drugs that administered to induce anaesthesia3-Drugs that administered to maintain anaesthesia
( the doctor say something but it is not clear at (10:10 min ) in the record )
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1-Induction of anaesthesia :what did we mean by induction ? To reach or to start anaesthesia .
this is done by administration ofIntravenous Drugs anesthetic in which
the time from anesthetic administration until the patient reach stage 3(which is the stage of surgical anesthesia and here the doctor can proceed the surgery ) .
2-maintain anaesthesia :Now , how we can maintain anaesthesia ? How can we maintain the
loss the consciousness , analgesia , amnesia , loss of muscle relaxation
and autonomic reflexes . HOW TO KEEP THE PATIENT IN All THESE
CONDITIONS OR HOW TO KEEP HIM IN STAGE 3 ??
this is done by Inhaled anesthetics
3- Recovery period:is the time of discontinuation of GA until the patient regains to his
consciousness.
At the end of the surgery ( this is important ) , the dose of inhaled
anesthetic is gradually reduced until it stop , during this time the
patient return to his/her consciousness ( this is the Recovery period)
So Recovery period it is the time from which the general anesthetic
administration is stopped, until the patient regain back to his
consciousness .
This is the phases :
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Summary
Administration of GA the period in which from the time of GA
administration until the patient go to stage 3 ( loss of consciousness
and other effects ) this is known as induction period
Then sustained GA is important for maintenance of anaesthesia to
keep the patient in stage 3 .
Then from the time of discontinuation of GA until return back the full
consciousness this is known as recovery period
Over-Dose comma or death , this is mean that no recovery period the
patient cant return back to his consciousness , this is mean the
paitient go to stage 4 the stage of medullary depression .
A student ask a Qs but i cant hear it ..The doctor answer :
((Ok >> analgesic drug , it is drugs that are administered in which we
have loss of pain without loss of consciousness , in local anesthetic
they produce the same effect , they produce the same wide the
analgesic but the term name as an anesthetic. we will talk about it
Insha-Allah in next lecture , local anesthetic although there are noloss of consciousness but they are named as anesthetic))
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Pre-anesthetic medications
From their name , pre- : mean before
So it is a group of drugs that are administered before GA to get multiplepurposes .
1) Sedation and amnesia. ex: Benzodiazepaines derivatives like Diazepam2) Analgesic . ex: Drugs opioids and its derivatives for example morphine .3) inhibition of parasympathetic reflexes . ex: Atropine or hyoscine4) H1 receptor antagonist. ex: diphenhydramine5) H2 receptor antagonist. ex: cimetidine or ratitidine6) Antiemetics drugs. ex: Metochlopramide
1)Sedation and amnesia.First of all we are looking to sedate the patient and relief anxiety , it is
normal that anyone know that he will go to a surgery procedure he will
become anxious , in order to relief an anxiety and induce sedation we
will give him pre-anesthetic medication .
Benzodiazepaines derivatives like Diazepam is administered as apre-anesthetic medication to relief anxiety , apprehension , to reduce
fear . Benzodiazepaines administration
2)analgesic Drugsanalgesic agent or pain killer are administered . we should not wait
until patient will complain from pain , the post-operative pain , in
which an analgesic agent is administered before and at the end of
surgery in order to reduce pain . The best analgesic drug is opioidsDerivatives as Morphine and Pethidine , and specially they are used
with the anesthetic if the anesthetic has a low analgesic effect we
should use another analgesic like for example opioids and its
derivatives for example morphine .
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3) inhibition of parasympathetic reflexesBy using ofantimuscarinic drugs in order to:
The lungs in order to reduce the bronchial secretion as a way as we looking toreduce the salivary secretion once we have ??? the salivary secretion will
induce laryngospasm that may enter the larynx to will induce laryngospasm.
Antimuscarinic agent are also administered with other aim to reduce the riskofcardiac arrhythmia , example ofantimuscarinic agent are either Atropine
or hyoscine .
Which one did you think is preferred ? Atropine or hyoscine ?The best is hyoscine . Ok why hyoscine ? Bcz hyoscine is responsible to cause
more CNS depression that is required in anaesthesia ( hyoscine is more
preferred for CNS depression , loss of memory which is amnesia ) so it is
preferred due to its CNS effect and also peripheral affect .
4)H1 receptor antagonist:
They are used to prevent allergic reaction ex: diphenhydramine5)H2 receptor antagonist:
They decrease acid secretion ( I am looking to suppress gastric acidsecretion In order to prevent the retention of gastric content back to the
lungs that may induce a aspiration pneumonia .
( : Aspiration pneumonia isbronchopneumoniathat develops due to the entranceof foreign materials into the bronchial tree, usually oral or gastric contents including
food, saliva, or nasal secretions. ) . ex: cimetidine or ranitidine
6)Antiemetic drugs : it is the drugs that prevent emesis ,in which
emesis can be a verse effect of GA
ex: Metochlopramide
H is related To histamine
H1 receptor responsible for allergic manifestation
H2 rece tor if the are stimulated the induce astric acid secretion
http://en.wikipedia.org/wiki/Antimuscarinichttp://en.wikipedia.org/wiki/Antimuscarinichttp://en.wikipedia.org/wiki/Antimuscarinichttp://en.wikipedia.org/wiki/Bronchopneumoniahttp://en.wikipedia.org/wiki/Bronchopneumoniahttp://en.wikipedia.org/wiki/Antimuscarinichttp://en.wikipedia.org/wiki/Antimuscarinichttp://en.wikipedia.org/wiki/Antimuscarinic -
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general anesthetic are represent in 2 main groups :1)inhaled anesthetic
They are given through the respiratory track and they are used
for maintenance of anaesthesia . either they are volatile liquids ,
or Gases like Nitrous oxide .
a)Volatile liquids : in which they are liquids under pressure once the pressure isreleased they are evaporated.
Example of the volatile liquid is the halogenated compounds . what did we mean by halogen ? halogens which are in group 7 .So halogenated compound they are the groups of drugs that contain
(Cl , Br ,I , F ) .
These are examples of halogenated general anesthetic :Halothane/ Isoflurane / Methoxyflurane / Sevoflurane
b)Gases : example is : Nitrous oxide . I think you know about nitrous oxide , commonly used by Dentistas an analgesic and it has a powerful analgesic effect , which is N2O
and known as a laughing gas bcz it induce laughing.
2)intravenous anesthetic drugs They are given intravenously To induce GA. They are different groups :
a)Barbiturate derivatives like : Thiopentalb)Benzodiazepaines derivatives like :Midazolamc)Opioid derivitives like : Fentanyld)Ketaminee)Propofol
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Ideal Characteristics of Inhalational Anesthetics:
Rapid & pleasant induction & recovery . Be potent, stable, non irritant and non inflammable
(( Now Ether , you know either? it is a general anesthetic drug by inhalation
but one of the most important problem of Ether that it is Flammable . and
this is the most thing that make us afraid and carefull in surgery rooms ,
that the anesthetic drug may become flammable and induce fire.))
Adequate relaxation of smooth muscle Wide margin of safety Absence of toxic effect ( or adverse drug reaction ) (( keep in your mind that during anaesthesia in some cases , if the
general anesthetic drug has inadequate relaxation of smooth
muscle effect , we will use a neuromuscular blocking agent like
Tubocurarine . Also neuromuscular blocking agent are useful in
Tracheal intubation for general anesthetic administration .
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Mechanism of Action of inhaled anesthetics
Now the mechanism is little difficult , but the general mechanism(?)
they produce CNS depression , they will inhibit neuronal excitation in
the CNS by different mechanism
First mechanism :With the increase in threshold, there is a decrease in neuronal activity.
(they will rise the neuronal firing threshold , this is mean they make
the neuron difficult for excitation )
Second mechanism :- At the cellular level, anesthetic agents affect synaptic transmission
rather than axonal conduction. The release of excitatory transmitters
and the response of the postsynaptic receptors are both inhibited.
- (They will inhibit the release of excitatory neurotransmitter in theCNS)
Third mechanism :- In general the previous 2 mechanisms will induce the CNS
depression . BUT the third mechanism will enhance the GABA
effect
- ( as u remember GABA is a inhibitory neurotransmitter that willcause opening the chloride channels so induce neuronal
hyperpolarization this is mean inducing neuronal excitation
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The pre-synapticneuron for example will inhibit calciumentrance , by that I will inhibit the release of excitatory
neurotransmitter .
The Post-synaptic neuron they either increase chlorideinflux , or they will increase potassium efflux , ya3ni they willinduce hyper-polarization or re-polarization ( respectively ) ,
and by that will inhibit neuronal excitation.
Rout of admimistration :
1) Inhaled anesthetic :-the anesthetic drug is given by inhalation , the site ofaction is in the CNS , this is mean given by inhalation theyshould be absorbed through the alveoli , reaching the
blood , distributed through the body , until it reach the
site of action which is CNS or the brain .
-Keep in your mind that the site of action is the CNS THEY
SHOULD REACH THE BRAIN ( CNS )
2) IV anesthetic
They go directly to the blood , reach the CNS in order to produce theanesthetic effect
So, regardless to their route of administration(inhaled or IV anesthetic )
BOTH of them , their site of action is the CNS to cause CNS depression
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Inhaled anesthetic-How they are taken ? they are taken by inhalation , usually they are mixture
with Gas , with oxygen , carrier gas , ok ? with air or with oxygen .
- Ok , these anesthetic as we said they should be transferred from thealveolar space to the blood and from the blood they should reach the brain .
How fast ? this is the pathway
So, inspired Gas to the alveoli arterial blood other tissue andfinally it should reach the brain and in the brain to produce their site
of action
Vice versa , or the opposite way , or redistribution process is the way of their
elimination .
How they are eliminated ? what will be the pathway for their elimination ?
From , the brain blood vessels other tissues the major way fromthe blood return back to the lungs to the alveoli finally by expiration
. This is known as ( redistribution process ) for the ( elimination ).
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To get a therapeutic effect the drug should reach the brain
from the alveolar space to the blood and from the blood to the brain
and this depends on many factors :
First factor : Drug solubility :
Something that u have to know ( blood : gas partition coefficient)which will determine the solubility of the drug in the blood .
What did u think , if the drug has a high drug solubility does this
mean that its induction will be faster or slower ?? SLOW .
As we increase (blood : gas partition coefficient) and increase in gas
solubility in the blood increase the onset of induction will be slower
bcz as the solubility increase the drug will need more time to reach the
partial pressure in the blood .
So there are reverse relationship between drug lipid solubility andits onset of induction ,as it is more the induction onset will be slow.
The more soluble the anesthetic in the blood , the more it shouldbe dissolved in order to reach the desired partial pressure
( bcz we r talking about Gases , the gases is measured with partial pressure Not in mg ) .
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In the figure : Different anesthetic drugs , you will see the ratio of
partial pressure of the anesthetic in the blood compared to the alveoli ,
we find that
1)Nitrous oxide :has low blood solubility / halothane is medium /
methoxyflurane is high , this is the type of induction.
- This is mean bcz of low blood solubility of Nitrous oxide itsonset of induction will be FAST .
- At the same time the onset of the speed of recovery will beFAST , this is ,mean the drug will leave the brain and returned
back to the blood , from the blood to the alveoli to get a
recovery phase Also will be fast .
2)Halothane:It has a high blood gas partial coefficient in which the solubility in
the blood higher than Nitrous oxide , so it will induce a slow speed
of induction or for anaesthesia comparing with nitrous oxide .
- These is the differences . There is a reverse relationshipcomparing between nitrous oxide and Halothane . ok? Lowsolubility in the blood fast induction . comparing with
halothane
- usually nitrous oxide is mixed with halothane to fasten its onsetof action , So are given in combination .
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Second Factor : Anesthetic Concentration in the inspired air
This factor That depend or that can control or that affect onset of drug
effect is its concentration in the inspired Air
What did you think the relationship ? direct ? or reverse ? DIRECT**this is mean as its concentration of the inspired air increase
this is mean it will reach the blood very fast , this is mean it will
reach the brain in very fast onset , the speed of induction or onset
of action will be FAST .
SO , increase the concentration of the anesthetic in the inspired air willincrease the speed of induction on anaesthesia , by increasing the rate
of transfer to the blood ( DIRECT RELATIONSHIP )
Thirs Factor : Pulmonary Ventilation
What did u think ? direct or indirect ? DIRECT .
Hyperventilation , this is mean the amount of anesthetic drug thatgo to the lungs will be more , so it will reach the blood very fast ,
and also the amount that reach the CNS also will be very FAST .
So , increasing Pulmonary Ventilation will increase in arterial tension
( Tension here mean concentration but bcz we are talking about gases we
substitute concentration with tension )
The more Pulmonary Ventilation the more the drug that go to the blood so its
tension will be more ( its conc. Will be more ) and this will induce( NOT Clear) effect.
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Fourth Factor : Pulmonary Blood Flow
What did u think ? direct or reverse ? REVERSE / INDIRECT As there is an increase in the blood flow to the lungs this is mean
the volume of the blood will be more , this is mean the amount of
anesthetic that should be dissolved also should be more ( high
anesthetic concentration ) , so the onset of speed of induction will
be slow . So ..
As pulmonary blood flow increase the Onset of induction will decrease
SUMMARY
So they are 4 factors 2 of them Direct and 2 of them Indirect L
2 factors with DIRECT relationship
2 factors with INDIRECT relationship
another factor : blood capacity
Increasing in blood capacity this is mean more anesthetic concentration
, more tension will rises very slowly .
concentration of anesthetic inspired air
pulmonary ventilation
pulmonary blood flow .
solubility of the drug in the blood.
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Elimination
The ways of elimination as we said they are eliminated mainly by the lungs by expiration
Other way of clearance is done by other tissue like liver liver play an important rule in drug metabolism
like in case of halothane and methoxyflurane in which these
metabolize are excreted by kidney , but the major process of their
elimination is by the lungs
- This is seen specially in Nitrous oxide bcz it is inorganic , No
need for metabolism and mainly eliminated by the lungs .
Duration is very important :Duration of the exposure of the inhaled anesthetic will affect the
time of recovery , as the duration of exposure will be more the
recovery ( returning back of consciousness) will be slow .
AGAIN as we said , If the drug has low blood gas partition coefficient this is meanits onset of action will be fast on the same time its recovery also will be fast .
So , it is very important , KEEP this in your mind .
NOW Comparing between Nitrous oxide and halothane
which one has the fastonset of action ? Nitrous oxide . why?- Bcz it has low blood gas partition coefficient and low blood
solubility , it has fast induction or fast onset of action .
Which one will produce a fast recovery ? Nitrous oxide .
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compare between them in the case ofpotency- potency is how much of drug is required to produce an effect , for drugs the potency
it is expressed by mg / units , in case of inhaled drugs partial pressure)
- drug potency is depend on drug lipid solubility as there is an increase in solubilitythe potency will be more this is mean that the amount of drug that needed to
produce an effect will be small .
So
Onset of action depend on the blood solubility , Potency of the drug depends on its lipid solubility
( as it is more the potency will be more )
Minimum Alveolar concentration (MAC)
The potency is measured by Minimum Alveolar concentration (MAC) which is :
The minimum concentration of the inhaled anesthetic that is looking to induce
immobility or prevent movement in response to surgical incision in 50% of patient
Comparing with other drug , the potency of other drug is expressed byED50 ( effective dose in 50% of population ) .
While in the inhaled anesthetic its potency is expressed by or dependson MAC 50 . it is defined as how much is the anesthetic is needed to
produce immobility or prevent movement or response to such
stimulus like surgical incision in 50% of population .
- As it Is small the potency of the drug will be more , and as it is high ,the potency of the drug will be low .
The MAC depends on the drug lipid solubility- high lipid solubility Low MAC the drug will be highly potent
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Now we finish from the introduction and we will talk about examples :
** INHALED ANESTHETIC
1) Halothane
- It is one of the inhaled anesthetic- it is halogenated- not irritant- Colorless- High blood solubility slow induction and recovery .- High fat solubility low MAC highly potent .- Mainly this drug can be metabolized by liver enzymes Cyt-P450- One of its adverse effect Sensitize the myocardium to the effect of catecholamine
and it will induce cardiac arrhythmia.
- Repeated administration over a short period of time has been implicated toproduce halothane hepatitis , and induce the liver damage .
why?They said that halothane metabolism will induce reactive metabolites , and
these reactive metabolites either cause direct damage to the liver cells or they will
induce immune-mediated response ( all of this due to the reactive metabolites ) .
2)Nitrous Oxide (N2O) laughing gas -
It is a good analgesic drug- Low blood solubility rapid induction and recovery- Most rapid induction- Most rapid rate of recovery- least potent, highest MAC value bcz of low lipid solubility- Not metabolized, totally eliminated by lungs- Bcz of its good analgesic effect it can be used in dental procedure and
obstetrics.
- Given by inhalation and mixed with oxygen 50 to 50 percent bcz of itspowerful analgesic effect .
- One of its problems is its short duration of action , you put the mask and ifthere is pain you must return the mask ( y3ni it needs repetitive
administration bcz of its short duration of action )
- Multiple adverse effect ( bcz of rapid recovering it may cause washout ofoxygen from the alveoli and this will induce hypoxia , it is very important to
prevent hypoxia development by administration of significant amount of pure
oxygen.
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** INTRAVENOUS ANESTHETIC :
1) Barbiturates : thiopental it is ultra short acting barbiturates in which its onset of
action within seconds , can be induce unconsciousness very rapid .
rapid onset induction and recoverygood anesthetic with poor analgesic effect
( in opposite to Nitrous oxide in which nitrous oxide is a poor
anesthetic with good analgesic effect ).
Dissociative Anesthesia
This term is defined in which we have analgesic effect as well as we have
amnesia , minimal effect of the respiratory function .
The patient is conscious , analgesic ,amnesic But he can open his eyes and
can swallow , but doesnt process any information ( decrees of awareness
of external environment )
Howwe get Dissociative Anesthesia ?
This is seen by the administration ofKetamine HCl . and its effects are :
1)muscular relaxation is poor2) this drug can increase Stimulates central sympathetic outflow
increasing HR, BP and CO.
3)Not used in hypertensive patients2)Propofol
It is a dug that produces anesthesia at a rate similar to that ofbarbiturates ( in compared with thiopental) in which it has a fast onset
of action .
post operative vomiting is less common and may have anti-emeticproperty
hypersensitivity is less common
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3)BENZODIAZEPINES
Benzodiazepine derivatives (Diazepam, midazolam, lorazepam )
Not complete GA produces amnesia , muscle relaxation , sedation , no analgesia . Used for:
1) Premedication To relieve anxiety & prevent sympathetic activity.
2) Conscious sedation along with Opioids (for short surgical & diagnostic
procedures e.g : Endoscopy and Bronchoscopy
Neuroleptanalgesia:
It is a state in which there is an analgesia , amnesia , sedation
BUT he is consciousness and cooperative that mean he is able to respond to
commands or external orders .
Anxiety, motor activity, and sensitivity to painful stimuli are reduced;
the person is quiet and indifferent to surroundings
How we get Neuroleptanalgesia?
by administration of 2 drugs :
1)narcotic analgesics (Opioids derivatives) like Fantanyl2) Neuroleptic drugs (antipsychoticdrugs) like Droperidol
Droperidol+ Fantanyl Neuroleptanalgesia
If we add Nitrous Oxide to Droperidol and Fantanyl we will have
Neurolept anaesthesia ( NOT Neurolept analgesia)
Droperidol+ Fantanyl + Nitrous Oxide Neurolept anaesthesia
http://en.wikipedia.org/wiki/Antipsychotichttp://en.wikipedia.org/wiki/Antipsychotichttp://en.wikipedia.org/wiki/Antipsychotichttp://en.wikipedia.org/wiki/Antipsychotic -
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THE END
GOOD LUCK
Im sorry for any mistake ..
Done By : Eman Nazzal