Lab # 2 Local Anesthetic

Drugs

Definition of local anesthetic drugs

They are drugs used to abolish pain sensation in

certaion area of the body.

They depress the afferent nerve impulses which

travel to the CNS.

They cause reversible block of nerve conduction

when applied locally to the nerve tissue in

appropriate concentration.

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Mechanism of action of L.A1) (-) the generation & propagation of the nerve

impulses at its site of action on the cell

membrane.

2) (-) Na+/ k+ ATPase, so no Na+ influx & no K+

outflux → membrane stabilization.

3) the activity of Na+ / Ca+ exchange causing

membrane stabilization. (block Na channle →

prevent depolrization)

4) the threshold of excitability or block the

conduction of nerve impulses. Samiah AL-shehri 3

Method for administration of L.A

1) Surface anesthesia.

2) Infiltration anesthesia.

3) Nerve block anesthesia.

4) Spinal anesthesia.

Method for administration of L.A

1 .Surface Anesthesia: By direct application of the drug to the

surface. E.g. eye, skin, cornea. E.g. Lidocaine , coccaine

2 .Infiltration Anesthesia : The local anesthetic is injectected (S.C)in

order to paralyze nerve ending at the site of

operation.E.g. Lidocain, Procaine

Method for administration of L.A

3 .Nerve Block Anesthesia:

The local anesthetic is injected in the vicinity of the

major nerve trunks e.g. trachea plexus (neck)

e.g. lidocaine,

procaine

4 .Spinal Anesthesia:

The local anesthetic is injected in the subarachnoid

space so that it reaches the roots of the spinal

nerves between

Lumber (L1 & L2 ) e.g. procaine

Identification & Evaluation of L.A:

1) Corneal method (surface).

2) Intradermal wheel method (infilteration).

3) Nerve block ( frog plexus method).

1-Corneal method (Surface):

Principle:

The L.A. is applied & the change in the response

of the animal to the painful stimulus is recorded.

Animal: Rabbit .

Painful stimulus: is induced by a fine cotton

applicators applied on the cornea.

1-Corneal method (Surface):

Anesthetic used: Lidocaine 1%

Response: blinking of the eye.

N.B. The response is compared Before and after

application of lidocaine .

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1-Corneal method (Surface):

Procedure:

1- clip the eye laches of the rabbit

2- check the normal coroneal reflex

3- aplply 0.2 ml Lidocain to eye & other eye is used as

control

4- after every min check corneal reflex in both eyes 5 times

2-Intradermal wheel method(infiltration):

Animal: Guinea pig .

Painful stimulus: Pin prick .

Anesthetic used: Lidocaine 0.2 %

Response: shrinkage of the skin (L.A. will prevent

feeling of pain during the prick) .

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2-Intradermal wheel method(infiltration):

Procedur:

1- clip the hair of the back of G.P & shave the skin

2- apply painful stimuli (using pin prick) to the skin

of Rt or Lt sides, the animal response by

shrinking of the skin

3- inj. Lidocain 0.2% to the Rt side only intradermal

where the Lt side leaved control

4- pin prick are made every 5” until loss of pain

sensation

3-Nerve Block Method (frog plexus method):

Animal: Frog .

Painful stimulus: dil. Hcl .( 0.05% , 0.1% , 0.2%)

Anesthetic used: Procaine .(0.1% , 0.2%)

Response: Withdrawal of the leg .

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3-Nerve Block Method (frog plexus method):

Procedure:

1- decapitate the frog with out pithing of the spinal

cord

2- atransverse incision is made in the abdominal

below the sternum, where the viscera is removed,

through this opening . Becarful not to damage the

nerve

3- hang the frog by a hook

4- test each leg with tap water , the frog should no

give reflex action to tap water (indicate loss

conscious movement)

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3-Nerve Block Method (frog plexus method):

5- immerse the foot in 0.05 N Hcl , observe the

withdrawel reflex within 10 sec ,then wash the

foot till the muscle are relaxed

6- inj. L.A into the abd. Cavity , so that the plexus is

sub merged with the drug

7- test the withdrawal reflex every min ,always to

wash the leg after acid apply

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3-Nerve Block Method (frog plexus method):

the foot is immersed to dil.Hcl for no longer than

10” to avoid damage of the skin

When aresponse is no longer obtained with 10”

try with 0.2 N Hcl for 10”

8- determine the total onset time of L.A

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3-Nerve Block Method (frog plexus method):

Result:

Onset time of 0.1% Procaine =Onset time of 0.2% Procaine =

Total 0.2 N Hcl

0.1 N Hcl

0.05 N Hcl

0.1 procaine

0.2 procaine

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