Definition
Local anaesthesia: Local anaesthesia is a transient and reversible loss of sensation in a localized or circumscribed area of the body without impairing the degree of consciousness.
Local anaesthetics: Local anaesthetics are the agents which are used for producing transient and reversible loss of sensation in a localized area of the body without affecting the degree of consciousness.
Ideal properties of local anesthetics
1.) Local anesthetics should produce effective local anesthesia when administered correctly and in a adequate doses.
2.) The action of local anesthesia should be reversible.
3.) It should have rapid onset of action.
4.) It should have sufficient duration of action.
5.) It should be isotonic and have ph compatible with that of the tissues.
6.) It should not produce any injury or irritation of the tissue at site of injection.
7.) It should have no or minimal local or systemic toxicity.
8.) Local anesthetics solution must have adequate shelf life.
Methods of local anesthesia
1.) By application of cold.
2.) By application of pressure to nerve trunk.
3.) By rendering the tissue anemic.
4.) By paralyzing the sensory nerve endings or nerve fibers with drugs.
Routes of administration of local anaesthesia
1.) Topical or surface anesthesia: It is present in the form of ointment(eg. 5% lignocaine HCL) , emulsion (eg.2% HCL ), spray (eg.10% lignocaine HCL )etc.
2.) Infiltration anaesthesia: It is applied near the terminal fibres of any nerve to produce anaesthesia of the localized area.
3.) Regional or block anaesthesia: In this technique nerve trunk is blocked.
4.) Spinal anaesthesia: It is applied in the subarachnoid space between lumbar 2-3 or lumbar 3-4.
5.) Epidural block: It is applied in the potential space present in between the dura mater and the connective tissue lining of the vertebral canal.
6.) Intravenous injection
Preparation and composition of local anaesthesia
1.) Local anesthetic agent: Lignocaine, prilocaine
2.) The vehicle modified Ringers isotonic solution
3.) Vasoconstrictor adrenaline, nor-adrenaline
4.) Reducing agent: Sodium meta bisulphate
5.) Preservatives: Capryl-hydro-caprienotoxin
6.) Fungicidal agent: Thymol
7.) Diluting agent: Distilled water
Classification of local anaesthesia
a.) According to sources
1.) Natural : Cocaine
2.) Synthetic:
- Nitrogenous: procaine, lidocaine, cinthocaine
- Non-nitrogenous: ethyl alcohol, benzyl alcohol
- Others: ice, clove oil, phenol
B.) According to chemistry
1.) Ester type: basic structure(-coo-)
a.) Benzoic acid derivatives:
- Natural: cocain
- Synthetic: Benzocain
b.) PABA( Para Amino Benzoic Acid)
- . Procaine
- Tetracaine
- Propoxycaine
2.) Amide type
- Lidocaine
- Prilocain
- Mepivacaine
- Bupivacaine
The pharmacological action of local anaesthesia
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Mechanism of action of local anaesthesia
Indication of local anaesthesia
1.) Extraction of tooth.
2.) Root canal treatment in vital tooth.
3.) Curettage of dry socket.
4.) Excisional and incisional biopsy of oral tissue.
5.) Apicectomy.
6.) Removal of cyst.
7.) Drainage of abscess.
8.) Laser surgery.
9.) Implant surgery.
Contraindication of local anaesthesia
1.) History of allergy to local anesthetics agents.
2.) History of bleeding disorder.
3.) Patient of anti coagulant disorder.
4.) Severe form of liver disease.
5.) Haemangioma.
6.) Cardiovascualr disease.
7.) Hyperthyroidism
8.) Epilepsy
9.) Patient under long term steroid therapy.
10.) Mentally retarded patient.
Advantage of local anaesthesia
1.) Simple technique.
2.) No elaborate pre-operative of patient is required.
3.) It is more safe as it is does not involve CNS.
4.) No elaborate arrangement on apparatus is needed.
5.) Transportable
Disadvantages of local anaesthesia
1.) There are individual variations in response to local anesthetic drugs.
2.) Rapid absorption of the drug into the blood stream can cause severe, potentially fatal reactions.
3.) Direct damage of nerve.
4.) Post dural headache from CSF leak.
5.) Not suitable for extremes of ages.
The adverse effect of local anaesthesia
1.) Hypersensitivity reaction( mainly ester group products)
2.) Toxic effect on CNS ( unconsciousness, respiratory arrest, death due to overdose)
3.) Toxic effect on CVS ( decreases of cardiac output and hear rate, bupivacaine in high dose can cause cardiac arrythmia, etc)
4.) Adrenaline toxicity such as anxiety, restlessness, headache, palpitation, sweating with pallor, respiratory distress.
Causes of failure of local anaesthesia
1.) Deposition of anesthesia solution in wrong site.
2.) Deposition of in appropriate amount of anesthetics solution.
3.) Incorrect technique.
4.) Intravascular injection
5.) Variations of individual response.
How to overcome the failure
1.) Adequate amount of local anesthesia should be given.
2.) Purulent pus forming infection should be avoided as local anesthesia cannot dissociate in the acid media.
3.) Local anesthesia should be discarded after expire date.
4.) If necessary individual dose should be measured for different person.
5.) Do not deposit anesthesia solution in wrong site.
