Local anesthesia is any technique to render part of the body insensitive to pain without affecting consciousness. Local anesthetics are drugs, which upon topical application or local injection cause reversible loss of sensory perception, especially pain, in a restricted area of the body.

Composition of Local Anesthesia

1.    Local anesthetic agent- this is the active ingredient in the solution eg. Lignocaine.

2.   Vasoconstrictor- adrenaline reduces toxicity and confines anesthetic agent to a localized area thus increasing depth and duration of anesthesia.

3.   Anti-oxidant- vasoconstrictors are unstable in solution and may oxidize, especially on a prolonged exposure to sunlight. Sodium meta-bisulfite, which competes for the available oxygen, protects solution from oxidation.

4.   Preservative- methyl paraben keeps the solution in stable form.

5.   Fungicide- thymol is used.

6.   Vehicle- normal saline or ringer’s lactate solution is used. Isotonic vehicle minimizes discomfort during injection.

Types of local anesthetics

Basically there are 2 groups:

1.ESTERS- 

(1).  Butacaine
(2).  Cocaine
(3).  Benzocaine
(4).  Tetracaine
(5).  Piperocaine
(6).  Procaine
(7).  Chloroprocaine
(8).  Propoxycaine

(1).  Articaine
(2).  Bupivacaine
(3).  Dibucaine
(4).  Etidocaine
(5).  Lidocaine
(6).  Mepivacaine
(7).  Prilocain

Dosage of Local Anesthesia in Dentistry

1.    Most commonly used local anesthetic is Lidocaine as 2% lignocaine with 1:200,000 adrenaline.

2.    Lidocaine without adrenaline can be given 4.5mg/kg body weight not to exceed 300 mg.

3.    With adrenaline it can be given upto 7mg/kg body weight not to exceed 500 mg.

4.    The maximum dose for local anesthetic solutions is somewhere between 70 mg to 500 mg for an average 70 kg patient.

5.    Of course, the maximum dose is dependent upon the age, weight and health of the patient, the type of solution used, and whether vasoconstrictor is present or not.

6.    The dose of local anesthetic should be lowered when children are sedated

Uses of Local Anesthesia in Dental Procedures

Various procedures in dentistry cannot be made painless without the use of a local anesthetic and also at times the patient is so anxious with the fear of pain during the dental procedure that even if there is no need of an anesthetic injection they would purposely ask for it.

The procedures requiring local anesthesia in dental clinic are:

1.  Root canal treatment
2.  Removal of teeth
3.  Deep dental fillings
4.  Periodontal gum surgeries
5.  Cosmetic dentistry procedures
6.  Crown and bridge work
7.  Implants
8.  Oral surgical procedure

The availability of various anesthetic agents has made the dental procedures almost entirely painless.

Complications of Local Anesthesia

An anesthetic complication may be defined as any deviation from the normally expected pattern during or after the securing of regional analgesia.

Classified as follows:

1. Primary or secondary
2. Mild or severe
3. Transient or permanent

Primary complication is one that is caused and manifested at the time of anesthesia.

Secondary complication is one that is manifested later, even though it may be caused at the time of insertion of the needle and injection of the solution.

Mild complication is one that exhibits a slight change from the normally expected pattern and reverses without any specific treatment.

Severe complication manifests  itself by a pronounced deviation from the normally expected pattern and requires a definite plan of treatment.

Transient complication is one that, although severe at the time of occurrence, leaves no residual effect.

Permanent complication would leave a residual effect, even though mild in nature.

Complication may also be divided into

Those attributed to the solution used. This group includes those complication that result from absorption of the anesthetic solution.

1. Toxicity
2. Idiosyncrasy
3. Allergy
4. Anaphlactoid reactions
5. Infection caused by contaminated solution
6. Local irritations or tissue reaction’s caused by solution

Those attributed to the insertion of the needle.

1. Syncope
2. Muscle trismus
3. Pain
4. Edema
5. Infections
6. Broken needles
7. Prolonged anesthesia
8. Hematoma
9. Sloughing
10. Bizzare neurological symptoms

Allergy to Local Anesthesia

Defined as hypersensitive state acquired through exposure to particular antigen, re-exposure to which brings about a heightened capacity to react.

Symptoms:

1. Rashes
2. Urticaria
3. Angioneurotic edema
4. Mucous membrane congestion
   a. Rhinitis
   b. Asthmatic symptoms

SYNCOPE (Fainting) with Local Anesthesia

Partial or complete loss of consciousness with interruption of awareness of oneself and ones surroundings. When the loss of consciousness is temporary and there is spontaneous recovery, it is referred to as syncope or, in nonmedical terms, Fainting.

Syncope is due to a temporary reduction in blood flow and therefore a shortage of oxygen to the brain. This leads to lightheadedness or a “black out” episode, a loss of consciousness.

Most frequent complication. This is a form of neurogenic shock and is caused by cererbral ischemia secondary to vaso-dilation or an increase in peripheral vascular bed, with a corresponding drop in blood pressure.