- Local anesthesia is the reversible loss of sensation in a particular are of the body caused nerve ending depression or inhibit peripheral nerve conduction.
Types of anesthesia
- Surface anesthesia
- Infiltration anesthesia
- Epidural anesthesia
- Spinal anesthesia
1. Surface anesthesia
- It produce by locally only topical action and there is no loss of motor function.
- Example: Lidocaine in throat acts in 2-5 min and produced anesthesia for 30-45 min.
2. Infiltration anesthesia
- LA anesthesia (dilution solution) administered under the skin at the operation area.
- Immediate onset of action, duration of action – shorter than the nerve block.
- Example: Lidocaine – 30 – 60 min. Bupivacaine – 120 -180 min.
3. Conduction block
- The LA is injected around nerve trunks so that the area distal to injection is anaesthetized and paralyzed.
4. Spinal anesthesia
- It blocks the pain in a particular region.
- Epidurals block the nerve impulses from the lower spinal segments.
- This results decreased sensation in the lower half of the body.
A. Injectable anesthesia
- Low potency, short duration
Example: procaine, chlorprocaine
2. Intermediate potency and duration
Example: lidocaine (Lignocaine), Prilocaine
3. High potency, long duration
Example: tetracaine, bupivacaine, ropivacaine dibucaine (cinchocaine)
B. Surface anesthesia
Example: cocaine, lidocaine, tetracaine, benoxinate
Example: benzocaine, butylaminobenzoate (Butamben)
C. Ester – linked Las
Example: cocaine, procaine, chlorprocaine, tetracaine, benzocaine
D. Amino – linked Las
Example: Lidocaine, bupivacaine, dibucaine, prilocaine, ropivacaine.
Mechanism of action
- M-gate and “h” gate (halt gate) is present at the extra and intra cellular mouth of the membrane.
- The gates are closed in the resting state.
- Threshold depolarization of the membrane opens the activation gate allowing Na+ ions.
- The local anesthetics receptor is located within the channel in its intracellular half.
- The unionized form of local anesthetics traverses the membrane.
- Re-ionized in the axoplasm and binds at the LA receptor.
- The cationic form (BH+) of the local anesthetics which primarily binds to the receptor.
- The LA receptors are more affinity, so more accessible of LAs, thus reduce the opening of channels and Na+ ions does not enter.