Local Anesthesia-Tips

 

Few tips about local anesthesia

Intraoral techniques  for Mandibular Nerve Block:

  1. Gow gates technique
  2. Akinosi technique

Extra oral technique for Mandibular nerve block:

The needle is inserted from below the zygomatic arch. Then it is directed posterior to the lateral pterygoid plate below the foramen ovale.

Extra oral technique for Maxillary nerve block:

The needle is directed anterior to the lateral pterygoid plate into the pterygopalatine fossa.

Except cocaine which is a naturally occurring local anaesthetic agent and vasoconstrictive, all other local anesthetics are synthetic compounds that are vasodilating in nature.

Walking time bomb:

The vasoconstrictive action of adrenaline is augmented when cocaine is used as a local anesthetic agent due to its vasoconstrictive property. So, if cocaine is given as LA agent with adrenaline, the risk of death increases in cocaine users. Therefore, they are known as walking time bombs.

The reaction that occurs in the submucosa at the normal tissue level ph is:

la-break

RN is lipophilic and is responsible for penetration into the nerve. If the tissue ph is decreased due to infection or pus, it results in abundance of H+ ions outside the nerve sheath. Therefore, the equilibrium of reaction in formation of lipophilic molecule (RN) shifts towards left. So, the RN+ fails to enter the nerve and can not block the nerve conduction.

 

Local anaesthetics as an example of the situation above

Local anaesthetics block action potential generated by blocking Na+ channels

Most local anaesthetics  are weak bases, with a pKa between 8 and 9, so that they are mainly but not completely ionised at physiological pH. The un-charged species (B) penetrates the nerve sheath and axonal membrane and is then converted to the BH+ active form, which then blocks the Na+ channels. Increasing the acidity of the external solution would favour ionisation and render local anaesthetics ineffective.

LOCAL ANAESTHETICS ARE INEFFECTIVE IN INFECTED TISSUE (ACIDIC).

Quaternary derivatives of local anaesthetics (Q+) do not work when applied outside but can block channels if introduced directly into cytoplasm.*

 

Nitrous Oxide Gas

  • 5-25%- causes moderate sedation, diminution of fear and anxiety, marked relaxation.
  • 25-45%- causes dissociation sedation and analgesia, floating sensation, reduced blink rate, euphoric state (laughing gas).
  • 45-65%- causes total anesthesia, complete analgesia, marked amnesia.
  • 45-65%- causes total anesthesia, complete analgesia, marked amnesia.

Advantages of addition of vaconstritive agent (Adrenaline) with local anesthetic agent:

  • Prevents rapid absorption of the local anesthetic agents and thus increases the concentration at the site of action.
  • Prolongs the duration of action
  • reduced absorption rate and increased efficiency in small doses of LA results in reduced toxicity of the LA agent.
  • Reduced bleeding in the area of surgery.

Types of local anesthetic block:

Nerve block– local anesthetic agent is deposited near main trunk of the nerve. e.g. Inferior nerve block, blocks sensation of all the teeth of the lower jaw including the labial buccal mucosa anterior to the mental nerve.

Field block-local anesthetic agent is deposited near the large branch of the peripheral nerve; e.g. mental nerve block.

Local infiltration– local anesthetic agent is deposited near the small nerve endings; e.g. Deposition of LA agent near the root apex of lower central incisor.

 

*Source: http://www.frca.co.uk/article.aspx?articleid=220

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