Local anesthesiaLocal anesthesia has been defined as a loss of sensation in a circumscribed area ofthe body caused by a depression of excitation in nerve endings or an inhibition of conduction process in peripheral nerves.Local anesthetic: produce loss of sensation to pain in a specific area of the body without the loss of consciousness
Solution contained within a dental cartridge1. Local anesthetic solution2. Vasopressor3. Sodium chloride4. Distilled water.
Action of local anesthetic The conceptThey prevent both the generation and theconduction of a nerve impulse. It sets up a chemicalroadblock between thesource of impulse (e.g. the scalpel incision in soft tissues) and the brain.
Physiology of the peripheral nerves. The function of a nerve is to carrymessages from one part of the bodyto another. These messages, in theform of electrical action potentials, are called impulses. Action potentials are transient membrane depolarization that result from a brief increase in the permeability of the membrane to sodium, and usually also from a delayed increase in the permeability to potassium.
Mode and site of action of local anesthetics The nervemembrane is thesite at which localanesthetic agents exert their pharmacological actions. The primary action of local anesthetic in producing a conduction block is to decease the permeability of the ion channels to sodium ions (N+)
•All local anesthetics are amphipathic,•Local anesthetics without a hydrophilic part are not suited for injection but are good topical anesthetics.•The nature of the linkage is important in defining several properties of the local anesthetic, including the basic mode of biotransformation.
Local anesthetic are availabe as salts for clinical use.Within the solution it exists simultaneously as1. Uncharged molecules (RN) also called the base and2. positively charged molecules (RNH+), called the cation. RNH+ RN + H+ The uncharged, lipid-soluble, free base form (RN) of the anesthetic is responsible for diffusion through the nerve sheath.
In the presence of a high concentration of hydrogen ions (low pH) the equilibrium shifts to the left and most of the anesthetic solution exists in cationic form. RNH+ > RN + H+ As hydrogen ion concentration decreases (higher pH), the equilibrium shifts toward the free base form. RNH+ < RN + H+
Local anesthetics Esters Amides Quinoline Esters of Esters of para- benzoic aminobenzoic Articaine centbucridine acid acid Bupivacaine Dibucaine Etidocaine Butacaine Lidocaine Cocaine Chloroprocaine MepivacaineBenzocaine Procaine prilocaineHedylcaine propoxycainePiperocaineTetracaine.
the doses of local anesthetic drugs are presented in terms of milligrams of drug per unit of body weight, mg/kg.Maximum dose for an individual is usually between70mg to 500mgThe amount of dose also varied based on the type ofsolution used and the presence of vasoconstrictorExample:---For adult whose weight is 150lbs and up,maximum dose Articaine and lidocaine is about500mg---For children, the dosage reduced to about 1/3 to½ depending on their weight. .