Local anesthetics

A local anesthetic is a drug that can locally inhibit the occurrence and conduction of nerve impulses. The chemical structure of these drugs is closely related to the local anesthetic effect. The chemical structure must have three components: 1 aromatic ring; 2 intermediate part, some are ester type (such as procaine), some are Amide type (such as lidocaine); 3 amine moiety, mostly tertiary amine, a few secondary amines. The effect of local anesthetics on the nerve trunk is to first suppress the sensory nerve and then inhibit the impulse conduction of the motor nerve, and its effect is reversible. It causes the loss of sensory function to be the first to affect pain, followed by temperature, and finally touch and pressure. The local anesthetic effect is because the drug prevents the influx of sodium ions, so that the nerve cell membrane can not be depolarized, the action potential can not be generated, and the conduction of nerve impulse is blocked. Local anesthetics act on the inner side of the membrane in a dissociative form. Because they belong to organic bases, they have higher fat solubility in an alkaline environment and a stronger ability to penetrate the cell membrane to the inside of the membrane. Conversely, in an acidic environment (for example, Under inflammatory conditions) their ability to pass the membrane is poor and the local anesthetic potency is diminished. The mechanism of local anesthesia is still inconclusive. It is currently believed that it may compete with calcium ions to synthesize phospholipids in the cell membrane of nerve fibers, forming a stronger complex of local anesthetics and phospholipids, destroying the role of phospholipids in carrying sodium ions. This hinders the influx of sodium ions. Local anesthetics are absorbed to stimulate the central nervous system and inhibit the cardiovascular system. The former manifests as convulsions, which in turn leads to medullary paralysis and respiratory failure; the latter manifests as myocardial depression and vasodilation, which in severe cases leads to cardiovascular collapse and death. Therefore, the absorption of drugs into the blood should be prevented or reduced when applying local anesthetics.