Chapter 15 Local Anesthetics Local anesthetics reversibly block impulse conduction along axons and other excitable membranes that utilize sodium channels as the primary means of action potential generation. This action can be used clinically to block pain sensation.

Mechanism of Action The primary mechanism of action of local anesthetics is blockade of voltage-gated sodium channels. Local anesthetics bind to receptors near the intracellular end of the channel and block the channel in a time- and voltage-dependent fashion.

Classification of local anesthetics Esters 酯类 Amides酰胺类 1. Procaine (普鲁卡因） Lidocaine（利多卡因） 2. Chloroprocaine Mepivacaine马比佛卡因 3. Trtracaine丁卡因 Bupivacaine 布比卡因 4. Cocaine 可卡因 Etidocaine依替卡因 ropivacaine罗哌卡因

局麻方法

Types of local anesthetics and clinical application 1.surface/topical anesthesia is often used for eye, ear, nose, and throat procedures. Satisfactory anesthesia requires an agent capable of rapid penetration of the skin or mucosa. Tetracaine, because of its excellent penetration . 2. Infiltration anesthesia: Local anesthetics is injected in the vicinity of peripheral nerve endings (such as area of the surgical incision). 3.conduction anesthesia Local anesthetics is injected in the vicinity of major nerve trunks.

4 Spinalan (Subarachnoid) anesthesia : Local anesthetics is instilled within the subarachnoid spaces surrounding the spinal cord. 5.Epidural anesthesia Local anesthetics is instilled within the epidural spaces surrounding the spinal cord.

Toxicity of Local Anesthetics Ultimately, local anesthetic agents are absorbed from the site of administration. If blood levels rise too high, effects on several organ system may be observed. 1.Hypersensitivity(allergic) 2. Central Nervous System: Central nervous system effects at low doses include sleepiness, light- headedness, visual 视and auditory 听disturbances, and restlessness. At higher concentration, nystagmus muscular twitching眼震 may occur.Finally overt tonic-clonic convulsions followed by central nervous system depression and death may occur.

3. Cardiovascular System: Local anesthetics block cardiac sodium channels and thus depress excitability and conduction. At very high concentration, because they may also block calcium channels, they depress the strength of cardiac contraction and cause arteriolar dilation. Both effects leads to hypotension.