Anesthesia/anesthetics specific agents

Specific Local Anesthetic Agents. Clinically used local anesthetics and the methods of appHcation are summarized in Table 5. Procaine hydrochloride [51-05-8] (Novocain), introduced in 1905, is a relatively weak anesthetic having along onset and short duration of action. Its primary use is in infiltration anesthesia and differential spinal blocks. The low potency and low systemic toxicity result from rapid hydrolysis. The 4-arninobenzoic acid... 

Both the inhaled and the intravenous anesthetics can depress spontaneous and evoked activity of neurons in many regions of the brain. Older concepts of the mechanism of anesthesia evoked nonspecific interactions of these agents with the lipid matrix of the nerve membrane (the so-called Meyer-Overton principle)—interactions that were thought to lead to secondary changes in ion flux. More recently, evidence has accumulated suggesting that the modification of ion currents by anesthetics results from more direct interactions with specific nerve membrane components. The ionic mechanisms involved for different anesthetics may vary, but at clinically relevant concentrations they appear to involve interactions with members of the ligand-gated ion channel family. 

Current anesthesia protocols usually include several agents in combinations that vary according to the depth of anesthesia required for specific procedures. Inhalational anesthetics, which include nitrous oxide and six halogenated hydrocarbons, have varying potency in proportion to their lipid solubilities. MAC value, a measure of anesthetic potency, is defined as the minimal alveolar anesthetic concentration (% of inspired air) at which 50% of patients do not respond to a surgical stimulus. MAC values are additive, lower in elderly patients, and lower in the presence of opioid analgesics and sedative hypnotics. 

Local anesthetics are used to locally anesthetize a wide range of specific body parts or areas to allow painless surgery. Local anesthetics are most commonly used for dental procedures and repair of lacerations. They can also be used to provide neural blockade for larger, more painful procedures. Sites of LA application include localized injection, peripheral nerve blocks as well as central nerve blockade. The only safe agents which can be utilized for intravenous regional anesthesia (Bier block) are lidocaine and prilocaine. Other typical indications are outlined in Table 64.1. 

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