Chapter 21: Local and General Anesthetics

Local and General Anesthetics overview examines the pharmacological agents used to induce the loss of sensation and consciousness, distinguishing between local anesthetics and general anesthetics. Local anesthetics function by reversibly obstructing the conduction of nerve impulses, primarily through the blockade of voltage-gated sodium channels within peripheral nerves or the spinal cord. Chemically, these substances are classified as either ester-type or amide-type, and their efficacy is notably influenced by tissue pH; for instance, the presence of inflammation or acidosis can hinder their ability to penetrate neuronal membranes. Clinical application varies from topical surface treatments and local infiltration to more complex regional techniques like spinal intrathecal and epidural anesthesia. The sensitivity of nerve fibers to these blocks is dependent on their size and myelination, where smaller pain-transmitting fibers are typically affected before larger motor fibers. In contrast, general anesthetics act on the central nervous system to facilitate major surgical procedures by producing unconsciousness, amnesia, and analgesia. The text evaluates inhalational agents, such as nitrous oxide and halogenated hydrocarbons, through metrics like the minimum alveolar concentration (MAC) for potency and the blood:gas partition coefficient for the speed of induction. These gaseous agents generally enhance inhibitory neurotransmission at GABA receptors. Significant clinical risks associated with halogenated gases, such as malignant hyperthermia, are highlighted alongside the use of dantrolene as a corrective treatment. Furthermore, the chapter details parenteral options, including rapid-acting induction agents like propofol and etomidate, benzodiazepines for sedation, and potent opioids like fentanyl for balanced anesthesia. It also covers unique states such as dissociative anesthesia produced by ketamine, which targets glutamate receptors. By integrating these various chemical classes and delivery methods, the material provides a thorough understanding of how anesthetic practice manages patient safety and comfort during medical interventions.