Anesthetic Agents: What They Are and How They Work
Anesthetic agents are drugs that produce a loss of sensation, including pain, by acting on the brain or peripheral nervous system. They can be given by different routes, such as injection, inhalation, or topical application. Anesthetic agents have different chemical structures and can be classified into various groups, such as barbiturate anesthetics, nonbarbiturate general anesthetics, anesthetic gases, and volatile liquids . Anesthetic potency is closely correlated to lipid solubility and there are two main theories of how they interact with the cell membrane: the lipid theory and the protein theory.
Anesthetic agents can be divided into two broad classes: general anesthetics and local anesthetics. General anesthetics induce anesthesia throughout the body and can be administered either by inhalation or by direct injection into the bloodstream. General anesthesia involves loss of consciousness, usually for the purpose of relieving the pain of surgery. Local anesthetics prevent the transmission of nerve impulses without causing unconsciousness. They act by reversibly binding to fast sodium channels from within nerve fibers, thereby preventing sodium from entering the fibers, stabilizing the cell membrane and preventing action potential propagation. Local anesthetics can be either ester- or amide-based. Ester local anesthetics are generally unstable in solution and fast-acting, while amide local anesthetics are generally heat-stable, with a long shelf life and a slower onset and longer half-life .
Anesthetic agents have many benefits for patients and healthcare providers, such as reducing pain, anxiety, and stress during medical procedures. However, they also have some risks and side effects, such as allergic reactions, respiratory depression, cardiovascular instability, nausea, vomiting, and postoperative cognitive dysfunction. Therefore, careful selection, administration, monitoring, and reversal of anesthetic agents are essential for ensuring patient safety and optimal outcomes.
Examples of Specific Anesthetic Agents
There are many different anesthetic agents available for various purposes and procedures. Some examples of specific anesthetic agents are:
- Inhalational anesthetics: These are gases or vapors that are breathed in by the patient to induce and maintain general anesthesia. They are usually administered in combination with oxygen and other drugs, such as opioids or muscle relaxants. Some examples of inhalational anesthetics are nitrous oxide, sevoflurane, isoflurane, desflurane, and xenon .
- Intravenous anesthetics: These are drugs that are injected into a vein to induce and maintain general anesthesia. They are often used for short procedures or as induction agents before switching to inhalational anesthetics. Some examples of intravenous anesthetics are propofol, ketamine, thiopental, etomidate, and midazolam .
- Ester local anesthetics: These are drugs that are metabolized by enzymes called cholinesterases in the blood and tissues. They have a short duration of action and are more likely to cause allergic reactions than amide local anesthetics. Some examples of ester local anesthetics are procaine, cocaine, benzocaine, and tetracaine .
- Amide local anesthetics: These are drugs that are metabolized by enzymes in the liver. They have a longer duration of action and are less likely to cause allergic reactions than ester local anesthetics. Some examples of amide local anesthetics are lidocaine, prilocaine, bupivacaine, ropivacaine, and mepivacaine .