There are two broad types of general anesthetics: The inhalation agents and the intravenous agents. It is not the purpose of this subcourse to provide a complete listing or a detailed discussion of the agents that are presented. If you desire additional information on these agents, you should consult a pharmacology text.
a. Inhalation Agents. Inhalation anesthetic agents are gases or volatile liquids. These substances are often mixed with oxygen and the patient is allowed to breathe the mixture. After a period, a sufficient level of the anesthetic agent is obtained in the blood and anesthesia is produced. In general, anesthesia can be well controlled with these agents because the concentration of the agent in the blood can be increased or decreased easily by either increasing or decreasing the concentration of the agent in the air the patient is breathing. It is relatively uncommon for a patient to have an allergic reaction to one of the inhalation general anesthetic agents. However, the side effects of some of these agents can be quite serious. There is rapid recovery for the patient when this type of agent is used. That is, when the patient is no longer allowed to breathe the agent, the depression of the central nervous system quickly disappears.
(1) Nitrous oxide. Nitrous oxide is a gas supplied in blue metal cylinders. Nitrous oxide is commonly referred to as laughing gas. Although nitrous oxide is a safe general anesthetic, it is relatively weak in terms of producing anesthesia and muscle relaxation. Consequently, nitrous oxide is often used in conjunction with other agents. Nitrous oxide is often used in dental surgery and in obstetrical practice during delivery.
(2) Halothane (Fluothane®). Halothane is a volatile liquid inhalation anesthetic. It is one of the most widely used general anesthetics. Since halothane does not produce potent analgesia and muscle relaxation, other agents are sometimes administered with halothane on an as-needed basis. Halothane has popularity because it is nonexplosive, rapid acting, pleasant smelling, and is compatible with other drugs.
(3) Enflurane (Erthrane®. Enflurane is a volatile liquid inhalation anesthetic with many of the properties of halothane. It produces greater muscle relaxation than halothane, but like halothane, it is a poor analgesic.
b. Intravenous Agents. Intravenous general anesthetics are sterile solutions intended to be administered into the patient's circulatory system. Intravenous anesthetic agents do produce loss of consciousness; however, most of these agents lack the ability to produce complete analgesia. In general, the level of anesthesia is more difficult to control with intravenous anesthetics than with inhalation anesthetics.
(1) Thiopental sodium (Pentothal®) Thiopental sodium is an ultrashort acting barbiturate. That is, this agent acts very quickly to produce anesthesia. Sometimes this agent is used alone for minor surgical procedures. In other cases, the drug is used to initiate anesthesia. Then, other anesthetic agents are used to maintain the anesthesia. Thiopental sodium is a NOTE Q item. That is, it is a controlled substance.
(2) Fentanyl (Sublimaze®) and droperidol (Innovar®). This agent is an intravenously administered product, which combines the narcotic analgesic effect of fentanyl with the sedative and antiemetic effects of droperidol. This agent produces a semiconscious state in the patient, and it is used in types of surgery in which the surgeon needs the cooperation of the patient. Innovar is usually used in combination with nitrous oxide because of its slow induction. Innovar may also be used for various diagnostic procedures. This product is a controlled substance (Note R item).
(3) Ketamine (Ketalar®) is a nonbarbiturate anesthetic that can be administered either intravenously or intramuscularly. Ketamine produces a dissociative type anesthesia in which the patient becomes detached mentally from the environment. Ketamine may be used for induction anesthesia or for diagnostic or minor surgical procedures in children.
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