Anesthetics Essays (842 words) - General Anesthetics,

Anesthetics Introduction Anesthetics are depressant drugs that cause a total or partial loss of the sense of pain. The effect an anesthetic has on the body depends on several factors. What type of anesthetic is used determines the effect along with the dosage and a person (or animals) body weight. The word anesthesia was first introduced by Oliver Wendell Holmes in 1846 about four weeks after the first demonstration of ether anesthesia at the Massachusetts General Hospital. Ether was the first type of anesthesia used and was demonstrated as a means of allowing a patient to be unconscious and free from surgical pain. Stages of Anesthesia Stage one is known as analgesia and results from an increase in circulating endorphins. There is a mild depression of cortical centers and this type of anesthesia is also known as twilight sleep. Stage two is characterized by a loss of consciousness. It is a critical period because delirium and increased involuntary activity, as well as hypersecretion, can occur. It is best to get through stage one and stage two as quickly as possible and this stage, along with stage one, are known as induction. Stage three is the stage of anesthesia known as surgical anesthesia, and most surgical procedures are performed in this stage. There is usually a loss of spinal reflexes and muscle tone. Stage four is an undesirable stage and is characterized by respiratory depression and other manifestations of overdose. Most general anesthetics are non-specific agents, meaning that their activity depends on their lipid solubility rather that their structure. Inhaled and exhaled gas containing the agents equilibrates with the lung tissue, and then with the blood. In the brain, the agent equilibrates between the blood and neural tissue, depressing neurons and causing the pharmacological effect. Types of Anesthesia Though ether was the first type of anesthesia, there are now many different types. Ether, along with chloroform, are known as the anesthetics from hell because they have all of the negative traits of this class of drugs. Ethyl ether is potent and fairly safe, but it is also flammable and explosive. It forms peroxides and it produces a very unpleasant induction phase. Also, it is irritating and causes nausea and vomiting during recovery. Chloroform is just as potent and relaxes the skeletal muscle fairly effectively, but has a narrow margin of safety, produces liver and kidney toxicity, and has been known to fairly frequently cause cardiac arrest. In addition, it can also cause severe hypertension. Another type of general anesthetic agent is non halogenated hydrocarbons. All of these work well and the longer the chain, the higher the potency. However, these have a tendency to produce cardiovascular toxicity. Cyclopropane is the only one still in use and is explosive. Ethyl ether was the first anesthetic, but is not used anymore because of its negative effects, but other ethers came along throughout the past century and a half as well. Like hydrocarbons, the longer the chain, the more potent the anesthetic. However, the longer the chain, the higher the toxicity. Also having a longer chain reduces induction time. Ethyl ether is very rarely used and divinyl ether is explosive and produces deep anesthesia too quickly. Another type of general anesthetic is halogenated hydrocarbons. When a halogen is added to an anesthesia, flammability is greatly reduced, and in some cases, eliminated. In addition, the halogen can also add potency. Depending on the halogen, some of these compounds can cause arrhythmia and/or renal or hepatic toxicity. Compounds containing only bromine are usually not useful and compounds containing only chlorine are limited in use, are toxic, and can cause arrhythmia. The best of the chlorinated agents are ethyl chloride and trichloroethylene. Fluorinated hydrocarbons are the most useful general anesthetics, and were first discovered as offshoots of the nuclear weapons program. Adding a fluorine to an anesthetic decreases flammability and boiling point. It also decreases the rate of catechol- induced arrhythmia (these increase as the size of the halogen increases). Listed below are a few different types of fluorinate hydrocarbons: Halothane (Fluothane) was the first fluorinated hydrocarbon to be used. It is a poor muscle relaxant, and has some toxicity and has been shown to cause catechol- induced arrhythmia. Methoxyflurane (Penthrane) is somewhat better than the above, but still causes some arrhythmia and toxicity. It also causes a slow induction period. Enflurane (Enthrane) is a pretty good anesthetic in stage one (see topic below). Isoflurane (Forane) is the best general anesthetic found so far and has no common ill effects. Another type of general anesthetics is nitrous oxide. This is the least toxic anesthetic, but is also the least potent. It causes good analgesia. but is a poor muscle relaxant. Ketamine hydrochloride is also