Oxidation anesthetic agents

Ethylene is slightly more potent as an anesthetic than nitrous oxide, and the smell of ethylene causes choking. Diffusion through the alveolar membrane is sufficiendy rapid for equilibrium to be estabUshed between the alveolar and the pulmonary capillary blood with a single exposure. Ethylene is held both ia cells and ia plasma ia simple physical solution. The Hpoid stroma of the red blood cells absorb ethylene, but it does not combine with hemoglobin. The concentration ia the blood is 1.4 mg/mL when ethylene is used by itself for anesthesia. However, ia the 1990s it is not used as an anesthetic agent. 

Uses. As anesthetic agent as foaming agent for whipped cream as oxidant for organic compounds in rocket fuels... 

Usually various anesthetic agents are combined to increase efficacy and at the same time decrease toxicity and shorten the time to recovery. For example induction of anesthesia is obtained with an intravenous agent with a rapid onset of action like thiopentone and then anesthesia is maintained with a nitrous oxide/oxygen mixture in combination with halothane or a comparable volatile anesthetic. 

Contrast-enhanced MRI with Gd-DTPA has been applied to the evaluation of several compounds in man, some focusing on the hemodynamic effects of the drugs on cerebral blood volumes. Kolbtisch and others compared the anesthetic agents nitrous oxide and sevofhirane, noting them to produce compound-specific patterns of diffuse increases in cerebral blood volume (Kolbitsch et al., 2001). Intravenous cocaine, on the other hand, was observed to produce dose-dependent vasoconstriction of cerebral blood vessels (Kaufman et ul., 1998). 

Depth of anesthesia is determined by the concentration of anesthetic agent that reaches the brain. Brain concentration, in turn, depends on the solubility and transport of the anesthetic agent in the bloodstream and on its partial pressure in inhaled air. Anesthetic potency is usually expressed as a minimum alveolar concentration (MAC), defined as the percent concentration of anesthetic in inhaled air that results in anesthesia in 50% of patients. As shown in Table 9.6, nitrous oxide, N2O, is the least potent of the common anesthetics. Fewer than 50% of patients are immobilized by breathing an 80 20 mix of nitrous oxide and oxygen. Methoxyflurane is the most potent agent a partial pressure of only 1.2 mm Hg is sufficient to anesthetize 50% of patients, and a partial pressure of 1.4 mm Hg will anesthetize 95%. 

Inhaled anesthetics currently in use include halo-genated volatile liquids such as desflurane, enflurane, halothane, isoflurane, methoxyflurane, and sevoflurane (Table 11-1). These volatile liquids are all chemically similar, but newer agents such as desflurane and sevoflurane are often used preferentially because they permit a more rapid onset, a faster recovery, and better control during anesthesia compared to older agents such as halothane.915 These volatile liquids likewise represent the primary form of inhaled anesthetics. The only gaseous anesthetic currently in widespread use is nitrous oxide, which is usually reserved for relatively short-term procedures (e.g., tooth extractions). Earlier inhaled anesthetics, such as ether, chloroform, and cyclopropane, are not currently used because they are explosive in nature or produce toxic effects that do not occur with the more modern anesthetic agents. 

Postoperatively, the anesthesiologist withdraws the anesthetic mixture and monitors the immediate return of the patient to consciousness. For most anesthetic agents, recovery is the reverse of induction that is, redistribution from the site of action rather than metabolism underlies recovery. The anesthesiologist continues to monitor the patient to be sure that there are no delayed toxic reactions, for example, diffusion hypoxia for nitrous oxide, and hepato-toxicity with halogenated hydrocarbons. 

Chloroform, which was discovered in 1833, was a third compound whose intoxicating properties were discovered before it was used as an anesthetic agent. Chloroform addiction was easily concealed, with addicts sniffing from a handkerchief throughout the day. The use of nitrous oxide, ether, and chloroform continue to a lesser extent today, occuring in... 

This patient had multiple risk factors for anesthesia-induced hepatitis, including obesity, middle age, female sex, a history of drug allergies, and multiple exposures to fluorinated anesthetic agents. Desflurane has a very low rate of hepatic oxidative metabolism (0.02 versus 20% for halothane), and is considered to be one of the safest volatile agents as far as hepatotoxicity is concerned. Nevertheless, this case shows that it can cause severe hepatotoxicity. 

A selective inhibitor of neuronal nitric oxide synthase, 7-nitroindazole, prolonged the duration of methohexital-induced narcosis in rats (3). This finding is consistent with previous work showing potentiation of anesthetic agents by non-specific nitric oxide synthase inhibitors. 

The inhalation anesthetics in use arc halothanc. enfluranc. isofluranc. methoxyriurane. sevullurane. desfluranc. and nitrous oxide. Older agents such as ethylene and cyclopropane are obsolete because of a fundamental chemical prop-eny—they are explo.sive and flammable when mixed with oxygen. This adds an unacceptable level uf danger tu the production of anesthesia. 

Initial metabolism of inhaled anesthetics involves the cytochrome P-450 enzymes, located in the mi-crosomes of the liver and the kidneys [30, 31], most commonly by oxidation. Some agents, i.e. halothane, may under certain circumstances, also undergo reduction. In addition to their primary metabolism, some agents, for instance sevoflurane, also undergo phase II conjugation reactions prior to excretion. 

A multigas monitor for anesthesia was reported by Engstrom of Sweden. The Engstrom EMMA is an inexpensive, on-line monitor for volatile anesthetic agents and can measure levels of halothane, enflurane, isoflurane, trichloroethylene, and methoxyflurane in any type of breathing circuit breath by breath. It is reported that no clinically significant interference was realized from nitrous oxide and water has only a small effect. 

Ketamine is used as a sole anesthetic agent for diagnostic and surgical procedures that do not require skeletal muscle relaxation. It is best suited for short procedures, but it can be used with additional doses for longer procedures. It is also used for the induction of anesthesia prior to the administration of other general anesthetics and to supplement low-potency agents, such as nitrous oxide. 

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