Volatile anesthetic agents

See also Anesthetic Agents Volatile Organic Compounds (VOC). 

Volatile anesthetic agents - Close perioperative monitoring is recommended in patients undergoing general anesthesia who are on amiodarone therapy as they may be more sensitive to the myocardial depressant and conduction effects of halogenated inhalational anesthetics. 

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. 

No difference has been observed in the interactions of the two enantiomers of isoflurane with hpid bilayers. But the (5)-enantiomer of isoflurane is two times more active than the (7 )-enantiomer toward a calcium channel receptor, that is sensitive to volatile anesthetic agents, while nodifference in activity has been observed toward an anesthetic nonsensitive receptor. The (5)-enantiomer of isoflurane is also more active than the (R)-enantiomer toward acetylcholine nicotinic receptor and GABA receptor. These data strongly suggest that fluoroethers interact not only with cerebral membranous lipids but also with receptor proteins. 

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. 

No studies were located in humans or animals regarding the absorption of inhaled 1,1-dichloroethane. However, its use as a gaseous anesthetic agent in humans provides evidence of its absorption. Furthermore, the volatile and lipophilic nature of 1,1-dichloroethane favors pulmonary absorption. Structurally related chlorinated aliphatics and gaseous anesthetics are known to be rapidly and extensively absorbed from the lung. The total amount absorbed from the lungs will be directly proportional to the concentration in inspired air, the duration of exposure, the blood/air partition coefficient of 1,1-dichloroethane, its solubility in tissues, and the individual s ventilation rate and cardiac output. One of the most important factors controlling pulmonary absorption is the blood/air partition coefficient of the chemical. The concentration of the chemical and the duration of exposure are also important determinants of the extent of systemic absorption. 

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. 

In patients who have been exposed to volatile anesthetic agents for 30 minutes or so there is an increase in potency of pipecuronium to such an extent that doses can be reduced by about one-third with isoflurane (16) or... 

The main applications of enantiomeric separation by GC concern precise determination of enantiomeric composition of chiral research chemicals, drugs, intermediates, metabolites, pesticides, flavors and fragrances, etc. CHIRBASE, a database of chiral compounds, provides comprehensive structural, experimental, and bibliographic information on successful and unsuccessful chiral separations, and rule sets for each CSP and information about the processes of chiral separations. According to CHIRBASE, an appropriate CSP is available for almost every racemic mixture of compounds ranging form apolar to polar. Some 22,000 separations of enantiomers, involving 5,500 basic chiral compounds and documented in 2,200 publications, have been achieved by GC. This method is particularly suitable for volatile compounds such as inhalation anesthetic agents, e.g., enflurane, isoflurane, desflurane, and racemic a-ionone. 

Although gas chromatography (GC) is a well established method for the analytical determination of enantiomeric purity, the number of preparative applications is quite limited. Most of these preparative applications by gas chromatography have been recently reviewed [181] and were performed on a relatively small scale. The method is particularly suited for volatile compounds such as the inhalation anesthetic agents enflurane, isoflurane and desflurane [182] and it has also been recently applied to the resolution of racemic a-ionone [183]. The feasibility of separating the enantiomers by gas phase simulated moving bed chromatography has also been demonstrated for the first time and was applied to the anesthetic enflurane (Fig. 6.18) [184]. However, the productivity of the system was relatively low. 

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. 

The minimum alveolar concentration (MAC) is defined as the conoentration at 1 atmosphere of anesthetic in the alveoli that is required to produce immobility in 50% of adult patients subjected to a surgical incision. A further inorease to 1.3 MAC frequently will oause immobility in 99% of patients. At equilibrium, the conoentration (or partial pressure) of an anesthetic in the alveoli is equal to that in the brain, and it is this concentration in the brain that probably most olosely reflects the concentration at the site responsible for the anesthetio aotions. Thus, the MAC often is used as a measure of the potenoy of individual anesthetic agents. The MAC of many of the volatile and gaseous anesthetics in use today is shown in Table 18.2. 

The structure and physical properties of the volatile anesthetics are given in Table 18.5. Toxic degradation products are formed by reaction of the anesthetic agent with the... 

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