Inhalation anaesthetics isoflurane

What are the advantages of the inhalation anaesthetics isoflurane, desflurane and sevoflurane over the older ones ether, chloroform and halothane ... 

Ti LK, Pua HL, Lee XL. Single vital capacity inhalational anaesthetic induction in adults—isoflurane vs sevoflurane. Can J Anaesth 1998 45(10) 949-53. 

Inhalation anaesthetics are either gases or volatile liquids. Apart from nitrous oxide, which is still widely used, earlier inhalation anaesthetics are no longer used. Ether is not suitable because it is explosive and irritant to the respiratory tract. Chloroform cannot be used because it is toxic to the liver. Inhalation anaesthetics currently in use are the volatile liquids halothane (since 1956) and more recently isoflurane, desflurane and sevoflurane and nitrous oxide gas. 

Inhalation anaesthetics are gases or volatile liquids. Nitrous oxide and isoflurane are commonly used. 

In a study in 20 healthy patients the concurrent use of either halothane or isoflurane increased the serum concentrations of propofol by about 20% during the maintenance of general anaesthesia. The US manufacturer of propofol notes that inhalational anaesthetics (such as halothane or isoflurane) would be expected to increase the effects of propofol. The man-... 

It used to be thought that beta bloekers should be withdrawn from patients before surgery beeause of the risk that their cardiac depressant effects would be additive with those of inhalational anaesthetics, resulting in a reduction in cardiac output and blood pressure, but it seems that any effect depends on the anaesthetic used. It has been suggested that the ranking order of compatibility (from the least to the most compatible with beta blockers) is as follows methoxyflurane, ether, cyclopropane, trichloroethylene, enflurane, halothane, isoflurane. ... 

Patients anaesthetised with inhalational anaesthetics (particularly cyclopropane and halothane, and to a lesser extent desflurane, enflurane, ether, isoflurane, methoxyflurane, and sevoflurane) can develop cardiac arrhythmias if they are given adrenaline (epinephrine) or noradrenaline (norepinephrine), unless the dosages are very low. Children appear to be less susceptible to this interaction. file addition of adrenaline to intrathecal tetracaine enhances the sedative effects of propofol. 

The effects of neuromuscular blockers are increased by inhalational anaesthetics, the greater the dosage of the anaesthetic the greater the increase in blockade. In broad terms desflurane, ether, enflurane, isoflurane, methoxyllurane and sevoflurane have a greater effect than halothane, which is more potent than cyclopropane, whereas nitrous oxide appears not to interact significantly with competitive blockers. " ... 

Two methods of anaesthesia are currently in use, the application of inhaled gaseous or volatile anaesthetics such as halothane, sevoflurane and isoflurane to maintain a level of anaesthesia. Older compounds in this category include nitrous oxide and chloroform. 

An increase in alveolar ventilation will cause an increase in the alveolar concentration of inhaled agent when semi-closed or open breathing circuits are employed. The effect is most noticeable with a highly soluble anaesthetic, such as diethyl ether. With modern, relatively insoluble agents, such as isoflurane and desflurane, the effects of changes in alveolar ventilation are less pronounced. 

Halothane was introduced into clinical practice in 1956. It was not the first fluorinated anaesthetic— fluoroxene (Fluoromar) holds that distinction—but it was the first to achieve widespread acceptability. Halothane is a fluorinated alkane 1-bromo, 1-chloro -2,2,2-trifluoroethane (Figure 3.2). It has a characteristic odour, similar to chloroform, and requires a stabiliser, thymol (0.01%), to prevent degradation by light. Halothane has a blood/gas partition coefficient of 2.4 able 3.2) but its lack of irritant qualities makes possible the use of relatively high inspired concentrations (2-4%). For that reason, inhalation induction is characteristically smooth and rapid. Compared to sevoflurane, and possibly isoflurane, recovery from halothane anaesthesia is delayed. 

Isoflurane is a volatile colourless liquid, which is not flanamable at normal anaesthetic concentrations. It is relatively insoluble, and has a lower blood/gas coefficient than halothane or enflurane, which allows rapid adjustment of the depth of anaesthesia. It has a pungent odour and can cause bronchial irritation, which makes inhalational induction unpleasant. Isoflurane is minimally metabolised (0.2%), and none of the breakdown products has been related to anaesthetic toxicity. 

Sevoflurane is a chemical analogue of isoflurane. It is less chemically stable than the other volatile anaesthetics in current use. About 3% is metabolised in the body and it is degraded by contact with carbon dioxide absorbents, such as soda lime. The reaction with soda lime causes the formation of a vinyl ether (Compound A), which may be nephrotoxic. Sevoflurane is less soluble than isoflurane and is very pleasant to breathe, which makes it an excellent choice for inhalational induction of anaesthesia, particularly in children. The respiratory and cardiovascular effects of sevoflurane are very similar to isoflurane. 

Gases of interest are nitrous oxide and the inhalation vapours (or volatile halogenated anaesthetics) such as halothane (CF3CHBrCl), isoflurane (CHF2OCHCICF3) and enflurane (CHCIFCF2OCHF2). In this section electrochemical studies on nitrous oxide, halothane and isoflurane will be discussed. 

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