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Desflurane ( 1,2,2,2-tetrafluoroethyl difluoromethyl ether) is a highly fluorinated methyl ethyl ether used for induction and maintenance of general anesthesia. Desflurane was developed in the 1980's and approved by the FDA in 1992 as a faster acting and clearing inhalant anesthetic compared to previously used inhalant anesthetics. Like halothane, enflurane, and isoflurane, it is a racemic mixture of ( R) and ( S) optical isomers (). Together with sevoflurane, it is gradually replacing isoflurane for human use, except in economically undeveloped areas, where its high cost precludes its use. It has the most rapid onset and offset of the volatile anesthetic drugs used for general anesthesia due to its low solubility in blood.
Some drawbacks of desflurane are its low potency, its pungency and its high cost (though at low flow fresh gas rates, the cost difference between desflurane and isoflurane appears to be insignificant). It may cause tachycardia and airway irritability when administered at concentrations greater than 10% by volume. Due to this airway irritability, desflurane is infrequently used to induce anesthesia via inhalation techniques.
Though it vaporizes very readily, it is a liquid at room temperature. Anaesthetic machines are fitted with a specialized anaesthetic vaporiser unit that heats liquid desflurane at a constant temperature and pressure. This enables the agent to be available at a constant vapor pressure, negating the effects fluctuating ambient temperatures would otherwise have on its concentration imparted into the fresh gas flow of the anesthesia machine.
Desflurane, along with enflurane and to a lesser extent isoflurane, has been shown to react with the carbon dioxide absorbent in anesthesia circuits to produce detectable levels of carbon monoxide through degradation of the anesthetic agent. The absorbent Baralyme, when dried, is most culpable for the production of carbon monoxide from desflurane degradation, although it is also seen with soda lime absorbent as well. Dry conditions in the carbon dioxide absorbent are conducive to this phenomenon, such as those resulting from high fresh gas flows.
the exact mechanism of the action of general anaesthetics has not been delineated. Inhalant anesthetics work on the central and peripheral nervous systems by blocking excitatory ion channels and enhancing the activity of inhibitory ion channels. Desflurane is known to act as a positive allosteric modulator of the [[GABAA|GABAA receptor]] and [[glycine receptor]]s, and as a negative allosteric modulator of the nicotinic acetylcholine receptor, as well as affecting other ligand-gated ion channels.
Desflurane induces a dose dependent reduction in blood pressure due to reduced systemic vascular resistance. However, rapid increases in desflurane may induce a transient sympathetic response secondary to catecholamine release. Even though it is highly pungent, it is still a bronchodilator. It reduces the ventilatory response to hypoxia and hypercapnia. Like sevoflurane, desflurane vasodilatory properties also cause it to increase intracranial pressure and cerebral blood flow. However, it reduces cerebral metabolic rate. It also promotes muscle relaxation and potentiate neuromuscular blockade at a greater level than sevoflurane.
( R)-Enantiomer | ( S)-Enantiomer |
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However unlike nitrous oxide, which is also used as an anaesthetic and remains in the atmosphere for over a century, the atmospheric lifetime of desflurane at 14.1 years is similar to methane at 12.4 years. Some argue that GWP is not a suitable metric for such SLCP, and that due to its negligible radiative forcing desflurane is not a significant part of greenhouse gas emissions from the healthcare sector.
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