Isoflurane, sold under the brand name Forane among others, is a halogenated ether used as a general anesthetic. It can be used to start or maintain anesthesia; however, other medications are often used to start anesthesia, due to airway irritation with isoflurane. Isoflurane is a inhalational anesthetic given via inhalation. It is on the World Health Organization's List of Essential Medicines.

Medical uses

Isoflurane is indicated for induction and maintenance of general anesthesia. its pungency can irritate the respiratory system, negating any possible advantage conferred by its physical properties. Thus, it is mostly used in general anesthesia as a maintenance agent after induction of general anesthesia with an intravenous agent such as thiopentone or propofol.

Mechanism of action

Similar to many general anesthetics, the exact mechanism of the action has not been clearly delineated. Isoflurane reduces pain sensitivity (analgesia) and relaxes muscles. Isoflurane likely binds to GABA, glutamate and glycine receptors, but has different effects on each receptor. Isoflurane acts as a positive allosteric modulator of the GABA<sub>A</sub> receptor in electrophysiology studies of neurons and recombinant receptors. It potentiates glycine receptor activity, which decreases motor function. It inhibits receptor activity in the NMDA glutamate receptor subtypes. Isoflurane inhibits conduction in activated potassium channels. Isoflurane also affects intracellular molecules. It inhibits plasma membrane calcium ATPases (PMCAs) which affects membrane fluidity by hindering the flow of (calcium ions) out across the membrane, this in turn affects neuron depolarization. It binds to the D subunit of ATP synthase and NADH dehydrogenase.

General anaesthesia with isoflurane reduces plasma endocannabinoid AEA concentrations, and this could be a consequence of stress reduction after loss of consciousness.

Adverse effects

Side effects of isoflurane include a decreased ability to breathe (respiratory depression), low blood pressure, and an irregular heartbeat. Whether these concerns occur in humans is unclear. This area is important as "some of the commonly used inhaled anesthetics may cause brain damage that accelerates the onset of Alzheimer's disease".

Anesthetic physical properties

Isoflurane has a minimum alveolar concentration (MAC) of 1.15 vol %. The blood/gas partition coefficient is 1.4, and the oil/gas partition coefficient is 98. Its vapor pressure at is . It is non-combustible but can give off irritable and toxic fumes when exposed to flame. Its name comes from being a structural isomer of enflurane, hence they have the same empirical formula.

Environment

The average lifetime of isoflurane in the atmosphere is 3.2 years, its global warming potential is 510 (times greater than carbon dioxide) and yearly emissions as of 2015 were 880 tons.

Veterinary use

Isoflurane is used for the induction and maintenance of general anesthesia in horses and dogs. It is also used on koalas.

Isoflurane is also commonly used in lab settings as general anesthesia for work on laboratory mice and rats.

References

  • - 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether
  • - 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether as an anesthetic agent