Isoflurane is a potent anaesthetic agent of low solubility, allowing rapid changes to be made to the level of anaesthesia. For this reason it should only be administered using an adequately calibrated vaporiser in an appropriate anaesthetic circuit. Isoflurane should be used to effect by a suitably skilled anaesthetist. Administration may be performed in oxygen only or in a mixture of nitrous oxide and oxygen at a ratio of 2:1.

Minimum alveolar concentration The MAC value of isoflurane is 1.28% in the dog and 1.63% in the cat.

Premedication A preanaesthetic regime should be chosen to suit the patient. Isoflurane use has been shown to be compatible with common preanaesthetic agents such as acepromazine, opioids, benzodiazepines, alpha-2-adrenoreceptor agonists (and their reversal agents) and anticholinergics.

Induction of anaesthesia Dogs and cats may be induced by inspired isoflurane concentrations between 2 and 4%. Premedication and/or concurrent use of nitrous oxide reduces the concentration of isoflurane required.

If anaesthesia is induced with an injectable agent, an initial isoflurane concentration slightly above that required for maintenance should usually be administered to aid the transition to gaseous anaesthesia.

Maintenance of anaesthesia As a general rule, concentrations of around 1.5 MAC are necessary for anaesthetic maintenance. In practice, levels of 1.5-2.5% in the dog and 1.5-3.0% in the cat are used. Again, premedication and/or concurrent use of nitrous oxide reduces the concentration of isoflurane required.