The delivered concentration of isoflurane must be regulated accurately. Vaporisers specially calibrated for the agent should be used.

Isoflurane may be vaporised from a flow-over vaporiser specifically calibrated for isoflurane. Vaporisers delivering a saturated vapour which is then diluted (flow-through vaporisers) may also be used. Levels of anaesthesia may be altered rapidly and easily. Isoflurane may be administered in oxygen or oxygen/nitrous oxide mixtures.

The potency of inhalation anaesthetics is expressed by their required Minimum Alveolar Concentration (MAC) which prevents gross purposeful movements in response to a pain stimulus in 50% of the animals. For adult dogs, this MAC for isoflurane is 1.28; for cats it is 1.63; and for horses it is 1.31.

Healthy dogs, cats and horses should not receive food 8 to 12 hours before anaesthesia. Water should be allowed by free choice. Animals should be examined clinically before anaesthesia. Other factors such as age, pre-existing disease, medication and surgical sites should also be considered before using isoflurane.

Depending upon the patient status, a short-acting barbiturate or an anticholinergic, a tranquilliser or a muscle relaxant may be used to avert excitement during induction (see interactions).

Acepromazine or xylazine can be used as preanaesthetic agents, while in certain patients an anticholinergic may also be indicated.

Following a barbiturate anaesthetic dose, mask induction using inspired concentrations of 2.0-2.5% isoflurane alone with oxygen is usually employed. Pure mask induction with isoflurane alone with oxygen may require concentrations of up to 5.0% in dogs or 4.0% in cats. These concentrations can be expected to produce surgical anaesthesia within 5 to 10 minutes. Pharyngeal and laryngeal reflexes are rapidly diminished, as a result of which tracheal intubation is made easy. Intubation in cats should be performed quickly before anaesthesia lightens and the glottis closes.

Anaesthesia may be induced using intravenous administration of glyceryl guaiacolate followed by either a short acting barbiturate or ketamine hydrochloride. In unweaned foals, anaesthesia can be induced by face mask delivery of isoflurane at the maximum vaporiser concentration (5%) with an oxygen flow of 8 l/min.

The concentration of isoflurane necessary to maintain anaesthesia is less than the required concentration for induction.

Surgical anaesthesia may be maintained during surgery using a concentration of 1.5-1.8% isoflurane alone with oxygen.

Surgical anaesthesia may be maintained during surgery using a concentration of 1.5-3.0% isoflurane alone with oxygen.

After induction and intubation, isoflurane may be delivered in either 100% oxygen or oxygen/nitrous oxide mixture (1:1). At the start isoflurane concentrations in the inspired air should usually be set at the maximum level allowed by the vaporiser (4-5%). Oxygen flow rates of 13-22 ml/min/kg are used to fill the anaesthetic machine rapidly with isoflurane. The vaporiser setting should then, based on the horse's reactions, be gradually decreased to 3.5% and further down to reach the optimum concentration, to 2%, or between 1.5% and 2.5%.

Body temperature, blood pressure and respiration should be monitored during anaesthesia. These effects are dose dependent, and the anaesthetic flow should be adjusted to compensate for changes.

Consideration should be given to the analgesic requirements of the patients before recovery from anaesthesia takes place.

When used in excitable horses, consideration should be given to the administration of a sedative to cover the period of recovery from isoflurane anaesthesia.

The concentration of isoflurane must be reduced to 0% at the end of surgery to allow prompt recovery. This recovery from isoflurane anaesthesia is typically uneventful. When the administration of isoflurane has been stopped, the air passages of the patient should be ventilated several times with 100% oxygen until complete awakening.

Due to the low solubility of isoflurane in blood, rapid changes in anaesthetic depth and a rapid recovery may be seen. Isoflurane administration should therefore not be discontinued until the completion of the surgical procedure and the preparations for recovery.