Inhalation use.
Isoflurane should be administered using an accurately calibrated vaporiser in an appropriate anaesthetic circuit, since levels of anaesthesia may be altered rapidly and easily.
Isoflurane may be administered in oxygen or oxygen/nitrous oxide mixtures.
The MAC (minimal alveolar concentration in oxygen) or effective dose ED50 values and suggested concentrations given below for the target species should be used as a guide or starting point only. The actual concentrations required in practice will depend on many variables, including the concomitant use of other drugs during the anaesthetic procedure and the clinical status of the patient.
Isoflurane may be used in conjunction with other drugs commonly used in veterinary anaesthetic regimes for premedication, induction and analgesia. Some specific examples are given in the individual species information. The use of analgesia for painful procedures is consistent with good veterinary practice.
Recovery from isoflurane anaesthesia is usually smooth and rapid. The analgesic requirements of the patient should be considered before the termination of general anaesthesia.
Horse
The MAC for isoflurane in the horse is approximately 1.31%.
Premedication
Isoflurane may be used with other drugs commonly used in veterinary anaesthetic regimes. The following drugs have been found to be compatible with isoflurane: acepromazine, alfentanil, atracurium, butorphanol, detomidine, diazepam, dobutamine, dopamine, guaiphenesin, ketamine, morphine, pentazocine, pethidine, thiamylal, thiopentone and xylazine. Drugs used for premedication should be selected for the individual patient. However, the potential interactions below should be noted.
Interactions
Detomidine and xylazine have been reported to reduce the MAC for isoflurane in horses.
Induction
As it is not normally practicable to induce anaesthesia in adult horses using isoflurane, induction should be by the use of a short acting barbiturate such as thiopentone sodium, ketamine or guaiphenesin. Concentrations of 3 to 5% isoflurane may then be used to achieve the desired depth of anaesthesia in 5 to 10 minutes.
Isoflurane at a concentration of 3 to 5% in a high flow oxygen may be used for induction in foals.
Maintenance
Anaesthesia may be maintained using 1.5% to 2.5% isoflurane.
Recovery
Recovery is usually smooth and rapid.
Dog
The MAC for isoflurane in the dog is approximately 1.28%.
Premedication
Isoflurane may be used with other drugs commonly used in veterinary anaesthetic regimes. The following drugs have been found to be compatible with isoflurane: acepromazine, atropine, butorphanol, buprenorphine, bupivacaine, diazepam, dobutamine, ephedrine, epinephrine, etomidate, glycopyrrolate, ketamine, medetomidine, midazolam, methoxamine, oxymorphone, propofol, thiamylal, thiopentone and xylazine. Drugs used for premedication should be selected for the individual patient. However, the potential interactions below should be noted.
Interactions
Morphine, oxymorphone, acepromazine, medetomidine, medetomidine plus midazolam have been reported to reduce the MAC for isoflurane in dogs.
The concomitant administration of midazolam/ketamine during isoflurane anaesthesia may result in marked cardiovascular effects, particularly arterial hypotension.
The depressant effects of propanolol on myocardial contractility are reduced during isoflurane anaesthesia, indicating a moderate degree of β-receptor activity.
Induction
Induction is possible by face mask using up to 5% isoflurane, with or without premedication.
Maintenance
Anaesthesia may be maintained using 1.5% to 2.5% isoflurane.
Recovery
Recovery is usually smooth and rapid.
Cat
The MAC for isoflurane in the cat is approximately 1.63%.
Premedication
Isoflurane may be used with other drugs commonly used in veterinary anaesthetic regimes. The following drugs have been found to be compatible with isoflurane: acepromazine, atracurium, atropine, diazepam, ketamine, and oxymorphone. Drugs used for premedication should be selected for the individual patient. However, the potential interactions below should be noted.
Interactions
Intravenous administration of midazolam- butorphanol has been reported to alter several cardio-respiratory parameters in isoflurane- induced cats as has epidural fentanyl and medetomidine. Isoflurane has been shown to reduce the sensitivity of the heart to adrenaline (epinephrine).
Induction
Induction is possible by face mask using up to 4% isoflurane, with or without premedication.
Maintenance
Anaesthesia may be maintained using 1.5% to 3% isoflurane.
Recovery
Recovery is usually smooth and rapid.
Ornamental birds
Few MAC/ED50 values have been recorded. Examples are 1.34% for the Sandhill crane, 1.45% for the racing pigeon, reduced to 0.89% by the administration of midazolam, and 1.44% for cockatoos, reduced to 1.08% by the administration of butorphanol analgesic.
The use of isoflurane anaesthesia has been reported for many species, from small birds such as zebra finches, to large birds such as vultures, eagles and swans.
Interactions
Propofol has been demonstrated in the literature to be compatible with isoflurane anaesthesia in swans. Butorphanol has been reported to reduce the MAC for isoflurane in cockatoos. Midazolam has been reported to reduce the MAC for isoflurane in pigeons.
Induction: Induction with 3 to 5% isoflurane is normally rapid. Induction of anaesthesia with propofol, followed by isoflurane maintenance, has been reported for swans.
Maintenance
The maintenance dose depends on the species and individual. Generally, 2 to 3% is suitable and safe.
Only 0.6 to 1% may be needed for some stork and heron species.
Up to 4 to 5% may be needed for some vultures and eagles.
3.5 to 4% may be needed for some ducks and geese.
Generally, birds respond very rapidly to changes in concentration of isoflurane.
Recovery
Recovery is usually smooth and rapid.
Reptiles
Isoflurane is considered by several authors to be the anaesthetic of choice for many species. The literature records its use on a wide variety of reptiles (e.g. various species of lizard, tortoise, iguanas, chameleon and snakes).
The ED50 was determined in the desert iguana to be 3.14% at 35°C and 2.83% at 20°C.
Interactions
No specific publications on reptiles have reviewed compatibilities or interactions of other drugs with isoflurane anaesthesia.
Induction
Induction is usually rapid at 2 to 4% isoflurane.
Maintenance
1 to 3% is a useful concentration.
Recovery
Recovery is usually smooth and rapid.
Rats, mice, hamsters, chinchillas, gerbils, guinea pigs & ferrets
Isoflurane has been recommended for anaesthesia of a wide variety of small mammals. The MAC for mice has been cited as 1.34%, and for the rat as 1.38%, 1.46% and 2.4%.
Interactions
No specific publications on small mammals have reviewed compatibilities or interactions of other drugs with isoflurane anaesthesia.
Induction
Isoflurane concentration 2 to 3%.
Maintenance
Isoflurane concentration 0.25 to 2%.
Recovery
Recovery is usually smooth and rapid.
Summary table containing anaethesia induction and maintenance data by species
Species | MAC (%) | Induction (%) | Maintenance (%) | Recovery |
Horses | 1.31 | 3.0 - 5.0 | 1.5 - 2.5 | Smooth and rapid |
Dogs | 1.28 | Up to 5.0 | 1.5 - 2.5 | Smooth and rapid |
Cats | 1.63 | Up to 4.0 | 1.5 - 3.0 | Smooth and rapid |
Ornamental birds | See dosage | 3.0 - 5.0 | See dosage | Smooth and rapid |
Reptiles | See dosage | 2.0 - 4.0 | 1.0 - 3.0 | Smooth and rapid |
Rats, mice, hamsters, chinchillas, gerbils, guinea pigs and ferrets | 1.34 (mouse) 1.38/1.46/2.40 (rat) | 2.0 - 3.0 | 0.25 - 2.0 | Smooth and rapid |