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.
The lowest effective dose should be administered, and, as with all anaesthetics, the correct dose is the minimum that achieves the desired anaesthetic.
Although anaesthetics have a low potential for damage to the atmosphere, it is good practice to use charcoal filters with scavenging equipment, rather than to discharge them into the air.
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.
Drug interactions/compatibilities: Propofol has been demonstrated in the literature to be compatible with isoflurane anaesthesia in swans.
Interactions: 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 (eg. 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.
Drug interactions/ compatibilities: 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 AND FERRETS
Isoflurane has been recommended for anaesthesia of a wide variety of ‘small mammals’ (eg. rats, mouse, hamster, chinchilla, gerbil, guinea pig and ferret).
The MAC for mice has been cited as 1.34%, and for the rat as 1.38%, 1.46% and 2.4%.
Drug interactions/ compatibilities: 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.
Species | MAC (%) | Induction (%) | Maintenance (%) | Recovery |
Horse | 1.31 | 3.0 - 5.0 (foals) | 1.5 - 2.5 | Smooth and rapid |
Dog | 1.28 | Up to 5.0 | 1.5 - 2.5 | Smooth and rapid |
Cat | 1.63 | Up to 4.0 | 1.5 - 3 | Smooth and rapid |
Ornamental birds | See posology | 3.0 - 5.0 | See posology | Smooth and rapid |
Reptiles | See posology | 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 |
PIGS (CASTRATION OF PIGLETS UP TO 7 DAYS OF AGE):
For piglets (up to 7 days of age)
Isoflurane concentration of up to 5Vol%, with oxygen as carrier gas with a flow rate of 2L/min.
The MAC value for isoflurane in pigs is 1.41-2.00%
Premedication:
Post-operative pain must be controlled by the timely parenteral administration of appropriate analgesics before the induction of anaesthesia.
Induction:
Isoflurane concentrations of up to 5 Vol % are used for the anaesthetic induction (with oxygen as carrier gas with a flow rate of 2L/min). After 70- 90 seconds a sufficient depth of anaesthesia is generally achieved. The actual duration required in practice depends on many variables. It is therefore imperative that the depth of anaesthesia be clinically checked by means of reflexes in each individual animal before castration is started. The inter- and dew claw reflexes are particularly suitable.
The castration may only be carried out under controlled supply of isoflurane, using a suitable inhalation device tested for the purpose. For the individual animal, it must be ensured that the mask used is leak-proof and that the exhaust air is filtered and discharged into a room (e.g. outdoors) where a sufficient rate of air exchange is achieved.
The product should only be used for uncomplicated castration procedures that are anticipated to be short in duration (maximum of 120 seconds for the entire procedure from the induction of anaesthesia to the end of castration of a piglet).
Recovery:
Recovery is usually smooth and rapid
Species | MAC (%) | Induction (%) | Maintenance (%) | Recovery |
Horse | 1.31 | 3.0 – 5.0 (foals) | 1.5 – 2.5 | Smooth and rapid |
Dog | 1.28 | Up to 5.0 | 1.5 – 2.5 | Smooth and rapid |
Cat | 1.63 | Up to 4.0 | 1.5 – 3.0 | Smooth and rapid |
Ornamental birds | See posology | 3.0 – 5.0 | See posology | Smooth and rapid |
Reptiles | See posology | 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 |
Pigs (piglets up to 7 days of age) | 1.41-2.00 | Up to 5.0 | | Smooth and rapid |