There are many inhalational anaesthetic agents. These include:
- Sevoflurane
- Methoxlyflurane
- Halothane
- Isoflurane
- Enflurane
- Ether
- Desflurane
Modern anaesthetic agents are very potent. All are liquids at room temperature and vaporise readily, so they must be delivered using a purpose-made vaporiser. The concentration of anaesthetic needed to induce and maintain anaesthesia varies between the different agents.
The most popular agents
The most widely used agents are Isoflurane and Sevoflurane.
- Ether is no longer available as an anaesthetic agent in the EU or North America and since it is unpleasant for animals to inhale and also poses a safety risk (as it forms explosive mixtures with air or oxygen) it should not be used.
- Halothane was a suitable anaesthetic, but it is no longer available commercially in many countries.
- Similarly, Methoxyflurane is now unavailable in most countries.
- Desflurane could be used for anaesthesia of laboratory animals, but it is significantly more expensive than the other agents that are available. It provides even more rapid onset and recovery from anaesthesia than do Sevoflurane and Isoflurane.
Isoflurane
Isoflurane produces rapid induction and recovery from anaesthesia, and the depth of anaesthesia can be altered easily and rapidly. It is non-irritant, non-explosive and non-flammable.
Isoflurane produces moderate respiratory and cardiovascular system depression. Its pungent odour has been reported to cause breath holding during induction in children, but this does not seem a significant problem in most species, except the rabbit. It appears to be irritant in guinea pigs, often causing signs of distress on induction in this species.
The main advantage of using Isoflurane in experimental animals is that it undergoes almost no bio-transformation and is almost completely eliminated in exhaled air. This suggests that there will be little effect on liver microsomal enzymes and, hence, minimal interference in drug metabolism or toxicology studies
Sevoflurane
Sevoflurane produces even more rapid induction and recovery from anaesthesia than does Isoflurane, and the depth of anaesthesia can be altered very easily and rapidly. It is non-explosive and non-flammable.
Sevoflurane is much less pungent than other agents, and mask induction is well tolerated in many species (except rabbits and guinea pigs).
The main advantage of sevoflurane is the even greater ease of matching the depth of anaesthesia to the degree of surgical stimulation, coupled with very rapid and smooth recovery. If undisturbed, many animals recover from sevoflurane without a period of involuntary excitement.
Desflurane
Induction of and recovery from anaesthesia with Desflurane is the most rapid of the volatile anaesthetics, and it is relatively non-irritant.
Desflurane undergoes the least degree of metabolism of modern inhalant anaesthetics. It requires a pressurised, temperature- controlled vaporiser because of its very low boiling point.
Desflurane has not yet been widely used in either veterinary clinical practice or laboratory species.