An inhaled anaesthetic gas
Isoflurane
An older inhaled anaesthetic used mainly to keep people asleep during surgery; pungent, so not used to send people to sleep by mask.
What is Isoflurane?
Isoflurane is an inhaled general anaesthetic, breathed in as a vapour to keep people asleep during surgery. It is given by an anaesthetist, who monitors breathing, heart rate, blood pressure and consciousness. It is an older, reliable and inexpensive agent used mainly to maintain anaesthesia once a person is already asleep. Because it is pungent and can irritate the airway, it is not pleasant to breathe and is not usually used to send people to sleep by mask. Like all anaesthetic vapours, it can lower blood pressure and, very rarely, trigger the inherited reaction malignant hyperthermia.
Education and reference only. This is a plain-language guide to Isoflurane — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Isoflurane is a general anaesthetic given as a vapour that the person breathes in, mixed with oxygen, usually through a breathing tube. It is given and supervised by anaesthetists, who monitor breathing, heart rate, blood pressure and consciousness. It is an older, long-established and inexpensive inhaled agent used mainly to keep people asleep during surgery (this is called maintenance) after they have been sent to sleep by another method. Because it has a sharp, pungent smell that can irritate the airway, it is not generally used to send people to sleep by breathing it from a mask.
How it works
Isoflurane is absorbed through the lungs into the blood and reaches the brain, where it maintains general anaesthesia by keeping awareness switched off. The anaesthetist adjusts how much is breathed to control the depth of sleep, and it wears off as it is breathed back out. Its pungency means it tends to irritate the airway and can cause coughing or breath-holding if used to send someone to sleep, which is why a gentler agent is usually chosen for that step and isoflurane is reserved for keeping the person asleep.
Company & origin
Originated / developed by: Generic (long-established).
An older, well-established inhaled anaesthetic used in the UK mainly to keep people asleep during surgery.
Practical use
How to take Isoflurane
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Isoflurane is breathed in as a vapour, given and adjusted by an anaesthetist, usually through a breathing tube; it is not something you take yourself.
- Tell the anaesthetic team about your medicines, allergies and any personal or family history of problems with anaesthesia beforehand.
- You will usually be sent to sleep by another method first, then kept asleep with isoflurane.
- You will be monitored throughout, with the depth of anaesthesia adjusted by changing how much you breathe.
- Tell staff if you feel sick or muddled on waking, as this can occur, settles, and can be treated.
Weighing it up
Advantages & disadvantages of Isoflurane
Advantages
- A reliable, well-understood agent for keeping people asleep during surgery.
- Inexpensive, with a long track record of safe use.
- Allows the depth of anaesthesia to be adjusted easily during an operation.
Disadvantages
- Pungent and irritating to breathe, so it is not suitable for sending people to sleep by mask.
- Can lower blood pressure, which the anaesthetic team manages.
- Like all anaesthetic vapours, it can very rarely trigger malignant hyperthermia in susceptible people.
Practical use
Good to know
Isoflurane is given by an anaesthetist who monitors you closely and adjusts the amount you breathe. Its strengths are that it is reliable, well understood from long use, and inexpensive, which keeps it in regular use for maintaining anaesthesia. Its main drawback is that it is pungent and irritating to breathe, so it is not used to send people to sleep by mask, only to keep them asleep once they already are. Like other anaesthetic vapours, it can lower blood pressure, which the team manages, and it can, very rarely, trigger the serious inherited reaction malignant hyperthermia; anaesthetists are trained to recognise and treat this and will ask about any family history of anaesthetic problems.
Who should not take it / use with caution
- People with a personal or family history of malignant hyperthermia must not be given isoflurane or other triggering anaesthetics.
- It is generally not used to send people to sleep by mask because it is too irritating to breathe.
- As with all anaesthetics, the team must know about any previous serious reactions to anaesthesia.
Monitoring
- Continuous monitoring of breathing, oxygen levels, the amount of vapour breathed, heart rate, blood pressure and consciousness.
- Watching closely for any early signs of malignant hyperthermia, such as a rising temperature.
- Reviewing recovery, including any nausea or confusion, after the anaesthetic.
Side effects
- A fall in blood pressure, managed by the anaesthetic team.
- Coughing or breath-holding if breathed in while still awake, which is why it is not used for gas induction.
- Nausea or confusion on waking, and very rarely the serious inherited reaction malignant hyperthermia.
Key interactions
- Its effects add to those of other anaesthetics, sedatives and strong painkillers; the team balances all of these.
- Care is taken alongside medicines that affect blood pressure or heart rate.
- The anaesthetic team manages its use with muscle relaxants and other agents during surgery.
Available as: Vapour breathed in through a breathing tube, given by an anaesthetist in hospital.
Answers
Isoflurane: frequently asked questions
What is isoflurane used for?
It is mainly used to keep people asleep during surgery after they have been sent to sleep by another method.
Why isn't it used to send me to sleep by mask?
Isoflurane is pungent and irritating to breathe, which can cause coughing, so a gentler agent is usually chosen to send you to sleep.
Is isoflurane an old anaesthetic?
Yes, it is an older, well-established agent that remains in regular use because it is reliable and inexpensive.
What is malignant hyperthermia?
It is a very rare, serious inherited reaction to certain anaesthetics in which temperature and muscle activity rise dangerously; anaesthetists are trained to recognise and treat it.
Will I be aware during my operation?
No. Isoflurane keeps you asleep, and the anaesthetist monitors you throughout to keep you at the right depth.
Authoritative sources
- BNF
- NICE CKS
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