Anaesthetic gases are an important part of modern general anaesthesia. They allow anaesthetists to maintain unconsciousness and, in some circumstances, provide analgesia during surgery and other procedures.

In UK hospitals, the main inhaled agents encountered are sevoflurane, isoflurane and nitrous oxide, while desflurane has been largely withdrawn from routine use in England because of its exceptionally high environmental impact.

It is worth noting that not all “anaesthetic gases” are gases at room temperature. Sevoflurane, isoflurane and desflurane are volatile liquids stored in bottles and converted into vapour by an anaesthetic machine. Nitrous oxide, by contrast, is supplied as a compressed/liquefied gas.

Sevoflurane

Sevoflurane is one of the principal volatile anaesthetic agents used in UK hospitals. It can be used for induction and maintenance of general anaesthesia and is particularly useful when inhalational induction is desirable, including in some children.

Advantages

A major advantage of sevoflurane is that it is relatively non-irritating to the airway. This makes it suitable for inhalational induction, where the patient breathes the anaesthetic vapour rather than receiving an intravenous induction drug.

It also has a relatively rapid onset and offset compared with older volatile agents. This allows anaesthetists to adjust the depth of anaesthesia relatively easily during an operation.

Sevoflurane is also considerably preferable to desflurane from an environmental perspective. Its global-warming impact is substantially lower, which is one reason UK hospitals have increasingly favoured it as desflurane use has been reduced.

Disadvantages

Sevoflurane is still a greenhouse gas, so it is not environmentally neutral. Anaesthetic vapour that is exhaled by the patient is normally removed through the hospital’s waste-anaesthetic-gas scavenging system, but some ultimately reaches the atmosphere.

It can also produce fluoride-containing degradation products in the anaesthetic breathing system, although modern clinical use has not generally made this a major practical limitation.

Another disadvantage is that, like all general anaesthetic agents, sevoflurane can contribute to low blood pressure and respiratory depression. Its use therefore requires continuous monitoring by appropriately trained anaesthetic staff.

Isoflurane

Isoflurane is an older volatile anaesthetic that remains clinically useful, although it is generally less favoured for routine modern anaesthesia than sevoflurane.

Advantages

Isoflurane is effective for maintaining general anaesthesia and has been used extensively for many years. It is potent, relatively inexpensive and familiar to anaesthetists.

Its long-established clinical use means there is extensive experience with the drug, including in situations where a volatile agent is required but rapid changes in anaesthetic depth are less important.

Disadvantages

The principal clinical disadvantage is its slower onset and recovery compared with some of the newer volatile agents. This can make it less attractive when rapid emergence from anaesthesia is desirable.

Isoflurane can also cause cardiovascular and respiratory depression, particularly at higher concentrations.

From an environmental perspective, isoflurane is worse than sevoflurane. Its global-warming potential is substantially higher than sevoflurane’s, although still considerably lower than that of desflurane.

Desflurane

Desflurane has historically been valued because its physical properties allow very rapid changes in anaesthetic concentration and relatively rapid emergence from anaesthesia.

However, its use in the NHS has changed dramatically because of its environmental impact.

Advantages

The main clinical advantage of desflurane is its rapid elimination from the body. This can make it useful when a particularly rapid and predictable emergence from anaesthesia is desirable.

It is also relatively easy to adjust the depth of anaesthesia rapidly because changes in the inspired concentration produce comparatively rapid changes in anaesthetic concentration in the patient.

Disadvantages

The major disadvantage today is its very high environmental impact. Desflurane has a much greater global-warming potential than sevoflurane and is persistent in the atmosphere. Professional guidance has therefore strongly encouraged avoiding it where clinically appropriate.

In England, NHS England announced the decommissioning of desflurane from routine practice, with only limited clinical exceptions permitted from April 2024. The policy was supported by the Association of Anaesthetists and the Royal College of Anaesthetists.

Consequently, desflurane should no longer be considered a routine first-choice volatile anaesthetic in NHS England.

Nitrous Oxide

Nitrous oxide (N₂O) is different from the volatile anaesthetic agents. It has relatively weak anaesthetic properties but provides useful analgesia and anxiolysis. It is therefore often used alongside other anaesthetic drugs rather than as the sole agent for general anaesthesia.

It is also familiar outside operating theatres, particularly in obstetric analgesia, where mixtures containing nitrous oxide and oxygen are commonly used.

Advantages

Nitrous oxide has a rapid onset and offset, making its effects relatively easy to control.

It provides useful analgesia and can reduce the amount of other anaesthetic agents required. It is also non-irritating to the airway and is relatively easy to administer.

Because it is supplied as a gas, it can be particularly useful for short procedures where rapid administration and recovery are desirable.

Disadvantages

Nitrous oxide is not sufficiently potent to produce surgical anaesthesia on its own at clinically practical concentrations. It therefore generally has to be combined with other anaesthetic drugs.

It can also cause nausea and vomiting and can expand closed air spaces within the body. For this reason, it may be inappropriate in some patients or procedures.

Its environmental impact is another increasingly important disadvantage. Nitrous oxide is a potent and long-lived greenhouse gas. In addition, significant quantities can be lost from hospital central-piping systems through leakage before the gas is ever administered to a patient. UK and international sustainability guidance consequently recommends reducing unnecessary nitrous oxide use and addressing leakage from central pipelines.

The environmental issue

The environmental consequences of anaesthetic gases have become increasingly important in UK healthcare. Inhaled anaesthetics contribute to the carbon footprint of operating theatres, and the agents differ considerably in their climate effects. Desflurane and nitrous oxide are particularly important targets for reduction.

Hospitals can reduce emissions by choosing anaesthetic gases with lower environmental impacts, using low fresh-gas flows where clinically appropriate, preventing leaks and avoiding unnecessary use of inhalational agents. Total intravenous anaesthesia (TIVA) and regional anaesthesia can also provide alternatives to inhalational general anaesthesia in appropriate patients.

Anaesthetic Gases: Conclusion

The choice of anaesthetic gas is based on more than simply how quickly a patient falls asleep or wakes up. Anaesthetists must consider the patient’s medical condition, the type and duration of surgery, airway considerations, recovery requirements and the characteristics of each drug.

In current UK practice, sevoflurane is an important general-purpose volatile agent, while isoflurane remains a useful established alternative. Desflurane has become uncommon in England because of its very high environmental impact, and nitrous oxide is increasingly used selectively because of both its clinical limitations and environmental consequences.

Ultimately, the best anaesthetic is the one that provides safe and effective patient care while minimising unnecessary drug use and environmental harm. Environmental considerations are increasingly part of that clinical decision-making process, but they should not override individual patient safety.

Due to potentially hazardous substances in these gases, staff safety should also be considered where they are in repeated contact with anaesthetic gases through their workday, and workplace exposure monitoring should be carried out to ensure that staff exposure is kept within recommended exposure limits.

For help with workplace exposure monitoring to comply with COSHH recommendations click here.