IHEEM 2019 REGIONAL CONFERENCE
commute of all 1.3 million NHS staff. He said: “While we clearly can’t make every member of the NHS’s staff cycle or walk to work, we can implement engineering good practice that might mitigate the GWP of these gases.” Moving to the atmospheric impact of some of the more widely used medical gases and anaesthetic agents, Mike Ralph explained that the abbreviation’, ‘TPL’ was short for the ‘Tropospheric Lifetime’ of such substances when released into the atmosphere, i.e. the period they were in the air before they ‘broke down’ and lost their impact. He said: “With, say, an evaporator liquid bottle, you may have just 250 mL of Sevoflurane – probably the least harmful inhalational anaesthetic agent, but with a GWP of 130 times its carbon equivalent, and a TPL of 1.1 years. Isoflurane has a GWP of 510 and a TPL of 3.2 years, and Desflurane a GWP of 2,540 and a TPL of 14 years. Nitrous oxide, however, has a GWP of 298, and a Tropospheric Lifetime of 110 years.” The speaker added that with Desflurane – ‘the most expensive’ inhalatory agent – a 250 mL bottle will generate nearly a tonne of carbon and, on average, if surgery is being undertaken in a healthcare facility treating a lot of patients with high co-morbidities, the anaesthetists may well use about 500 mL per average operating day. Graham Stanton asked Mike Ralph at this point about any potential ill-effects for surgical staff inhaling such gases. He responded: “One of Desflurane’s key advantages is that it has very low solubility in the blood, and accordingly the patient is induced very quickly, and the gases also leave the body very quickly.
“If you have a bad heart, or, for example, are very overweight, the anaesthetist will strive to ensure that you are ‘kept under’ for the minimum time, which explains why Desflurane is so popular. There is thus very little that the patient will exhale during ‘Recovery’, with the bulk of the agent extracted through the theatre’s AGSS system.” The bigger problem, the speaker said, was that Desflurane can be up in the atmosphere for 14 years, while although Nitrous oxide doesn’t have the highest Global Warming Potential, once released, it can be up in the air for 110 years before breaking down.
Proportional contributions Mike Ralph’s next slide – highlighting the proportional CO2
e contributions of the
various medical gases and inhalational agents used in anaesthesia – showed that Entonox accounted for some two-thirds of the total. He added: “The gas that is probably easiest to control is Nitrous oxide, because there are a lot of available options.” Against the backdrop of the alarming Global Warming Potential of some medical gases and agents, Mike
40 Health Estate Journal January 2020
Ambulance N2
Desflurane 16%
O and O2 16%
Isoflurane 1% Sevoflurane 2%
Emergency N2
O and O2 16%
Nitrous oxide for anaesthesia 18%
Maternity 31%
Figure 1: The proportional contribution to CO2 commonly used anaesthetic gases in 2017.
Ralph said the Association of Anaesthetists of Great Britain and Ireland (AAGBI), and some of its European counterparts, had got together to co-ordinate a study into how hospitals were using particular anaesthetics for different purposes. Pointing to a chart illustrating some of the findings, he explained: “In one instance you can see that there is a hospital not using Nitrous oxide as a carrier gas; it is inducing with Desflurane, and maintaining (anaesthesia) with Isoflurane. Its carbon footprint is thus quite low, and the combination (of agents) may suit the type of patients it has. In contrast, we found a different hospital using a very large volume of N2
O, and very little inhalatory
agent, so it may be performing lots of standard time operations. That healthcare facility is using more Desflurane and Isoflurane, and may also be employing low flow techniques, or using air and oxygen as a carrier gas. There are some significant differences in how anaesthetists work; practices may depend on the anaesthetist’s age. Younger and more recent cohorts are taught to work without Nitrous oxide, although it is still pretty widely used.”
Explanation of ‘MACs’
The next slide showed Minimum Alveolar Concentrations, or ‘MACs’. The ‘MAC’, Mike Ralph explained, was the standard unit of measurement for how anaesthetised a patient was. He said: “1 MAC is the concentration of the vapour in the lungs needed to prevent movement in 50 per cent of subjects in response to surgical stimulus; it allows comparison of the potency of anaesthetics.” The slide illustrated the levels of various gases and inhalational agents needed to effectively anaesthetise an individual, and their
emissions of the most
relative carbon emissions/hour, with Desflurane and Nitrous oxide ‘very high’. Mike Ralph said: “This is not attributable to the quantities of agent used, but rather to the depletion levels of these gases. Nitrous oxide will never truly anaesthetise somebody on its own – although it does have strong analgesic advantages, but Desflurane tends to be seen as the ‘genie in the box’; it is very easy to use it all the time.”
Potential mitigating actions Having set the scene on the different impacts and GWPs of some of the most commonly used medical gases and inhalational anaesthetic agents, Mike Ralph turned to consider what could be done to mitigate these effects. He said: “One potential option is to move from Desflurane to Sevoflurane, which seems a really obvious one, but there will always be a need for Desflurane. Some anaesthetists will actually lock it away, which means that when personnel want to use it, they may have to explain why to the senior anaesthetist. However, if you have an emergency patient that you need to induce quickly, you will need to locate Desflurane quickly. Its management can thus be difficult.”
Another potential action, Mike Ralph explained, was to reduce the use of surgical Nitrous oxide – either through lower flow anaesthesia, or by using Medical air and Oxygen blended as a carrier gas. He added: “Another alternative is to use more intravenous or local/regional anaesthesia. Intravenous and total intravenous anaesthesia do, however, have their problems. Some Relative anaesthesia and ‘blocks’ may, however, offer a way forward as alternative solutions for gas and air in
The Sustainable Development Unit
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