Two New Zealand anaesthesiologists have spent decades refining their practice to safely reduce use of anaesthetic agents that contribute to global warming.

In the developed world, says Associate Professor Ross Kennedy from the University of Otago in Christchurch, between 10 and 12 per cent of the total population will have an anaesthetic each year. “Christchurch is a region of about half a million people, so that means 50,000 to 60,000 anaesthetics every year across our public and private hospitals,” says Professor Kennedy, a specialist anaesthetist who is also equipment officer and director of research in the Department of Anaesthesia at Christchurch Hospital, part of the Waitaha Canterbury district of Te Whatu Ora Health New Zealand.

Using data to both improve patient safety and reduce waste in anaesthesia – which can include volatile chlorofluorocarbons which are potent greenhouse gases – has been something of a passion project for Professor Kennedy and his colleague Dr Richard French, who’s also an anaesthetist and now Chief Medical Officer for the local hospital network. Beginning in 2016, the pair used GE Healthcare’s Carestation Insights for a pilot project at Christchurch Hospital. The project demonstrated that anaesthetists could be encouraged to reduce the flow of these volatile inhaled agents earlier in procedures, which resulted in additional cost savings and lower emissions.


Since the pilot analysing the anonymising data relating to 5000 patients concluded five years ago, Professor Kennedy says there has been considerable growth in the deployment of Caresation Insights. “Beginning in late 2018, we installed it across 10 of our anaesthetic and then in late 2020 when we opened a major new building, we installed it in another 10 locations, so it’s now running in 20 operating theatres across our main campus.”

Prior to installing Carestation Insights, Professor Kennedy collected data from anaesthetic machines, via a very labour-intensive process, for more than 15 years. “That meant we only sampled every year or two,” he says. “Now we have up-to-date data on tap and can combine info from across several Insights dashboards. Over 50 months, we have gathered data on more than 15,000 cases.” The data is for public-hospital patients only, and Professor Kennedy estimates they are now capturing more than half of all anaesthetic procedures, which will grow in time.

“It’s been interesting because our original pilot was on only four machines, and every time we have scaled, the overall patterns of what we’re seeing have been quite similar,” he says. “It’s a useful illustration that good sampling gives you really good insights into what’s going on.”

The data has also revealed changing patterns, with about 60 per cent of procedures using total intravenous anaesthesia (TIVA) instead of inhaled agents – data that’s easy to extract by combining the dashboards. As Professor Kennedy notes, the focus of the original pilot was to help encourage low-flow procedures to reduce use of volatile inhaled agents. Comparing data across dashboards helped demonstrate to anaesthetists that low-flow was both safe and effective. The pilot confirmed they were already “a low-flow shop”, but the insights drove them to do better, saving money and significantly reducing emissions from volatile anaesthetic inhalants.

According to the UK’s Association of Anaesthetists, these gases account for 5 per cent of the CO2 equivalent emissions of acute NHS hospitals. The main inhalant climate-conscious anaesthetists have in their sights is Desflurane, which Professor Kennedy says is rarely used in their hospitals.

In a recent GE Healthcare webinar discussing using data to make institutional-level changes in anaesthesia, Belgian anaesthesiologist and biomedical engineer Dr Alain Kalmar said that legislation is already in the pipeline that by 2025 will require special permission to use Desflurane.

Dr Kalmar has published several papers on the environmental impact of inhaled anaesthetics. The Global Warming Potential (GWP) of these anaesthetic gases have been calculated, and it’s startling. “We calculate that one bottle of Sevoflurane equals about 266kg of CO2 emissions, and one bottle of Desflurane about 2.5 tonnes of CO2,” Dr Kalmar told the webinar audience. “For reference, one bottle of Sevoflurane equals burning 111 litres of gasoline or flying 2600km or driving 1700 kilometres in an average car.”

As well as reducing the emissions footprint, Dr Kalmar shared some compelling statistics on cost savings, based on his benchmarking study analysing the Sevoflurane use by 22 anaesthetists and 40,000 general anaesthesia procedures. “It showed a huge variability in consumption of Sevoflurane,” he said. “In only eight minutes, the consumption varies between 3ml and 20ml. This analysis shows very significant savings opportunities – if extrapolated over a whole year, the additional consumption by some anaesthetists is between 100 and 800 bottles per year for equal anaesthesia. This corresponds with an additional cost between 10,000 and 80,000 euros, or an additional emission of 27 to 213 tonnes of co2. If all anaesthetists would assume the most economical methodology, this would result in savings of up to 400,000 euros a year and almost 1000 tonnes of CO2.”

Dr Kalmar said discussing the data with the 22 anaesthetists as a group was a powerful way to motivate changes in behaviour. That’s similar to what Professor Kennedy and Dr French learned in their New Zealand pilot, where text messages were sent to anaesthetists and assistants on days where they were working in a theatre with Carestation Insights installed, to remind them to reduce their flow as soon as possible after the start of a case.

Professor Kennedy said today in their hospitals there’s no need for even these gentle prompts. “We still present on low-flow a couple of times a year, but focusing on flow rates at the start of a procedure has become a part of the culture if we are using a volatile anaesthetic,” he says. “People use low-flows as the norm. To be honest, as much as the data it’s the advances in gas-flow technology.”

The Christchurch hospitals where he works use GE Healthcare’s Aisys CS2 with End-tidal control software. “We’ve had this technology for 12 years and it makes using low-flows straightforward for most of the case,” explains Professor Kennedy. “During our pilot, we discovered the impact of the way anaesthetists managed the beginning of the case has on the overall sevoflurane consumption, which is where we came up with the two-box model. That’s where we’re still concentrating our attention.”

Behaviours can take time to change when there’s an entrenched culture. “Although low-flow volatile anaesthesia is the norm in Christchurch, and indeed much of New Zealand, there are certainly pockets of resistance, even when low-flow equipment is available,” says Professor Kennedy.

“For us now, I think we are pretty close to the best we can be,” says Professor Kennedy of their low-flow culture. “Because a lot of the machines are automated, we know that a lot of our machines are running at pretty low flow during the body of the case. Where we can make a big difference is that period at the beginning, and the data shows that our anaesthetists are pretty diligent. Actually, there’s a suggestion that some of the more junior members of the department are outperforming the older members of the department – I need to drill down on that data!”

That makes him very happy. “These more junior doctors have carried on with implementing the concepts behind the so-called two-box model – they really get it and in five years they’ll be teaching the next lot. That’s a positive and exciting thing.”

The data shows the way but in the end it’s the humans who deliver results.