
Anaesthesia has a large environmental impact, what can vets do to reduce this?
It is now 7 months since we started making changes in the practice to reduce our environmental impact. One of the things that set us on our journey was a paper from Science 2009; 326:123–5, by Ravishankara and Daniel: Nitrous Oxide; the dominant ozone depleting substance emitted in the 21st Century.
Further investigation also revealed that nitrous oxide is a very powerful green house gas. In a more recent paper by Jones and West on Environmental Sustainability in Veterinary Anaesthesia (Veterinary Anaesthesia and Analgesia July 2019 Volume 46 ) they calculate that nitrous oxide has a high carbon footprint ( CO2e.kg of 36) due to its long persistence in the atmosphere- up to 110 years. Shocking.
Why do we use nitrous oxide? Nitrous oxide is used to enhance pain relief during surgery. The standard anaesthetic protocol that we would use for a dog or cat would be to give a premedication injection, of different types but usually a sedative type drug and pain killer. This helps the patient to relax and feel sleepy. An intravenous induction agent (such as propofol) is given. This renders the patient unconscious, and then a tube can be placed in the patient’s trachea which is connected to the anaesthetic gas delivery circuit. Patients are kept under surgical anaesthesia with a mix of oxygen, nitrous oxide (sometimes) and a volatile anaesthetic agent such as isofluorane. There are different sorts of circuits that can deliver the gaseous mix, but there are always waste gases at the end which are either expelled from a scavenging system into the outside environment, or which are captured by an activated charcoal absorber which has to be disposed of later. The latter does not absorb nitrous oxide.
The analgesic effect of Nitrous oxide has been very important to us, but over the years we have used additional techniques such as local anaesthetic blocks and CRI ( constant rate infusions) of analgesics such as ketamine to help with the management of surgical pain. Given the massive environmental impact of using Nitrous Oxide it seemed an obvious step to take to abandon its use at the practice. We organised a clinical staff meeting to discuss this and found there was a mixed response from them and a concern about reducing analgesia. With this in mind we set up a small trial to help our staff develop confidence. In dogs having a standard stifle procedure, who had both a local block and a CRI we asked them not to use nitrous oxide, but the rescue procedure would be that if it was clear analgesia was inadequate then they could add nitrous. After 20 procedures we found that the use of nitrous had been unnecessary. Great news, we could confidently end our contract with our supplier.
The added benefit of making more use of local anaesthetic blocks is that in combination with CRI it can massively reduce the use of the anaesthetic agent isofluorane. Isofluorane is a volatile liquid which is delivered to the anaesthetic circuit via a vaporiser. Isofluorane is also one of the greenhouse gases. We have calculated that we now use 50% less isofluorane per patient than we did before we were using the blocks. Not only is this good news for the environment, it is also saving a considerable amount of money for the practice and for our clients. There are also the types of anaesthetic circuits to consider. Less gas and agent is used with rebreathing circuits where the CO2 is removed from the exhaled gas via sodalime so that the remaining oxygen can be redelivered. We use Humphrey ADE circuits which are low flow compared to older types of circuit which need higher flow rates.
Do we need to use isofluorane? There are techniques such as TIVA ( Total Intravenous Anaesthesia) which do not require the use of such volatile agents. They do require some investment in electronic syringe drivers , which deliver a predetermined amount of intravenous anaesthetic agent very slowly over time to keep the patient asleep. This also requires some retraining of staff as the parameters for measuring anaesthetic depth are somewhat different and the response to increasing or reducing the anaesthetic is not as immediate as would be seen with gas.
And the future? in Canada there are capture systems developed which use scavengers to collect waste isofluorane from the expelled gas, which is then retrieved at specialist plants. There are also newer electronic systems to control flow rates of gases to reduce the quantities of waste gas production. The cost of these is likely to be prohibitive for the veterinary market during the early phase of development, but if successful the cost would hopefully reduce and make these more available.
It is likely that we may all need to consider the use of TIVA as standard at some point in the future.
We have been pleased with the massive reduction in Green House Gases that we have already achieved by taking relatively easy measures, and would encourage other practices to do the same.
