Carbon footprint of total intravenous vs. inhalational sevoflurane anaesthesia in adults: a reply

We welcome the correspondence from O'Sullivan and Shah [1], which comments on our study [2]. I agree broadly with their points and wish to emphasise that our results should not be interpreted as a minimum carbon footprint for total intravenous anaesthesia (TIVA). A common concern about TIVA is the high consumption of single-use plastic compared with volatile inhalational anaesthesia [3]. Anaesthetists might conclude that TIVA has a greater carbon footprint than sevoflurane anaesthesia and our model assumed ‘worst case’ use of consumables for each of our TIVA scenarios. We included all possible consumables that were used so that our calculations of the total carbon footprint of TIVA overestimated actual practices. By using this approach, and by publishing the carbon footprints of individual items used in our scenarios, clinicians can identify how the footprint of their practice might vary from the scenarios we modelled, as O'Sullivan and Shah have done. In our modelling, we assumed that all TIVA cases use processed electroencephalogram (pEEG), as many anaesthetists, particularly during training, choose to use this to minimise the risk of accidental awareness even in the absence of neuromuscular blockade [4]. As discussed in our study, if pEEG is not used for TIVA, the carbon footprint will reduce by 0.83 kgCO2e (excluding the energy required for the pEEG monitor), equating up to 28.1% of the total carbon footprint of TIVA. In this case, after 11 min, both TIVA scenarios have lower total carbon footprints than median consumption inhalational anaesthesia using sevoflurane. Conversely, if pEEG is also used for volatile anaesthesia to reduce recovery time and volatile anaesthetic agent consumption as highlighted by O'Sullivan and Shah [1] and to reduce accidental awareness [4], then the total carbon footprint of volatile sevoflurane anaesthesia will increase by at least 0.83 kgCO2e. Using our modelled scenarios, if pEEG is used for both TIVA and sevoflurane anaesthesia, then, after 20 min, the highest emitting TIVA scenario has a lower total carbon footprint than the most economical sevoflurane scenario. This 20-min threshold is drastically lower than the 44 min for our original high-emission TIVA scenario vs. minimal consumption sevoflurane without pEEG. It should be noted that data used for sevoflurane consumption were derived from a study that did not use pEEG to titrate sevoflurane but instead measured actual consumption using low fresh gas flow [5]. O'Sullivan and Shah highlight several TIVA practices that use resources more efficiently than our modelled scenarios and we encourage anaesthetists to consider how their practices can be leaner and greener while maintaining patient safety.