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

We read with interest the study by Elson et al. [1] and would like to highlight several areas where future studies could refine their modelling, particularly because we believe that the benefits of total intravenous anaesthesia (TIVA) may have been underestimated. The study assumes that a new syringe is used for every reload of propofol or remifentanil during TIVA. While this approach minimises the theoretical risk of contamination, it does not reflect real-world practice accurately. In many clinical settings, anaesthetists rotate two syringes for the same patient, refilling each only when empty, thus reducing plastic waste. By modelling each reload as a completely new single-use syringe, the study likely overestimates the consumable footprint associated with TIVA. Lorenz et al. found comparable contamination rates when syringes were refilled and reused, even for consecutive cases, compared with strict single-use replacement [2]. While reuse between patients cannot be endorsed, this finding highlights that syringe refilling within a single case under strict aseptic conditions can be performed with low additional contamination risk and supports more resource-efficient practices. A further reduction in plastic consumption could be achieved through bypassing syringes altogether. As shown elsewhere [3], TIVA can be administered directly from the propofol bottle, eliminating the need for disposable syringes entirely. Incorporating such innovations would decrease the environmental footprint of TIVA significantly, suggesting that the authors' already careful modelling likely understates its real-world sustainability advantage. Elson et al. reference the use of processed electroencephalogram (pEEG) monitoring exclusively in TIVA scenarios. In our institution, pEEG is recommended for TIVA cases where neuromuscular blockade is used, which is in keeping with recommendations from the Association of Anaesthetists [4]. Thus, not all cases of TIVA require pEEG. Moreover, it is used increasingly in volatile inhalational anaesthesia for various advantages including shortening recovery time and reducing volatile anaesthetic agent consumption [5]. The study assumes that remifentanil and metaraminol infusions are used exclusively in TIVA scenarios. In many clinical settings, remifentanil target-controlled infusions are combined with volatile anaesthesia. Metaraminol was a significant contributor to the environmental cost of TIVA cases (up to 21.5%) and is used frequently in both TIVA and inhalational anaesthesia. By modelling these drugs only in the TIVA group, the authors may again bias the environmental cost in favour of inhalational techniques. The authors report that beyond 22 min, TIVA becomes environmentally favourable and beyond 44 min, all inhalational anaesthesia scenarios exceed even the worst TIVA footprint. We suggest that even with fresh syringes, pEEG monitoring and metaraminol infusions used in all TIVA cases, the true crossover point may well be much earlier. This is particularly relevant since most adult general anaesthetic cases exceed this duration.