A climate perspective on spinal anaesthesia with sedation versus total intravenous anaesthesia for lower limb arthroplasty

Editor, Clinical evidence comparing spinal and general anaesthesia for lower limb arthroplasty generally favours spinal anaesthesia; however, the real-world advantages appear to be modest.1 Consequently, the decision between anaesthetic modalities is often driven by organisational and systemic considerations. Climate-related outcomes have emerged as an important factor in healthcare planning and are increasingly being integrated into both clinical guidelines and research frameworks.2 We aimed to quantify CO2 equivalent (CO2e) emissions (primary outcome) and plastic- and total waste generation associated with spinal versus total intravenous anaesthesia (TIVA) for total hip or knee arthroplasty in a Danish public hospital setting. We only included climate impact directly related to the choice of anaesthesia, e.g. the carbon footprint from the hospital admission itself was not included. Medical devices used for anaesthesia were assessed by CO2e estimates and by weighing both total waste and plastic waste. CO2e estimates were obtained primarily from manufacturers of medical equipment who had performed and were willing to share product life cycle assessments (cradle-to-grave). When such were unavailable, we used The Capital Region's CO2e reference list (the largely price-based FLIS-system), which is a screening-level tool and not a verified life-cycle source. The mean duration of anaesthesia was 1 h and 20 min. The anaesthesia ventilator was estimated to generate 0.06 kg CO2e per case, based on 80 min, 0.2 kWh consumption and 0.21 kg CO2e/kWh (Danish numbers). General waste and plastic from hospitals is typically incinerated, but with increased inclination to reuse plastic waste. To facilitate local interpretations, we reported general waste- or plastic as separate outcomes and did not add their incineration to the CO2e estimate. For products where the CO2e value was provided by the manufacturer, incineration was included in the calculation. Drug use was recorded as total volume in millilitres, regardless of type. Spinal anaesthesia was analysed with and without sedation. As the majority of patients prefer sedation adjunct to a spinal when undergoing arthroplasties, conclusions were based on the comparison TIVA versus spinal + sedation. A round-trip from Copenhagen-New York was set at 1100 kg CO2e.3 We identified 16 medical devices and six drugs required to carry out TIVA and spinal anaesthesia (Table 1). CO2e values for seven medical devices were provided by manufacturers, three medical devices via published literature and six via the Capital Region in Denmark's CO2e reference list. Table 1 - Waste and CO2e from anaesthesia to single hip or knee arthroplasty Anaesthesia type and item Total waste (g) Plastic waste (g) Medicine (ml) CO2e kg Total intravenous anaesthesia (TIVA) Ventilator tubes 160 126 0.69 Filter 23 21 0.21* CO2 sample tube 22 22 0.40* Face mask size 4 24 24 0.33 Reusable laryngeal mask size 4 57 57 0.28̈ TIVA extension set 18 18 0.8* Spaceline infusion line ×2 54 54 2.64§ Syringes (20 + 2 + 10 + 5 ml) 32 32 0.12* Draw-up needles (3 pcs) 6 4 0.10* Draw up spike 7 7 0.42* Nasal oxygen catheter 44 44 0.15 Propofol 10 mg ml −1, bolus 20 ml + infusion 40 ml# 56 0 60 Remifentanil 50 μg ml −1, infusion 40 ml# 8 4 40 Morphine 5 mg ml−1 (two vials), bolus 15 mg€ 8 0 4 Ondansetron 2 mg ml−1 (one vial), bolus 4 mg 4 0 2 Energy/oxygen/soda lime: anaesthesia ventilator 0.13 Total 523 g 413 g 106 ml 6.35 kg Spinal anaesthesia without sedation Spinal set 145 56 2.23* Spinal needle 3 1 0.06 Sterile gloves 26 5 0.44 Lidocaine 10 mg ml−1 s.c.€ 8 6 10 Bupivacaine 5 mg ml−1 vial€ 12 0 5 Morphine 5 mg ml−1 ×2 8 0 4 Total 202 g 68 g 19 ml 2.73 kg Spinal anaesthesia + sedation Spinal (as above) 202 68 19 2.73 Spaceline ×1 27 27 1.32§ Nasal oxygen catheter + CO2 sensor 66 66 0.51 Propofol 10 mg ml−1, infusion 20 ml h−1, 27 ml# 25 0 27 Total 320 g 161 g 46 ml 4.56 kg *CO2e based on “FLIS”-reference values (the integrated management information system). In this system, carbon emission is directly linked to the item price by a constant of 0.0785 kg CO2e/DKK.§CO2e based on https://journals.lww.com/ejanaesthesiology/fulltext/2024/12000/bacterial_contamination_and_greenhouse_gas.6.aspx.̈CO2e based on Sherman JD, Eckelman MJ. Comparative life cycle assessment of disposable and reusable laryngeal mask airways. Anesth Analg. 2012;114:1067–72.#Waste weight adjusted for the proportion of the medicine cannister that is used.€Full vial volume was used regardless of how much was used as the remaining volume was thrown out.Minimal impact from compressed oxygen and ventilator gas flow (0.01–0.04 kg CO2e) and soda lime (0.04 kg CO2e) were accounted for.The spinal set consisted of a large and a small tray, three syringes, two needles, antiseptic wipes and a cover. All values are reported in Table 1 and summarised in Table 2. The climate impact was higher for TIVA on all parameters compared with spinal + sedation (total waste: +203 g, plastic waste: +252 g, medicine use: +60 ml, CO2e: +1.79 kg). Table 2 - Summarised climate impact of total intravenous anaesthesia versus spinal with sedation Total waste (g) Plastic waste (g) Medicine (ml) CO2e Total intravenous anaesthesia 523 g 413 g 106 ml 6.35 kg Spinal anaesthesia + sedation 320 g 161 g 46 ml 4.56 kg Increased climate impact by using TIVA compared with spinal + sedation Total waste (g) Plastic waste (g) Medicine (ml) CO2e Proportionate increase 63% 157% 130% 39% Absolute increase/case 203 g 252 g 60 ml 1.79 kg Absolute increase DK/year (20 000 cases) 4.06 tons 5.04 tons 1200 l 35.8 tons TIVA was associated with a 38 to 156% higher climate impact across the assessed parameters. At the single-procedure level, the difference was minimal, but when extrapolated to a Danish national annual level, switching from always using TIVA to spinal + sedation could save the equivalent of 31 round-trip flights between Copenhagen and New York in addition to approximately 1200 l of medication. When assessing the direct environmental effect of anaesthesia, spinal + sedation is therefore superior to TIVA. Combined with its slight advantage in postoperative outcomes, this represents a meaningful argument for preferring spinal + sedation when there are no other arguments for choosing one strategy over the other. Generalisability of our results is not universal and they should be extrapolated to other countries with care, because: if general anaesthesia is performed with volatile anaesthetics, the CO2e markedly increases with 5.9 to 11.8 kg, given the circumstances used in this article.4 Therefore, from a climate perspective, prioritising the transition from volatile anaesthetics to TIVA where clinically appropriate should be prioritised over shifting from TIVA to spinal anaesthesia. In countries with less renewable energy, the ventilator will yield higher CO2e. In settings where spinal anaesthesia leads to prolonged oxygen therapy the environmental impact may even shift to favour TIVA.5 Screening-level tools like the ‘FLIS-system’ have limited precision and should, where possible, be replaced by manufacturer-specific cradle-to-grave calculations.6 If our estimates are used to calculate environmental impact in clinical trials,2 we urge that potential secondary effects from the choice of anaesthesia, e.g. shorter time to surgery or length of post-anaesthesia care unit stay, are translated into CO2e and added to the calculation.7