The Optimal Fresh Gas Flow when employing Total Intravenous Anaesthesia.
basic_science · Level V
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- Record sourced from PubMed, PMID 41805695.
- Also identified by DOI 10.1097/ALN.0000000000006025.
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Abstract
Fresh gas flow (FGF) during total intravenous anaesthesia (TIVA) is uncoupled from anaesthetic agent delivery. Higher FGFs reduce carbon dioxide (CO2) absorber consumption, but the overall costs and environmental trade-offs are unclear. We aimed to develop a context-specific calculator to estimate the "optimal" FGF during TIVA across different settings. We conducted a life-cycle assessment (LCA) of oxygen and air production, and CO2 absorbent production and disposal, quantifying environmental impact as global warming potential in 100 years (GWP100). The component costs (oxygen, air and CO2 absorbers) were obtained from institutional data. Annual costs and total GWP100 were modelled across FGFs of 1-10 L/min and FiO2 of 30-60%. Subsequently, we developed a web-based calculator (https://fgfcalculator.com) allowing users to input context-specific parameters, including grid emissions factors (GEF), to identify a FGF that best meets local objectives. We assessed the annual proportion of TIVA cases in our institution and applied local inputs to determine our optimal range. In our institution (GEF 0.599 kgCO2e/kWh; 36.4% TIVA), increasing FGF (FiO2 30%) reduced annual cost from S$12,948 (1 L/min) to S$1,572 (10 L min-1), but increased annual GWP100 near-linearly from 1,939 kgCO2e (1 L/min) to 5910 kgCO2e (10 L/min). The largest cost reduction occurred between 2-4 L/min, beyond which savings plateaued.Globally (assuming landfill disposal), the FGF that minimised GWP100 depended strongly on GEF: higher FGF decreased GWP100 when GEF ≤0.011 kgCO2e/kWh; was favourable up to 6 L/min when GEF 0.011-0.080; up to 4 L/min when GEF 0.080-0.20; and increased GWP100 at all higher-GEF settings (≥0.200). The optimal FGF is context specific. It is highly dependent on a country's GEF and the method of CO₂ absorbent disposal. By factoring in these variables, our calculator provides an evidence-based suggestion for FGF during TIVA, balancing economic and environmental considerations across the globe.