Greenhouse gas emissions of sevoflurane outweigh those of carrier gas and CO2 absorbers across the fresh gas flow spectrum.

Abstract

The absolute and relative effects of lowering fresh gas flows (FGF) on the CO2 equivalent (CO2e) emissions of sevoflurane, carrier gases (O2/air) and prepacked CO2 canister remain poorly quantified. We quantified these factors across a 0.2-4 L/min FGF range during the first hour of anesthesia. Data were compiled from 3 studies including 132 ASA I-III patients receiving a constant end-tidal sevoflurane concentration (FETsevo) using manual (n = 50) or target controlled delivery (n = 48) with 0.2 to 4 L/min FGF or during automated closed-circuit delivery (CCA) (n=34). Sevoflurane consumption was normalized to both 1.3 and 2.0% FETsevo, and carrier gas use to an inspired O2 concentration (FIO2) of 30 and 60%. Prepacked CO2 absorbent usage was calculated using a previously described model for both 130 and 160 mL/min exhaled CO2 (VCO2). Published CO2e values were used to derive CO2e of sevoflurane. Sevoflurane CO2e increases linearly with FGF (range 2.4 -18.6 kg CO2e), except when a brief wash-in period was used due to low FGF (FGF < 1 L/min). Carrier gas CO2e decreases with lower FGF but in a more complex manner, and increases with higher FIO2. (range 0.010 - 0.124 kg CO2e). Absorbent CO2e decreases linearly with FGF (range 0 - 0.070 kg CO2e). The CO2e of sevoflurane is two orders of magnitude higher than CO2e of carrier gas and CO2 absorbent, which are similar. When delivering sevoflurane in O2/air, the CO2e contribution of the carrier gas and CO2 absorbent is less than 3%, even during CCA. While CO2e is only one element of a comprehensive life cycle analysis, the presented CO2e data underscore that the key to minimizing the global warming potential of sevoflurane is lowering FGF and decreasing FETsevo.