Environmental and economic impact of using increased fresh gas flow to reduce carbon dioxide absorbent consumption in the absence of inhalational anaesthetics.

Abstract

Increasing fresh gas flow (FGF) to a circle breathing system reduces carbon dioxide (CO₂) absorbent consumption. We assessed the environmental and economic impacts of this trade-off between gas flow and absorbent consumption when no inhalational anaesthetic agent is used. A test lung with fixed CO₂ inflow was ventilated via a circle breathing system of an anaesthetic machine (Dräger Primus or GE Aisys CS²) using an FGF of 1, 2, 4, or 6 L min^-1. We recorded the time to exhaustion of the CO₂ absorbent canister, defined as when inspired partial pressure of CO₂ exceeded 0.3 kPa. For each FGF, we calculated the economic costs and the environmental impact associated with the manufacture of the CO₂ absorbent canister and the supply of medical air and oxygen. Environmental impact was measured in 100 yr global-warming potential, analysed using a life cycle assessment 'cradle to grave' approach. Increasing FGF from 1 to 6 L min^-1 was associated with up to 93% reduction in the combined running cost with minimal net change to the 100 yr global-warming potential. Most of the reduction in cost occurred between 4 and 6 L min^-1. Removing the CO₂ absorbent from the circle system, and further increasing FGF to control CO₂ rebreathing, afforded minimal further economic benefit, but more than doubled the global-warming potential. In the absence of inhalational anaesthetic agents, increasing FGF to 6 L min^-1 reduces running cost compared with lower FGFs, with minimal impact to the environment.