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Higher fresh gas flows during TIVA reduce costs without increasing environmental impact compared to low-flow techniques.
pearl- George Zhong, Ali Abbas, Joseph Jones, Sarah Kong, and Tim McCulloch.
- Department of Anaesthesia, Concord Repatriation General Hospital, Sydney, Australia. Electronic address: drgzhong@gmail.com.
- Br J Anaesth. 2020 Nov 1; 125 (5): 773778773-778.
BackgroundIncreasing 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.MethodsA 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.ResultsIncreasing 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.ConclusionsIn 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.Copyright © 2020 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.
Notes
What's the deal?
This lab study from Zhong et al. challenges the assumption that low-flow anaesthesia is economically and environmentally superior during TIVA anaesthetics when volatile agents are not used.
What did they do?
Zhong used a test lung model with fixed CO2 inflow (250 ml/min) ventilated via circle systems of two anaesthetic machines (Dräger Primus and GE Aisys CS2). FGF rates of 1, 2, 4, and 6 L/min were tested, measuring the time to CO2 absorbent exhaustion (when inspired CO2 >0.3 kPa).
An inspired 30% O2/air mixture was used, with the test lung volume-control-ventilated at 12 bpm with 500 mL tidal volumes.
Findings
Results showed that increasing FGF from 1 to 6 L/min resulted in over 90% reduction in running costs with minimal net change to global warming potential. The time to absorbent exhaustion increased non-linearly with higher FGFs, taking over 5-8 days at 6 L/min. Notably, removing the CO2 absorbent entirely and using very high FGF (15-18 L/min) provided minimal additional economic benefit while more than doubling the environmental impact.
"We suggest that 'high-flow anaesthesia', with FGF around 6 L/min, is a viable cost-saving strategy when using a circle system for anaesthetic maintenance without inhalational anaesthetic agents in adults."
Hang-on...
The absolute cost saving (due to reduced soda lime consumption) was actually pretty small, being less than 4% of the total non-staff anaesthetic cost. Although this might still be economically significant when scaled across an entire health system, especially given the simplicity of implementation and the lack of drawback.
Bottom-line
When using total intravenous anaesthesia with modern HME filters, higher fresh gas flows (~6 L/min) are more cost-effective than traditional low-flow techniques, without compromising environmental impact or patient safety.
Daniel Jolley
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