British journal of anaesthesia
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Letter Comparative Study
How do anaesthetist and geriatrician perioperative frailty assessments compare?
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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.
summary