Textbooks of anaesthesia describe in detail the calculations associated with splitting ratios created in variable bypass vapourisers. These calculations are based on assumptions of carrier gas flow (eg:assume 150 ml) as practised with measured flow vaporizers[1,2]. Carrier gas flow in a variable bypass vaporizer is agent specific,dynamic,unknown and operator independent.Therefore assuming carrier gas flow in calculations related to variable bypass vaporisers is without rationale[3]. In spite of technological advance,the amount of vapour produced is calculated based on clinically impractical assumptions. A simple method and formula is suggested for the quick estimate of vapour output, carrier gas flow and determine the splitting ratio while operating a sevoflurane variable bypass vaporizer.

The authors have declared no competing interest.

This study did not receive any funding

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