Splitting ratio in sevoflurane vapouriser-a relook on calculations

Abstract

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.