A randomised prospective comparison of equilibration point and changing gas composition during low-flow anaesthesia...

Safety and economy are the main concerns while using low- flow anaesthesia with newer inhalational agents. The main objective of this study was to use and compare 'equilibration time' of sevoflurane and desflurane after change-over from high-to-low flow anaesthesia.

This prospective study included consenting adult patients between 18-70 years undergoing elective surgery under general anaesthesia. Patients were randomised initially to receive high-flow anaesthesia with 1.3 MAC of either desflurane or sevoflurane with nitrous oxide. After equilibration point, low-flow anaesthesia was initiated. Heart rate, non-invasive blood pressure, pulse oximeter, 5 electrode ECG and gas monitoring was done. Statistical analysis was done with the help of Med CalC version 12.5.0.0 (student version) and IBM SPSS Version 20.0.

Mean equilibration time in sevoflurane group was higher (4.59 ± 0.77 minutes) than desflurane group (3.78 ± 0.56 minutes, P < 0.001). Inspired concentrations of both inhalational agents varied from their vaporiser settings over 2 hours, more so with sevoflurane than desflurane. Inspired oxygen concentration (FiO2) remained above 30% during anaesthesia in both groups with stable haemodynamics.

Change-over from high-to-low flow anaesthesia is faster in desflurane. With fresh gas flow (FGF) of 1 L with 50% oxygen and dial concentration of 1-1.5% of sevoflurane and 3.8-4.4% of desflurane, the risk of hypoxia is minimal. The disparity between the set and delivered concentrations is more (20%) in sevoflurane than desflurane (12%).