Minimal and medium flow anaesthesia with isoflurane and desflurane: Effects on inspired and expired oxygen and anaesthetic gas concentrations

Background: In this study we aimed to compare haemodynamics, body temperature, inspired and expired oxygen and anaesthetic gas concentrations in minimal and medium flow anaesthesia with isoflurane and desflurane. Methods: We studied 60 ASA 1-2 patients undergoing elective surgical procedures Patients were randomly divided to two equal main groups to receive isoflurane and desflurane. Then these main groups were randomly divided to 3 equal sub-groups such as to receive isoflurane or desflurane in 500, 1000 and 2000 ml.min fresh gas flow (FGF) respectively. FGF was applied 4 L min in initial phase (10 min) after standard anaesthetic induction, then isoflurane and desflurane concentrations were adjusted as 1.5 % and 6 % respectively and FGF was adjusted according to groups. HR, MAP, SpO oesophageal temperature, vaporizer settings, inspired and expired anaesthetic gas concentrations were recorded at regular intervals throughout the study. Results: Inspired and expired anaesthetic concentrations were decreased significantly in minimal flow groups compared to medium and high flow groups. FiO2 values were decreased parallel to duration of anaesthesia. Low FiO occurred in 2 cases in minimal flow isoflurane group and 8 cases in minimal flow desflurane group. Conclusion: Isoflurane and desflurane could be used safely with minimal and medium FGF, but we decided that isoflurane was superior to desflurane regarding oxygenation. We thought that there was hypoxia risk in cases which desflurane was used as inhalant agent in minimal flow with 50 % NO in O. However, we concluded that the increasing FiO % ratio can prevent hypoxia.