Modern inhalation agents and effects of anaesthesia equipment during low-flow anaesthesia

University dissertation from Department of Anaesthesiology and Intensive Care, Lund University Hospital, SE 221 85 Lund, Sweden

Abstract: Volatile agents are economically and ecologically acceptable only when administered via low-flow systems. However, sevoflurane degrades during low-flow anaesthesia to compound A, and a high carbon dioxide absorber temperature increases this degradation. This thesis suggests that there is a correlation between apparatus dead-space volume and absorber temperature during low- and minimal-flow sevoflurane anaesthesia. Increasing the dead-space volume reduces absorber temperature during low- and minimal-flow sevoflurane anaesthesia. The main disadvantage of low-flow techniques is that inspired (In) and end-tidal (Et) anaesthetic agent concentrations are not directly related to the vaporiser setting. In the present studies, with desflurane and sevoflurane, there was a significant difference between Et and In concentrations at fresh gas flows (FGFs) of 1.0 and 2.0 l/min. However, the ratio of Et to In concentration remained fairly constant. Excessive respiratory heat loss may lower body temperature. Artificial humidification of dry inspired gases reduces loss of body heat during anaesthesia, hence the popularity of heat and moisture exchangers (HMEs). In this study, HMEs improved the humidity of the anaesthetic gases at different FGFs, but did not improve maintenance of body temperature during low-flow anaesthesia in adults undergoing elective general or urologic surgery.

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