How does different fresh gas flows affect stress in rats during anaesthesia induction with sevoflurane in a chamber?

Abstract: The rat is one of the most used laboratory animals in Europe today. When replacement of live animals in research is not feasible, the aim is to improve the welfare of those animals by reducing stress and suffering. Anaesthesia in laboratory rats is a common procedure, and induction with inhalant agents is often associated with stress and discomfort in the animals. Therefore, one way to improve welfare would be to improve the induction quality. Additionally, research is lacking in the area about which factors influence stress in rats during inhalant anaesthesia induction. The behaviour of ten Wistar rats was studied during induction of anaesthesia with sevoflurane using an inhalation chamber. The rats were randomized into two groups, receiving a fresh gas flow of three and six litres per minutes, respectively. The vaporizer was set to 8%. The behaviours were recorded inside the chamber during preoxygenation and during the induction and recovery. Latency to, frequency and duration of several behaviours were observed and compared between the two groups. Also, time to recumbency, first movement and regain of righting reflex was noted and compared between both groups. No significant differences were found in frequency, latency or duration of the observed behaviours between groups, except for latency to ‘lie’ being longer in the low flow group. Stress-related behaviours were frequent in all rats during preoxygenation and induction. Rats induced with higher flow had a significantly faster induction than those in the low flow group.