Is carbon dioxide (CO2) a useful short acting anaesthetic for small laboratory animals?

The anaesthetic effect of carbon dioxide (CO(2) was investigated under predetermined exposure times in rats, mice and guineapigs with admixture of 20% of oxygen (O(2)), and with 20% of ambient air in rats. In rats first symptoms (median) were detectable between 7 and 9.5 s, the induction time (median) varied between 16 and 20.5 s and the surgical tolerance (median) was 40 s (after 60 s of exposure) and 53.5 s (after 120 s of exposure) to 80% CO(2)/20% O(2). When O(2) was replaced by ambient air, a surgical tolerance of 53.5 s (after 60 s of exposure) and 77 s (after 120 s of exposure) was measured. In mice the induction time to 80% CO(2)/20% O(2) was 10 s and the surgical tolerance 19.5 s (after 120 s of exposure). Guineapigs showed an induction period of 20 s and a surgical tolerance of 50 s (after 30 s of exposure) to 80% CO(2)/O(2). Recovery was short and smooth in all species. This method of general anaesthesia seems to be suitable for short and painful interventions, mainly in rats, but also in guineapigs.