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

The anaesthetic effect of carbon dioxide (CO2) was investigated under prede termined 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 symptom s (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 lafter 60 s of exposure) and 53.5 s (after 120 s of exposure) to 80% CO2/20 % 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% CO2/20% O-2 was 10 s and the surgical tol erance 19.5 s (after 120 s of exposure). Guineapigs showed an induction per iod of 20 s and a surgical tolerance of 50 s (after 30 s of exposure) to 80 % CO2/O-2. Recovery was shout and smooth in all species. This method of gen eral anaesthesia seems to be suitable for short and painful interventions, mainly in rats, but also in guineapigs.