The aim of this study was to assess unconsciousness in pigs during exposure to CO 2 through changes in the middle latency auditory evoke potentials (MLAEP) of the central nervous system (CNS), blood parameters (pH, carbon dioxide partial pressure [ p CO 2 ], oxygen partial pressure [ p O 2 ], oxygen saturation [SatO 2 ] and bicarbonate [HCO 3 - ]), behaviour and the corneal reflex. The MLEAP did not decrease significantly until after 60 s exposure to CO 2 . The blood parameters (decreased pH, p O 2 and SatO 2 and increased p CO 2 and HCO 3 - ) changed 53 s after the onset of immersion. The burst suppression index (BS