Philipp Villiger

SGV Meeting 2026 · Scientific Programme

CHUV, Lausanne

• 25 November 2026 · 11:55Inhalant Anesthesia before Euthanasia with CO2 in Laboratory Mice: improvement or change for the worse?
  Abstract

  Controlled atmosphere stunning (CAS) with carbon dioxide (CO₂) remains the most widely used method for euthanasia of laboratory rodents worldwide. However, its use raises important animal welfare concerns because it is aversive and induces respiratory distress that may result in anxiety and pain before loss of consciousness (LOC). Identifying other gases that minimize distress while ensuring rapid LOC therefore remains a key refinement objective to improve CAS. We recently conducted a comprehensive multimodal assessment of two CO₂ volume displacement rates, nitrogen (N₂), and carbon monoxide (CO) euthanasia in female and male C57BL/6N mice. By integrating electroencephalography (EEG), electromyography (EMG), cardiovascular and respiratory measurements, behavioral analysis, locomotor activity, and biochemical stress markers, we established objective endpoints for loss of posture and LOC and evaluated the overall welfare impact of different euthanasia protocols. These data provided important insights into the relationship between physiological, neurological, and behavioral responses during CAS gas euthanasia.

  Building on this framework, we additionally investigated whether the welfare burden associated with CO₂ euthanasia can be further reduced through prior induction with gaseous anesthetic agents. Specifically, we evaluate nitrous oxide (N₂O), isoflurane, and sevoflurane before CO₂ euthanasia, assessing their effects on behavioral, respiratory, cardiovascular, neurological, and biochemical indicators in female and male C57BL/6J and BALB/c mice. This approach allows direct comparison of euthanasia protocols across different sexes and strains while addressing the critical question of whether anesthetic induction reduces overall distress or merely shifts it to an earlier phase. Together, these studies provide a comprehensive evaluation of current and proposed refinement strategies and contribute evidence-based recommendations for improving the welfare of laboratory mice during euthanasia.