ZDAR.htm

NR ZDAR

AU Martoft,L.

TI Neurophysiological effects of high concentration CO2-inhalation in swine

QU Vet. med. Dissertation Universität Frederiksberg, Denmark, 2001

PT Dissertation

AB Carbon dioxide is used extensively for induction of pre-slaughter anaesthesia in swine and poultry as well as to induce anaesthesia during short-lasting surgical interventions and euthanasia in small laboratory animals. Loss of consciousness is not instantaneous during induction of CO2 anaesthesia, a fact that has prompted a debate concerning animal welfare and CO2 anaesthesia. The aim of this thesis was to study the neurophysiological effects of CO2 particularly the electrophysiological activity and intracellular pH during induction of CO2 anaesthesia, and to discuss the findings in relation to animal welfare. In the studies forming the basis of this thesis it was found that MLAEP (Middle-latency auditory evoked potentials) could be extracted from consciously awake, non-premedicated swine by using surface electrodes, and that the MLAEP trace looked much like that in man, dogs and rats. Furthermore, the alterations seen during induction of thiopentone anaesthesia were found to be similar to those seen in man. Inhalation of 90% CO2 was found to lead to changes in electrophysiological parameters from the very start of induction, and severe muscular activity from 13 to 30 sec after start of CO2 inhalation, i.e. after the start of depression of EEG and MLAEP parameters. The electrophysiological alterations seen during induction of CO2 anaesthesia and during induction of thiopentone anaesthesia in swine occurred at approximately the same pace. However, some differences were seen and these differences were thought to be attributable to the diverse neurochemical effects of the two compounds. As the electrophysiological parameters, the intracellular pH in the brain was found to change rapidly from the start of CO2 inhalation; from 7.3 to 6.7 after 60 s inhalation of 90% CO2. The electrophysiological activity started to normalize in the time span from 60 to 90 s after the end of CO2 inhalation. Muscular activity also reoccurred in this interval of time, which is in good agreement with other studies. In conclusion CO2, like thiopentone, is capable of inducing fast changes in CNS activity, but also in intracellular pH, and most probably CO2 promotes anaesthesia rapidly during inhalation of the gas. It does so in a complex manner likely to consist of both inhibitive and excitatory activity. In the short period prior to loss of consciousness it is possible that the animals can experience stress.
SP englisch

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